WO2015132844A1 - Positive electrode material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Positive electrode material for lithium ion secondary batteries, and lithium ion secondary battery Download PDF

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WO2015132844A1
WO2015132844A1 PCT/JP2014/055216 JP2014055216W WO2015132844A1 WO 2015132844 A1 WO2015132844 A1 WO 2015132844A1 JP 2014055216 W JP2014055216 W JP 2014055216W WO 2015132844 A1 WO2015132844 A1 WO 2015132844A1
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positive electrode
ion secondary
lithium ion
active material
secondary battery
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PCT/JP2014/055216
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French (fr)
Japanese (ja)
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小西　宏明
小林　満
豊隆 湯浅
所　久人
秀一 高野
崇 中林
章 軍司
達哉 遠山
孝亮 馮
翔 古月
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株式会社日立製作所
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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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery including the same.
  • the problem with electric vehicles is that the energy density of the driving battery is low and the travel distance for one charge is short. Therefore, there is a demand for an inexpensive secondary battery with high energy density.
  • Lithium ion secondary batteries have a higher energy density per weight than secondary batteries such as nickel hydrogen batteries and lead batteries. Therefore, the application to an electric vehicle and a power storage system is expected. However, in order to meet the demand for electric vehicles, it is necessary to further increase the energy density. In order to realize high energy density, it is necessary to increase the energy density of the positive electrode and the negative electrode.
  • a layered solid solution represented by Li 2 MO 3 -LiM′O 2 attracts attention.
  • the layered solid solution can also be represented by the composition formula Li 1 + x M 1-x O 2 as a lithium-enriched cathode active material of the layered oxide.
  • the molar ratio Co / Me (x / (x + y + z)) is 0.020 to 0.230
  • the molar ratio Mn / Me (z / (x + y + z)) is 0.625 to 0.
  • the positive electrode active material characterized in that it is .719 is described.
  • Patent Document 2 discloses a lithium manganese oxide having a layered structure and a lithium manganese having a spinel structure in order to provide a lithium ion secondary battery having a high capacity without a sharp decrease in output over a wide SOC (State of Charge) section.
  • the oxide is mixed.
  • JP 2012-151084 A Japanese Patent Publication No. 2013-520782
  • the layered solid solution has high resistance as compared with the layered oxide LiMO 2 , the reduction of the resistance is desired. Moreover, since the positive electrode active material currently disclosed by patent document 1 has low electrode density, improvement of volume energy density is desired.
  • the positive electrode material disclosed in Patent Document 2 has a high electrode density, and high volume energy density can be expected. However, high volumetric energy density can be obtained when the lower limit potential is lowered to 2.0 V.
  • an object of the present invention is to provide a lithium ion secondary battery with high output and high volumetric energy density.
  • the positive electrode material for a lithium ion secondary battery according to the present invention is made of a lithium transition metal oxide containing Li and a metal element, contains at least Ni and Mn as the metal element, and an atom of Li to the metal element
  • a first positive electrode active material having a ratio of 1.15 ⁇ Li / metal element ⁇ 1.5 and an atomic ratio of Ni to Mn of 0.334 ⁇ Ni / Mn ⁇ 1, and a composition formula LiMn 2 ⁇ y M ′ y O 4 (0 ⁇ y ⁇ 0.2, M ′ is represented by at least one element of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti and Cu)
  • a second positive electrode active material is included, and the content of the second positive electrode active material is 5% by mass or more and less than 30% by mass with respect to the positive electrode material.
  • ⁇ Positive material> When using a lithium ion secondary battery for an electric vehicle, it is desirable that the travel distance per charge be long. In order to increase the travel distance per charge, it is necessary to improve the energy density per unit volume.
  • a lithium ion secondary battery using a layered solid solution as a positive electrode active material is expected to have a high capacity and a high weight energy density.
