WO2024190592A1 - Electrode for secondary battery, method for producing same, and all-solid-state secondary battery - Google Patents

Electrode for secondary battery, method for producing same, and all-solid-state secondary battery Download PDF

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WO2024190592A1
WO2024190592A1 PCT/JP2024/008731 JP2024008731W WO2024190592A1 WO 2024190592 A1 WO2024190592 A1 WO 2024190592A1 JP 2024008731 W JP2024008731 W JP 2024008731W WO 2024190592 A1 WO2024190592 A1 WO 2024190592A1
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electrode
secondary battery
active material
electrode active
positive electrode
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PCT/JP2024/008731
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French (fr)
Japanese (ja)
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歩 田中
啓 角田
純一 池尻
英郎 山内
巌大郎 狩野
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日本電気硝子株式会社
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Publication of WO2024190592A1 publication Critical patent/WO2024190592A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers

Definitions

  • the present invention relates to an electrode for a secondary battery, a method for producing the same, and an all-solid-state secondary battery using the electrode for the secondary battery.
  • the electrodes used in lithium-ion secondary batteries are made up of an electrode active material that absorbs and releases lithium ions during charging and discharging, a conductive additive that aids in electronic conduction, and a binder required to bind these to the base material that collects electricity.
  • binders used in this process include polyvinylidene fluoride and styrene butadiene rubber.
  • Patent Document 1 discloses a positive electrode for a secondary battery having a positive electrode active material layer that contains at least a positive electrode active material and a solid electrolyte.
  • the binder When the battery is exposed to high temperatures of 60°C or higher, the binder reacts with the electrolyte and swells, reducing its binding properties. This causes the electrode mixture to peel off from the base material used for collecting current, resulting in rapid deterioration of the battery.
  • the object of the present invention is to provide an electrode for a secondary battery, a manufacturing method thereof, and an all-solid-state secondary battery that can effectively increase the capacity of the secondary battery and has excellent charge/discharge cycle characteristics.
  • This article describes the electrodes for secondary batteries and their manufacturing methods that solve the above problems, as well as various aspects of all-solid-state secondary batteries.
  • the secondary battery electrode according to aspect 1 of the present invention is characterized by comprising a current collector and an electrode layer made of an electrode active material that essentially contains an electrode active material crystal and an amorphous phase, and a conductive assistant.
  • the electrode layer is substantially free of ⁇ ''-alumina, ⁇ -alumina, and NASICON crystals.
  • the electrode layer is composed of only inorganic materials.
  • the electrode layer is formed on both main surfaces of the current collector.
  • the method for manufacturing an electrode for a secondary battery according to aspect 5 of the present invention is a method for manufacturing an electrode for a secondary battery according to any one of aspects 1 to 4, characterized in that an electrode material layer containing an electrode active material precursor and a conductive assistant is formed on a main surface of a current collector, and the electrode layer is formed by firing the electrode material layer.
  • the all-solid-state secondary battery according to aspect 6 of the present invention is characterized in that it comprises a secondary battery electrode according to any one of aspects 1 to 4.
  • the present invention provides an electrode for a secondary battery, a manufacturing method thereof, and an all-solid-state secondary battery that can effectively increase the capacity of the secondary battery and has excellent charge/discharge cycle characteristics.
  • FIG. 1 is a schematic cross-sectional view showing an electrode for a secondary battery according to one embodiment of the present invention.
  • FIG. 2 is a schematic cross-sectional view showing a secondary battery electrode according to another embodiment of the present invention.
  • FIG. 3 is a schematic cross-sectional view showing an all-solid-state secondary battery according to one embodiment of the present invention.
  • Fig. 1 is a schematic cross-sectional view showing a secondary battery electrode according to one embodiment of the present invention.
  • a secondary battery electrode 10 of this embodiment includes a current collector 2 and an electrode layer 3.
  • the electrode layer 3 is substantially composed of an electrode active material 4 and a conductive assistant 5.
  • Substantially consisting of electrode active material 4 and conductive assistant 5" means that the main components are electrode active material 4 and conductive assistant 5, and for example, that the total content of electrode active material 4 and conductive assistant 5 in electrode layer 3 is 99 mass% or more.
  • the current collector 2 is not particularly limited as long as it has electronic conductivity.
  • the current collector include metal materials such as aluminum, titanium, silver, copper, stainless steel, and alloys thereof.
  • the above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals.
  • the above metal materials have high electronic conductivity and are less likely to undergo chemical reactions during charging and discharging of the secondary battery, so that the capacity of the secondary battery can be effectively increased and the charging and discharging cycle characteristics are excellent.
  • the current collector 2 is made of aluminum or an alloy containing aluminum.
  • Aluminum or an alloy containing aluminum has a low density among metal materials, and therefore can effectively increase the capacity of the secondary battery.
  • the surface of the current collector made of aluminum or an alloy containing aluminum is carbon-coated. This can prevent the formation of a passive oxide film on the surface of the current collector 2 during firing of the electrode, and therefore the secondary battery has excellent cycle characteristics during charge and discharge.
  • the current collector 2 is preferably a metal foil.
  • Metal foil is flexible, which allows for a large contact area with the electrode layer, and when used as a secondary battery, it can be integrated with the extraction electrode, effectively increasing the capacity of the secondary battery and providing excellent cycle characteristics during charging and discharging.
  • the current collector is preferably made of foamed metal. Because foamed metal has a high specific surface area, it is possible to increase the contact area with the electrode layer, resulting in excellent cycle characteristics during charging and discharging of the secondary battery.
  • the thickness of the current collector 2 is preferably 10 nm or more and 100 ⁇ m or less.
  • the thickness of the current collector 2 is preferably 50 ⁇ m or less, and more preferably 30 ⁇ m or less. In this case, the energy density of the secondary battery can be further increased.
  • the thickness of the current collector 2 is preferably 30 nm or more, and more preferably 50 nm or more. In this case, the increase in the internal resistance of the battery due to the decrease in conductivity and the decrease in discharge capacity, as well as the resulting decrease in weight energy density and volume energy density, can be further suppressed.
  • the electrode active material 4 is a positive electrode active material or a negative electrode active material.
  • the electrode active material 4 is composed of electrode active material crystals (positive electrode active material crystals or negative electrode active material crystals) and an amorphous phase.
  • the positive electrode active material is not particularly limited as long as it is made of positive electrode active material crystals capable of absorbing and releasing alkali ions such as sodium ions and lithium ions and an amorphous phase, and functions as an electrode layer.
  • the positive electrode active material may be formed, for example, by firing a positive electrode active material precursor powder such as a glass powder. By firing the positive electrode active material precursor powder, positive electrode active material crystals are precipitated. In addition, an amorphous phase is formed together with the positive electrode active material crystals by firing. By forming the amorphous phase, the alkali ion conductivity in the electrode layer 3 can be improved. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
  • the positive electrode active material crystal acting as the positive electrode active material is preferably a positive electrode active material crystal containing sodium, and examples thereof include sodium transition metal phosphate crystals containing Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O.
  • Na 2 FeP 2 O 7 Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Fe 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Fe 2.18 (P 2 O 7 ) 2 , Na 3 Fe 2 (P O 4 ) (P 2 O 7 ), NaFePO 4 , Na 2 MnP 2 O 7 , Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Mn 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Mn 2.18 (P 2 O 7 ) 2 , Na 3 V 2 (PO 4 ) 3 , NaNiPO 4 , Na 2 NiP 2 O 7 , Na 4 Ni 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Ni 2.18 (P 2 O 7 ) 2 , Na 4 Ni 7 (PO 4 ) 6 , Na 3 Ni 3 (PO 4
  • the sodium transition metal phosphate crystal is preferred because it has a high capacity and excellent chemical stability.
  • triclinic crystals belonging to the space group P1 or P-1 particularly crystals represented by the general formula Na x M y P 2 O z (1.2 ⁇ x ⁇ 2.8, 0.95 ⁇ y ⁇ 1.6, 6.5 ⁇ z ⁇ 8), are preferred because they have excellent cycle characteristics.
  • Other examples of the positive electrode active material crystal that acts as a positive electrode active material include layered sodium transition metal oxide crystals such as NaCrO 2 , Na 0.7 MnO 2 , and NaFe 0.2 Mn 0.4 Ni 0.4 O 2 .
  • the negative electrode active material is not particularly limited as long as it contains negative electrode active material crystals and an amorphous phase capable of absorbing and releasing alkali ions such as sodium ions and lithium ions, and functions as an electrode layer.
  • the negative electrode active material may be formed, for example, by firing a negative electrode active material precursor powder such as a glass powder. By firing the negative electrode active material precursor powder, negative electrode active material crystals are precipitated. Furthermore, by firing, an amorphous phase is formed together with the negative electrode active material crystals. By forming the amorphous phase, the alkali ion conductivity in the electrode layer 3 can be improved. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
  • negative electrode active material crystals that act as negative electrode active materials include crystals containing at least one selected from Nb and Ti and O, metal crystals containing at least one selected from Sn, Bi, and Sb, and alloy crystals containing at least one selected from Sn, Bi, and Sb.
  • Crystals containing at least one selected from Nb and Ti and O are preferred because they have excellent cycle characteristics. Furthermore, when the crystals containing at least one selected from Nb and Ti and O contain Na and/or Li, the charge/discharge efficiency (ratio of discharge capacity to charge capacity) is increased, and a high charge/discharge capacity can be maintained, which is preferred.
  • crystals containing at least one selected from Nb and Ti and O are orthorhombic crystals, hexagonal crystals, cubic crystals, or monoclinic crystals, particularly monoclinic crystals belonging to the space group P21/m, which are more preferred because they are less likely to reduce capacity even when charged and discharged at a large current.
  • orthorhombic crystals examples include NaTi2O4 , etc.
  • hexagonal crystals examples include Na2TiO3 , NaTi8O13 , NaTiO2 , LiNbO3 , LiNbO2 , Li7NbO6 , Li2Ti3O7 , etc.
  • cubic crystals examples include Na2TiO3 , NaNbO3 , Li4Ti5O12 , Li3NbO4 , etc.
  • Examples of monoclinic crystals include Na2Ti6O13 , NaTi2O4 , Na2TiO3 , Na4Ti5O12 , Na2Ti4O9 , Na2Ti9O19 , Na2Ti3O7 , Na2Ti3O7 , Li1.7Nb2O5 , Li1.9Nb2O5 , Li12Nb13O33 , and LiNb3O8 .
  • Examples of monoclinic crystals belonging to the space group P21 / m include Na2Ti3O7 .
  • the crystals containing at least one selected from Nb and Ti and O preferably further contain at least one selected from B, Si, P, and Ge. These components facilitate the formation of an amorphous phase together with the negative electrode active material crystals, and have the effect of further improving sodium ion conductivity.
  • Other materials that can be used include metal crystals of at least one type selected from Sn, Bi, and Sb, alloy crystals containing at least one type selected from Sn, Bi, and Sb (e.g., Sn-Cu alloy, Bi-Cu alloy, Bi-Zn alloy), and glass containing at least one type selected from Sn, Bi, and Sb. These are preferred because they have high capacity and are less likely to decrease in capacity even when charged and discharged at a large current.
  • conductive carbon can be used as the conductive assistant 5.
  • conductive carbon include acetylene black, carbon black, ketjen black, vapor grown carbon fiber carbon conductive assistant (VGCF), carbon nanotubes, etc. It is preferable that the conductive assistant is such a carbon-based conductive assistant.
  • the content of the conductive assistant in the electrode layer 3 is, in mass %, preferably 0.05% or more, more preferably 0.1% or more, even more preferably 0.5% or more, particularly preferably 1% or more, and preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, particularly preferably 5% or less.
  • content of the conductive assistant in the electrode layer 3 is within the above range, it is possible to further improve ionic conductivity while ensuring high electronic conductivity within the electrode, and it is possible to further effectively improve the battery characteristics of the secondary battery.
  • the thickness of the electrode layer 3 is preferably in the range of 3 ⁇ m to 300 ⁇ m, and more preferably in the range of 10 ⁇ m to 150 ⁇ m. If the electrode layer 3 is too thin, the capacity of the secondary battery itself will be small, and the energy density may decrease. If the electrode layer 3 is too thick, the resistance to electronic conduction will be large, and the discharge capacity and operating voltage will tend to decrease.
  • the thickness of the electrode layer 3 is preferably in the range of 0.3 ⁇ m to 300 ⁇ m, and more preferably in the range of 3 ⁇ m to 150 ⁇ m. If the thickness of the electrode layer 3 is too thin, the absolute capacity (mAh) of the negative electrode tends to decrease. If the thickness of the electrode layer 3 is too thick, the resistance increases, and the capacity (mAh/g) tends to decrease.
  • the electrode layer 3 preferably does not substantially contain solid electrolytes such as ⁇ ''-alumina, ⁇ -alumina, and NASICON crystals. These solid electrolytes may reduce the sinterability of the electrode active material 4 and reduce the adhesion between the current collector 2 and the electrode layer 3 when the positive electrode active material precursor powder or the negative electrode active material precursor powder is fired to form the electrode active material crystals and amorphous phase.
  • solid electrolytes such as ⁇ ''-alumina, ⁇ -alumina, and NASICON crystals.
  • substantially free of solid electrolyte means that the content of solid electrolyte in electrode layer 3 is less than 1 mass %, for example.
  • the electrode layer 3 is preferably composed only of inorganic materials such as metal oxides, conductive carbon, and metals. If it contains organic materials such as binders, the binders will react with the electrolyte when the secondary battery is exposed to high temperatures of 60°C or higher, causing the binders to swell and reduce the binding properties, and the electrode mixture will peel off from the base material used for collecting current, causing the battery to deteriorate rapidly. In addition, the density of the electrode layer 3 will decrease, tending to reduce the discharge capacity.
  • inorganic materials such as metal oxides, conductive carbon, and metals. If it contains organic materials such as binders, the binders will react with the electrolyte when the secondary battery is exposed to high temperatures of 60°C or higher, causing the binders to swell and reduce the binding properties, and the electrode mixture will peel off from the base material used for collecting current, causing the battery to deteriorate rapidly. In addition, the density of the electrode layer 3 will decrease, tending to reduce the discharge capacity.
  • the ratio of the thickness of the electrode layer 3 to the thickness of the current collector 2 is preferably 1 or more, more preferably 2 or more, even more preferably 5 or more, and particularly preferably 10 or more, and is preferably 1000 or less, more preferably 500 or less, even more preferably 200 or less, and particularly preferably 100 or less.
  • the main surface of the current collector 2 has a structure with holes or is mesh-shaped.
  • the electrode layers 3 provided on both main surfaces of the current collector 2 can be fused together, further increasing adhesion and making it easier to homogenize the reaction distribution inside the electrode, thereby improving input/output characteristics.
  • the secondary battery electrode 10 of the present invention can be formed, for example, by forming an electrode material layer containing an electrode active material precursor (positive electrode active material precursor or negative electrode active material precursor) and a conductive assistant on one main surface of a current collector 2, and firing the electrode material layer to form the electrode layer 3.
  • the electrode material layer can be obtained, for example, by applying a paste containing an electrode active material precursor and a conductive assistant, and drying the paste.
  • the paste may contain a binder, a plasticizer, a solvent, or the like, as necessary.
  • the electrode material layer may be a powder compact.
  • the drying temperature of the paste is not particularly limited, but can be, for example, 40°C or higher and 120°C or lower.
  • the drying time of the paste is not particularly limited, but can be, for example, 3 minutes or higher and 600 minutes or lower.
  • the atmosphere during firing is preferably an inert atmosphere or a reducing atmosphere.
  • the firing temperature can be, for example, 400°C to 800°C, and the holding time at that temperature can be, for example, 1 minute to 2 hours.
  • the positive electrode active material precursor powder may contain, in terms of mole percent of oxide, 8% to 55% Na 2 O, 10% to 70% CrO+FeO+MnO+CoO+NiO, and 15% to 70% P 2 O 5 +SiO 2 +B 2 O 3 .
  • % means “mol %” unless otherwise specified.
  • ⁇ + ⁇ + means the total amount of the corresponding components.
  • Na 2 O is a source of sodium ions that move between the positive electrode active material and the negative electrode active material during charging and discharging.
  • the content of Na 2 O is preferably 8% to 55%, more preferably 15% to 45%, and even more preferably 25% to 35%. If the content of Na 2 O is too small, the amount of sodium ions that contribute to absorption and release tends to decrease, and the discharge capacity tends to decrease. On the other hand, if the content of Na 2 O is too large, heterogeneous crystals that do not contribute to charging and discharging, such as Na 3 PO 4, tend to precipitate, and the discharge capacity tends to decrease.
  • CrO, FeO, MnO, CoO, and NiO are components that act as a driving force for the absorption and release of sodium ions by causing a redox reaction due to the change in the valence of each transition element during charging and discharging.
  • NiO and MnO have a large effect of increasing the redox potential.
  • FeO is particularly easy to stabilize the structure during charging and discharging, and is easy to improve cycle characteristics.
  • the content of CrO+FeO+MnO+CoO+NiO is preferably 10% to 70%, more preferably 15% to 60%, even more preferably 20% to 55%, even more preferably 23% to 50%, particularly preferably 25% to 40%, and most preferably 26% to 36%.
  • each of the P 2 O 5 , SiO 2 and B 2 O 3 components is preferably 0% to 70%, more preferably 15% to 70%, further preferably 20% to 60%, and particularly preferably 25% to 45%.
  • various components can be added in addition to the above components to facilitate vitrification within a range that does not impair the effect as a positive electrode active material.
  • examples of such components include, in oxide notation, MgO, CaO, SrO, BaO, ZnO, CuO, Al 2 O 3 , GeO 2 , Nb 2 O 5 , TiO 2 , ZrO 2 , V 2 O 5 , and Sb 2 O 5 , and in particular, Al 2 O 3, which acts as a network-forming oxide, and V 2 O 5, which is an active material component, are preferred.
  • the content of the above components is preferably 0% to 30%, more preferably 0.1% to 20%, and even more preferably 0.5% to 10%, in total.
  • an amorphous phase is formed along with the positive electrode active material crystals.
  • the formation of the amorphous phase can improve the sodium ion conductivity in the electrode layer 3.
  • the adhesion between the current collector 2 and the electrode layer 3 can be improved.
  • the average particle size of the positive electrode active material precursor powder is preferably 0.01 ⁇ m to 15 ⁇ m, more preferably 0.05 ⁇ m to 12 ⁇ m, and even more preferably 0.1 ⁇ m to 10 ⁇ m. If the average particle size of the positive electrode active material precursor powder is too small, the positive electrode active material precursor powder will have a strong cohesive force, and will tend to have poor dispersibility when made into a paste. As a result, the internal resistance of the battery will increase and the operating voltage will tend to decrease. In addition, the electrode density will decrease, and the capacity per unit volume of the battery will tend to decrease. On the other hand, if the average particle size of the active material precursor powder is too large, sodium ions will be less likely to diffuse and the internal resistance will tend to increase. In addition, the surface smoothness of the electrode will tend to be poor.
  • the average particle size means D 50 (volume-based average particle size) and indicates a value measured by a laser diffraction scattering method.
  • the negative electrode active material precursor powder preferably contains, in terms of mole percent of oxide, 0% to 90% SnO, 0% to 90% Bi 2 O 3 , 0% to 90% TiO 2 , 0% to 90% Fe 2 O 3 , 0% to 90% Nb 2 O 5 , 0% to 90% SiO 2 +B 2 O 3 +P 2 O 5 5% to 75%, and 0% to 80% Na 2 O.
  • Sn ions, Bi ions, Ti ions, Fe ions, or Nb ions are more uniformly dispersed in the oxide matrix containing Si, B, or P.
  • Na 2 O the material becomes more excellent in sodium ion conductivity. As a result, it is possible to suppress the volume change when absorbing and releasing sodium ions, and it is possible to obtain a negative electrode active material with more excellent cycle characteristics.
  • SnO, Bi 2 O 3 , TiO 2 , Fe 2 O 3 and Nb 2 O 5 are negative electrode active material components that become sites for absorbing and releasing alkali ions.
  • the discharge capacity per unit mass of the negative electrode active material becomes larger, and the charge/discharge efficiency (ratio of discharge capacity to charge capacity) during the initial charge/discharge is more likely to be improved.
  • the content of these components is too high, the volume change associated with the absorption and release of sodium ions during charge/discharge cannot be alleviated, and cycle characteristics tend to deteriorate.
  • it is preferable to set the content range of each component as follows.
  • the SnO content is preferably 0% to 90%, more preferably 45% to 85%, even more preferably 55% to 75%, and particularly preferably 60% to 72%.
  • the content of Bi 2 O 3 is preferably 0% to 90%, more preferably 10% to 70%, further preferably 15% to 65%, and particularly preferably 25% to 55%.
  • the TiO2 content is preferably 0% to 90%, more preferably 5% to 72%, even more preferably 10% to 68%, even more preferably 12% to 58%, particularly preferably 15% to 49%, and most preferably 15% to 39%.
  • the content of Fe 2 O 3 is preferably 0% to 90%, more preferably 15% to 85%, even more preferably 20% to 80%, and particularly preferably 25% to 75%.
  • the content of Nb 2 O 5 is preferably 0% to 90%, more preferably 7% to 79%, even more preferably 9% to 69%, even more preferably 11% to 59%, particularly preferably 13% to 49%, and most preferably 15% to 39%.
  • the content of SnO+Bi 2 O 3 +TiO 2 +Fe 2 O 3 +Nb 2 O 5 is preferably 0% to 90%, more preferably 5% to 85%, and even more preferably 10% to 80%.
  • SiO2 , B2O3 and P2O5 are network-forming oxides that surround the sites in the negative electrode active material that store and release sodium ions, and thus further improve the cycle characteristics.
  • SiO2 and P2O5 not only further improve the cycle characteristics, but also have excellent sodium ion conductivity, and therefore have the effect of further improving the rate characteristics.
  • SiO 2 +B 2 O 3 +P 2 O 5 is preferably 5% to 85%, more preferably 6% to 79%, even more preferably 7% to 69%, even more preferably 8% to 59%, particularly preferably 9% to 49%, and most preferably 10% to 39%. If SiO 2 +B 2 O 3 +P 2 O 5 is too small, the volume change of the negative electrode active material component accompanying the absorption and release of sodium ions during charging and discharging cannot be alleviated, causing structural destruction, and the cycle characteristics tend to decrease. On the other hand, if SiO 2 +B 2 O 3 +P 2 O 5 is too large, the content of the negative electrode active material component becomes relatively small, and the charge and discharge capacity per unit mass of the negative electrode active material tends to become small.
  • the content of SiO2 is preferably 0% to 75%, more preferably 5% to 75%, even more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of SiO2 is too high, the discharge capacity tends to decrease.
  • the content of P 2 O 5 is preferably 5% to 75%, more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of P 2 O 5 is too low, it is difficult to obtain the above cycle characteristics. On the other hand, if the content of P 2 O 5 is too high, the discharge capacity is likely to decrease and the water resistance is likely to decrease. In addition, when an aqueous electrode paste is produced, unwanted heterogeneous crystals are generated and the P 2 O 5 network is broken, so that the cycle characteristics are likely to decrease.
  • the content of B 2 O 3 is preferably 0% to 75%, more preferably 5% to 75%, even more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of B 2 O 3 is too high, the discharge capacity is likely to decrease and the chemical durability is likely to decrease.
  • an amorphous phase is formed along with the negative electrode active material crystals.
  • the formation of the amorphous phase can improve the sodium ion conductivity in the electrode layer 3.
  • the adhesion between the current collector 2 and the electrode layer 3 can be improved.
  • the average particle size of the negative electrode active material precursor powder is preferably 0.01 ⁇ m to 15 ⁇ m, more preferably 0.05 ⁇ m to 12 ⁇ m, and even more preferably 0.1 ⁇ m to 10 ⁇ m. If the average particle size of the negative electrode active material precursor powder is too small, the agglomeration force between the negative electrode active material precursor powders becomes strong, and dispersibility tends to be poor when made into a paste. As a result, the internal resistance of the battery increases and the operating voltage tends to decrease. In addition, the electrode density decreases, and the capacity per unit volume of the battery tends to decrease. On the other hand, if the average particle size of the negative electrode active material precursor powder is too large, sodium ions become difficult to diffuse and the internal resistance tends to increase. In addition, the surface smoothness of the electrode tends to be poor.
  • the electrode active material precursor powder is preferably prepared by melting and molding a raw material batch. This preparation method is preferable because it makes it easier to obtain an amorphous electrode active material precursor powder with excellent homogeneity.
  • the electrode active material precursor powder can be prepared as follows.
  • the raw materials are prepared to obtain a raw material batch having the desired composition.
  • the obtained raw material batch is then melted.
  • the melting temperature may be adjusted as appropriate so that the raw material batch is homogeneously melted.
  • the melting temperature is preferably 800°C or higher, and more preferably 900°C or higher.
  • the upper limit of the melting temperature it is preferably 1500°C or lower, and more preferably 1400°C or lower.
  • the obtained molten material is molded.
  • the molten material may be poured between a pair of cooling rolls and molded into a film while being rapidly cooled, or the molten material may be poured into a mold and molded into an ingot.
  • the obtained molded body is then pulverized to obtain an electrode active material precursor powder.
  • the electrode active material precursor powder may be produced by press-molding the raw material batch and then sintering it. Specifically, it can be produced as follows.
  • the raw materials are prepared to have the desired composition to obtain a raw material batch.
  • the obtained raw material batch is pre-calcined to obtain a pre-calcined raw material.
  • the pre-calcination temperature and pre-calcination time may be appropriately adjusted so that the raw material batch can be appropriately degassed.
  • the pre-calcination temperature is preferably 800°C or higher, and more preferably 900°C or higher.
  • the upper limit of the pre-calcination temperature it is preferably 1500°C or lower, and more preferably 1400°C or lower.
  • the obtained calcined raw material is pressure-molded to obtain a green compact.
  • the pressure for pressure molding may be appropriately adjusted so as to obtain a dense green compact.
  • the pressure is preferably 200 kgf/ cm2 or more, and more preferably 400 kgf/cm2 or more .
  • the obtained compact is sintered to obtain a sintered body.
  • the sintering temperature and sintering time may be adjusted as appropriate so that the compact reacts homogeneously.
  • the sintering temperature is preferably 800°C or higher, and more preferably 900°C or higher.
  • There is no particular upper limit to the sintering temperature but since a sintering temperature that is too high can lead to energy loss and evaporation of sodium components, etc., it is preferably 1500°C or lower, and more preferably 1400°C or lower.
  • the obtained sintered body is pulverized to obtain an electrode active material precursor powder.
  • (All-solid-state secondary battery) 3 is a schematic cross-sectional view showing an all-solid-state secondary battery according to one embodiment of the present invention. As shown in Fig. 3, the all-solid-state secondary battery 30 includes a current collector 2, an electrode layer 3, a solid electrolyte layer 34, a counter electrode layer 35, and a second current collector 36.
  • An electrode layer 3 is provided on both main surfaces of the current collector 2.
  • a solid electrolyte layer 34 is provided on the main surface of each electrode layer 3 opposite the current collector 2.
  • a counter electrode layer 35 is provided on the main surface of each solid electrolyte layer 34 opposite the electrode layer 3.
  • a second current collector 36 is provided on the main surface of each counter electrode layer 35 opposite the solid electrolyte layer 34. The second current collector 36 does not necessarily have to be provided.
  • the solid electrolyte constituting the solid electrolyte layer 34 is preferably formed from a sodium ion conductive oxide.
  • the sodium ion conductive oxide include compounds containing at least one selected from Al, Y, Zr, Si, and P, Na, and O.
  • Specific examples of the sodium ion conductive oxide include beta-alumina or NASICON crystal, which have excellent sodium ion conductivity.
  • the sodium ion conductive oxide is preferably at least one sodium ion conductive oxide selected from the group consisting of ⁇ ''-alumina, ⁇ -alumina, and NASICON crystal.
  • the sodium ion conductive oxide is more preferably ⁇ -alumina or ⁇ ''-alumina. These have even better sodium ion conductivity.
  • Beta alumina has two crystal forms, ⁇ -alumina (theoretical formula: Na 2 O ⁇ 11Al 2 O 3 ) and ⁇ ′′-alumina (theoretical formula: Na 2 O ⁇ 5.3Al 2 O 3 ).
  • ⁇ ′′-alumina is a metastable substance, and is usually used with Li 2 O or MgO added as a stabilizer.
  • ⁇ ′′-alumina has a higher sodium ion conductivity than ⁇ -alumina, it is preferable to use ⁇ ′′-alumina alone or a mixture of ⁇ ′′-alumina and ⁇ -alumina, and it is more preferable to use Li 2 O-stabilized ⁇ ′′-alumina (Na 1.7 Li 0.3 Al 10.7 O 17 ) or MgO-stabilized ⁇ ′′-alumina ((Al 10.32 Mg 0.68 O 16 )(Na 1.68 O)).
  • NASICON crystals include Na 3 Zr 2 Si 2 PO 12 , Na 3.2 Zr 1.3 Si 2.2 P 0.8 O 10.5 , Na 3 Zr 1.6 Ti 0.4 Si 2 PO 12 , Na 3 Hf 2 Si 2 PO 12 , Na 3.4 Zr 0.9 Hf 1.4 A 10.6 Si 1.2 P 1.8 O 12 , Na 3 Zr 1.7 Nb 0.24 Si 2 PO 12 , Na 3.6 Ti 0.2 Y 0.8 Si 2.8 O 9 , Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.12 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.05 Zr 2 Si 2.06 P 0.95 O 12 , Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 , Na 3.4 Zr 1.9 Zn 0.1 Si 2.4 P 0.6 O 12 , Na 3.4 Zr 1.9 Mg 0.1 Si 2.2 P 0.8 O 12 , Na 2 .8 Zr 2 Si 2.4 P 0.6 O 12 , Na 3.6 Zr 0.13 Yb
  • the solid electrolyte layer 34 can be manufactured by mixing raw material powders, molding the mixed raw material powders, and then firing them. For example, it can be manufactured by forming a green sheet by turning the raw material powders into a slurry, and then firing the green sheet. It may also be manufactured by the sol-gel method.
  • the thickness of the solid electrolyte layer 34 is preferably 1 ⁇ m or more, more preferably 3 ⁇ m or more, even more preferably 5 ⁇ m or more, and preferably 1000 ⁇ m or less, more preferably 800 ⁇ m or less, and even more preferably 500 ⁇ m or less. If the thickness of the solid electrolyte layer 34 is too thin, the mechanical strength decreases and it becomes more susceptible to breakage, making it more likely for an internal short circuit to occur. If the thickness of the solid electrolyte layer 34 is too thick, the sodium ion conduction distance associated with charging and discharging becomes longer, increasing the internal resistance, and making it more likely for the discharge capacity and operating voltage to decrease. In addition, the energy density per unit volume of the all-solid-state secondary battery 30 also becomes more likely to decrease.
  • the solid electrolyte layer 34 may include a first solid electrolyte layer that is a dense layer and a second solid electrolyte layer that is a porous layer.
  • the first solid electrolyte layer and the second solid electrolyte layer may be made of the same material as the solid electrolyte layer 34.
  • the first solid electrolyte layer not only plays the role of a solid electrolyte, but also functions as a base layer to ensure the mechanical strength of the solid electrolyte layer 34. Therefore, the first solid electrolyte layer has a denser structure than the second solid electrolyte layer.
  • the first solid electrolyte layer has a smaller porosity than the second solid electrolyte layer.
  • the first solid electrolyte layer has a porosity defined by the following formula (1) of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less.
  • the lower limit of the porosity is not particularly limited, but can be, for example, 0.1%.
  • p is the bulk density and p0 is the true density.
  • the thickness of the first solid electrolyte layer is preferably 0.01 ⁇ m or more, more preferably 0.1 ⁇ m or more, even more preferably 1 ⁇ m or more, particularly preferably 5 ⁇ m or more, preferably 300 ⁇ m or less, more preferably 200 ⁇ m or less, even more preferably 150 ⁇ m or less, and particularly preferably 100 ⁇ m or less. If the thickness of the first solid electrolyte layer is too small, the mechanical strength may decrease, or the electrode layer 3 and the counter electrode layer 35 may be short-circuited. On the other hand, if the thickness of the first solid electrolyte layer is too large, the ionic conductivity of the solid electrolyte layer 34 is likely to decrease. In addition, the energy density per unit volume of the all-solid-state secondary battery 30 tends to be high.
  • the second solid electrolyte layer is a porous layer having voids that are three-dimensionally connected to the solid electrolyte.
  • the electrode layer 3 and the counter electrode layer 35 are provided on the surface of the second solid electrolyte layer. Since the second solid electrolyte layer has voids that are three-dimensionally connected, the materials (active material powder, etc.) that make up the electrode layer 3 and the counter electrode layer 35 can easily enter the voids. Therefore, by providing the second solid electrolyte layer, which is a porous layer, on the first solid electrolyte layer, which is a dense layer, the adhesion between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 can be increased.
  • the second solid electrolyte layer has a porosity defined by the above formula (1) of preferably 25% or more, more preferably 30% or more, even more preferably 40% or more, and preferably 97% or less, more preferably 95% or less, and even more preferably 90% or less.
  • a porosity defined by the above formula (1) preferably 25% or more, more preferably 30% or more, even more preferably 40% or more, and preferably 97% or less, more preferably 95% or less, and even more preferably 90% or less.
  • the thickness of the second solid electrolyte layer is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more, even more preferably 5 ⁇ m or more, particularly preferably 10 ⁇ m or more, preferably 1000 ⁇ m or less, more preferably 800 ⁇ m or less, even more preferably 500 ⁇ m or less, particularly preferably 300 ⁇ m or less.
  • the thickness of the second solid electrolyte layer is too small, the amount of material constituting the electrode layer 3 and the counter electrode layer 35 that penetrates into the voids in the second solid electrolyte layer is reduced, so that the contact area between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 is reduced, and adhesion is likely to decrease.
  • the ion conduction paths at the interfaces between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 are reduced, so the internal resistance of the all-solid-state secondary battery 30 tends to increase. As a result, the rapid charge/discharge characteristics of the all-solid-state secondary battery 30 are likely to decrease.
  • the solid electrolyte layer 34 which includes a first solid electrolyte layer that is a dense layer and a second solid electrolyte layer that is a porous layer, can be formed, for example, by the method for manufacturing a solid electrolyte sheet described in WO 2021/045039.
  • the electrode active material contained in the counter electrode layer 35 is a negative electrode active material when the electrode active material contained in the electrode layer 3 of the secondary battery electrode 10 is a positive electrode active material, and is a positive electrode active material when the electrode active material contained in the electrode layer 3 of the secondary battery electrode 10 is a negative electrode active material.
  • the negative electrode active material contained in the counter electrode layer 35 is not particularly limited, but may be, for example, a carbon electrode material such as hard carbon or soft carbon.
  • the carbon electrode material is preferably hard carbon.
  • the negative electrode active material may contain metallic sodium or an alloy-based negative electrode active material capable of absorbing sodium, such as tin, bismuth, lead, or phosphorus. It is preferable that the counter electrode layer 35 is not metallic sodium or a negative electrode layer containing metallic sodium.
  • the counter electrode layer 35 containing the negative electrode active material may further contain a sodium ion conductive solid electrolyte and a conductive assistant.
  • the ratio of each material in the counter electrode layer 35 containing the negative electrode active material may be, for example, in mass %, 60% to 95% negative electrode active material, 5% to 35% sodium ion conductive solid electrolyte, and 0% to 5% conductive assistant.
  • the sodium ion conductive solid electrolyte may be, for example, the sodium ion conductive oxide described in the section on the solid electrolyte layer 34.
  • the conductive assistant may be, for example, one described in the section on the electrode layer 3.
  • the thickness of the counter electrode layer 35 containing the negative electrode active material is preferably 0.3 ⁇ m or more, more preferably 3 ⁇ m or more, even more preferably 10 ⁇ m or more, and preferably 500 ⁇ m or less, and more preferably 300 ⁇ m or less.
  • the thickness of the counter electrode layer 35 containing the negative electrode active material is equal to or greater than the above lower limit, the charge/discharge capacity of the all-solid-state secondary battery 30 can be further increased.
  • the thickness of the counter electrode layer 35 containing the negative electrode active material is too thick, the resistance to electronic conduction increases, and the discharge capacity and operating voltage of the all-solid-state secondary battery 30 may decrease.
  • the positive electrode active material contained in the counter electrode layer 35 is not particularly limited, but is preferably a positive electrode active material made of crystallized glass containing crystals represented by the general formula Na x M y P 2 O z (1 ⁇ x ⁇ 2.8, 0.95 ⁇ y ⁇ 1.6, 6.5 ⁇ z ⁇ 8, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr).
  • M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr.
  • the positive electrode active material is made of crystallized glass containing crystals represented by the general formula Na x MP 2 O 7 (1 ⁇ x ⁇ 2, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr).
  • a positive electrode active material crystal for example, Na 2 FeP 2 O 7 , Na 2 CoP 2 O 7 , Na 2 NiP 2 O 7, etc. can be used.
  • the counter electrode layer 35 containing the positive electrode active material may also contain a solid electrolyte and a conductive additive.
  • the ratio of each material in the counter electrode layer 35 containing the positive electrode active material can be, for example, in mass %, 30% to 95% positive electrode active material, 5% to 70% solid electrolyte, and 0% to 20% conductive additive.
  • the solid electrolyte the one described in the section on solid electrolyte layer 34 can be used.
  • conductive carbon can be used. Examples of conductive carbon include acetylene black, carbon black, ketjen black, vapor grown carbon fiber carbon conductive additive (VGCF), etc. It is preferable that the conductive additive is a carbon-based conductive additive made of the above-mentioned materials.
  • the thickness of the counter electrode layer 35 containing the positive electrode active material is preferably 10 ⁇ m or more, more preferably 50 ⁇ m or more, even more preferably 100 ⁇ m or more, and preferably 1000 ⁇ m or less, and more preferably 700 ⁇ m or less.
  • the thickness of the counter electrode layer 35 containing the positive electrode active material is equal to or greater than the above lower limit, the charge/discharge capacity of the all-solid-state secondary battery 30 can be further increased.
  • the counter electrode layer 35 containing the positive electrode active material is too thick, the resistance to electronic conduction increases, which may reduce the discharge capacity and operating voltage of the all-solid-state secondary battery 30, and the stress due to shrinkage during firing may increase, leading to peeling.
  • the material of the second current collector 36 is not particularly limited, but may be a metal material such as aluminum, titanium, silver, copper, stainless steel, or an alloy thereof.
  • the above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals.
  • the thickness of the second current collector 36 is not particularly limited, but may be 0.01 ⁇ m or more and 1000 ⁇ m or less.
  • the method for forming the second current collector 36 is not particularly limited, and examples of the method include physical vapor phase methods such as vapor deposition or sputtering, and chemical vapor phase methods such as thermal CVD, MOCVD, and plasma CVD. Other methods for forming the second current collector 36 include plating, the sol-gel method, and liquid phase film formation methods using spin coating. However, it is preferable to form the second current collector 36 on the counter electrode layer 35 by sputtering, as this provides excellent adhesion.
  • test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery.
  • the test battery was assembled in an environment with a dew point temperature of -70°C or lower.
  • the obtained test battery was CC (constant current) charged from the open circuit voltage to 4.5 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained.
  • CC discharge was performed from 4.5 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained.
  • the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge.
  • the "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity.
  • the C rate was set to 0.2 C. The results are shown in Table 1.
  • Electrode Layer Formation of Positive Electrode Layer (Electrode Layer)
  • the positive electrode paste was applied to a thickness of 80 ⁇ m on one main surface of a 20 ⁇ m thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer.
  • the positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 2 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
  • test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery.
  • the test battery was assembled in an environment with a dew point temperature of -70°C or lower.
  • Electrode Layer Formation of Positive Electrode Layer (Electrode Layer)
  • the positive electrode paste was applied to a thickness of 80 ⁇ m on one main surface of a 20 ⁇ m thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer.
  • the positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 3 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
  • test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery.
  • the test battery was assembled in an environment with a dew point temperature of -70°C or lower.
  • raw material powders were prepared using sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), nickel oxide (NiO), and orthophosphoric acid (H 3 PO 4 ) as raw materials to obtain the compositions shown in Table 4, and melted in an air atmosphere at 1200 to 1500° C. for 90 minutes. The melt was then poured between a pair of rotating rollers and shaped while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized using a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.5 ⁇ m.
  • D 50 average particle size
  • Electrode Layer Formation of Positive Electrode Layer (Electrode Layer)
  • the positive electrode paste was applied to a thickness of 80 ⁇ m on one main surface of a 20 ⁇ m thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer.
  • the positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 4 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
  • test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery.
  • the test battery was assembled in an environment with a dew point temperature of -70°C or lower.
  • the obtained test battery was CC (constant current) charged from the open circuit voltage to 5.2 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained.
  • CC discharge was performed from 5.2 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained.
  • the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge.
  • the "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity.
  • the C rate was set to 0.2 C. The results are shown in Table 4.
  • the pre-firing raw material batch was pressurized at 500 kgf/cm 2 , and fired at 900°C for 12 hours in a nitrogen/hydrogen mixed atmosphere for Comparative Example 1 and in a nitrogen atmosphere for Comparative Examples 2 and 3 to obtain a sintered body.
  • the obtained sintered body was pulverized in a ball mill and a planetary ball mill to obtain a positive electrode active material precursor powder having an average particle size (D 50 ) of 0.5 ⁇ m.
  • Electrode Layer Formation of Positive Electrode Layer (Electrode Layer)
  • the positive electrode paste was applied to a thickness of 80 ⁇ m on one main surface of a 20 ⁇ m thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode layer.
  • the positive electrode layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and a positive electrode layer (electrode layer) was formed on one main surface of the current collector to obtain an electrode for a secondary battery.
  • test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery.
  • the test battery was assembled in an environment with a dew point temperature of -70°C or lower.
  • the energy density of the electrode layer was 210 Wh/kg or more, and the capacity retention rate at 50 cycles was 67% or more.
  • the energy density of the electrode layer was 183 Wh/kg or less, and the capacity retention rate at 50 cycles was 23% or less.
  • Example 17 (a) Preparation of green sheet for forming first solid electrolyte layer Sodium carbonate (Na 2 CO 3 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), zirconium oxide (ZrO 2 ), and yttrium oxide (Y 2 O 3 ) were used as raw materials, and raw material powder was prepared so that, in mole percent, Na 2 O 14.2%, Al 2 O 3 75.4%, MgO 5.4%, ZrO 2 4.9%, and Y 2 O 3 0.1% was obtained. The raw material powder was calcined at 1250 ° C. for 4 hours, and then pulverized to an average particle size of 2 ⁇ m.
  • the negative electrode paste was applied to the center of one main surface of a 38 mm square, 75 ⁇ m thick solid electrolyte layer so that the negative electrode paste was 33 mm square and 70 ⁇ m thick. Drying was performed in a thermostatic chamber at 80° C. for 1 hour. Then, firing was performed in an N 2 (99.99%) atmosphere at 800° C. for 2 hours to form a negative electrode.
  • the weight of the negative electrode was calculated by (weight of the laminate after the negative electrode formation) minus (weight of the solid electrolyte layer).
  • the weight of the hard carbon active material was calculated by multiplying the weight of the active material by 0.8.
  • the capacity of the hard carbon was calculated by setting the capacity of the hard carbon to 385 mAh/g. As a result, the capacity of the negative electrode was 0.3 mAh/cm 2 .
  • the weight of the positive electrode was calculated from (weight of the laminate after the positive electrode was formed) - (weight of the laminate before the positive electrode was formed) - (weight of the aluminum foil).
  • the weight of the Na 2 FeP 2 O 7 active material was calculated by multiplying the calculated weight of the support by the ratio of the active material among them, 0.865.
  • the capacity of the positive electrode was calculated by assuming the capacity of Na2FeP2O7 crystallized glass ( Na2FeP2O7 active material) to be the theoretical capacity of 97mAh/g. As a result, the capacity of the positive electrode was 0.5mAh/ cm2 .
  • the capacity of the negative electrode was divided by the capacity of the positive electrode to obtain the N/P ratio (negative electrode capacity/positive electrode capacity), which was 0.6.
  • the all-solid-state secondary battery of Example 17 had an energy density of 70 Wh/kg and a capacity retention rate of 95% after 50 cycles.

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Abstract

Provided are an electrode for a secondary battery which makes it possible to effectively increase the capacity of a secondary battery and has excellent charge/discharge cycle characteristics, a method for producing the electrode for a secondary battery, and an all-solid-state secondary battery.　The electrode for a secondary battery is characterized by comprising: an electrode layer substantially comprising an electrode active material including electrode active material crystals and an amorphous phase, and a conductive auxiliary agent; and a current collector.

Description

二次電池用電極及びその製造方法、並びに全固体二次電池Electrode for secondary battery, manufacturing method thereof, and all-solid-state secondary battery
　本発明は、二次電池用電極及びその製造方法、並びに該二次電池用電極を用いた全固体二次電池に関する。 The present invention relates to an electrode for a secondary battery, a method for producing the same, and an all-solid-state secondary battery using the electrode for the secondary battery.
　リチウムイオン二次電池に用いられる電極は、充放電によりリチウムイオンを吸蔵・放出する電極活物質、電子伝導を助ける導電助剤、これらを集電する基材に結着させるために必要な結着剤で構成される。この結着剤にはポリフッ化ビニリデンやスチレンブタジエンゴムなどが使用されている。 The electrodes used in lithium-ion secondary batteries are made up of an electrode active material that absorbs and releases lithium ions during charging and discharging, a conductive additive that aids in electronic conduction, and a binder required to bind these to the base material that collects electricity. Examples of binders used in this process include polyvinylidene fluoride and styrene butadiene rubber.