  • the electrode density is low, there is a problem in volume energy density. Since layered solid solutions have high resistance, they need to be micronized to obtain high capacity. However, when the particles are made finer, the electrode density decreases due to interparticle friction and the like. As a result, the volumetric energy density is reduced. Therefore, in order to obtain high volumetric energy density, it is necessary to improve the electrode density.
  • a positive electrode active material having a spinel structure capable of obtaining a large capacity even with a large particle size can be mixed to achieve high density.
  • layered solid solutions generally do not have high capacity unless the lower limit potential is lowered to 2.0 V.
  • a lithium manganese oxide having a spinel structure represented by LiMn 2 O 4 is accompanied by a change in the abundance of Mn 3+ and a change in crystal structure at 3.2 V or less, so the lower limit potential is up to 2.0 V If it is lowered, LiMn 2 O 4 may be degraded and the cycle characteristics may be degraded.
  • FIG. 1 is a discharge curve of Li 1.05 Ni 0.35 Mn 0.45 O 2 and 2 is a discharge curve of Li 1.2 Ni 0.2 Mn 0.6 O 2 .
  • 1 is a discharge curve of Li 1.05 Ni 0.35 Mn 0.45 O 2
  • 2 is a discharge curve of Li 1.2 Ni 0.2 Mn 0.6 O 2 .
  • lithium manganese oxide having a spinel structure represented by LiMn 2 O 4 has high output. Accordingly, the reaction area of the LiMn 2 O 4 (3.9 ⁇ 4.1V ), because LiMn 2 O 4 also react, thus improving the cell output.
  • the first positive electrode active material is made of a lithium transition metal oxide containing Li and a metal element, contains at least Ni and Mn as the metal element, and the atomic ratio of Li to the metal element is 1 It is characterized in that 15 ⁇ Li / metal element ⁇ 1.5, and the atomic ratio of Ni to Mn is 0.334 ⁇ Ni / Mn ⁇ 1.
  • the ratio of lithium element to metal element Li / metal element
  • the amount of Li contributing to the reaction is reduced and high capacity can not be obtained.
  • Li / metal element is larger than 1.5, the crystal lattice becomes unstable and the discharge capacity is reduced.
  • Ni / Mn is lower than 0.334, the discharge potential decreases, and a large difference occurs between the reaction end potential and the reaction potential of the second positive electrode active material, and the second positive electrode active material improves the resistance at the discharge end Can not.
  • Ni / Mn is larger than 1, almost no charge / discharge reaction involving oxygen occurs, and the capacity decreases.
  • the amount of oxygen contained in the first positive electrode active material is maintained while maintaining the layered solid solution structure by the valence of the metal and the amount of Li on the basis that the total molar number of the metal element and lithium is equivalent. Since it is considered that the amount of oxygen to be supplied is appropriately increased or decreased, -1.ltoreq..delta..ltoreq.1.
  • the metal element may further contain an additive element M.
  • the atomic ratio of Ni and Mn to the metal element is preferably 0.975 ⁇ (Ni + Mn) / metal element ⁇ 1.0.
  • the additive element M is an additive or an impurity added within a range not affecting the present invention, and at least one element selected from Co, V, Mo, W, Zr, Nb, Ti, Cu, Al, Fe It is.
  • y represents the content ratio (the mass ratio of substance) of M ′.
  • M ′ is an element to be added appropriately, and the addition amount thereof needs to be suppressed to the range of 0 ⁇ y ⁇ 0.2 so that the effect of the present invention is not suppressed.
  • the content of the second positive electrode active material is preferably 5% by mass or more and less than 30% by mass with respect to the positive electrode material.
  • the content of the second positive electrode active material is less than 5% by mass, the effect of improving the electrode density is small, and a high volume energy density can not be obtained.
  • the content of the second positive electrode active material is 30% by mass or more, the proportion of the first positive electrode active material from which high capacity can be obtained decreases, so that high energy density can not be obtained.
  • the content of the second positive electrode active material is preferably 5% by mass or more and 20% by mass or less.
  • the particle diameter of the first positive electrode active material is preferably 100 to 400 nm.
  • the resistance can be reduced by reducing the particle size.
  • the particle diameter of the second positive electrode active material is preferably 5 to 15 ⁇ m.
  • the second positive electrode active material represented by LiMn 2 O 4 can obtain high capacity even if the particle size is large.
  • the positive electrode material according to the present invention can be produced by a method generally used in the technical field to which the present invention belongs.
  • the first positive electrode active material can be produced, for example, by mixing and firing compounds containing Li, Ni, and Mn in appropriate proportions.
  • the composition of the positive electrode material can be appropriately adjusted by changing the ratio of the compounds to be mixed.
  • the compound containing Li include lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium oxide and the like.
  • the compound containing Ni include nickel acetate, nickel nitrate, nickel carbonate, nickel sulfate, nickel hydroxide and the like.
  • Mn manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide etc. can be mentioned, for example.
  • the second positive electrode active material can be produced by mixing and calcining compounds containing Li and Mn respectively in appropriate proportions.
  • the compound containing Li include lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium oxide and the like.
  • Mn manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide etc. can be mentioned, for example.
  • composition of the positive electrode material can be determined, for example, by elemental analysis using inductively coupled plasma (ICP) or the like.
  • ICP inductively coupled plasma
  • the lithium ion secondary battery according to the present invention is characterized by containing the above-mentioned positive electrode material.
  • positive electrode material for the positive electrode, high volume energy density and high output can be achieved.
  • the cycle characteristics may be degraded. Therefore, in use, by setting the lower limit potential to 3.3 V or more based on Li metal, deterioration of the second positive electrode active material can be suppressed, and high cycle characteristics can be maintained.
  • the lithium ion secondary battery according to the present invention can be preferably used for an electric vehicle.
  • the positive electrode active material occludes and releases lithium ions by charge and discharge. Since not all lithium ions released from the positive electrode active material return to the positive electrode, the composition of the positive electrode active material after charge and discharge is expected to be different from that before charge and discharge.
  • the positive electrode active material of a layered compound represented by LiMO 2 has a composition ratio of Li in a full discharge state (2.0 V) when used in a potential range of 2.0 to 4.3 V based on Li metal. It is known to be about 0.75.
  • the substance mass of Li after charging and discharging of the layered solid solution is also reduced by about 20% in the fully discharged state compared to before charging and discharging. Therefore, when a lithium secondary battery is manufactured using the positive electrode material according to the present invention and charged and discharged, the first positive electrode active material is represented by the composition formula Li x Ni a Mn b M c O 2 + in a full discharge state.
  • the atomic ratio of Li to metal elements other than Li in the first positive electrode active material satisfies the relationship 0.90 ⁇ Li / metal element ⁇ 1.5.
  • the lithium ion secondary battery is composed of a positive electrode containing a positive electrode material, a negative electrode containing a negative electrode material, a separator, an electrolytic solution, an electrolyte and the like.
  • the negative electrode material is not particularly limited as long as it is a substance capable of inserting and extracting lithium ions.
  • Materials generally used in lithium ion secondary batteries can be used as the negative electrode material.
  • graphite, lithium alloy and the like can be exemplified.
  • a separator those generally used in lithium ion secondary batteries can be used.
  • a microporous film or non-woven fabric made of polyolefin such as polypropylene, polyethylene, and a copolymer of propylene and ethylene can be exemplified.
  • the electrolytic solution and the electrolyte those generally used in lithium ion secondary batteries can be used.
  • the electrolytic solution diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, methyl acetate, ethyl methyl carbonate, methyl propyl carbonate, dimethoxyethane and the like can be exemplified.
  • the electrolyte LiClO 4, LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) can be exemplified 3 or the like.
  • the lithium ion secondary battery 12 includes an electrode group including a positive electrode 3 having a positive electrode material coated on both sides of a current collector, a negative electrode 4 having a negative electrode material coated on both sides of the current collector, and a separator 5.
  • the positive electrode 3 and the negative electrode 4 are wound via the separator 5 to form a wound electrode group.