　また、下記の特許文献１には、正極活物質と固体電解質とを少なくとも含む正極活物質層を有する二次電池用正極が開示されている。 In addition, the following Patent Document 1 discloses a positive electrode for a secondary battery having a positive electrode active material layer that contains at least a positive electrode active material and a solid electrolyte.
特開２０１４－１４３１３３号公報JP 2014-143133 A
　上記のような結着剤は、電池が６０℃以上の高温にさらされると結着剤が電解液と反応し、膨潤するため結着性が低下し、集電するための基材から電極合材が剥離してしまうため電池が急激に劣化する原因となっていた。 When the battery is exposed to high temperatures of 60°C or higher, the binder reacts with the electrolyte and swells, reducing its binding properties. This causes the electrode mixture to peel off from the base material used for collecting current, resulting in rapid deterioration of the battery.
　また、特許文献１に記載の二次電池用正極は、エネルギー密度があまり高くなかった。 In addition, the secondary battery positive electrode described in Patent Document 1 did not have a very high energy density.
　本発明の目的は、二次電池の容量を効果的に高めることができ、充放電によるサイクル特性に優れる、二次電池用電極及びその製造方法、並びに全固体二次電池を提供することにある。 The object of the present invention is to provide an electrode for a secondary battery, a manufacturing method thereof, and an all-solid-state secondary battery that can effectively increase the capacity of the secondary battery and has excellent charge/discharge cycle characteristics.
　上記課題を解決する二次電池用電極及びその製造方法、並びに全固体二次電池の各態様について説明する。 This article describes the electrodes for secondary batteries and their manufacturing methods that solve the above problems, as well as various aspects of all-solid-state secondary batteries.
　本発明の態様１に係る二次電池用電極は、集電体と、実質的に電極活物質結晶及び非晶質相を含む電極活物質と導電助剤からなる電極層とからなることを特徴としている。 The secondary battery electrode according to aspect 1 of the present invention is characterized by comprising a current collector and an electrode layer made of an electrode active material that essentially contains an electrode active material crystal and an amorphous phase, and a conductive assistant.
　態様２に係る二次電池用電極では、態様１において、前記電極層には、β’’－アルミナ、β－アルミナ、及びＮＡＳＩＣＯＮ結晶を実質的に含まないことが好ましい。 In the secondary battery electrode according to aspect 2, in aspect 1, it is preferable that the electrode layer is substantially free of β''-alumina, β-alumina, and NASICON crystals.
　態様３に係る二次電池用電極では、態様１又は態様２において、前記電極層は、無機材料のみで構成されていることが好ましい。 In the secondary battery electrode according to aspect 3, in aspect 1 or aspect 2, it is preferable that the electrode layer is composed of only inorganic materials.
　態様４に係る二次電池用電極では、態様１から態様３のいずれか一つの態様において、前記集電体の両主面上に前記電極層が形成されていることが好ましい。 In the secondary battery electrode according to aspect 4, in any one of aspects 1 to 3, it is preferable that the electrode layer is formed on both main surfaces of the current collector.
　本発明の態様５に係る二次電池用電極の製造方法は、態様１から態様４のいずれか一つの態様の二次電池用電極の製造方法であって、集電体の主面上に、電極活物質前駆体及び導電助剤とを含んだ電極材料層を形成し、該電極材料層を焼成することにより前記電極層が形成されることを特徴とする。 The method for manufacturing an electrode for a secondary battery according to aspect 5 of the present invention is a method for manufacturing an electrode for a secondary battery according to any one of aspects 1 to 4, characterized in that an electrode material layer containing an electrode active material precursor and a conductive assistant is formed on a main surface of a current collector, and the electrode layer is formed by firing the electrode material layer.
　本発明の態様６に係る全固体二次電池は、態様１から態様４のいずれか一つの態様の二次電池用電極を備えることを特徴としている。 The all-solid-state secondary battery according to aspect 6 of the present invention is characterized in that it comprises a secondary battery electrode according to any one of aspects 1 to 4.
　本発明によれば、二次電池の容量を効果的に高めることができ、充放電によるサイクル特性に優れる、二次電池用電極及びその製造方法、並びに全固体二次電池を提供することができる。 The present invention provides an electrode for a secondary battery, a manufacturing method thereof, and an all-solid-state secondary battery that can effectively increase the capacity of the secondary battery and has excellent charge/discharge cycle characteristics.
図１は、本発明の一実施形態に係る二次電池用電極を示す模式的断面図である。FIG. 1 is a schematic cross-sectional view showing an electrode for a secondary battery according to one embodiment of the present invention. 図２は、本発明の別の実施形態に係る二次電池用電極を示す模式的断面図である。FIG. 2 is a schematic cross-sectional view showing a secondary battery electrode according to another embodiment of the present invention. 図３は、本発明の一実施形態に係る全固体二次電池を示す模式的断面図である。FIG. 3 is a schematic cross-sectional view showing an all-solid-state secondary battery according to one embodiment of the present invention.
　以下、好ましい実施形態について説明する。但し、以下の実施形態は単なる例示であり、本発明は以下の実施形態に限定されるものではない。また、各図面において、実質的に同一の機能を有する部材は同一の符号で参照する場合がある。 Below, preferred embodiments are described. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.
　（二次電池用電極）
　図１は、本発明の一実施形態に係る二次電池用電極を示す模式的断面図である。図１に示すように、本実施形態の二次電池用電極１０は、集電体２及び電極層３を備える。電極層３は実質的に電極活物質４及び導電助剤５からなる。 (Electrodes for secondary batteries)
Fig. 1 is a schematic cross-sectional view showing a secondary battery electrode according to one embodiment of the present invention. As shown in Fig. 1, a secondary battery electrode 10 of this embodiment includes a current collector 2 and an electrode layer 3. The electrode layer 3 is substantially composed of an electrode active material 4 and a conductive assistant 5.
　なお、「実質的に電極活物質４及び導電助剤５からなる」とは、主成分が電極活物質４及び導電助剤５であることを意味し、例えば、電極層３における電極活物質４及び導電助剤５の含有量の合計が９９質量％以上であることを意味する。 "Substantially consisting of electrode active material 4 and conductive assistant 5" means that the main components are electrode active material 4 and conductive assistant 5, and for example, that the total content of electrode active material 4 and conductive assistant 5 in electrode layer 3 is 99 mass% or more.
　（集電体）
　本実施形態において、集電体２は、電子伝導性を有するものであれば、特に限定されない。集電体としては、アルミニウム、チタン、銀、銅、ステンレス鋼又はこれらの合金などの金属材料が挙げられる。上記金属材料は、単独で用いてもよく、複数を併用してもよい。なお、これらの合金とは、少なくとも１種の上記金属を含む合金である。上記金属材料は、電子伝導性が高く、二次電池の充放電の際に化学反応が起こりにくいため、二次電池の容量を効果的に高めることができ、充放電によるサイクル特性に優れる。 (Current collector)
In this embodiment, the current collector 2 is not particularly limited as long as it has electronic conductivity. Examples of the current collector include metal materials such as aluminum, titanium, silver, copper, stainless steel, and alloys thereof. The above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals. The above metal materials have high electronic conductivity and are less likely to undergo chemical reactions during charging and discharging of the secondary battery, so that the capacity of the secondary battery can be effectively increased and the charging and discharging cycle characteristics are excellent.
　この中でも、集電体２は、アルミニウム又は該アルミニウムを含む合金により構成されていることが好ましい。アルミニウム又は該アルミニウムを含む合金は、金属材料の中でも低密度であるため、二次電池の容量を効果的に高めることができる。また、アルミニウム又は該アルミニウムを含む合金により構成されている集電体は、表面にカーボンコートされていることが好ましい。このようにすることにより、電極の焼成時に集電体２の表面に不動態酸化皮膜を形成することを防止できるため、二次電池の充放電によるサイクル特性に優れる。 Among these, it is preferable that the current collector 2 is made of aluminum or an alloy containing aluminum. Aluminum or an alloy containing aluminum has a low density among metal materials, and therefore can effectively increase the capacity of the secondary battery. In addition, it is preferable that the surface of the current collector made of aluminum or an alloy containing aluminum is carbon-coated. This can prevent the formation of a passive oxide film on the surface of the current collector 2 during firing of the electrode, and therefore the secondary battery has excellent cycle characteristics during charge and discharge.
　集電体２は、金属箔であることが好ましい。金属箔は柔軟性があるため、電極層との接触面積を高めることができ、二次電池として使用した時に取り出し電極と一体化できるため、二次電池の容量を効果的に高めることができ、充放電によるサイクル特性に優れる。 The current collector 2 is preferably a metal foil. Metal foil is flexible, which allows for a large contact area with the electrode layer, and when used as a secondary battery, it can be integrated with the extraction electrode, effectively increasing the capacity of the secondary battery and providing excellent cycle characteristics during charging and discharging.
　また、集電体は、発泡金属であることが好ましい。発泡金属は比表面積が高いため、電極層との接触面積を高めることができ、二次電池の充放電によるサイクル特性に優れる。 The current collector is preferably made of foamed metal. Because foamed metal has a high specific surface area, it is possible to increase the contact area with the electrode layer, resulting in excellent cycle characteristics during charging and discharging of the secondary battery.
　集電体２の厚みは、１０ｎｍ以上、１００μｍ以下であることが好ましい。集電体２の厚みは、好ましくは５０μｍ以下であり、より好ましくは３０μｍ以下である。この場合、二次電池のエネルギー密度をより一層高めることができる。また、集電体２の厚みは、好ましくは３０ｎｍ以上であり、より好ましくは５０ｎｍ以上である。この場合、導電性の低下により電池の内部抵抗が増加して放電容量が低下すること、及び、それに起因する重量エネルギー密度及び体積エネルギー密度の低下をより一層抑制することができる。 The thickness of the current collector 2 is preferably 10 nm or more and 100 μm or less. The thickness of the current collector 2 is preferably 50 μm or less, and more preferably 30 μm or less. In this case, the energy density of the secondary battery can be further increased. In addition, the thickness of the current collector 2 is preferably 30 nm or more, and more preferably 50 nm or more. In this case, the increase in the internal resistance of the battery due to the decrease in conductivity and the decrease in discharge capacity, as well as the resulting decrease in weight energy density and volume energy density, can be further suppressed.
　（電極活物質）
　電極活物質４は、正極活物質又は負極活物質である。電極活物質４は、電極活物質結晶（正極活物質結晶または負極活物質結晶）と非晶質相からなる。 (Electrode active material)
The electrode active material 4 is a positive electrode active material or a negative electrode active material. The electrode active material 4 is composed of electrode active material crystals (positive electrode active material crystals or negative electrode active material crystals) and an amorphous phase.
　（正極活物質）
　正極活物質としては、ナトリウムイオンやリチウムイオン等のアルカリイオンを吸蔵・放出可能な正極活物質結晶と非晶質相からなり、電極層として機能するものであれば特に限定されない。正極活物質は、例えば、ガラス粉末等の正極活物質前駆体粉末を焼成して形成してもよい。正極活物質前駆体粉末を焼成することにより、正極活物質結晶が析出する。また、焼成により、正極活物質結晶とともに非晶質相が形成される。非晶質相が形成されることにより、電極層３内におけるアルカリイオン伝導性を向上させることができる。また、集電体２と電極層３との密着性を向上させることができる。 (Positive Electrode Active Material)
The positive electrode active material is not particularly limited as long as it is made of positive electrode active material crystals capable of absorbing and releasing alkali ions such as sodium ions and lithium ions and an amorphous phase, and functions as an electrode layer. The positive electrode active material may be formed, for example, by firing a positive electrode active material precursor powder such as a glass powder. By firing the positive electrode active material precursor powder, positive electrode active material crystals are precipitated. In addition, an amorphous phase is formed together with the positive electrode active material crystals by firing. By forming the amorphous phase, the alkali ion conductivity in the electrode layer 3 can be improved. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
　正極活物質として作用する正極活物質結晶としては、ナトリウムを含む正極活物質結晶であることが好ましく、Ｎａ、Ｍ（ＭはＣｒ、Ｆｅ、Ｍｎ、Ｃｏ、Ｖ及びＮｉからから選ばれる少なくとも１種の遷移金属元素）、Ｐ及びＯを含むナトリウム遷移金属リン酸塩結晶が挙げられる。具体例としては、Ｎａ２ＦｅＰ２Ｏ７、Ｎａ４Ｆｅ３（ＰＯ４）２（Ｐ２Ｏ７）、Ｎａ４Ｆｅ５（ＰＯ４）２（Ｐ２Ｏ７）２、Ｎａ３．６４Ｆｅ２．１８（Ｐ２Ｏ７）２、Ｎａ３Ｆｅ２（ＰＯ４）（Ｐ２Ｏ７）、ＮａＦｅＰＯ４、Ｎａ２ＭｎＰ２Ｏ７、Ｎａ４Ｍｎ３（ＰＯ４）２（Ｐ２Ｏ７）、Ｎａ４Ｍｎ５（ＰＯ４）２（Ｐ２Ｏ７）２、Ｎａ３．６４Ｍｎ２．１８（Ｐ２Ｏ７）２、Ｎａ３Ｖ２（ＰＯ４）３、ＮａＮｉＰＯ４、Ｎａ２ＮｉＰ２Ｏ７、Ｎａ４Ｎｉ３（ＰＯ４）２（Ｐ２Ｏ７）、Ｎａ４Ｎｉ５（ＰＯ４）２（Ｐ２Ｏ７）２、Ｎａ３．６４Ｎｉ２．１８（Ｐ２Ｏ７）２、Ｎａ４Ｎｉ７（ＰＯ４）６、Ｎａ３Ｎｉ３（ＰＯ４）２（Ｐ２Ｏ７）、ＮａＣｏＰＯ４、Ｎａ２ＣｏＰ２Ｏ７、Ｎａ４Ｃｏ３（ＰＯ４）２（Ｐ２Ｏ７）、Ｎａ４Ｃｏ５（ＰＯ４）２（Ｐ２Ｏ７）２、Ｎａ３．６４Ｃｏ２．１８（Ｐ２Ｏ７）２等が挙げられる。当該ナトリウム遷移金属リン酸塩結晶は、高容量で化学的安定性に優れるため好ましい。なかでも空間群Ｐ１またはＰ－１に属する三斜晶系結晶、特に一般式ＮａｘＭｙＰ２Ｏｚ（１．２≦ｘ≦２．８、０．９５≦ｙ≦１．６、６．５≦ｚ≦８）で表される結晶がサイクル特性に優れるため好ましい。その他に正極活物質として作用する正極活物質結晶としては、ＮａＣｒＯ２、Ｎａ０．７ＭｎＯ２、ＮａＦｅ０．２Ｍｎ０．４Ｎｉ０．４Ｏ２等の層状ナトリウム遷移金属酸化物結晶が挙げられる。 The positive electrode active material crystal acting as the positive electrode active material is preferably a positive electrode active material crystal containing sodium, and examples thereof include sodium transition metal phosphate crystals containing Na, M (M is at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O. Specific examples include Na 2 FeP 2 O 7 , Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Fe 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Fe 2.18 (P 2 O 7 ) 2 , Na 3 Fe 2 (P O 4 ) (P 2 O 7 ), NaFePO 4 , Na 2 MnP 2 O 7 , Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Mn 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Mn 2.18 (P 2 O 7 ) 2 , Na 3 V 2 (PO 4 ) 3 , NaNiPO 4 , Na 2 NiP 2 O 7 , Na 4 Ni 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Ni 5 (PO 4 ) 2 (P 2 O 7 ) 2 , Na 3.64 Ni 2.18 (P 2 O 7 ) 2 , Na 4 Ni 7 (PO 4 ) 6 , Na 3 Ni 3 (PO 4 ) 2 (P 2 O 7 ), NaCoPO 4 , Na 2 CoP 2 O 7 , Na 4 Co 3 (PO 4 ) 2 (P 2 O 7 ), Na 4 Examples of the sodium transition metal phosphate crystal include Na 5 (PO 4 ) 2 (P 2 O 7 ) 2 and Na 3.64 Co 2.18 (P 2 O 7 ) 2. The sodium transition metal phosphate crystal is preferred because it has a high capacity and excellent chemical stability. Among them, triclinic crystals belonging to the space group P1 or P-1, particularly crystals represented by the general formula Na x M y P 2 O z (1.2≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8), are preferred because they have excellent cycle characteristics. Other examples of the positive electrode active material crystal that acts as a positive electrode active material include layered sodium transition metal oxide crystals such as NaCrO 2 , Na 0.7 MnO 2 , and NaFe 0.2 Mn 0.4 Ni 0.4 O 2 .
　（負極活物質）
　負極活物質としては、ナトリウムイオンやリチウムイオン等のアルカリイオンを吸蔵・放出可能な負極活物質結晶と非晶質相を含み、電極層として機能するものであれば特に限定されない。負極活物質は、例えば、ガラス粉末等の負極活物質前駆体粉末を焼成して形成してもよい。負極活物質前駆体粉末を焼成することにより、負極活物質結晶が析出する。さらに、焼成により、負極活物質結晶とともに非晶質相が形成される。非晶質相が形成されることにより、電極層３内におけるアルカリイオン伝導性を向上させることができる。また、集電体２と電極層３との密着性を向上させることができる。 (Negative Electrode Active Material)
The negative electrode active material is not particularly limited as long as it contains negative electrode active material crystals and an amorphous phase capable of absorbing and releasing alkali ions such as sodium ions and lithium ions, and functions as an electrode layer. The negative electrode active material may be formed, for example, by firing a negative electrode active material precursor powder such as a glass powder. By firing the negative electrode active material precursor powder, negative electrode active material crystals are precipitated. Furthermore, by firing, an amorphous phase is formed together with the negative electrode active material crystals. By forming the amorphous phase, the alkali ion conductivity in the electrode layer 3 can be improved. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
　負極活物質として作用する負極活物質結晶としては、例えば、Ｎｂ及びＴｉから選ばれる少なくとも１種及びＯを含む結晶、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種の金属結晶、またはＳｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種を含む合金結晶を挙げることができる。 Examples of negative electrode active material crystals that act as negative electrode active materials include crystals containing at least one selected from Nb and Ti and O, metal crystals containing at least one selected from Sn, Bi, and Sb, and alloy crystals containing at least one selected from Sn, Bi, and Sb.
　Ｎｂ及びＴｉから選ばれる少なくとも１種及びＯを含む結晶は、サイクル特性に優れるため好ましい。さらに、Ｎｂ及びＴｉから選ばれる少なくとも１種及びＯを含む結晶が、Ｎａ及び／又はＬｉを含むと、充放電効率（充電容量に対する放電容量の比率）が高まり、高い充放電容量を維持することができるため好ましい。なかでも、Ｎｂ及びＴｉから選ばれる少なくとも１種及びＯを含む結晶が、斜方晶系結晶、六方晶系結晶、立方晶系結晶又は単斜晶系結晶、特に空間群Ｐ２１／ｍに属する単斜晶系結晶であれば、大電流で充放電しても容量の低下が起こりにくいため、より好ましい。 Crystals containing at least one selected from Nb and Ti and O are preferred because they have excellent cycle characteristics. Furthermore, when the crystals containing at least one selected from Nb and Ti and O contain Na and/or Li, the charge/discharge efficiency (ratio of discharge capacity to charge capacity) is increased, and a high charge/discharge capacity can be maintained, which is preferred. Among these, crystals containing at least one selected from Nb and Ti and O are orthorhombic crystals, hexagonal crystals, cubic crystals, or monoclinic crystals, particularly monoclinic crystals belonging to the space group P21/m, which are more preferred because they are less likely to reduce capacity even when charged and discharged at a large current.
　斜方晶系結晶としては、ＮａＴｉ２Ｏ４等が挙げられる。六方晶系結晶としては、Ｎａ２ＴｉＯ３、ＮａＴｉ８Ｏ１３、ＮａＴｉＯ２、ＬｉＮｂＯ３、ＬｉＮｂＯ２、Ｌｉ７ＮｂＯ６、Ｌｉ２Ｔｉ３Ｏ７等が挙げられる。立方晶系結晶としては、Ｎａ２ＴｉＯ３、ＮａＮｂＯ３、Ｌｉ４Ｔｉ５Ｏ１２、Ｌｉ３ＮｂＯ４等が挙げられる。単斜晶系結晶としては、Ｎａ２Ｔｉ６Ｏ１３、ＮａＴｉ２Ｏ４、Ｎａ２ＴｉＯ３、Ｎａ４Ｔｉ５Ｏ１２、Ｎａ２Ｔｉ４Ｏ９、Ｎａ２Ｔｉ９Ｏ１９、Ｎａ２Ｔｉ３Ｏ７、Ｎａ２Ｔｉ３Ｏ７、Ｌｉ１．７Ｎｂ２Ｏ５、Ｌｉ１．９Ｎｂ２Ｏ５、Ｌｉ１２Ｎｂ１３Ｏ３３、ＬｉＮｂ３Ｏ８等が挙げられる。空間群Ｐ２１／ｍに属する単斜晶系結晶としては、Ｎａ２Ｔｉ３Ｏ７等が挙げられる。 Examples of orthorhombic crystals include NaTi2O4 , etc. Examples of hexagonal crystals include Na2TiO3 , NaTi8O13 , NaTiO2 , LiNbO3 , LiNbO2 , Li7NbO6 , Li2Ti3O7 , etc. Examples of cubic crystals include Na2TiO3 , NaNbO3 , Li4Ti5O12 , Li3NbO4 , etc. Examples of monoclinic crystals include Na2Ti6O13 , NaTi2O4 , Na2TiO3 , Na4Ti5O12 , Na2Ti4O9 , Na2Ti9O19 , Na2Ti3O7 , Na2Ti3O7 , Li1.7Nb2O5 , Li1.9Nb2O5 , Li12Nb13O33 , and LiNb3O8 . Examples of monoclinic crystals belonging to the space group P21 / m include Na2Ti3O7 .
　Ｎｂ及びＴｉから選ばれる少なくとも１種及びＯを含む結晶は、さらに、Ｂ、Ｓｉ、Ｐ及びＧｅから選ばれる少なくとも１種を含むことが好ましい。これらの成分は、負極活物質結晶とともに非晶質相を形成させやすくし、ナトリウムイオン伝導性をより一層向上させる効果を有する。 The crystals containing at least one selected from Nb and Ti and O preferably further contain at least one selected from B, Si, P, and Ge. These components facilitate the formation of an amorphous phase together with the negative electrode active material crystals, and have the effect of further improving sodium ion conductivity.
　その他に、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種の金属結晶や、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種を含む合金結晶（例えばＳｎ－Ｃｕ合金、Ｂｉ－Ｃｕ合金、Ｂｉ－Ｚｎ合金）、Ｓｎ、Ｂｉ及びＳｂから選ばれる少なくとも１種を含有するガラスを用いることができる。これらは、高容量であり、大電流で充放電しても容量の低下が起こりにくいため好ましい。 Other materials that can be used include metal crystals of at least one type selected from Sn, Bi, and Sb, alloy crystals containing at least one type selected from Sn, Bi, and Sb (e.g., Sn-Cu alloy, Bi-Cu alloy, Bi-Zn alloy), and glass containing at least one type selected from Sn, Bi, and Sb. These are preferred because they have high capacity and are less likely to decrease in capacity even when charged and discharged at a large current.