  • the wound body is inserted into the battery can 6.
  • the negative electrode 4 is electrically connected to the battery can 6 via the negative electrode lead piece 8.
  • a sealing lid 9 is attached to the battery can 6 via a packing 10.
  • the positive electrode 3 is electrically connected to the sealing lid 9 through the positive electrode lead piece 7.
  • the wound body is insulated by the insulating plate 11.
  • the electrode group may not be a wound body shown in FIG. 2, and may be a laminate in which the positive electrode 3 and the negative electrode 4 are stacked via the separator 5.
  • the first positive electrode active material was produced by the following method. Lithium carbonate, nickel carbonate and manganese carbonate were mixed in a ball mill to obtain a precursor. The obtained precursor was calcined at 500 ° C. for 12 hours in the air to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then fired at 850 to 1050 ° C. for 12 hours in the air. The fired pellet was ground in an agate mortar to obtain a first positive electrode active material represented by the composition formula Li x Ni a Mn b M c O 2 + ⁇ .
  • the second positive electrode active material was produced by the following method. Lithium hydroxide and manganese oxide were mixed in a ball mill to obtain a precursor. The obtained precursor was calcined at 500 ° C. for 12 hours in the air to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then fired at 800 ° C. for 12 hours in the air. The fired pellet was crushed in an agate mortar to obtain LiMn 2 O 4 . This was used as a second positive electrode active material.
  • the first positive electrode active material and the second positive electrode active material were mixed to obtain a positive electrode material.
  • the composition of the first positive electrode active material and the content of the second positive electrode active material in the manufactured positive electrode material are shown in Table 1.
  • a positive electrode was produced using the above-mentioned positive electrode material, and trial batteries of Examples 1 to 12 and Comparative Examples 1 to 6 were produced.
  • a positive electrode slurry was prepared by uniformly mixing the positive electrode material of the battery used in the trial battery, the conductive agent, and the binder. The positive electrode slurry was applied onto a 20 ⁇ m thick aluminum current collector foil and dried at 120 ° C. After drying, it was pressed at a pressure of 40 MPa to obtain an electrode plate. Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.
  • the negative electrode was produced using metallic lithium.
  • a non-aqueous electrolytic solution one in which LiPF 6 was dissolved at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 2 was used.
  • the experimental battery of Example 12 measured the discharge capacity in the same manner as in Example 1 except that the upper limit voltage for charge and discharge was 4.6 V and the lower limit voltage was 2.0 V.
  • the measured discharge capacities are shown in Table 1.
  • the upper limit voltage is 4.6 V at a current of 0.05 C equivalent and the lower limit voltage is 3.3 V at a current of 0.05 C equivalent for discharging.
  • a charge and discharge test was conducted, and the discharge capacity at the second cycle was taken as the rated capacity.
  • the prototype battery after two cycles was charged to 4.6 V and then discharged to a capacity of 50% of the rated capacity. Thereafter, a current of 1.2 mA was applied for 10 seconds to measure the direct current resistance. The value obtained by dividing the potential difference before and after applying the current for 10 seconds by the applied current value (1.2 mA) was defined as the DC resistance value.
  • the experimental battery of Example 12 measured DC resistance in the same manner as in Example 1 except that the upper limit voltage for charging and discharging was set to 4.6 V and the lower limit voltage was set to 2.0 V.
  • the measured DC resistance values are shown in Table 1. ⁇ Measurement of capacity retention rate> The capacity retention rate after 100 cycles was determined for the trial batteries of each example and comparative example.
  • the upper limit voltage is 4.6 V at a current of 0.05 C equivalent and the lower limit voltage is 3.3 V at a current of 0.05 C equivalent for discharging.
  • a charge and discharge test was conducted, and the discharge capacity at the second cycle was taken as the rated capacity. Thereafter, after 99 cycles of charge 1 C and discharge 1 C, charge and discharge were carried out at 0.05 C, and the capacity after 100 cycles was measured. A value obtained by dividing the discharge capacity after 100 cycles by the rated capacity was defined as a capacity retention rate.
  • the capacity retention ratio of the prototype battery manufactured using the positive electrode material of Example 12 was measured in the same manner as in Example 1 except that the upper limit voltage for charging and discharging was set to 4.6 V and the lower limit voltage was set to 2.0 V.
  • Example 1 has a higher capacity than Comparative Example 1 in the potential range of 3.3 V or more.
  • Example 1 has a higher potential than Comparative Example 1. Therefore, Example 1 can obtain higher energy density than Comparative Example 1.
  • the same results as in Example 1 were obtained for the discharge curves of Examples 2 to 12. Therefore, Examples 1 to 12 can obtain higher energy density as compared to the Comparative Example.
  • the discharge capacity per unit volume is higher than in Comparative Examples 1 to 6. Furthermore, in Examples 1 to 12, the direct current resistance is equal to or less than Comparative Example 2 in which the second positive electrode active material is not contained.
  • Comparative Examples 2 to 6 it was not possible to simultaneously achieve high capacity and low resistance.
  • Comparative Example 1 since Li / (Ni + Mn) of the first positive electrode active material is as high as 1.5 and Ni / Mn is as small as 0.33, discharge per unit volume in the region of 4.6 to 3.3 V Capacity is low.
  • Comparative Example 2 since only the first positive electrode active material with low electrode density is formed, the discharge capacity per unit volume is low.
  • the discharge capacity per unit volume is low because only the second positive electrode active material with low capacity is used.
  • Comparative Example 4 since the content of the second positive electrode active material having a low capacity is as large as 30%, the discharge capacity per unit volume is low.
  • Comparative Example 5 since Li / (Ni + Mn) of the first positive electrode active material is as low as 1.125, the discharge capacity is low and the discharge capacity per unit volume is low. In Comparative Example 6, since Li / (Ni + Mn) of the first positive electrode active material is as high as 1.50, the discharge capacity is low and the discharge capacity per unit volume is low.
  • the first positive electrode active material satisfying the relationship of atomic weight ratios of Li, Ni, and Mn of 1.15 ⁇ Li / (Ni + Mn) ⁇ 1.5 and 0.334 ⁇ Ni / Mn ⁇ 1, and the composition formula LiMn 2 -y M ' y O 4 (0 y y 0.2 0.2, M' is represented by Fe, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti, Cu, or any other element)
  • Per unit volume of a lithium ion secondary battery by using a positive electrode material containing a second positive electrode active material and having a content of the second positive electrode active material to the positive electrode material of 5% by mass or more and less than 30% by mass. Discharge capacity is improved and resistance is reduced. As a result, it is possible to provide a lithium ion secondary battery having a high volumetric energy density and a high output.
  • Example 1 has a higher capacity retention rate than Example 12. This is because the lower limit potentials of charge and discharge are different. In Example 12, since the lower limit potential of charge and discharge was as low as 2.0 V, when the cycle was repeated, the second positive electrode active material was deteriorated, and the capacity retention rate was lowered. On the other hand, in Example 1, by setting the lower limit potential of charge and discharge to 3.3 V, deterioration of the second positive electrode active material was suppressed, and a high capacity retention rate could be achieved.
  • Li / (Ni + Mn) and Ni / Mn of the lithium transition metal oxide having a metal element containing at least Ni and at least Ni and Mn are optimized, and the composition formula LiMn 1 ⁇ y M ′ y O 4 (0 ⁇ y ⁇ 0.2, M ′ is represented by at least one element of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti and Cu)

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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

The objective of the present invention is to provide a lithium ion secondary battery which has high energy density and high output power. The objective can be achieved by a positive electrode material which is characterized by containing a first positive electrode active material that is composed of a lithium transition metal oxide containing Li and metal elements including at least Ni and Mn, with the atomic ratio of Li to the metal elements being 1.15 < Li/(metal elements) < 1.5 and the atomic ratio of Ni to Mn being 0.334 < Ni/Mn ≤ 1, and a second positive electrode active material that is represented by composition formula LiMn2-yM'yO4 (wherein 0 ≤ y ≤ 0.2 and M' represents at least one element selected from among Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti and Cu), and which is also characterized in that the content of the second positive electrode active material is 5% by mass or more but less than 30% by mass relative to the positive electrode material.