　（導電助剤）
　導電助剤５としては、例えば、導電性炭素を用いることができる。導電性炭素としては、例えば、アセチレンブラック、カーボンブラック、ケッチェンブラック、気相法炭素繊維炭素導電助剤（ＶＧＣＦ）、カーボンナノチューブ等を挙げることができる。導電助剤は、このような炭素系導電助剤であることが好ましい。 (Conductive assistant)
For example, conductive carbon can be used as the conductive assistant 5. Examples of conductive carbon include acetylene black, carbon black, ketjen black, vapor grown carbon fiber carbon conductive assistant (VGCF), carbon nanotubes, etc. It is preferable that the conductive assistant is such a carbon-based conductive assistant.
　電極層３中の導電助剤の含有量は、質量％で、好ましくは０．０５％以上、より好ましくは０．１％以上、さらに好ましくは０．５％以上であり、特に好ましくは１％以上であり、好ましくは２０％以下、より好ましくは１５％以下、さらに好ましくは１０％以下、特に好ましくは５％以下である。電極層３中の導電助剤の含有量が上記範囲内にある場合、電極内における高い電子伝導性を確保しつつ、イオン伝導性をより一層向上させることができ、二次電池の電池特性をより一層効果的に向上させることができる。 The content of the conductive assistant in the electrode layer 3 is, in mass %, preferably 0.05% or more, more preferably 0.1% or more, even more preferably 0.5% or more, particularly preferably 1% or more, and preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, particularly preferably 5% or less. When the content of the conductive assistant in the electrode layer 3 is within the above range, it is possible to further improve ionic conductivity while ensuring high electronic conductivity within the electrode, and it is possible to further effectively improve the battery characteristics of the secondary battery.
　電極活物質４が正極活物質の場合、電極層３の厚みは、３μｍ～３００μｍの範囲であることが好ましく、１０μｍ～１５０μｍの範囲であることがより好ましい。電極層３の厚みが薄すぎると、二次電池自体の容量が小さくなることから、エネルギー密度が低下する場合がある。電極層３の厚みが厚すぎると、電子伝導に対する抵抗が大きくなるため放電容量及び作動電圧が低下する傾向にある。 When the electrode active material 4 is a positive electrode active material, the thickness of the electrode layer 3 is preferably in the range of 3 μm to 300 μm, and more preferably in the range of 10 μm to 150 μm. If the electrode layer 3 is too thin, the capacity of the secondary battery itself will be small, and the energy density may decrease. If the electrode layer 3 is too thick, the resistance to electronic conduction will be large, and the discharge capacity and operating voltage will tend to decrease.
　電極活物質４が負極活物質の場合、電極層３の厚みは、０．３μｍ～３００μｍの範囲であることが好ましく、３μｍ～１５０μｍの範囲であることがより好ましい。電極層３の厚みが薄すぎると、負極の絶対容量（ｍＡｈ）が低下する傾向にある。電極層３の厚みが厚すぎると、抵抗が大きくなるため容量（ｍＡｈ／ｇ）が低下する傾向にある。 When the electrode active material 4 is a negative electrode active material, the thickness of the electrode layer 3 is preferably in the range of 0.3 μm to 300 μm, and more preferably in the range of 3 μm to 150 μm. If the thickness of the electrode layer 3 is too thin, the absolute capacity (mAh) of the negative electrode tends to decrease. If the thickness of the electrode layer 3 is too thick, the resistance increases, and the capacity (mAh/g) tends to decrease.
　電極層３には、β’’－アルミナ、β－アルミナ、及びＮＡＳＩＣＯＮ結晶等の固体電解質を実質的に含まないことが好ましい。これらの固体電解質は、正極活物質前駆体粉末や負極活物質前駆体粉末を焼成して、電極活物質結晶と非晶質相が形成される際に、電極活物質４の焼結性を低下させ、集電体２と電極層３との密着性を低下させる虞がある。 The electrode layer 3 preferably does not substantially contain solid electrolytes such as β''-alumina, β-alumina, and NASICON crystals. These solid electrolytes may reduce the sinterability of the electrode active material 4 and reduce the adhesion between the current collector 2 and the electrode layer 3 when the positive electrode active material precursor powder or the negative electrode active material precursor powder is fired to form the electrode active material crystals and amorphous phase.
　なお、「固体電解質を実質的に含まない」とは、例えば、電極層３における固体電解質の含有量が１質量％未満であることを意味する。 Note that "substantially free of solid electrolyte" means that the content of solid electrolyte in electrode layer 3 is less than 1 mass %, for example.
　電極層３は、金属酸化物や導電性炭素や金属等の無機材料のみで構成されていることが好ましい。結着剤等の有機材料が含まれていると、二次電池が６０℃以上の高温にさらされると結着剤が電解液と反応し、膨潤するため結着性が低下し、集電するための基材から電極合材が剥離してしまうため電池が急激に劣化する原因になる。また、電極層３の緻密性が低下し放電容量が低下する傾向にある。 The electrode layer 3 is preferably composed only of inorganic materials such as metal oxides, conductive carbon, and metals. If it contains organic materials such as binders, the binders will react with the electrolyte when the secondary battery is exposed to high temperatures of 60°C or higher, causing the binders to swell and reduce the binding properties, and the electrode mixture will peel off from the base material used for collecting current, causing the battery to deteriorate rapidly. In addition, the density of the electrode layer 3 will decrease, tending to reduce the discharge capacity.
　集電体２の厚みに対する電極層３の厚みの比（電極層／集電体）は、１以上であることが好ましく、２以上であることがより好ましく、５以上であることがさらに好ましく、１０以上であることが特に好ましく、１０００以下であることが好ましく、５００以下であることがより好ましく、２００以下であることがさらに好ましく、１００以下であることが特に好ましい。このような範囲にすることにより、二次電池用電極１０の反りを防止して機械的強度を高めたり、集電体２と電極層３との密着性を向上させたり、残留歪を低減させたりできるため、二次電池の容量を効果的に高めることができ、充放電によるサイクル特性に優れる。 The ratio of the thickness of the electrode layer 3 to the thickness of the current collector 2 (electrode layer/current collector) is preferably 1 or more, more preferably 2 or more, even more preferably 5 or more, and particularly preferably 10 or more, and is preferably 1000 or less, more preferably 500 or less, even more preferably 200 or less, and particularly preferably 100 or less. By setting it in such a range, it is possible to prevent warping of the secondary battery electrode 10 and increase its mechanical strength, improve the adhesion between the current collector 2 and the electrode layer 3, and reduce residual distortion, so that the capacity of the secondary battery can be effectively increased and the charge/discharge cycle characteristics are excellent.
　図２は、本発明の別の実施形態に係る二次電池用電極を示す模式的断面図である。図２に示すように、本実施形態の二次電池用電極２０は、集電体２及び電極層３からなる。ここで、集電体２の両主面上に電極層３を備える。それぞれの電極層３は電極活物質４及び導電助剤５からなる。このような構成にすることにより、１つの集電体２に対し２つの電極層３を形成することができるので、二次電池の容量をさらに効果的に高めることができる。 FIG. 2 is a schematic cross-sectional view showing an electrode for a secondary battery according to another embodiment of the present invention. As shown in FIG. 2, the electrode for a secondary battery 20 of this embodiment is composed of a current collector 2 and an electrode layer 3. Here, the electrode layers 3 are provided on both main surfaces of the current collector 2. Each electrode layer 3 is composed of an electrode active material 4 and a conductive assistant 5. With this configuration, two electrode layers 3 can be formed for one current collector 2, so that the capacity of the secondary battery can be further effectively increased.
　本実施形態では、集電体２の主面に穴が開いた構造を有する、あるいは集電体２がメッシュ状であることが好ましい。このような構成にすることにより、集電体２の両主面上に設けられた電極層３同士も融着することができ、密着性がさらに高められるとともに、電極内部の反応分布が均質化しやすくなるため、入出力特性を向上させることができる。 In this embodiment, it is preferable that the main surface of the current collector 2 has a structure with holes or is mesh-shaped. With such a configuration, the electrode layers 3 provided on both main surfaces of the current collector 2 can be fused together, further increasing adhesion and making it easier to homogenize the reaction distribution inside the electrode, thereby improving input/output characteristics.
　（二次電池用電極の製造方法）
　本発明の二次電池用電極１０は、例えば、集電体２の一方側の主面上に、電極活物質前駆体（正極活物質前駆体または負極活物質前駆体）及び導電助剤とを含んだ電極材料層を形成し、該電極材料層を焼成することにより電極層３を形成することができる。電極材料層は、例えば、電極活物質前駆体及び導電助剤とを含んだペーストを塗布し、乾燥することにより得ることができる。なお、ペーストには、必要に応じて、バインダー、可塑剤、又は溶剤等が含まれていてもよい。なお、電極材料層は、圧粉体であってもよい。 (Method of manufacturing secondary battery electrodes)
The secondary battery electrode 10 of the present invention can be formed, for example, by forming an electrode material layer containing an electrode active material precursor (positive electrode active material precursor or negative electrode active material precursor) and a conductive assistant on one main surface of a current collector 2, and firing the electrode material layer to form the electrode layer 3. The electrode material layer can be obtained, for example, by applying a paste containing an electrode active material precursor and a conductive assistant, and drying the paste. The paste may contain a binder, a plasticizer, a solvent, or the like, as necessary. The electrode material layer may be a powder compact.
　ペーストの乾燥温度としては、特に限定されないが、例えば、４０℃以上、１２０℃以下とすることができる。また、ペーストの乾燥時間としては、特に限定されないが、例えば、３分以上、６００分以下とすることができる。 The drying temperature of the paste is not particularly limited, but can be, for example, 40°C or higher and 120°C or lower. The drying time of the paste is not particularly limited, but can be, for example, 3 minutes or higher and 600 minutes or lower.
　焼成時の雰囲気は不活性雰囲気または還元雰囲気であることが好ましい。焼成温度（最高温度）は、例えば、４００℃～８００℃とすることができ、その温度での保持時間は、例えば、１分間～２時間とすることができる。 The atmosphere during firing is preferably an inert atmosphere or a reducing atmosphere. The firing temperature (maximum temperature) can be, for example, 400°C to 800°C, and the holding time at that temperature can be, for example, 1 minute to 2 hours.
　正極活物質前駆体粉末としては、（ｉ）Ｃｒ、Ｆｅ、Ｍｎ、Ｃｏ、Ｎｉ、Ｔｉ及びＮｂからなる群より選ばれた少なくとも１種の遷移金属元素、（ｉｉ）Ｐ、Ｓｉ及びＢから選択される少なくとも１種の元素、並びに（ｉｉｉ）Ｏを含むものが挙げられる。 Positive electrode active material precursor powders include those containing (i) at least one transition metal element selected from the group consisting of Cr, Fe, Mn, Co, Ni, Ti, and Nb, (ii) at least one element selected from P, Si, and B, and (iii) O.
　正極活物質前駆体粉末としては、特に酸化物換算のモル％で、Ｎａ２Ｏ　８％～５５％、ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯ　１０％～７０％、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３　１５％～７０％を含有するものが挙げられる。各成分をこのように限定した理由を以下に説明する。なお、以下の各成分の含有量に関する説明において、特に断りのない限り、「％」は「モル％」を意味する。また、「○＋○＋・・・」は該当する各成分の合量を意味する。 The positive electrode active material precursor powder may contain, in terms of mole percent of oxide, 8% to 55% Na 2 O, 10% to 70% CrO+FeO+MnO+CoO+NiO, and 15% to 70% P 2 O 5 +SiO 2 +B 2 O 3 . The reasons for limiting each component in this way are explained below. In the following explanation of the content of each component, "%" means "mol %" unless otherwise specified. In addition, "○+○+..." means the total amount of the corresponding components.
　Ｎａ２Ｏは、充放電の際に正極活物質と負極活物質との間を移動するナトリウムイオンの供給源となる。Ｎａ２Ｏの含有量は、好ましくは８％～５５％、より好ましくは１５％～４５％、さらに好ましくは２５％～３５％である。Ｎａ２Ｏが少なすぎると、吸蔵及び放出に寄与するナトリウムイオンが少なくなるため、放電容量が低下する傾向にある。一方、Ｎａ２Ｏが多すぎると、Ｎａ３ＰＯ４等の充放電に寄与しない異種結晶が析出しやすくなるため、放電容量が低下する傾向にある。 Na 2 O is a source of sodium ions that move between the positive electrode active material and the negative electrode active material during charging and discharging. The content of Na 2 O is preferably 8% to 55%, more preferably 15% to 45%, and even more preferably 25% to 35%. If the content of Na 2 O is too small, the amount of sodium ions that contribute to absorption and release tends to decrease, and the discharge capacity tends to decrease. On the other hand, if the content of Na 2 O is too large, heterogeneous crystals that do not contribute to charging and discharging, such as Na 3 PO 4, tend to precipitate, and the discharge capacity tends to decrease.
　ＣｒＯ、ＦｅＯ、ＭｎＯ、ＣｏＯ、ＮｉＯは、充放電の際に各遷移元素の価数が変化してレドックス反応を起こすことにより、ナトリウムイオンの吸蔵及び放出の駆動力として作用する成分である。なかでも、ＮｉＯ及びＭｎＯは酸化還元電位を高める効果が大きい。また、ＦｅＯは充放電において特に構造を安定化させやすく、サイクル特性を向上させやすい。ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯの含有量は、好ましくは１０％～７０％、より好ましくは１５％～６０％、さらに好ましくは２０％～５５％、さらに好ましくは２３％～５０％、特に好ましくは２５％～４０％、最も好ましくは２６％～３６％である。ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯが少なすぎると、充放電に伴うレドックス反応が起こりにくくなり、吸蔵及び放出されるナトリウムイオンが少なくなるため放電容量が低下する傾向にある。一方、ＣｒＯ＋ＦｅＯ＋ＭｎＯ＋ＣｏＯ＋ＮｉＯが多すぎると、異種結晶が析出して放電容量が低下する傾向にある。 CrO, FeO, MnO, CoO, and NiO are components that act as a driving force for the absorption and release of sodium ions by causing a redox reaction due to the change in the valence of each transition element during charging and discharging. Among them, NiO and MnO have a large effect of increasing the redox potential. FeO is particularly easy to stabilize the structure during charging and discharging, and is easy to improve cycle characteristics. The content of CrO+FeO+MnO+CoO+NiO is preferably 10% to 70%, more preferably 15% to 60%, even more preferably 20% to 55%, even more preferably 23% to 50%, particularly preferably 25% to 40%, and most preferably 26% to 36%. If the amount of CrO+FeO+MnO+CoO+NiO is too small, the redox reaction accompanying charging and discharging is difficult to occur, and the discharge capacity tends to decrease because fewer sodium ions are absorbed and released. On the other hand, if there is too much CrO+FeO+MnO+CoO+NiO, foreign crystals tend to precipitate and the discharge capacity tends to decrease.
　Ｐ２Ｏ５、ＳｉＯ２及びＢ２Ｏ３は３次元網目構造を形成するため、正極活物質の構造を安定化させる効果を有する。特に、Ｐ２Ｏ５、ＳｉＯ２がナトリウムイオン伝導性に優れるために好ましく、Ｐ２Ｏ５がより好ましい。Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３の含有量は、好ましくは１５％～７０％、より好ましくは２０％～６０％、さらに好ましくは２５％～４５％である。Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３が少なすぎると、繰り返し充放電した際に放電容量が低下しやすくなる傾向にある。一方、Ｐ２Ｏ５＋ＳｉＯ２＋Ｂ２Ｏ３が多すぎると、Ｐ２Ｏ５等の充放電に寄与しない異種結晶が析出する傾向にある。なお、Ｐ２Ｏ５、ＳｉＯ２及びＢ２Ｏ３の各成分の含有量は各々好ましくは０％～７０％、より好ましくは１５％～７０％、さらに好ましくは２０％～６０％、特に好ましくは２５％～４５％である。 P 2 O 5 , SiO 2 and B 2 O 3 form a three-dimensional network structure, and therefore have the effect of stabilizing the structure of the positive electrode active material. In particular, P 2 O 5 and SiO 2 are preferred because they have excellent sodium ion conductivity, and P 2 O 5 is more preferred. The content of P 2 O 5 + SiO 2 + B 2 O 3 is preferably 15% to 70%, more preferably 20% to 60%, and even more preferably 25% to 45%. If P 2 O 5 + SiO 2 + B 2 O 3 is too small, the discharge capacity tends to decrease when repeatedly charged and discharged. On the other hand, if P 2 O 5 + SiO 2 + B 2 O 3 is too much, heterogeneous crystals that do not contribute to charging and discharging, such as P 2 O 5, tend to precipitate. The content of each of the P 2 O 5 , SiO 2 and B 2 O 3 components is preferably 0% to 70%, more preferably 15% to 70%, further preferably 20% to 60%, and particularly preferably 25% to 45%.
　また、正極活物質としての効果を損なわない範囲で、上記成分に加えて種々の成分を含有させることでガラス化を容易にすることができる。このような成分としては、酸化物表記でＭｇＯ、ＣａＯ、ＳｒＯ、ＢａＯ、ＺｎＯ、ＣｕＯ、Ａｌ２Ｏ３、ＧｅＯ２、Ｎｂ２Ｏ５、ＴｉＯ２、ＺｒＯ２、Ｖ２Ｏ５、Ｓｂ２Ｏ５が挙げられ、特に網目形成酸化物として働くＡｌ２Ｏ３や活物質成分となるＶ２Ｏ５が好ましい。上記成分の含有量は、合量で、好ましくは０％～３０％、より好ましくは０．１％～２０％、さらに好ましくは０．５％～１０％である。 In addition, various components can be added in addition to the above components to facilitate vitrification within a range that does not impair the effect as a positive electrode active material. Examples of such components include, in oxide notation, MgO, CaO, SrO, BaO, ZnO, CuO, Al 2 O 3 , GeO 2 , Nb 2 O 5 , TiO 2 , ZrO 2 , V 2 O 5 , and Sb 2 O 5 , and in particular, Al 2 O 3, which acts as a network-forming oxide, and V 2 O 5, which is an active material component, are preferred. The content of the above components is preferably 0% to 30%, more preferably 0.1% to 20%, and even more preferably 0.5% to 10%, in total.
　正極活物質前駆体粉末は、焼成により、正極活物質結晶とともに非晶質相が形成される。非晶質相が形成されることにより、電極層３内におけるナトリウムイオン伝導性を向上させることができる。また、集電体２と電極層３との密着性を向上させることができる。 When the positive electrode active material precursor powder is sintered, an amorphous phase is formed along with the positive electrode active material crystals. The formation of the amorphous phase can improve the sodium ion conductivity in the electrode layer 3. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
　正極活物質前駆体粉末の平均粒子径は、好ましくは０．０１μｍ～１５μｍ、より好ましくは０．０５μｍ～１２μｍ、さらに好ましくは０．１μｍ～１０μｍである。正極活物質前駆体粉末の平均粒子径が小さすぎると、正極活物質前駆体粉末同士の凝集力が強くなり、ペースト化した際に分散性に劣る傾向がある。その結果、電池の内部抵抗が高くなり作動電圧が低下しやすくなる。また、電極密度が低下して電池の単位体積あたりの容量が低下する傾向がある。一方、活物質前駆体粉末の平均粒子径が大きすぎると、ナトリウムイオンが拡散しにくくなるとともに、内部抵抗が大きくなる傾向がある。また、電極の表面平滑性に劣る傾向がある。 The average particle size of the positive electrode active material precursor powder is preferably 0.01 μm to 15 μm, more preferably 0.05 μm to 12 μm, and even more preferably 0.1 μm to 10 μm. If the average particle size of the positive electrode active material precursor powder is too small, the positive electrode active material precursor powder will have a strong cohesive force, and will tend to have poor dispersibility when made into a paste. As a result, the internal resistance of the battery will increase and the operating voltage will tend to decrease. In addition, the electrode density will decrease, and the capacity per unit volume of the battery will tend to decrease. On the other hand, if the average particle size of the active material precursor powder is too large, sodium ions will be less likely to diffuse and the internal resistance will tend to increase. In addition, the surface smoothness of the electrode will tend to be poor.
　なお、本発明において、平均粒子径は、Ｄ５０（体積基準の平均粒子径）を意味し、レーザー回折散乱法により測定された値を指すものとする。 In the present invention, the average particle size means D 50 (volume-based average particle size) and indicates a value measured by a laser diffraction scattering method.
　負極活物質前駆体粉末としては、酸化物換算のモル％で、ＳｎＯ　０％～９０％、Ｂｉ２Ｏ３　０％～９０％、ＴｉＯ２　０％～９０％、Ｆｅ２Ｏ３　０％～９０％、Ｎｂ２Ｏ５　０％～９０％、ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５　５％～７５％、Ｎａ２Ｏ　０％～８０％を含有することが好ましい。上記構成にすることにより、負極活物質成分であるＳｎイオン、Ｂｉイオン、Ｔｉイオン、Ｆｅイオン又はＮｂイオンが、Ｓｉ、Ｂ又はＰを含有する酸化物マトリクス中により均一に分散した構造が形成される。また、Ｎａ２Ｏを含有することにより、ナトリウムイオン伝導性により一層優れた材料となる。結果として、ナトリウムイオンを吸蔵及び放出する際の体積変化を抑制でき、サイクル特性により一層優れた負極活物質を得ることが可能となる。 The negative electrode active material precursor powder preferably contains, in terms of mole percent of oxide, 0% to 90% SnO, 0% to 90% Bi 2 O 3 , 0% to 90% TiO 2 , 0% to 90% Fe 2 O 3 , 0% to 90% Nb 2 O 5 , 0% to 90% SiO 2 +B 2 O 3 +P 2 O 5 5% to 75%, and 0% to 80% Na 2 O. By making the above configuration, a structure is formed in which the negative electrode active material components Sn ions, Bi ions, Ti ions, Fe ions, or Nb ions are more uniformly dispersed in the oxide matrix containing Si, B, or P. In addition, by containing Na 2 O, the material becomes more excellent in sodium ion conductivity. As a result, it is possible to suppress the volume change when absorbing and releasing sodium ions, and it is possible to obtain a negative electrode active material with more excellent cycle characteristics.
　負極活物質前駆体粉末の組成を上記の通り限定した理由を以下に説明する。なお、以下の説明において、特に断りのない限り、「％」は「モル％」を意味する。また、「○＋○＋・・・」は該当する各成分の合量を意味する。 The reasons for limiting the composition of the negative electrode active material precursor powder as described above are explained below. In the following explanation, unless otherwise specified, "%" means "mol %." Also, "○ + ○ + ..." means the total amount of the corresponding components.