Description

リチウムイオン二次電池用正極材料およびリチウムイオン二次電池Positive electrode material for lithium ion secondary battery and lithium ion secondary battery
　本発明は、リチウムイオン二次電池用の正極材料、及びそれを含むリチウムイオン二次電池に関する。 The present invention relates to a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery including the same.
　電気自動車の課題は、駆動用電池のエネルギー密度が低く、一充電での走行距離が短いことである。そこで、安価で高エネルギー密度をもつ二次電池が求められている。 The problem with electric vehicles is that the energy density of the driving battery is low and the travel distance for one charge is short. Therefore, there is a demand for an inexpensive secondary battery with high energy density.
　リチウムイオン二次電池は、ニッケル水素電池や鉛電池等の二次電池に比べて重量当たりのエネルギー密度が高い。そのため、電気自動車や電力貯蔵システムへの応用が期待されている。しかし、電気自動車の要請に応えるためには、さらなる高エネルギー密度化が必要である。高エネルギー密度化を実現するためには、正極及び負極のエネルギー密度を高める必要がある。 Lithium ion secondary batteries have a higher energy density per weight than secondary batteries such as nickel hydrogen batteries and lead batteries. Therefore, the application to an electric vehicle and a power storage system is expected. However, in order to meet the demand for electric vehicles, it is necessary to further increase the energy density. In order to realize high energy density, it is necessary to increase the energy density of the positive electrode and the negative electrode.
　高いエネルギー密度が得られる正極活物質として、Ｌｉ2ＭＯ3－ＬｉＭ′Ｏ2で表される層状固溶体が注目されている。層状固溶体は、層状酸化物のＬｉを富化した正極活物質として、組成式Ｌｉ1+xＭ1-xＯ2で表すこともできる。 As a positive electrode active material capable of obtaining high energy density, a layered solid solution represented by Li 2 MO 3 -LiM′O 2 attracts attention. The layered solid solution can also be represented by the composition formula Li 1 + x M 1-x O 2 as a lithium-enriched cathode active material of the layered oxide.
　特許文献１には、一般式ＬｉaＣｏxＮｉyＭｎzＯ2（ａ＋ｘ＋ｙ＋ｚ＝２）で構成され、その全遷移金属元素Ｍｅに対するＬｉのモル比Ｌｉ／Ｍｅ（ａ／（ｘ＋ｙ＋ｚ））が１．２５～１．４０であり、モル比Ｃｏ／Ｍｅ（ｘ／（ｘ＋ｙ＋ｚ））が０．０２０～０．２３０であり、モル比Ｍｎ／Ｍｅ（ｚ／（ｘ＋ｙ＋ｚ））が０．６２５～０．７１９であることを特徴とする正極活物質が記載されている。 Patent Document 1, the general formula Li a Co x Ni y Mn z O 2 (a + x + y + z = 2) consists of, its Li to all transition metal element Me mole ratio Li / Me (a / (x + y + z)) is 1 The molar ratio Co / Me (x / (x + y + z)) is 0.020 to 0.230, and the molar ratio Mn / Me (z / (x + y + z)) is 0.625 to 0. The positive electrode active material characterized in that it is .719 is described.
　特許文献２には、広いＳＯＣ（Ｓｔａｔｅ　ｏｆ　Ｃｈａｒｇｅ）区間にわたって急激な出力低下がなく、高容量を有するリチウムイオン二次電池を提供するため、層状構造のリチウムマンガン酸化物とスピネル構造を有するリチウムマンガン酸化物を混合している。 Patent Document 2 discloses a lithium manganese oxide having a layered structure and a lithium manganese having a spinel structure in order to provide a lithium ion secondary battery having a high capacity without a sharp decrease in output over a wide SOC (State of Charge) section. The oxide is mixed.