　ＳｎＯ、Ｂｉ２Ｏ３、ＴｉＯ２、Ｆｅ２Ｏ３及びＮｂ２Ｏ５は、アルカリイオンを吸蔵及び放出するサイトとなる負極活物質成分である。これらの成分を含有させることにより、負極活物質の単位質量当たりの放電容量がより大きくなり、かつ、初回充放電時の充放電効率（充電容量に対する放電容量の比率）がより向上しやすくなる。但し、これらの成分の含有量が多すぎると、充放電時のナトリウムイオンの吸蔵及び放出に伴う体積変化を緩和できずに、サイクル特性が低下する傾向がある。以上に鑑み、各成分の含有量範囲は以下の通りとすることが好ましい。 SnO, Bi 2 O 3 , TiO 2 , Fe 2 O 3 and Nb 2 O 5 are negative electrode active material components that become sites for absorbing and releasing alkali ions. By including these components, the discharge capacity per unit mass of the negative electrode active material becomes larger, and the charge/discharge efficiency (ratio of discharge capacity to charge capacity) during the initial charge/discharge is more likely to be improved. However, if the content of these components is too high, the volume change associated with the absorption and release of sodium ions during charge/discharge cannot be alleviated, and cycle characteristics tend to deteriorate. In view of the above, it is preferable to set the content range of each component as follows.
　ＳｎＯの含有量は、好ましくは０％～９０％、より好ましくは４５％～８５％、さらに好ましくは５５％～７５％、特に好ましくは６０％～７２％である。 The SnO content is preferably 0% to 90%, more preferably 45% to 85%, even more preferably 55% to 75%, and particularly preferably 60% to 72%.
　Ｂｉ２Ｏ３の含有量は、好ましくは０％～９０％、より好ましくは１０％～７０％、さらに好ましくは１５％～６５％、特に好ましくは２５％～５５％である。 The content of Bi 2 O 3 is preferably 0% to 90%, more preferably 10% to 70%, further preferably 15% to 65%, and particularly preferably 25% to 55%.
　ＴｉＯ２の含有量は、好ましくは０％～９０％、より好ましくは５％～７２％、さらに好ましくは１０％～６８％、さらに好ましくは１２％～５８％、特に好ましくは１５％～４９％、最も好ましくは１５％～３９％である。 The TiO2 content is preferably 0% to 90%, more preferably 5% to 72%, even more preferably 10% to 68%, even more preferably 12% to 58%, particularly preferably 15% to 49%, and most preferably 15% to 39%.
　Ｆｅ２Ｏ３の含有量は、好ましくは０％～９０％、より好ましくは１５％～８５％、さらに好ましくは２０％～８０％、特に好ましくは２５％～７５％である。 The content of Fe 2 O 3 is preferably 0% to 90%, more preferably 15% to 85%, even more preferably 20% to 80%, and particularly preferably 25% to 75%.
　Ｎｂ２Ｏ５の含有量は、好ましくは０％～９０％、より好ましくは７％～７９％、さらに好ましくは９％～６９％、さらに好ましくは１１％～５９％、特に好ましくは１３％～４９％、最も好ましくは１５％～３９％である。なお、ＳｎＯ＋Ｂｉ２Ｏ３＋ＴｉＯ２＋Ｆｅ２Ｏ３＋Ｎｂ２Ｏ５は、好ましくは０％～９０％、より好ましくは５％～８５％、さらに好ましくは１０％～８０％である。 The content of Nb 2 O 5 is preferably 0% to 90%, more preferably 7% to 79%, even more preferably 9% to 69%, even more preferably 11% to 59%, particularly preferably 13% to 49%, and most preferably 15% to 39%. The content of SnO+Bi 2 O 3 +TiO 2 +Fe 2 O 3 +Nb 2 O 5 is preferably 0% to 90%, more preferably 5% to 85%, and even more preferably 10% to 80%.
　また、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５は、網目形成酸化物であり、上記負極活物質成分におけるナトリウムイオンの吸蔵及び放出するサイトを取り囲み、サイクル特性をより一層向上させる作用がある。なかでも、ＳｉＯ２及びＰ２Ｏ５は、サイクル特性をより一層向上させるだけでなく、ナトリウムイオン伝導性に優れるため、レート特性をより一層向上させる効果がある。 In addition, SiO2 , B2O3 and P2O5 are network-forming oxides that surround the sites in the negative electrode active material that store and release sodium ions, and thus further improve the cycle characteristics. Among these, SiO2 and P2O5 not only further improve the cycle characteristics, but also have excellent sodium ion conductivity, and therefore have the effect of further improving the rate characteristics.
　ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５は、好ましくは５％～８５％、より好ましくは６％～７９％、さらに好ましくは７％～６９％、さらに好ましくは８％～５９％、特に好ましくは９％～４９％、最も好ましくは１０％～３９％である。ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５が少なすぎると、充放電時のナトリウムイオンの吸蔵及び放出に伴う負極活物質成分の体積変化を緩和できず構造破壊を起こすため、サイクル特性が低下しやすくなる。一方、ＳｉＯ２＋Ｂ２Ｏ３＋Ｐ２Ｏ５が多すぎると、相対的に負極活物質成分の含有量が少なくなり、負極活物質の単位質量当たりの充放電容量が小さくなる傾向がある。 SiO 2 +B 2 O 3 +P 2 O 5 is preferably 5% to 85%, more preferably 6% to 79%, even more preferably 7% to 69%, even more preferably 8% to 59%, particularly preferably 9% to 49%, and most preferably 10% to 39%. If SiO 2 +B 2 O 3 +P 2 O 5 is too small, the volume change of the negative electrode active material component accompanying the absorption and release of sodium ions during charging and discharging cannot be alleviated, causing structural destruction, and the cycle characteristics tend to decrease. On the other hand, if SiO 2 +B 2 O 3 +P 2 O 5 is too large, the content of the negative electrode active material component becomes relatively small, and the charge and discharge capacity per unit mass of the negative electrode active material tends to become small.
　なお、ＳｉＯ２、Ｂ２Ｏ３及びＰ２Ｏ５の各々の含有量の好ましい範囲は以下の通りである。 The preferred ranges of the respective contents of SiO 2 , B 2 O 3 and P 2 O 5 are as follows.
　ＳｉＯ２の含有量は、好ましくは０％～７５％、より好ましくは５％～７５％、さらに好ましくは７％～６０％、さらに好ましくは１０％～５０％、特に好ましくは１２％～４０％、最も好ましくは２０％～３５％である。ＳｉＯ２の含有量が多すぎると、放電容量が低下しやすくなる。 The content of SiO2 is preferably 0% to 75%, more preferably 5% to 75%, even more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of SiO2 is too high, the discharge capacity tends to decrease.
　Ｐ２Ｏ５の含有量は、好ましくは５％～７５％、より好ましくは７％～６０％、さらに好ましくは１０％～５０％、特に好ましくは１２％～４０％、最も好ましくは２０％～３５％である。Ｐ２Ｏ５の含有量が少なすぎると、上記サイクル特性が得られにくくなる。一方、Ｐ２Ｏ５の含有量が多すぎると、放電容量が低下しやすくなるとともに、耐水性が低下しやすくなる。また、水系電極ペーストを作製した際に、望まない異種結晶が生じてＰ２Ｏ５ネットワークが切断されるため、サイクル特性が低下しやすくなる。 The content of P 2 O 5 is preferably 5% to 75%, more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of P 2 O 5 is too low, it is difficult to obtain the above cycle characteristics. On the other hand, if the content of P 2 O 5 is too high, the discharge capacity is likely to decrease and the water resistance is likely to decrease. In addition, when an aqueous electrode paste is produced, unwanted heterogeneous crystals are generated and the P 2 O 5 network is broken, so that the cycle characteristics are likely to decrease.
　Ｂ２Ｏ３の含有量は、好ましくは０％～７５％、より好ましくは５％～７５％、さらに好ましくは７％～６０％、さらに好ましくは１０％～５０％、特に好ましくは１２％～４０％、最も好ましくは２０％～３５％である。Ｂ２Ｏ３の含有量が多すぎると、放電容量が低下しやすくなるとともに、化学的耐久性が低下しやすくなる。 The content of B 2 O 3 is preferably 0% to 75%, more preferably 5% to 75%, even more preferably 7% to 60%, even more preferably 10% to 50%, particularly preferably 12% to 40%, and most preferably 20% to 35%. If the content of B 2 O 3 is too high, the discharge capacity is likely to decrease and the chemical durability is likely to decrease.
　負極活物質前駆体粉末は、焼成により、負極活物質結晶とともに非晶質相が形成される。非晶質相が形成されることにより、電極層３内におけるナトリウムイオン伝導性を向上させることができる。また、集電体２と電極層３との密着性を向上させることができる。 When the negative electrode active material precursor powder is fired, an amorphous phase is formed along with the negative electrode active material crystals. The formation of the amorphous phase can improve the sodium ion conductivity in the electrode layer 3. In addition, the adhesion between the current collector 2 and the electrode layer 3 can be improved.
　負極活物質前駆体粉末の平均粒子径は、好ましくは０．０１μｍ～１５μｍ、より好ましくは０．０５μｍ～１２μｍ、さらに好ましくは０．１μｍ～１０μｍである。負極活物質前駆体粉末の平均粒子径が小さすぎると、負極活物質前駆体粉末同士の凝集力が強くなり、ペースト化した際に分散性に劣る傾向がある。その結果、電池の内部抵抗が高くなり作動電圧が低下しやすくなる。また、電極密度が低下して電池の単位体積あたりの容量が低下する傾向がある。一方、負極活物質前駆体粉末の平均粒子径が大きすぎると、ナトリウムイオンが拡散しにくくなるとともに、内部抵抗が大きくなる傾向がある。また、電極の表面平滑性に劣る傾向がある。 The average particle size of the negative electrode active material precursor powder is preferably 0.01 μm to 15 μm, more preferably 0.05 μm to 12 μm, and even more preferably 0.1 μm to 10 μm. If the average particle size of the negative electrode active material precursor powder is too small, the agglomeration force between the negative electrode active material precursor powders becomes strong, and dispersibility tends to be poor when made into a paste. As a result, the internal resistance of the battery increases and the operating voltage tends to decrease. In addition, the electrode density decreases, and the capacity per unit volume of the battery tends to decrease. On the other hand, if the average particle size of the negative electrode active material precursor powder is too large, sodium ions become difficult to diffuse and the internal resistance tends to increase. In addition, the surface smoothness of the electrode tends to be poor.
　電極活物質前駆体粉末は、原料バッチを溶融、成形することにより作製することが好ましい。当該作製方法によれば、均質性に優れた非晶質の電極活物質前駆体粉末を得やすくなるため好ましい。具体的には、電極活物質前駆体粉末は以下のようにして作製することができる。 The electrode active material precursor powder is preferably prepared by melting and molding a raw material batch. This preparation method is preferable because it makes it easier to obtain an amorphous electrode active material precursor powder with excellent homogeneity. Specifically, the electrode active material precursor powder can be prepared as follows.
　まず、所望の組成となるように原料を調製して原料バッチを得る。次に、得られた原料バッチを溶融する。溶融温度は、原料バッチが均質に溶融されるよう適宜調整すればよい。例えば、溶融温度は８００℃以上であることが好ましく、９００℃以上であることがより好ましい。溶融温度の上限は、特に限定されないが、溶融温度が高すぎるとエネルギーロスや、ナトリウム成分等の蒸発につながることから、１５００℃以下であることが好ましく、１４００℃以下であることがより好ましい。 First, the raw materials are prepared to obtain a raw material batch having the desired composition. The obtained raw material batch is then melted. The melting temperature may be adjusted as appropriate so that the raw material batch is homogeneously melted. For example, the melting temperature is preferably 800°C or higher, and more preferably 900°C or higher. There are no particular limitations on the upper limit of the melting temperature, but since a melting temperature that is too high can lead to energy loss and evaporation of sodium components, etc., it is preferably 1500°C or lower, and more preferably 1400°C or lower.
　次に、得られた溶融物を成形する。成形方法としては、特に限定されず、例えば、溶融物を一対の冷却ロール間に流し込み、急冷しながらフィルム状に成形してもよいし、あるいは、溶融物を鋳型に流し出し、インゴット状に成形してもよい。続いて、得られた成形体を粉砕することにより電極活物質前駆体粉末を得る。 Then, the obtained molten material is molded. There are no particular limitations on the molding method, and for example, the molten material may be poured between a pair of cooling rolls and molded into a film while being rapidly cooled, or the molten material may be poured into a mold and molded into an ingot. The obtained molded body is then pulverized to obtain an electrode active material precursor powder.
　また、電極活物質前駆体粉末は、原料バッチを加圧成形後、焼成することにより作成してもよい。具体的には、以下のようにして作製することができる。 Alternatively, the electrode active material precursor powder may be produced by press-molding the raw material batch and then sintering it. Specifically, it can be produced as follows.
　まず、所望の組成となるように原料を調製して原料バッチを得る。次に、得られた原料バッチを仮焼成して仮焼成原料を得る。仮焼成温度及び仮焼成時間は、原料バッチの脱ガスが適切にできるよう適宜調整すればよい。例えば、仮焼成温度は８００℃以上であることが好ましく、９００℃以上であることがより好ましい。仮焼成温度の上限は、特に限定されないが、仮焼成温度が高すぎるとエネルギーロスや、ナトリウム成分等の蒸発につながることから、１５００℃以下であることが好ましく、１４００℃以下であることがより好ましい。 First, the raw materials are prepared to have the desired composition to obtain a raw material batch. Next, the obtained raw material batch is pre-calcined to obtain a pre-calcined raw material. The pre-calcination temperature and pre-calcination time may be appropriately adjusted so that the raw material batch can be appropriately degassed. For example, the pre-calcination temperature is preferably 800°C or higher, and more preferably 900°C or higher. There are no particular limitations on the upper limit of the pre-calcination temperature, but since a pre-calcination temperature that is too high can lead to energy loss and evaporation of sodium components, etc., it is preferably 1500°C or lower, and more preferably 1400°C or lower.
　次に、得られた仮焼成原料を加圧成形して圧粉体を得る。加圧成形する圧力は、緻密な圧粉体ができるよう適宜調整すればよい。例えば、圧力は２００ｋｇｆ／ｃｍ２以上であることが好ましく、４００ｋｇｆ／ｃｍ２以上であることがより好ましい。 Next, the obtained calcined raw material is pressure-molded to obtain a green compact. The pressure for pressure molding may be appropriately adjusted so as to obtain a dense green compact. For example, the pressure is preferably 200 kgf/ cm2 or more, and more preferably 400 kgf/cm2 or more .
　次に、得られた圧粉体を焼成して焼成体を得る。焼成温度及び焼成時間は、圧粉体が均質に反応されるよう適宜調整すればよい。例えば、焼成温度は８００℃以上であることが好ましく、９００℃以上であることがより好ましい。焼成温度の上限は、特に限定されないが、焼成温度が高すぎるとエネルギーロスや、ナトリウム成分等の蒸発につながることから、１５００℃以下であることが好ましく、１４００℃以下であることがより好ましい。続いて、得られた焼成体を粉砕することにより電極活物質前駆体粉末を得る。 Then, the obtained compact is sintered to obtain a sintered body. The sintering temperature and sintering time may be adjusted as appropriate so that the compact reacts homogeneously. For example, the sintering temperature is preferably 800°C or higher, and more preferably 900°C or higher. There is no particular upper limit to the sintering temperature, but since a sintering temperature that is too high can lead to energy loss and evaporation of sodium components, etc., it is preferably 1500°C or lower, and more preferably 1400°C or lower. Next, the obtained sintered body is pulverized to obtain an electrode active material precursor powder.
　（全固体二次電池）
　図３は、本発明の一実施形態に係る全固体二次電池を示す模式的断面図である。図３に示すように、全固体二次電池３０は、集電体２と、電極層３と、固体電解質層３４と、対極層３５と、第２の集電体３６とを備える。 (All-solid-state secondary battery)
3 is a schematic cross-sectional view showing an all-solid-state secondary battery according to one embodiment of the present invention. As shown in Fig. 3, the all-solid-state secondary battery 30 includes a current collector 2, an electrode layer 3, a solid electrolyte layer 34, a counter electrode layer 35, and a second current collector 36.
　集電体２の両方の主面上に、電極層３が設けられている。また、それぞれの電極層３の集電体２とは反対側の主面上に固体電解質層３４が設けられている。それぞれの固体電解質層３４の電極層３とは反対側の主面上に対極層３５が設けられている。それぞれの対極層３５の固体電解質層３４とは反対側の主面上に第２の集電体３６が設けられている。なお、第２の集電体３６は設けられていなくてもよい。 An electrode layer 3 is provided on both main surfaces of the current collector 2. A solid electrolyte layer 34 is provided on the main surface of each electrode layer 3 opposite the current collector 2. A counter electrode layer 35 is provided on the main surface of each solid electrolyte layer 34 opposite the electrode layer 3. A second current collector 36 is provided on the main surface of each counter electrode layer 35 opposite the solid electrolyte layer 34. The second current collector 36 does not necessarily have to be provided.
　以下、本発明の全固体ナトリウムイオン二次電池における各層の詳細について説明する。 The details of each layer in the all-solid-state sodium-ion secondary battery of the present invention are described below.
　（固体電解質層）
　固体電解質層３４を構成する固体電解質は、ナトリウムイオン伝導性酸化物から形成されていることが好ましい。ナトリウムイオン伝導性酸化物としては、Ａｌ、Ｙ、Ｚｒ、Ｓｉ、及びＰから選ばれる少なくとも１種、Ｎａ、並びにＯを含有する化合物が挙げられる。ナトリウムイオン伝導性酸化物の具体例としては、ナトリウムイオン伝導性に優れるベータアルミナまたはＮＡＳＩＣＯＮ結晶が挙げられる。なかでも、ナトリウムイオン伝導性酸化物は、β’’－アルミナ、β－アルミナ、及びＮＡＳＩＣＯＮ結晶からなる群から選択される少なくとも１種のナトリウムイオン伝導性酸化物であることが好ましい。ナトリウムイオン伝導性酸化物は、β－アルミナ又はβ’’－アルミナであることがより好ましい。これらは、ナトリウムイオン伝導性により一層優れている。 (Solid electrolyte layer)
The solid electrolyte constituting the solid electrolyte layer 34 is preferably formed from a sodium ion conductive oxide. Examples of the sodium ion conductive oxide include compounds containing at least one selected from Al, Y, Zr, Si, and P, Na, and O. Specific examples of the sodium ion conductive oxide include beta-alumina or NASICON crystal, which have excellent sodium ion conductivity. In particular, the sodium ion conductive oxide is preferably at least one sodium ion conductive oxide selected from the group consisting of β''-alumina, β-alumina, and NASICON crystal. The sodium ion conductive oxide is more preferably β-alumina or β''-alumina. These have even better sodium ion conductivity.
　ベータアルミナには、β－アルミナ（理論組成式：Ｎａ２Ｏ・１１Ａｌ２Ｏ３）とβ’’－アルミナ（理論組成式：Ｎａ２Ｏ・５．３Ａｌ２Ｏ３）の２種類の結晶型が存在する。β’’－アルミナは、準安定物質であるため、通常、Ｌｉ２ＯやＭｇＯを安定化剤として添加したものが用いられる。β－アルミナよりもβ’’－アルミナの方がナトリウムイオン伝導度が高いため、β’’－アルミナ単独、またはβ’’－アルミナとβ－アルミナとの混合物を用いることが好ましく、Ｌｉ２Ｏ安定化β’’－アルミナ（Ｎａ１．７Ｌｉ０．３Ａｌ１０．７Ｏ１７）またはＭｇＯ安定化β’’－アルミナ（（Ａｌ１０．３２Ｍｇ０．６８Ｏ１６）（Ｎａ１．６８Ｏ））を用いることがより好ましい。 Beta alumina has two crystal forms, β-alumina (theoretical formula: Na 2 O·11Al 2 O 3 ) and β″-alumina (theoretical formula: Na 2 O·5.3Al 2 O 3 ). β″-alumina is a metastable substance, and is usually used with Li 2 O or MgO added as a stabilizer. Since β″-alumina has a higher sodium ion conductivity than β-alumina, it is preferable to use β″-alumina alone or a mixture of β″-alumina and β-alumina, and it is more preferable to use Li 2 O-stabilized β″-alumina (Na 1.7 Li 0.3 Al 10.7 O 17 ) or MgO-stabilized β″-alumina ((Al 10.32 Mg 0.68 O 16 )(Na 1.68 O)).
　ＮＡＳＩＣＯＮ結晶としては、Ｎａ３Ｚｒ２Ｓｉ２ＰＯ１２、Ｎａ３．２Ｚｒ１．３Ｓｉ２．２Ｐ０．８Ｏ１０．５、Ｎａ３Ｚｒ１．６Ｔｉ０．４Ｓｉ２ＰＯ１２、Ｎａ３Ｈｆ２Ｓｉ２ＰＯ１２、Ｎａ３．４Ｚｒ０．９Ｈｆ１．４Ａｌ０．６Ｓｉ１．２Ｐ１．８Ｏ１２、Ｎａ３Ｚｒ１．７Ｎｂ０．２４Ｓｉ２ＰＯ１２、Ｎａ３．６Ｔｉ０．２Ｙ０．８Ｓｉ２．８Ｏ９、Ｎａ３Ｚｒ１．８８Ｙ０．１２Ｓｉ２ＰＯ１２、Ｎａ３．１２Ｚｒ１．８８Ｙ０．１２Ｓｉ２ＰＯ１２、Ｎａ３．０５Ｚｒ２Ｓｉ２．０６Ｐ０．９５Ｏ１２、Ｎａ３．４Ｚｒ２Ｓｉ２．４Ｐ０．６Ｏ１２、Ｎａ３．４Ｚｒ１．９Ｚｎ０．１Ｓｉ２．４Ｐ０．６Ｏ１２、Ｎａ３．４Ｚｒ１．９Ｍｇ０．１Ｓｉ２．２Ｐ０．８Ｏ１２、Ｎａ２．８Ｚｒ２Ｓｉ２．４Ｐ０．６Ｏ１２、Ｎａ３．６Ｚｒ０．１３Ｙｂ１．６７Ｓｉ０．１１Ｐ２．９Ｏ１２、Ｎａ５ＹＳｉ４Ｏ１２等の結晶が挙げられる。なかでも、ＮＡＳＩＣＯＮ結晶は、Ｎａ３．４Ｚｒ２Ｓｉ２．４Ｐ０．６Ｏ１２又はＮａ３．０５Ｚｒ２Ｓｉ２．０６Ｐ０．９５Ｏ１２であることが好ましい。この場合、ナトリウムイオン伝導性をより一層向上させることができる。 NASICON crystals include Na 3 Zr 2 Si 2 PO 12 , Na 3.2 Zr 1.3 Si 2.2 P 0.8 O 10.5 , Na 3 Zr 1.6 Ti 0.4 Si 2 PO 12 , Na 3 Hf 2 Si 2 PO 12 , Na 3.4 Zr 0.9 Hf 1.4 A 10.6 Si 1.2 P 1.8 O 12 , Na 3 Zr 1.7 Nb 0.24 Si 2 PO 12 , Na 3.6 Ti 0.2 Y 0.8 Si 2.8 O 9 , Na 3 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.12 Zr 1.88 Y 0.12 Si 2 PO 12 , Na 3.05 Zr 2 Si 2.06 P 0.95 O 12 , Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 , Na 3.4 Zr 1.9 Zn 0.1 Si 2.4 P 0.6 O 12 , Na 3.4 Zr 1.9 Mg 0.1 Si 2.2 P 0.8 O 12 , Na 2 .8 Zr 2 Si 2.4 P 0.6 O 12 , Na 3.6 Zr 0.13 Yb 1.67 Si 0.11 P 2.9 O 12 , Na 5 Among them , the NASICON crystal is Na3.4Zr2Si2.4P0.6O12 or Na3.05Zr2Si2.06P0.95O12 . It is preferable that the molecular weight is 12. In this case, the sodium ion conductivity can be further improved.