特開２０１２－１５１０８４号公報JP 2012-151084 A 特表２０１３－５２０７８２号公報Japanese Patent Publication No. 2013-520782
　層状固溶体は層状酸化物ＬｉＭＯ2と比して抵抗が高いため、低抵抗化が望まれている。また、特許文献１に開示されている正極活物質は電極密度が低いため、体積エネルギー密度の向上が望まれている。 Since the layered solid solution has high resistance as compared with the layered oxide LiMO 2 , the reduction of the resistance is desired. Moreover, since the positive electrode active material currently disclosed by patent document 1 has low electrode density, improvement of volume energy density is desired.
　特許文献２に示されている正極材料は、電極密度が高く、高い体積エネルギー密度が期待できる。しかしながら、高い体積エネルギー密度が得られるのは、下限電位を２．０Ｖまで下げた場合である。 The positive electrode material disclosed in Patent Document 2 has a high electrode density, and high volume energy density can be expected. However, high volumetric energy density can be obtained when the lower limit potential is lowered to 2.0 V.
　そこで、本発明は、出力が高く、かつ、体積エネルギー密度が高いリチウムイオン二次電池を提供することを目的とする。 Then, an object of the present invention is to provide a lithium ion secondary battery with high output and high volumetric energy density.
　本発明に係るリチウムイオン二次電池用正極材料は、Ｌｉと、金属元素と、を含むリチウム遷移金属酸化物よりなり、金属元素として少なくともＮｉと、Ｍｎと、を含み、金属元素に対するＬｉの原子比が、１．１５＜Ｌｉ／金属元素＜１．５であり、Ｍｎに対するＮｉの原子比が、０．３３４＜Ｎｉ／Ｍｎ≦１である第一の正極活物質と、組成式ＬｉＭｎ2-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＭｎ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表される第二の正極活物質を含み、第二の正極活物質の含有量は正極材料に対し５質量％以上３０質量％未満であることを特徴とする。 The positive electrode material for a lithium ion secondary battery according to the present invention is made of a lithium transition metal oxide containing Li and a metal element, contains at least Ni and Mn as the metal element, and an atom of Li to the metal element A first positive electrode active material having a ratio of 1.15 <Li / metal element <1.5 and an atomic ratio of Ni to Mn of 0.334 <Ni / Mn ≦ 1, and a composition formula LiMn 2− y M ′ y O 4 (0 ≦ y ≦ 0.2, M ′ is represented by at least one element of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti and Cu) A second positive electrode active material is included, and the content of the second positive electrode active material is 5% by mass or more and less than 30% by mass with respect to the positive electrode material.
　本発明によれば、高出力、かつ、体積エネルギー密度の高いリチウムイオン二次電池を提供することができる。 According to the present invention, it is possible to provide a lithium ion secondary battery with high output and high volumetric energy density.
層状固溶体の放電曲線を示すグラフである。It is a graph which shows the discharge curve of layered solid solution. リチウムイオン二次電池の構造を模式的に示す断面図である。It is sectional drawing which shows the structure of a lithium ion secondary battery typically. 実施例１及び比較例１の放電曲線を示すグラフである。5 is a graph showing discharge curves of Example 1 and Comparative Example 1;
　＜正極材料＞
　リチウムイオン二次電池を電気自動車に採用する場合、一充電当たりの走行距離が長いことが望まれる。一充電当たりの走行距離を長くするためには、単位体積当たりのエネルギー密度を向上させる必要がある。 <Positive material>
When using a lithium ion secondary battery for an electric vehicle, it is desirable that the travel distance per charge be long. In order to increase the travel distance per charge, it is necessary to improve the energy density per unit volume.