　固体電解質層３４は、原料粉末を混合し、混合した原料粉末を成形した後、焼成することにより製造することができる。例えば、原料粉末をスラリー化してグリーンシートを作製した後、グリーンシートを焼成することにより製造することができる。また、ゾルゲル法により製造してもよい。 The solid electrolyte layer 34 can be manufactured by mixing raw material powders, molding the mixed raw material powders, and then firing them. For example, it can be manufactured by forming a green sheet by turning the raw material powders into a slurry, and then firing the green sheet. It may also be manufactured by the sol-gel method.
　固体電解質層３４の厚みは、好ましくは１μｍ以上、より好ましくは３μｍ以上、さらに好ましくは５μｍ以上、好ましくは１０００μｍ以下、より好ましくは８００μｍ以下、さらに好ましくは５００μｍ以下である。固体電解質層３４の厚みが薄すぎると、機械的強度が低下して破損しやすくなるため、内部短絡が起こりやすくなる。固体電解質層３４の厚みが厚すぎると、充放電に伴うナトリウムイオン伝導距離が長くなるため内部抵抗が高くなり、放電容量及び作動電圧が低下しやすくなる。また、全固体二次電池３０の単位体積当たりのエネルギー密度も低下しやすくなる。 The thickness of the solid electrolyte layer 34 is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less. If the thickness of the solid electrolyte layer 34 is too thin, the mechanical strength decreases and it becomes more susceptible to breakage, making it more likely for an internal short circuit to occur. If the thickness of the solid electrolyte layer 34 is too thick, the sodium ion conduction distance associated with charging and discharging becomes longer, increasing the internal resistance, and making it more likely for the discharge capacity and operating voltage to decrease. In addition, the energy density per unit volume of the all-solid-state secondary battery 30 also becomes more likely to decrease.
　なお、固体電解質層３４は、緻密層である第１の固体電解質層と、多孔質層である第２の固体電解質層とを備えていてもよい。第１の固体電解質層及び第２の固体電解質層は、固体電解質層３４と同じ材料を用いることができる。 The solid electrolyte layer 34 may include a first solid electrolyte layer that is a dense layer and a second solid electrolyte layer that is a porous layer. The first solid electrolyte layer and the second solid electrolyte layer may be made of the same material as the solid electrolyte layer 34.
　第１の固体電解質層は、固体電解質本来の役割だけでなく、固体電解質層３４の機械的強度を確保するための基材層としての機能も有する。そのため、第１の固体電解質層は、第２の固体電解質層よりも緻密な構造を有している。 The first solid electrolyte layer not only plays the role of a solid electrolyte, but also functions as a base layer to ensure the mechanical strength of the solid electrolyte layer 34. Therefore, the first solid electrolyte layer has a denser structure than the second solid electrolyte layer.
　第１の固体電解質層は、第２の固体電解質層よりも空隙率が小さいことが望ましい。また、第１の固体電解質層は、下記式（１）により定義される空隙率が、好ましくは２０％以下、より好ましくは１０％以下、さらに好ましくは５％以下である。空隙率の下限値は、特に限定されないが、例えば、０．１％とすることができる。 It is desirable that the first solid electrolyte layer has a smaller porosity than the second solid electrolyte layer. In addition, the first solid electrolyte layer has a porosity defined by the following formula (1) of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit of the porosity is not particularly limited, but can be, for example, 0.1%.
　空隙率＝（１－ｐ／ｐ０）×１００（％）…式（１） Porosity = (1-p/p0) x 100 (%)...Formula (1)
　なお、式（１）中、ｐはかさ密度であり、ｐ０は真密度である。 In formula (1), p is the bulk density and p0 is the true density.
　第１の固体電解質層の厚みは、好ましくは０．０１μｍ以上、より好ましくは０．１μｍ以上、さらに好ましくは１μｍ以上、特に好ましくは５μｍ以上、好ましくは３００μｍ以下、より好ましくは２００μｍ以下、さらに好ましくは１５０μｍ以下、特に好ましくは１００μｍ以下である。第１の固体電解質層の厚みが小さすぎると、機械的強度が低下したり、電極層３と対極層３５とが短絡したりするおそれがある。一方、第１の固体電解質層の厚みが大きすぎると、固体電解質層３４のイオン伝導性が低下しやすくなる。また、全固体二次電池３０の単位体積当たりのエネルギー密度が高くなる傾向がある。 The thickness of the first solid electrolyte layer is preferably 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 1 μm or more, particularly preferably 5 μm or more, preferably 300 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, and particularly preferably 100 μm or less. If the thickness of the first solid electrolyte layer is too small, the mechanical strength may decrease, or the electrode layer 3 and the counter electrode layer 35 may be short-circuited. On the other hand, if the thickness of the first solid electrolyte layer is too large, the ionic conductivity of the solid electrolyte layer 34 is likely to decrease. In addition, the energy density per unit volume of the all-solid-state secondary battery 30 tends to be high.
　第２の固体電解質層は、固体電解質と３次元的に連通した空隙を有する多孔質層である。なお、第２の固体電解質層の表面上に、電極層３及び対極層３５が設けられる。この際、第２の固体電解質層は、３次元的に連通した空隙を有するため、電極層３及び対極層３５を構成する材料（活物質粉末等）が空隙に入り込み易くなる。従って、緻密層である第１の固体電解質層上に、多孔質層である第２の固体電解質層を設けることにより、固体電解質層３４と電極層３及び対極層３５との密着性を高めることができる。 The second solid electrolyte layer is a porous layer having voids that are three-dimensionally connected to the solid electrolyte. The electrode layer 3 and the counter electrode layer 35 are provided on the surface of the second solid electrolyte layer. Since the second solid electrolyte layer has voids that are three-dimensionally connected, the materials (active material powder, etc.) that make up the electrode layer 3 and the counter electrode layer 35 can easily enter the voids. Therefore, by providing the second solid electrolyte layer, which is a porous layer, on the first solid electrolyte layer, which is a dense layer, the adhesion between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 can be increased.
　第２の固体電解質層は、上記式（１）により定義される空隙率が、好ましくは２５％以上、より好ましくは３０％以上、さらに好ましくは４０％以上、好ましくは９７％以下、より好ましくは９５％以下、さらに好ましくは９０％以下である。第２の固体電解質層の空隙率が上記範囲内にある場合、３次元的に連通した空隙をより一層容易に形成することができ、固体電解質層３４と電極層３及び対極層３５との密着性をより一層高めることができる。 The second solid electrolyte layer has a porosity defined by the above formula (1) of preferably 25% or more, more preferably 30% or more, even more preferably 40% or more, and preferably 97% or less, more preferably 95% or less, and even more preferably 90% or less. When the porosity of the second solid electrolyte layer is within the above range, three-dimensionally connected voids can be formed more easily, and the adhesion between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 can be further improved.
　第２の固体電解質層の厚みは、好ましくは１μｍ以上、より好ましくは２μｍ以上、さらに好ましくは５μｍ以上、特に好ましくは１０μｍ以上、好ましくは１０００μｍ以下、より好ましくは８００μｍ以下、さらに好ましくは５００μｍ以下、特に好ましくは３００μｍ以下である。 The thickness of the second solid electrolyte layer is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 5 μm or more, particularly preferably 10 μm or more, preferably 1000 μm or less, more preferably 800 μm or less, even more preferably 500 μm or less, particularly preferably 300 μm or less.
　第２の固体電解質層の厚みが小さすぎると、電極層３及び対極層３５を構成する材料が第２の固体電解質層の空隙に入り込む量が少なくなるため、固体電解質層３４と電極層３及び対極層３５との接触面積が小さくなり密着性が低下し易くなる。この場合、固体電解質層３４と電極層３及び対極層３５との界面におけるイオン伝導パスが少なくなるため、全固体二次電池３０の内部抵抗が高くなる傾向にある。結果として、全固体二次電池３０の急速充放電特性が低下し易くなる。 If the thickness of the second solid electrolyte layer is too small, the amount of material constituting the electrode layer 3 and the counter electrode layer 35 that penetrates into the voids in the second solid electrolyte layer is reduced, so that the contact area between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 is reduced, and adhesion is likely to decrease. In this case, the ion conduction paths at the interfaces between the solid electrolyte layer 34 and the electrode layer 3 and the counter electrode layer 35 are reduced, so the internal resistance of the all-solid-state secondary battery 30 tends to increase. As a result, the rapid charge/discharge characteristics of the all-solid-state secondary battery 30 are likely to decrease.
　緻密層である第１の固体電解質層と、多孔質層である第２の固体電解質層とを備える、固体電解質層３４は、例えば、国際公開第２０２１／０４５０３９号に記載の固体電解質シートの製造方法により形成することができる。 The solid electrolyte layer 34, which includes a first solid electrolyte layer that is a dense layer and a second solid electrolyte layer that is a porous layer, can be formed, for example, by the method for manufacturing a solid electrolyte sheet described in WO 2021/045039.
　（対極層）
　対極層３５に含まれる電極活物質は、二次電池用電極１０の電極層３に含まれる電極活物質が正極活物質である場合は、負極活物質であり、二次電池用電極１０の電極層３に含まれる電極活物質が負極活物質である場合は、正極活物質である。 (Counter electrode layer)
The electrode active material contained in the counter electrode layer 35 is a negative electrode active material when the electrode active material contained in the electrode layer 3 of the secondary battery electrode 10 is a positive electrode active material, and is a positive electrode active material when the electrode active material contained in the electrode layer 3 of the secondary battery electrode 10 is a negative electrode active material.
　対極層３５に含まれる負極活物質としては、特に限定されないが、例えば、ハードカーボンやソフトカーボン等の炭素電極材料を用いることができる。炭素電極材料は、ハードカーボンであることが好ましい。もっとも、負極活物質は、スズやビスマス、鉛、リン等のナトリウムを吸蔵できる合金系負極活物質や金属ナトリウムを含んでいてもよい。なお、対極層３５は、金属ナトリウム及び金属ナトリウムを含む負極層ではないことが好ましい。 The negative electrode active material contained in the counter electrode layer 35 is not particularly limited, but may be, for example, a carbon electrode material such as hard carbon or soft carbon. The carbon electrode material is preferably hard carbon. However, the negative electrode active material may contain metallic sodium or an alloy-based negative electrode active material capable of absorbing sodium, such as tin, bismuth, lead, or phosphorus. It is preferable that the counter electrode layer 35 is not metallic sodium or a negative electrode layer containing metallic sodium.
　負極活物質を含む対極層３５は、さらにナトリウムイオン伝導性固体電解質や導電助剤を含んでいてもよい。負極活物質を含む対極層３５における各材料の比率は、例えば、質量％で、負極活物質　６０％～９５％、ナトリウムイオン伝導性固体電解質　５％～３５％、及び導電助剤　０％～５％とすることができる。なお、ナトリウムイオン伝導性固体電解質は、例えば、固体電解質層３４の欄で説明したナトリウムイオン伝導性酸化物を用いることができる。導電助剤は、例えば、電極層３の欄で説明したものを用いることができる。 The counter electrode layer 35 containing the negative electrode active material may further contain a sodium ion conductive solid electrolyte and a conductive assistant. The ratio of each material in the counter electrode layer 35 containing the negative electrode active material may be, for example, in mass %, 60% to 95% negative electrode active material, 5% to 35% sodium ion conductive solid electrolyte, and 0% to 5% conductive assistant. The sodium ion conductive solid electrolyte may be, for example, the sodium ion conductive oxide described in the section on the solid electrolyte layer 34. The conductive assistant may be, for example, one described in the section on the electrode layer 3.
　なお、負極活物質を含む対極層３５の厚みは、０．３μｍ以上であることが好ましく、３μｍ以上であることがより好ましく、１０μｍ以上であることがさらに好ましく、５００μｍ以下であることが好ましく、３００μｍ以下であることがより好ましい。負極活物質を含む対極層３５の厚みが上記下限値以上である場合、全固体二次電池３０の充放電容量をより一層高めることができる。他方、負極活物質を含む対極層３５の厚みが厚すぎると、電子伝導に対する抵抗が大きくなり、全固体二次電池３０の放電容量及び作動電圧が低下することがある。 The thickness of the counter electrode layer 35 containing the negative electrode active material is preferably 0.3 μm or more, more preferably 3 μm or more, even more preferably 10 μm or more, and preferably 500 μm or less, and more preferably 300 μm or less. When the thickness of the counter electrode layer 35 containing the negative electrode active material is equal to or greater than the above lower limit, the charge/discharge capacity of the all-solid-state secondary battery 30 can be further increased. On the other hand, if the thickness of the counter electrode layer 35 containing the negative electrode active material is too thick, the resistance to electronic conduction increases, and the discharge capacity and operating voltage of the all-solid-state secondary battery 30 may decrease.
　対極層３５に含まれる正極活物質としては、特に限定されないが、一般式ＮａｘＭｙＰ２Ｏｚ（１≦ｘ≦２．８、０．９５≦ｙ≦１．６、６．５≦ｚ≦８、ＭはＦｅ、Ｎｉ、Ｃｏ、Ｍｎ、及びＣｒからなる群から選択される少なくとも１種）で表される結晶を含む結晶化ガラスからなる正極活物質であることが好ましい。なかでも、一般式ＮａｘＭＰ２Ｏ７（１≦ｘ≦２、ＭはＦｅ、Ｎｉ、Ｃｏ、Ｍｎ、及びＣｒからなる群から選択される少なくとも１種）で表される結晶を含む結晶化ガラスからなる正極活物質であることがより好ましい。このような正極活物質結晶としては、例えば、Ｎａ２ＦｅＰ２Ｏ７、Ｎａ２ＣｏＰ２Ｏ７、Ｎａ２ＮｉＰ２Ｏ７等を用いることができる。 The positive electrode active material contained in the counter electrode layer 35 is not particularly limited, but is preferably a positive electrode active material made of crystallized glass containing crystals represented by the general formula Na x M y P 2 O z (1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). In particular, it is more preferable that the positive electrode active material is made of crystallized glass containing crystals represented by the general formula Na x MP 2 O 7 (1≦x≦2, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr). As such a positive electrode active material crystal, for example, Na 2 FeP 2 O 7 , Na 2 CoP 2 O 7 , Na 2 NiP 2 O 7, etc. can be used.
　また、正極活物質を含む対極層３５は、固体電解質や、導電助剤を含んでいてもよい。正極活物質を含む対極層３５における各材料の比率は、例えば、質量％で、正極活物質　３０％～９５％、固体電解質　５％～７０％、及び導電助剤　０％～２０％とすることができる。 The counter electrode layer 35 containing the positive electrode active material may also contain a solid electrolyte and a conductive additive. The ratio of each material in the counter electrode layer 35 containing the positive electrode active material can be, for example, in mass %, 30% to 95% positive electrode active material, 5% to 70% solid electrolyte, and 0% to 20% conductive additive.
　なお、固体電解質としては、固体電解質層３４の欄で説明したものを用いることができる。導電助剤としては、例えば、導電性炭素を用いることができる。導電性炭素としては、例えば、アセチレンブラック、カーボンブラック、ケッチェンブラック、気相法炭素繊維炭素導電助剤（ＶＧＣＦ）等を挙げることができる。導電助剤は、上記のような材料からなる、炭素系導電助剤であることが好ましい。 As the solid electrolyte, the one described in the section on solid electrolyte layer 34 can be used. As the conductive additive, for example, conductive carbon can be used. Examples of conductive carbon include acetylene black, carbon black, ketjen black, vapor grown carbon fiber carbon conductive additive (VGCF), etc. It is preferable that the conductive additive is a carbon-based conductive additive made of the above-mentioned materials.
　なお、正極活物質を含む対極層３５の厚みは、１０μｍ以上であることが好ましく、５０μｍ以上であることがより好ましく、１００μｍ以上であることがさらに好ましく、１０００μｍ以下であることが好ましく、７００μｍ以下であることがより好ましい。正極活物質を含む対極層３５の厚みが上記下限値以上である場合、全固体二次電池３０の充放電容量をより一層高めることができる。なお、正極活物質を含む対極層３５の厚みが厚すぎると、電子伝導に対する抵抗が大きくなり、全固体二次電池３０の放電容量及び作動電圧が低下することがあるほか、焼成時の収縮による応力が大きくなり剥離につながることがある。 The thickness of the counter electrode layer 35 containing the positive electrode active material is preferably 10 μm or more, more preferably 50 μm or more, even more preferably 100 μm or more, and preferably 1000 μm or less, and more preferably 700 μm or less. When the thickness of the counter electrode layer 35 containing the positive electrode active material is equal to or greater than the above lower limit, the charge/discharge capacity of the all-solid-state secondary battery 30 can be further increased. When the counter electrode layer 35 containing the positive electrode active material is too thick, the resistance to electronic conduction increases, which may reduce the discharge capacity and operating voltage of the all-solid-state secondary battery 30, and the stress due to shrinkage during firing may increase, leading to peeling.
　（第２の集電体）
　第２の集電体３６の材料としては、特に限定されないが、それぞれ、アルミニウム、チタン、銀、銅、ステンレス鋼又はこれらの合金などの金属材料を用いることができる。上記金属材料は、単独で用いてもよく、複数を併用してもよい。なお、これらの合金とは、少なくとも１種の上記金属を含む合金である。第２の集電体３６の厚みは、特に限定されないが、それぞれ、０．０１μｍ以上、１０００μｍ以下とすることができる。 (Second Current Collector)
The material of the second current collector 36 is not particularly limited, but may be a metal material such as aluminum, titanium, silver, copper, stainless steel, or an alloy thereof. The above metal materials may be used alone or in combination. These alloys are alloys containing at least one of the above metals. The thickness of the second current collector 36 is not particularly limited, but may be 0.01 μm or more and 1000 μm or less.
　第２の集電体３６の形成方法としては、特に限定されず、例えば、蒸着又はスパッタリング等の物理的気相法や、熱ＣＶＤ法、ＭＯＣＶＤ法、プラズマＣＶＤ法等の化学的気相法が挙げられる。第２の集電体３６のその他の形成方法としては、メッキ、ゾルゲル法、スピンコートによる液相成膜法が挙げられる。もっとも、第２の集電体３６は、それぞれ、対極層３５上にスパッタリング法により形成することが、密着性に優れるため好ましい。 The method for forming the second current collector 36 is not particularly limited, and examples of the method include physical vapor phase methods such as vapor deposition or sputtering, and chemical vapor phase methods such as thermal CVD, MOCVD, and plasma CVD. Other methods for forming the second current collector 36 include plating, the sol-gel method, and liquid phase film formation methods using spin coating. However, it is preferable to form the second current collector 36 on the counter electrode layer 35 by sputtering, as this provides excellent adhesion.
　以下、本発明について、具体的な実施例に基づいて、さらに詳細に説明するが、本発明は以下の実施例に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能である。 The present invention will be described in more detail below based on specific examples, but the present invention is not limited to the following examples and can be modified as appropriate within the scope of the gist of the invention.
　（実施例１～４）
　（ａ）正極活物質前駆体粉末の作製
　炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、酸化第二鉄（Ｆｅ２Ｏ３ ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表１に記載の組成となるように原料粉末を調合し、１２００～１５００℃にて９０分間、大気雰囲気中にて溶融を行った。その後、溶融物を一対の回転ローラー間に流し出し、急冷しながら成形し、厚み０．１ｍｍ～２ｍｍのフィルム状のガラスを得た。得られたフィルム状のガラスに対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．５μｍであるガラス粉末（正極活物質前駆体粉末）を得た。 (Examples 1 to 4)
(a) Preparation of Positive Electrode Active Material Precursor Powder Sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), ferric oxide (Fe 2 O 3 ), and orthophosphoric acid (H 3 PO 4 ) were used as raw materials, and raw material powders were prepared to have the compositions shown in Table 1, and melted in an air atmosphere at 1200 to 1500° C. for 90 minutes. The melt was then poured between a pair of rotating rollers and shaped while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized in a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.5 μm.
　（ｂ）正極ペーストの作製
　得られた正極活物質前駆体粉末と、導電性炭素（導電助剤）としてのアセチレンブラック（ＴＩＭＣＡＬ社製、ＳＵＰＥＲＣ６５）を表１に記載の組成となるようにそれぞれ秤量し、ビーズミルを用いて混合し、正極合材粉末を作製した。作製した正極合材粉末１００質量部に、ポリプロピレンカーボネート（ＰＰＣ）を１５質量部添加し、さらにＮ－メチルピロリドンを３０質量部添加した。これらを自転・公転ミキサーを用いて十分に撹拌し、スラリー化して正極ペーストを作製した。 (b) Preparation of Positive Electrode Paste The obtained positive electrode active material precursor powder and acetylene black (SUPERC65, manufactured by TIMCAL) as conductive carbon (conductive assistant) were weighed to have the composition shown in Table 1, and mixed using a bead mill to prepare a positive electrode composite powder. 15 parts by mass of polypropylene carbonate (PPC) was added to 100 parts by mass of the prepared positive electrode composite powder, and 30 parts by mass of N-methylpyrrolidone was further added. These were thoroughly stirred using a rotation/revolution mixer and slurried to prepare a positive electrode paste.
　（ｃ）正極層（電極層）の形成
　集電体である厚さ２０μｍのアルミニウム箔の一方側の主面上に、厚さ８０μｍで、正極ペーストを塗布し、７０℃で３時間乾燥させ、正極材料層を形成した。集電体の主面上に形成した正極材料層を、電極打ち抜き機で直径１１ｍｍに打ち抜き、表１に記載の条件で３０分間焼成することにより、集電体の一方側の主面上に、正極層（電極層）を形成し、二次電池用電極を得た。 (c) Formation of Positive Electrode Layer (Electrode Layer) The positive electrode paste was applied to a thickness of 80 μm on one main surface of a 20 μm thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer. The positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 1 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
　（ｄ）粉末Ｘ線回折測定
　得られた二次電池用電極の粉末Ｘ線回折測定を行った。Ｘ線源としては、ＣｕＫα線（波長１．５４１Å）を用いた。また、Ｘ線回折装置としては、リガク社製、品番「ＳｍａｒｔＬａｂ」を用いた。粉末Ｘ線回折測定に対しＲｉｅｔｖｅｌｄ解析を行うことにより結晶構造の同定と非晶質相の含有量を評価した。結果を表１に示す。 (d) Powder X-ray diffraction measurement Powder X-ray diffraction measurement of the obtained secondary battery electrode was performed. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. In addition, the X-ray diffraction device used was a Rigaku Corporation, product number "SmartLab". The crystal structure was identified and the content of the amorphous phase was evaluated by performing Rietveld analysis on the powder X-ray diffraction measurement. The results are shown in Table 1.
　（ｅ）試験電池組み立て
　得られた二次電池用電極を、アルミニウム箔面を下に向けてコインセルの下蓋の上に載置し、その上に７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜からなるセパレータ、対極である金属ナトリウム、さらにコインセルの上蓋をこの順に積層し、試験電池を作製した。電解液としては、１Ｍ　ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度－７０℃以下の環境で行った。 (e) Test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery. As the electrolyte, 1M NaPF 6 solution/EC:DEC=1:1 (EC=ethylene carbonate, DEC=diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of -70°C or lower.
　（ｆ）電池特性の評価
　得られた試験電池について、８０℃で開回路電圧から４．５ＶまでＣＣ（定電流）充電を行い、単位質量当たりの正極合材へ充電された電気量（初回充電容量）を求めた。次に、４．５Ｖから２ＶまでＣＣ放電を行い、単位質量当たりの電極層から放電された電気量（初回放電容量）を求めた。また、初回放電時の作動電圧と放電容量から電極層のエネルギー密度を求めた。「容量維持率」は初回放電容量に対する５０サイクル目の放電容量の割合で評価した。なお、Ｃレートは０．２Ｃとした。結果を表１に示す。 (f) Evaluation of Battery Characteristics The obtained test battery was CC (constant current) charged from the open circuit voltage to 4.5 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained. Next, CC discharge was performed from 4.5 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained. In addition, the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge. The "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity. The C rate was set to 0.2 C. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　（実施例５～８）
　（ａ）正極活物質前駆体粉末の作製
　炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、二酸化マンガン（ＭｎＯ２ ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表２に記載の組成となるように原料粉末を調合し、１２００～１５００℃にて９０分間、大気雰囲気中にて溶融を行った。その後、溶融物を一対の回転ローラー間に流し出し、急冷しながら成形し、厚み０．１ｍｍ～２ｍｍのフィルム状のガラスを得た。得られたフィルム状のガラスに対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．３μｍであるガラス粉末（正極活物質前駆体粉末）を得た。 (Examples 5 to 8)
(a) Preparation of Positive Electrode Active Material Precursor Powder Sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), manganese dioxide (MnO 2 ), and orthophosphoric acid (H 3 PO 4 ) were used as raw materials, and raw material powders were prepared to have the compositions shown in Table 2, and melted in an air atmosphere at 1200 to 1500°C for 90 minutes. The melt was then poured between a pair of rotating rollers and shaped while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized in a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.3 μm.
　（ｂ）正極ペーストの作製
　得られた正極活物質前駆体粉末と、導電性炭素（導電助剤）としてのカーボンナノチューブ（Ｃ－ｎａｎｏ社製、品番「ＬＢ１１６」、ＢＥＴ比表面積：３００ｍ２／ｇ、径：１０ｎｍ、長さ：２０μｍ）を表２に記載の組成となるようにそれぞれ秤量し、ビーズミルを用いて混合し、正極合材粉末を作製した。作製した正極合材粉末１００質量部に、ポリプロピレンカーボネート（ＰＰＣ）を１５質量部添加し、さらにＮ－メチルピロリドンを３０質量部添加した。これらを自転・公転ミキサーを用いて十分に撹拌し、スラリー化して正極ペーストを作製した。 (b) Preparation of Positive Electrode Paste The obtained positive electrode active material precursor powder and carbon nanotubes (manufactured by C-nano, product number "LB116", BET specific surface area: 300 m 2 /g, diameter: 10 nm, length: 20 μm) as conductive carbon (conductive assistant) were weighed to obtain the composition shown in Table 2, and mixed using a bead mill to prepare a positive electrode composite powder. 15 parts by mass of polypropylene carbonate (PPC) was added to 100 parts by mass of the prepared positive electrode composite powder, and 30 parts by mass of N-methylpyrrolidone was further added. These were thoroughly stirred using a rotation/revolution mixer and slurried to prepare a positive electrode paste.
　（ｃ）正極層（電極層）の形成
　集電体である厚さ２０μｍのアルミニウム箔の一方側の主面上に、厚さ８０μｍで、正極ペーストを塗布し、７０℃で３時間乾燥させ、正極材料層を形成した。集電体の主面上に形成した正極材料層を、電極打ち抜き機で直径１１ｍｍに打ち抜き、表２に記載の条件で３０分間焼成することにより、集電体の一方側の主面上に、正極層（電極層）を形成し、二次電池用電極を得た。 (c) Formation of Positive Electrode Layer (Electrode Layer) The positive electrode paste was applied to a thickness of 80 μm on one main surface of a 20 μm thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer. The positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 2 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
　（ｄ）粉末Ｘ線回折測定
　得られた二次電池用電極の粉末Ｘ線回折測定を行った。Ｘ線源としては、ＣｕＫα線（波長１．５４１Å）を用いた。また、Ｘ線回折装置としては、リガク社製、品番「ＳｍａｒｔＬａｂ」を用いた。粉末Ｘ線回折測定に対しＲｉｅｔｖｅｌｄ解析を行うことにより結晶構造の同定と非晶質相の含有量を評価した。結果を表２に示す。 (d) Powder X-ray diffraction measurement Powder X-ray diffraction measurement of the obtained secondary battery electrode was performed. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. In addition, the X-ray diffraction device used was a Rigaku Corporation, product number "SmartLab". The crystal structure was identified and the content of the amorphous phase was evaluated by performing Rietveld analysis on the powder X-ray diffraction measurement. The results are shown in Table 2.
　（ｅ）試験電池組み立て
　得られた二次電池用電極を、アルミニウム箔面を下に向けてコインセルの下蓋の上に載置し、その上に７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜からなるセパレータ、対極である金属ナトリウム、さらにコインセルの上蓋をこの順に積層し、試験電池を作製した。電解液としては、１Ｍ　ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度－７０℃以下の環境で行った。 (e) Test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery. As the electrolyte, 1M NaPF 6 solution/EC:DEC=1:1 (EC=ethylene carbonate, DEC=diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of -70°C or lower.
　（ｆ）電池特性の評価
　得られた試験電池について、８０℃で開回路電圧から４．５ＶまでＣＣ（定電流）充電を行い、単位質量当たりの正極合材へ充電された電気量（初回充電容量）を求めた。次に、４．５Ｖから２ＶまでＣＣ放電を行い、単位質量当たりの電極層から放電された電気量（初回放電容量）を求めた。また、初回放電時の作動電圧と放電容量から電極層のエネルギー密度を求めた。「容量維持率」は初回放電容量に対する５０サイクル目の放電容量の割合で評価した。なお、Ｃレートは０．２Ｃとした。結果を表２に示す。 (f) Evaluation of battery characteristics The obtained test battery was CC (constant current) charged from the open circuit voltage to 4.5 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained. Next, CC discharge was performed from 4.5 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained. In addition, the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge. The "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity. The C rate was set to 0.2 C. The results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　（実施例９～１３）
　（ａ）正極活物質前駆体粉末の作製
　炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、酸化ニッケル（ＮｉＯ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表３に記載の組成となるように原料粉末を調合し、１２００～１５００℃にて９０分間、大気雰囲気中にて溶融を行った。その後、溶融物を一対の回転ローラー間に流し出し、急冷しながら成形し、厚み０．１ｍｍ～２ｍｍのフィルム状のガラスを得た。得られたフィルム状のガラスに対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．５μｍであるガラス粉末（正極活物質前駆体粉末）を得た。 (Examples 9 to 13)
(a) Preparation of Positive Electrode Active Material Precursor Powder Sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), nickel oxide (NiO), and orthophosphoric acid (H 3 PO 4 ) were used as raw materials, and raw material powders were prepared to have the compositions shown in Table 3, and melted in an air atmosphere at 1200 to 1500°C for 90 minutes. The melt was then poured between a pair of rotating rollers and shaped while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized using a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.5 μm.
　（ｂ）正極ペーストの作製
　得られた正極活物質前駆体粉末と、導電性炭素（導電助剤）としてのアセチレンブラック（ＴＩＭＣＡＬ社製、ＳＵＰＥＲＣ６５）を表３に記載の組成となるようにそれぞれ秤量し、ビーズミルを用いて混合し、正極合材粉末を作製した。作製した正極合材粉末１００質量部に、ポリプロピレンカーボネート（ＰＰＣ）を１０質量部添加し、さらにＮ－メチルピロリドンを３０質量部添加した。これらを自転・公転ミキサーを用いて十分に撹拌し、スラリー化して正極ペーストを作製した。 (b) Preparation of Positive Electrode Paste The obtained positive electrode active material precursor powder and acetylene black (SUPERC65, manufactured by TIMCAL) as conductive carbon (conductive assistant) were weighed to have the composition shown in Table 3, and mixed using a bead mill to prepare a positive electrode composite powder. 10 parts by mass of polypropylene carbonate (PPC) was added to 100 parts by mass of the prepared positive electrode composite powder, and 30 parts by mass of N-methylpyrrolidone was further added. These were thoroughly stirred using a rotation/revolution mixer and slurried to prepare a positive electrode paste.
　（ｃ）正極層（電極層）の形成
　集電体である厚さ２０μｍのアルミニウム箔の一方側の主面上に、厚さ８０μｍで、正極ペーストを塗布し、７０℃で３時間乾燥させ、正極材料層を形成した。集電体の主面上に形成した正極材料層を、電極打ち抜き機で直径１１ｍｍに打ち抜き、表３に記載の条件で３０分間焼成することにより、集電体の一方側の主面上に、正極層（電極層）を形成し、二次電池用電極を得た。 (c) Formation of Positive Electrode Layer (Electrode Layer) The positive electrode paste was applied to a thickness of 80 μm on one main surface of a 20 μm thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer. The positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 3 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
　（ｄ）粉末Ｘ線回折測定
　得られた二次電池用電極の粉末Ｘ線回折測定を行った。Ｘ線源としては、ＣｕＫα線（波長１．５４１Å）を用いた。また、Ｘ線回折装置としては、リガク社製、品番「ＳｍａｒｔＬａｂ」を用いた。粉末Ｘ線回折測定に対しＲｉｅｔｖｅｌｄ解析を行うことにより結晶構造の同定と非晶質相の含有量を評価した。結果を表３に示す。 (d) Powder X-ray diffraction measurement Powder X-ray diffraction measurement of the obtained secondary battery electrode was performed. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. In addition, the X-ray diffraction device used was a Rigaku Corporation, product number "SmartLab". The crystal structure was identified and the content of the amorphous phase was evaluated by performing Rietveld analysis on the powder X-ray diffraction measurement. The results are shown in Table 3.
　（ｅ）試験電池組み立て
　得られた二次電池用電極を、アルミニウム箔面を下に向けてコインセルの下蓋の上に載置し、その上に７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜からなるセパレータ、対極である金属ナトリウム、さらにコインセルの上蓋をこの順に積層し、試験電池を作製した。電解液としては、１Ｍ　ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度－７０℃以下の環境で行った。 (e) Test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery. As the electrolyte, 1M NaPF 6 solution/EC:DEC=1:1 (EC=ethylene carbonate, DEC=diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of -70°C or lower.
　（ｆ）電池特性の評価
　得られた試験電池について、８０℃で開回路電圧から５．２ＶまでＣＣ（定電流）充電を行い、単位質量当たりの正極合材へ充電された電気量（初回充電容量）を求めた。次に、５．２Ｖから２ＶまでＣＣ放電を行い、単位質量当たりの電極層から放電された電気量（初回放電容量）を求めた。また、初回放電時の作動電圧と放電容量から電極層のエネルギー密度を求めた。「容量維持率」は初回放電容量に対する５０サイクル目の放電容量の割合で評価した。なお、Ｃレートは０．２Ｃとした。結果を表３に示す。 (f) Evaluation of Battery Characteristics The obtained test battery was subjected to CC (constant current) charging from the open circuit voltage to 5.2 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained. Next, CC discharge was performed from 5.2 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained. In addition, the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge. The "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity. The C rate was set to 0.2 C. The results are shown in Table 3.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　（実施例１４～１６）
　（ａ）正極活物質前駆体粉末の作製
　炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、酸化ニッケル（ＮｉＯ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表４に記載の組成となるように原料粉末を調合し、電気炉中にて１１００℃で６時間仮焼成することで脱ガスした。その後、仮焼成した原料バッチを５００ｋｇｆ／ｃｍ２で加圧成形して、大気雰囲気中、９００℃で１２時間焼成し、焼結体を得た。得られた焼結体に対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．５μｍである固相反応粉末（正極活物質前駆体粉末）を得た。 (Examples 14 to 16)
(a) Preparation of Positive Electrode Active Material Precursor Powder Sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), nickel oxide (NiO) and orthophosphoric acid (H 3 PO 4 ) were used as raw materials, and raw material powders were prepared to have the composition shown in Table 4, and degassed by pre-firing at 1100°C for 6 hours in an electric furnace. The pre-firing raw material batch was then pressurized at 500 kgf/cm 2 and fired at 900°C for 12 hours in an air atmosphere to obtain a sintered body. The obtained sintered body was pulverized in a ball mill and a planetary ball mill to obtain a solid-phase reaction powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.5 μm.
　また、炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、酸化ニッケル（ＮｉＯ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表４に記載の組成となるように原料粉末を調合し、１２００～１５００℃にて９０分間、大気雰囲気中にて溶融を行った。その後、溶融物を一対の回転ローラー間に流し出し、急冷しながら成形し、厚み０．１ｍｍ～２ｍｍのフィルム状のガラスを得た。得られたフィルム状のガラスに対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．５μｍであるガラス粉末（正極活物質前駆体粉末）を得た。 In addition, raw material powders were prepared using sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), nickel oxide (NiO), and orthophosphoric acid (H 3 PO 4 ) as raw materials to obtain the compositions shown in Table 4, and melted in an air atmosphere at 1200 to 1500° C. for 90 minutes. The melt was then poured between a pair of rotating rollers and shaped while being quenched to obtain a film-like glass having a thickness of 0.1 mm to 2 mm. The obtained film-like glass was pulverized using a ball mill and a planetary ball mill to obtain a glass powder (positive electrode active material precursor powder) having an average particle size (D 50 ) of 0.5 μm.
　（ｂ）正極ペーストの作製
　得られた正極活物質前駆体粉末（固相反応粉末とガラス粉末）と、導電性炭素（導電助剤）としてのアセチレンブラック（ＴＩＭＣＡＬ社製、ＳＵＰＥＲＣ６５）を表４に記載の組成となるようにそれぞれ秤量し、ビーズミルを用いて混合し、正極合材粉末を作製した。作製した正極合材粉末１００質量部に、ポリプロピレンカーボネート（ＰＰＣ）を１５質量部添加し、さらにＮ－メチルピロリドンを３０質量部添加した。これらを自転・公転ミキサーを用いて十分に撹拌し、スラリー化して正極ペーストを作製した。 (b) Preparation of Positive Electrode Paste The obtained positive electrode active material precursor powder (solid-phase reaction powder and glass powder) and acetylene black (SUPERC65, manufactured by TIMCAL) as conductive carbon (conductive assistant) were weighed to have the composition shown in Table 4, and mixed using a bead mill to prepare a positive electrode composite powder. 15 parts by mass of polypropylene carbonate (PPC) was added to 100 parts by mass of the prepared positive electrode composite powder, and 30 parts by mass of N-methylpyrrolidone was further added. These were thoroughly stirred using a rotation/revolution mixer and slurried to prepare a positive electrode paste.
　（ｃ）正極層（電極層）の形成
　集電体である厚さ２０μｍのアルミニウム箔の一方側の主面上に、厚さ８０μｍで、正極ペーストを塗布し、７０℃で３時間乾燥させ、正極材料層を形成した。集電体の主面上に形成した正極材料層を、電極打ち抜き機で直径１１ｍｍに打ち抜き、表４に記載の条件で３０分間焼成することにより、集電体の一方側の主面上に、正極層（電極層）を形成し、二次電池用電極を得た。 (c) Formation of Positive Electrode Layer (Electrode Layer) The positive electrode paste was applied to a thickness of 80 μm on one main surface of a 20 μm thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode material layer. The positive electrode material layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and fired for 30 minutes under the conditions shown in Table 4 to form a positive electrode layer (electrode layer) on one main surface of the current collector, thereby obtaining an electrode for a secondary battery.
　（ｄ）粉末Ｘ線回折測定
　得られた二次電池用電極の粉末Ｘ線回折測定を行った。Ｘ線源としては、ＣｕＫα線（波長１．５４１Å）を用いた。また、Ｘ線回折装置としては、リガク社製、品番「ＳｍａｒｔＬａｂ」を用いた。粉末Ｘ線回折測定に対しＲｉｅｔｖｅｌｄ解析を行うことにより結晶構造の同定と非晶質相の含有量を評価した。結果を表４に示す。 (d) Powder X-ray diffraction measurement Powder X-ray diffraction measurement of the obtained secondary battery electrode was performed. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. In addition, the X-ray diffraction device used was a Rigaku Corporation, product number "SmartLab". The crystal structure was identified and the content of the amorphous phase was evaluated by performing Rietveld analysis on the powder X-ray diffraction measurement. The results are shown in Table 4.
　（ｅ）試験電池組み立て
　得られた二次電池用電極を、アルミニウム箔面を下に向けてコインセルの下蓋の上に載置し、その上に７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜からなるセパレータ、対極である金属ナトリウム、さらにコインセルの上蓋をこの順に積層し、試験電池を作製した。電解液としては、１Ｍ　ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度－７０℃以下の環境で行った。 (e) Test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery. As the electrolyte, 1M NaPF 6 solution/EC:DEC=1:1 (EC=ethylene carbonate, DEC=diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of -70°C or lower.
　（ｆ）電池特性の評価
　得られた試験電池について、８０℃で開回路電圧から５．２ＶまでＣＣ（定電流）充電を行い、単位質量当たりの正極合材へ充電された電気量（初回充電容量）を求めた。次に、５．２Ｖから２ＶまでＣＣ放電を行い、単位質量当たりの電極層から放電された電気量（初回放電容量）を求めた。また、初回放電時の作動電圧と放電容量から電極層のエネルギー密度を求めた。「容量維持率」は初回放電容量に対する５０サイクル目の放電容量の割合で評価した。なお、Ｃレートは０．２Ｃとした。結果を表４に示す。 (f) Evaluation of Battery Characteristics The obtained test battery was CC (constant current) charged from the open circuit voltage to 5.2 V at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained. Next, CC discharge was performed from 5.2 V to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained. In addition, the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge. The "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity. The C rate was set to 0.2 C. The results are shown in Table 4.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　（比較例１～３）
　（ａ）正極活物質前駆体粉末の作製
　炭酸ナトリウム（Ｎａ２ ＣＯ３ ）、メタリン酸ナトリウム（ＮａＰＯ３ ）、酸化第二鉄（Ｆｅ２Ｏ３ ）、二酸化マンガン（ＭｎＯ２ ）、酸化ニッケル（ＮｉＯ）及びオルソリン酸（Ｈ３ ＰＯ４ ）を原料とし、表５に記載の組成となるように原料粉末を調合し、電気炉中にて１１００℃で６時間仮焼成することで脱ガスした。その後、仮焼成した原料バッチを５００ｋｇｆ／ｃｍ２で加圧成形して、比較例１については、窒素・水素混合雰囲気中、比較例２、３については、窒素雰囲気中、９００℃で１２時間焼成し、焼結体を得た。得られた焼結体に対し、ボールミル及び遊星ボールミルでの粉砕を行うことにより、平均粒子径（Ｄ５０）が０．５μｍである正極活物質前駆体粉末を得た。 (Comparative Examples 1 to 3)
(a) Preparation of Positive Electrode Active Material Precursor Powder Sodium carbonate (Na 2 CO 3 ), sodium metaphosphate (NaPO 3 ), ferric oxide (Fe 2 O 3 ), manganese dioxide (MnO 2 ), nickel oxide (NiO) and orthophosphoric acid (H 3 PO 4 ) were used as raw materials, and raw material powders were prepared to have the compositions shown in Table 5, and degassed by pre-firing at 1100°C for 6 hours in an electric furnace. Thereafter, the pre-firing raw material batch was pressurized at 500 kgf/cm 2 , and fired at 900°C for 12 hours in a nitrogen/hydrogen mixed atmosphere for Comparative Example 1 and in a nitrogen atmosphere for Comparative Examples 2 and 3 to obtain a sintered body. The obtained sintered body was pulverized in a ball mill and a planetary ball mill to obtain a positive electrode active material precursor powder having an average particle size (D 50 ) of 0.5 μm.
　（ｂ）正極ペーストの作製
　得られた正極活物質前駆体粉末（固相反応粉末とガラス粉末）と、導電性炭素（導電助剤）としてのアセチレンブラック（ＴＩＭＣＡＬ社製、ＳＵＰＥＲＣ６５）と、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）を表５に記載の組成となるようにそれぞれ秤量し、ビーズミルを用いて混合し、正極合材粉末を作製した。作製した正極合材粉末１００質量部に、さらにＮ－メチルピロリドンを３０質量部添加した。これらを自転・公転ミキサーを用いて十分に撹拌し、スラリー化して正極ペーストを作製した。 (b) Preparation of Positive Electrode Paste The obtained positive electrode active material precursor powder (solid-phase reaction powder and glass powder), acetylene black (SUPERC65, manufactured by TIMCAL) as conductive carbon (conductive assistant), and polyvinylidene fluoride (PVDF) as a binder were weighed to have the composition shown in Table 5, and mixed using a bead mill to prepare a positive electrode composite powder. 30 parts by mass of N-methylpyrrolidone was further added to 100 parts by mass of the prepared positive electrode composite powder. These were thoroughly stirred using a rotation/revolution mixer and slurried to prepare a positive electrode paste.
　（ｃ）正極層（電極層）の形成
　集電体である厚さ２０μｍのアルミニウム箔の一方側の主面上に、厚さ８０μｍで、正極ペーストを塗布し、７０℃で３時間乾燥させ、正極層を形成した。集電体の主面上に形成した正極層を、電極打ち抜き機で直径１１ｍｍに打ち抜き、集電体の一方側の主面上に、正極層（電極層）を形成し、二次電池用電極を得た。 (c) Formation of Positive Electrode Layer (Electrode Layer) The positive electrode paste was applied to a thickness of 80 μm on one main surface of a 20 μm thick aluminum foil current collector, and dried at 70° C. for 3 hours to form a positive electrode layer. The positive electrode layer formed on the main surface of the current collector was punched out to a diameter of 11 mm using an electrode punching machine, and a positive electrode layer (electrode layer) was formed on one main surface of the current collector to obtain an electrode for a secondary battery.
　（ｄ）粉末Ｘ線回折測定
　得られた二次電池用電極の粉末Ｘ線回折測定を行った。Ｘ線源としては、ＣｕＫα線（波長１．５４１Å）を用いた。また、Ｘ線回折装置としては、リガク社製、品番「ＳｍａｒｔＬａｂ」を用いた。粉末Ｘ線回折測定に対しＲｉｅｔｖｅｌｄ解析を行うことにより結晶構造の同定と非晶質相の含有量を評価した。結果を表５に示す。 (d) Powder X-ray diffraction measurement Powder X-ray diffraction measurement of the obtained secondary battery electrode was performed. CuKα rays (wavelength 1.541 Å) were used as the X-ray source. In addition, the X-ray diffraction device used was a Rigaku Corporation, product number "SmartLab". The crystal structure was identified and the content of the amorphous phase was evaluated by performing Rietveld analysis on the powder X-ray diffraction measurement. The results are shown in Table 5.
　（ｅ）試験電池組み立て
　得られた二次電池用電極を、アルミニウム箔面を下に向けてコインセルの下蓋の上に載置し、その上に７０℃で８時間減圧乾燥した直径１６ｍｍのポリプロピレン多孔質膜からなるセパレータ、対極である金属ナトリウム、さらにコインセルの上蓋をこの順に積層し、試験電池を作製した。電解液としては、１Ｍ　ＮａＰＦ６溶液／ＥＣ：ＤＥＣ＝１：１（ＥＣ＝エチレンカーボネート、ＤＥＣ＝ジエチルカーボネート）を用いた。なお試験電池の組み立ては露点温度－７０℃以下の環境で行った。 (e) Test Battery Assembly The obtained secondary battery electrode was placed on the bottom cover of a coin cell with the aluminum foil side facing down, and a separator made of a 16 mm diameter polypropylene porous film dried under reduced pressure at 70°C for 8 hours, metallic sodium as the counter electrode, and the top cover of the coin cell were laminated in this order on top of it to prepare a test battery. As the electrolyte, 1M NaPF 6 solution/EC:DEC=1:1 (EC=ethylene carbonate, DEC=diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of -70°C or lower.
　（ｆ）電池特性の評価
　得られた試験電池について、８０℃で開回路電圧から４．５Ｖまで（比較例３は５．２Ｖまで）ＣＣ（定電流）充電を行い、単位質量当たりの正極合材へ充電された電気量（初回充電容量）を求めた。次に、４．５Ｖから（比較例３は５．２Ｖから）２ＶまでＣＣ放電を行い、単位質量当たりの電極層から放電された電気量（初回放電容量）を求めた。また、初回放電時の作動電圧と放電容量から電極層のエネルギー密度を求めた。「容量維持率」は初回放電容量に対する５０サイクル目の放電容量の割合で評価した。なお、Ｃレートは０．２Ｃとした。結果を表５に示す。 (f) Evaluation of battery characteristics The obtained test battery was subjected to CC (constant current) charging from the open circuit voltage to 4.5 V (5.2 V in Comparative Example 3) at 80 ° C., and the amount of electricity charged to the positive electrode composite per unit mass (initial charge capacity) was obtained. Next, CC discharge was performed from 4.5 V (from 5.2 V in Comparative Example 3) to 2 V, and the amount of electricity discharged from the electrode layer per unit mass (initial discharge capacity) was obtained. In addition, the energy density of the electrode layer was obtained from the operating voltage and discharge capacity at the time of the initial discharge. The "capacity retention rate" was evaluated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity. The C rate was set to 0.2 C. The results are shown in Table 5.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　実施例１～１６の二次電池用電極では、電極層のエネルギー密度は２１０Ｗｈ／ｋｇ以上であり、５０サイクルの容量維持率は６７％以上であった。一方、比較例１～３の二次電池用電極では、電極層のエネルギー密度は１８３Ｗｈ／ｋｇ以下であり、５０サイクルの容量維持率は２３％以下であった。 In the secondary battery electrodes of Examples 1 to 16, the energy density of the electrode layer was 210 Wh/kg or more, and the capacity retention rate at 50 cycles was 67% or more. On the other hand, in the secondary battery electrodes of Comparative Examples 1 to 3, the energy density of the electrode layer was 183 Wh/kg or less, and the capacity retention rate at 50 cycles was 23% or less.
　（実施例１７）
　（ａ）第１の固体電解質層形成用グリーンシートの作製
　炭酸ナトリウム（Ｎａ２ＣＯ３）、酸化アルミニウム（Ａｌ２Ｏ３）及び酸化マグネシウム（ＭｇＯ）、酸化ジルコニウム（ＺｒＯ２）、酸化イットリウム（Ｙ２Ｏ３）を原料とし、モル％で、Ｎａ２Ｏ　１４．２％、Ａｌ２Ｏ３　７５．４％、ＭｇＯ　５．４％、ＺｒＯ２　４．９％、Ｙ２Ｏ３　０．１％となるように原料粉末を調製し、１２５０℃で４時間仮焼した後、平均粒径２μｍになるよう粉砕した。そして、この粉末１００質量部に対して、バインダーとしてのポリビニルブチラール樹脂（積水化学社製、商品名「ＢＭ－ＳＺ」）を１２．５質量部添加し、Ｎ－メチルピロリドンに分散させた後、自転・公転ミキサーで十分に撹拌してスラリー化した。得られたスラリーをポリエチレンテレフタレートフィルム（ＰＥＴフィルム）上に、ドクターブレードを用いて塗布し、７０℃で乾燥した後、ＰＥＴフィルムから剥離することにより第１の固体電解質層形成用グリーンシートを得た。 (Example 17)
(a) Preparation of green sheet for forming first solid electrolyte layer Sodium carbonate (Na 2 CO 3 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), zirconium oxide (ZrO 2 ), and yttrium oxide (Y 2 O 3 ) were used as raw materials, and raw material powder was prepared so that, in mole percent, Na 2 O 14.2%, Al 2 O 3 75.4%, MgO 5.4%, ZrO 2 4.9%, and Y 2 O 3 0.1% was obtained. The raw material powder was calcined at 1250 ° C. for 4 hours, and then pulverized to an average particle size of 2 μm. Then, 12.5 parts by mass of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name "BM-SZ") was added as a binder to 100 parts by mass of this powder, and the mixture was dispersed in N-methylpyrrolidone, and then sufficiently stirred with a rotation/revolution mixer to form a slurry. The obtained slurry was applied onto a polyethylene terephthalate film (PET film) using a doctor blade, dried at 70° C., and then peeled off from the PET film to obtain a green sheet for forming a first solid electrolyte layer.
　（ｂ）第２の固体電解質層形成用グリーンシートの作製
　炭酸ナトリウム（Ｎａ２ＣＯ３）、酸化アルミニウム（Ａｌ２Ｏ３）及び酸化マグネシウム（ＭｇＯ）、酸化ジルコニウム（ＺｒＯ２）、酸化イットリウム（Ｙ２Ｏ３）を原料とし、モル％で、Ｎａ２Ｏ　１４．２％、Ａｌ２Ｏ３　７５．４％、ＭｇＯ　５．４％、ＺｒＯ２　４．９％、Ｙ２Ｏ３　０．１％となるように原料粉末を調製し、１２５０℃で４時間仮焼した後、平均粒径２μｍになるよう粉砕した。そして、この粉末３５質量部と、高分子粒子としての架橋ポリメタクリル酸メチル粒子（積水化成品社製、品番「ＭＢＸ－５０」、平均粒子径５０μｍ）６５質量部を秤量し、混合した。これらの混合物１００質量部に対して、バインダーとしてのポリビニルブチラール樹脂（積水化学社製、商品名「ＢＭ－ＳＺ」）を１２．５質量部添加し、Ｎ－メチルピロリドンに分散させた後、自転・公転ミキサーで十分に撹拌してスラリー化した。得られたスラリーをＰＥＴフィルム上に、ドクターブレードを用いて塗布し、７０℃で乾燥した後、ＰＥＴフィルムから剥離することにより第２の固体電解質層形成用グリーンシートを得た。 (b) Preparation of green sheet for forming second solid electrolyte layer Sodium carbonate (Na 2 CO 3 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), zirconium oxide (ZrO 2 ), and yttrium oxide (Y 2 O 3 ) were used as raw materials, and raw material powder was prepared so that, in mole percent, Na 2 O 14.2%, Al 2 O 3 75.4%, MgO 5.4%, ZrO 2 4.9%, and Y 2 O 3 0.1% were prepared, calcined at 1250°C for 4 hours, and then pulverized to an average particle size of 2 μm. Then, 35 parts by mass of this powder and 65 parts by mass of crosslinked polymethylmethacrylate particles (manufactured by Sekisui Chemical Co., Ltd., product number "MBX-50", average particle size 50 μm) as polymer particles were weighed and mixed. To 100 parts by mass of the mixture, 12.5 parts by mass of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name "BM-SZ") was added as a binder, and the mixture was dispersed in N-methylpyrrolidone, and then sufficiently stirred with a rotation/revolution mixer to form a slurry. The obtained slurry was applied onto a PET film using a doctor blade, dried at 70°C, and then peeled off from the PET film to obtain a green sheet for forming a second solid electrolyte layer.
　（ｃ）積層体の作製
　得られた第１の固体電解質層形成用グリーンシートの両側の主面上に、得られた第２の固体電解質層形成用グリーンシートを積層し、９０℃、４０ＭＰａで５分間等方圧プレスすることにより、積層体を作製した。 (c) Preparation of Laminate The obtained green sheets for forming a second solid electrolyte layer were laminated on both main surfaces of the obtained green sheet for forming a first solid electrolyte layer, and the laminate was isostatically pressed at 90° C. and 40 MPa for 5 minutes to prepare a laminate.
　（ｄ）積層体の焼成
　得られた積層体を、□４７．２５ｍｍで打ち抜いた後、１５５０℃で３０分間焼成することにより、緻密層である第１の固体電解質層の両側の主面上に、多孔質層である第２の固体電解質層が設けられてなる固体電解質層（厚み７０μｍ）を作製した。なお、得られた固体電解質層の大きさは□３８ｍｍであり、第１の固体電解質層の厚みは２０μｍであり、第２の固体電解質層の厚みは、それぞれ、２５μｍであった。また、第１の固体電解質層の空隙率は、５％であり、第２の固体電解質層の空隙率は、７８％であった。 (d) Firing of the laminate The obtained laminate was punched out to 47.25 mm square and then fired at 1550° C. for 30 minutes to produce a solid electrolyte layer (thickness 70 μm) in which a second solid electrolyte layer, which is a porous layer, was provided on both main surfaces of the first solid electrolyte layer, which is a dense layer. The size of the obtained solid electrolyte layer was 38 mm square, the thickness of the first solid electrolyte layer was 20 μm, and the thickness of the second solid electrolyte layer was 25 μm. The porosity of the first solid electrolyte layer was 5%, and the porosity of the second solid electrolyte layer was 78%.
　（ｅ）正極ペーストの作製
　正極ペーストは、実施例１と同様にして得た。 (e) Preparation of Positive Electrode Paste The positive electrode paste was obtained in the same manner as in Example 1.
　（ｆ）負極ペーストの作製
　炭素電極材料前駆体である、ハードカーボン源のスクロース（ショ糖）と、β’’－アルミナ粉末とを、重量比で４：１となるように、スターラ中で１時間混合することにより、混合物を得た。次に、上記混合物を、６０℃の恒温槽において１２時間乾燥させ、その後、１００℃において６時間真空乾燥させることにより、ナトリウムイオン伝導性固体電解質前駆体及び炭素電極材料前駆体の混合物の粉末を得た。次に、上記混合物の粉末をメノウ乳鉢で粉砕して粉末状とした。 (f) Preparation of negative electrode paste A mixture was obtained by mixing sucrose (cane sugar) as a hard carbon source, which is a carbon electrode material precursor, and β''-alumina powder in a weight ratio of 4:1 in a stirrer for 1 hour. Next, the mixture was dried in a thermostatic chamber at 60°C for 12 hours, and then vacuum dried at 100°C for 6 hours to obtain a powder of a mixture of a sodium ion conductive solid electrolyte precursor and a carbon electrode material precursor. Next, the powder of the mixture was pulverized in an agate mortar to obtain a powder form.
　ナトリウムイオン伝導性固体電解質前駆体及び炭素電極材料前駆体の混合物の粉末とハードカーボン粉末（平均粒径Ｄ５０＝１μｍ）と導電助剤（アセチレンブラック）とを、重量比で５７：４０：３となるように秤量し、混合して混合粉末を得た。さらに、負極合材粉末１００質量％に対して、バインダーとしてのポリプロピレンカーボネート（ＰＰＣ）を１５質量％加え、負極合材粉末の濃度が５０質量％となるように、溶媒としてＮ－メチル－２－ピロリドンを加えた。これを自公転ミキサーで混合することで、負極ペーストを作製した。 The mixture of sodium ion conductive solid electrolyte precursor and carbon electrode material precursor powder, hard carbon powder (average particle size D50 = 1 μm), and conductive additive (acetylene black) were weighed out to a weight ratio of 57:40:3 and mixed to obtain a mixed powder. Furthermore, 15% by mass of polypropylene carbonate (PPC) was added as a binder to 100% by mass of the negative electrode composite powder, and N-methyl-2-pyrrolidone was added as a solvent so that the concentration of the negative electrode composite powder was 50% by mass. This was mixed in a planetary mixer to produce a negative electrode paste.
　（ｇ）負極の形成
　３８ｍｍ□、厚み７５μｍの固体電解質層の一方側主面中央に、３３ｍｍ□、厚みが７０μｍになるように負極ペーストを塗工した。８０℃の恒温槽で１時間乾燥を行った。その後、Ｎ２（９９．９９％）雰囲気中において、８００℃、２時間の条件で焼成を行い負極を形成した。負極の担持重量は、（負極形成後の積層体の重量）－（固体電解質層の重量）から求めた。求めた担持重量に、このうちの活物質の比率０．８をかけてハードカーボン活物質重量を算出した。また、ハードカーボンの容量を３８５ｍＡｈ／ｇとして、負極の容量を算出した。その結果、負極の容量は、０．３ｍＡｈ／ｃｍ２であった。 (g) Formation of negative electrode The negative electrode paste was applied to the center of one main surface of a 38 mm square, 75 μm thick solid electrolyte layer so that the negative electrode paste was 33 mm square and 70 μm thick. Drying was performed in a thermostatic chamber at 80° C. for 1 hour. Then, firing was performed in an N 2 (99.99%) atmosphere at 800° C. for 2 hours to form a negative electrode. The weight of the negative electrode was calculated by (weight of the laminate after the negative electrode formation) minus (weight of the solid electrolyte layer). The weight of the hard carbon active material was calculated by multiplying the weight of the active material by 0.8. The capacity of the hard carbon was calculated by setting the capacity of the hard carbon to 385 mAh/g. As a result, the capacity of the negative electrode was 0.3 mAh/cm 2 .
　（ｈ）正極ペーストの塗工
　固体電解質層の負極とは反対側の主面中央に、３３ｍｍ□、厚みが３００μｍになるように正極ペーストを塗工した。その後、８０℃の恒温槽で２時間乾燥した。 (h) Coating of Positive Electrode Paste The positive electrode paste was coated on the center of the main surface of the solid electrolyte layer opposite to the negative electrode to a size of 33 mm square and a thickness of 300 μm. Then, it was dried in a thermostatic chamber at 80° C. for 2 hours.
　（ｉ）正極の形成
　上記、正極ペースト塗工、乾燥後の固体電解質層を２枚、および、集電体としてのアルミ箔（厚さ２０μｍ）を用意し、固体電解質層―アルミ箔―固体電解質層の順番で重ねた。その際、いずれの固体電解質層も正極ペーストを塗工した主面がアルミ箔と接するように重ねた。その状態で、Ｎ２／Ｈ２（９６／４　体積％）雰囲気中において、５００℃、３０分間保持の条件で焼成を行った。これにより、二次電池用電極合材（正極）を形成するとともに、１枚のアルミ箔に対して２つの正極層が形成された全固体電池を作製した。なお、正極の担持重量は、（正極形成後の積層体の重量）－（正極形成前の積層体の重量）－（アルミ箔重量）から求めた。求めた担持重量に、このうちの活物質の比率０．８６５をかけてＮａ２ＦｅＰ２Ｏ７活物質の重量を算出した。Ｎａ２ＦｅＰ２Ｏ７結晶化ガラス（Ｎａ２ＦｅＰ２Ｏ７活物質）の容量を理論容量の９７ｍＡｈ／ｇとして、正極の容量を算出した。その結果、正極の容量は、０．５ｍＡｈ／ｃｍ２であった。また、負極の容量を正極の容量で除し、Ｎ／Ｐ比（負極容量／正極容量）を求めたところ、Ｎ／Ｐ比は、０．６であった。 (i) Formation of the positive electrode Two sheets of the above-mentioned solid electrolyte layer after coating and drying the positive electrode paste and aluminum foil (thickness 20 μm) as a current collector were prepared and stacked in the order of solid electrolyte layer-aluminum foil-solid electrolyte layer. At that time, both solid electrolyte layers were stacked so that the main surface coated with the positive electrode paste was in contact with the aluminum foil. In that state, firing was performed in an N 2 /H 2 (96/4 volume%) atmosphere at 500 ° C. for 30 minutes. As a result, a secondary battery electrode mixture (positive electrode) was formed, and an all-solid-state battery in which two positive electrode layers were formed on one aluminum foil was produced. The weight of the positive electrode was calculated from (weight of the laminate after the positive electrode was formed) - (weight of the laminate before the positive electrode was formed) - (weight of the aluminum foil). The weight of the Na 2 FeP 2 O 7 active material was calculated by multiplying the calculated weight of the support by the ratio of the active material among them, 0.865. The capacity of the positive electrode was calculated by assuming the capacity of Na2FeP2O7 crystallized glass ( Na2FeP2O7 active material) to be the theoretical capacity of 97mAh/g. As a result, the capacity of the positive electrode was 0.5mAh/ cm2 . In addition, the capacity of the negative electrode was divided by the capacity of the positive electrode to obtain the N/P ratio (negative electrode capacity/positive electrode capacity), which was 0.6.
　（ｊ）充放電試験
　全固体ナトリウムイオン二次電池を、アルミラミネートを用いて封入した。その際、正極層、負極層、第３の電極それぞれにタブを出した。次に、６０℃及び０．０２Ｃの条件で全固体ナトリウムイオン二次電池の充放電を行った。 (j) Charge/Discharge Test The all-solid-state sodium ion secondary battery was encapsulated using an aluminum laminate. At that time, tabs were exposed from the positive electrode layer, the negative electrode layer, and the third electrode. Next, the all-solid-state sodium ion secondary battery was charged and discharged under the conditions of 60° C. and 0.02 C.
　実施例１７の全固体二次電池では、エネルギー密度は７０Ｗｈ／ｋｇであり、５０サイクルの容量維持率は９５％であった。 The all-solid-state secondary battery of Example 17 had an energy density of 70 Wh/kg and a capacity retention rate of 95% after 50 cycles.
１０，２０…二次電池用電極
２…集電体
３…電極層
３０…全固体二次電池
３４…固体電解質層
３５…対極層
３６…第２の集電体 10, 20... secondary battery electrode 2... current collector 3... electrode layer 30... all-solid-state secondary battery 34... solid electrolyte layer 35... counter electrode layer 36... second current collector

Claims (6)

  1. 　集電体と、実質的に電極活物質結晶及び非晶質相を含む電極活物質と導電助剤からなる電極層とからなることを特徴とする二次電池用電極。 An electrode for a secondary battery, characterized by comprising a current collector and an electrode layer made of an electrode active material substantially including an electrode active material crystalline and amorphous phases, and a conductive additive.
  2. 　前記電極層には、β’’－アルミナ、β－アルミナ、及びＮＡＳＩＣＯＮ結晶を実質的に含まないことを特徴とする請求項１に記載の二次電池用電極。 The electrode for a secondary battery according to claim 1, characterized in that the electrode layer is substantially free of β''-alumina, β-alumina, and NASICON crystals.
  3. 　前記電極層は、無機材料のみで構成されていることを特徴とする請求項１又は２に記載の二次電池用電極。 The electrode for a secondary battery according to claim 1 or 2, characterized in that the electrode layer is composed only of inorganic materials.
  4. 　前記集電体の両主面上に前記電極層が形成されていることを特徴とする請求項１又は２に記載の二次電池用電極。 The electrode for a secondary battery according to claim 1 or 2, characterized in that the electrode layer is formed on both main surfaces of the current collector.
  5. 　請求項１又は２に記載の二次電池用電極の製造方法であって、
    　集電体の主面上に、電極活物質前駆体及び導電助剤とを含んだ電極材料層を形成し、該電極材料層を焼成することにより前記電極層が形成されることを特徴とする二次電池用電極の製造方法。     A method for producing the electrode for a secondary battery according to claim 1 or 2, comprising the steps of:
    1. A method for manufacturing an electrode for a secondary battery, comprising: forming an electrode material layer containing an electrode active material precursor and a conductive assistant on a main surface of a current collector; and firing the electrode material layer to form the electrode layer.
  6. 　請求項１又は２に記載の二次電池用電極を備える、全固体二次電池。 An all-solid-state secondary battery comprising the secondary battery electrode according to claim 1 or 2.
PCT/JP2024/008731 2023-03-13 2024-03-07 Electrode for secondary battery, method for producing same, and all-solid-state secondary battery WO2024190592A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017073457A1 (en) * 2015-10-28 2017-05-04 日本電気硝子株式会社 Positive electrode active material for sodium-ion secondary cell
WO2018235828A1 (en) * 2017-06-21 2018-12-27 株式会社村田製作所 Magnesium sulfide material, magnesium sulfide composite material, positive electrode member for secondary batteries, wide band gap semiconductor material, magnesium secondary battery, and method for producing zincblende magnesium sulfide
WO2019088139A1 (en) * 2017-11-02 2019-05-09 国立大学法人東京大学 Secondary battery negative electrode, secondary battery, and methods for manufacturing these
JP2019125547A (en) * 2018-01-19 2019-07-25 日本電気硝子株式会社 Solid electrolyte powder, electrode mixture using the same, and all-solid sodium ion secondary battery

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017073457A1 (en) * 2015-10-28 2017-05-04 日本電気硝子株式会社 Positive electrode active material for sodium-ion secondary cell
WO2018235828A1 (en) * 2017-06-21 2018-12-27 株式会社村田製作所 Magnesium sulfide material, magnesium sulfide composite material, positive electrode member for secondary batteries, wide band gap semiconductor material, magnesium secondary battery, and method for producing zincblende magnesium sulfide
WO2019088139A1 (en) * 2017-11-02 2019-05-09 国立大学法人東京大学 Secondary battery negative electrode, secondary battery, and methods for manufacturing these
JP2019125547A (en) * 2018-01-19 2019-07-25 日本電気硝子株式会社 Solid electrolyte powder, electrode mixture using the same, and all-solid sodium ion secondary battery

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