　正極活物質として層状固溶体を用いたリチウムイオン二次電池は、容量が高く、高い重量エネルギー密度が期待できる。しかしながら、電極密度が低いため，体積エネルギー密度に課題がある。層状固溶体は抵抗が高いため、高容量を得るためには微粒子化する必要がある。しかしながら、粒子を細かくすると、粒子間摩擦などにより電極密度が低下する。その結果、体積エネルギー密度が低下する。したがって、高い体積エネルギー密度を得るために、電極密度を向上させる必要がある。 A lithium ion secondary battery using a layered solid solution as a positive electrode active material is expected to have a high capacity and a high weight energy density. However, since the electrode density is low, there is a problem in volume energy density. Since layered solid solutions have high resistance, they need to be micronized to obtain high capacity. However, when the particles are made finer, the electrode density decreases due to interparticle friction and the like. As a result, the volumetric energy density is reduced. Therefore, in order to obtain high volumetric energy density, it is necessary to improve the electrode density.
　電極密度を向上させる手段として、粒子径の異なる正極活物質を混合する方法がある。大粒径でも高容量を得られるスピネル構造を有する正極活物質を混合し、高密度化を図ることができる。しかしながら、層状固溶体は、通常下限電位を２．０Ｖまで下げないと高い容量が得られない。一方、ＬｉＭｎ2Ｏ4に代表されるスピネル構造を有するリチウムマンガン酸化物は、３．２Ｖ以下でＭｎ3+の存在率の変化や結晶構造の変化などを伴うため、下限電位を２．０Ｖまで下げると、ＬｉＭｎ2Ｏ4が劣化し、サイクル特性が低下するおそれがある。 As a means for improving the electrode density, there is a method of mixing positive electrode active materials having different particle sizes. A positive electrode active material having a spinel structure capable of obtaining a large capacity even with a large particle size can be mixed to achieve high density. However, layered solid solutions generally do not have high capacity unless the lower limit potential is lowered to 2.0 V. On the other hand, a lithium manganese oxide having a spinel structure represented by LiMn 2 O 4 is accompanied by a change in the abundance of Mn 3+ and a change in crystal structure at 3.2 V or less, so the lower limit potential is up to 2.0 V If it is lowered, LiMn 2 O 4 may be degraded and the cycle characteristics may be degraded.
　発明者らが鋭意検討した結果、層状固溶体のＬｉ、Ｎｉ、Ｍｎの組成比を調整することによって、下限電位を２．０Ｖまで下げなくても高容量が得られることを見出した。層状固溶体は、充電初期に遷移金属がレドックスに関与した反応が起こり、充電末期では、酸素が関与したレドックス反応が起こる。一方、放電初期では、遷移金属がレドックスに関与した反応が起こり、放電末期では、酸素が関与したレドックス反応が起こる。遷移金属が関与する反応は、高電位であるが、酸素が関与した反応は低電位であり抵抗が高い。したがって、正極活物質中においてレドックス反応に主に寄与するＮｉの割合を増加させることで、遷移金属の反応領域を増やすことができ、高電位化が可能となる。その結果、電位が高い領域の容量が増大する。 As a result of intensive investigations by the inventors, it was found that by adjusting the composition ratio of Li, Ni and Mn in the layered solid solution, a high capacity can be obtained without lowering the lower limit potential to 2.0 V. In the layered solid solution, a reaction in which a transition metal participates in redox occurs in the early stage of charging, and a redox reaction in which oxygen participates in the late stage of charging. On the other hand, at the beginning of the discharge, a reaction involving the transition metal occurs, and at the end of the discharge, a redox reaction involving the oxygen occurs. Reactions involving transition metals are at high potential while reactions involving oxygen are at low potential and high resistance. Therefore, by increasing the proportion of Ni that mainly contributes to the redox reaction in the positive electrode active material, the reaction region of the transition metal can be increased, and the potential can be increased. As a result, the capacitance of the high potential region is increased.
　図１にＬｉ1.05Ｎｉ0.35Ｍｎ0.45Ｏ2とＬｉ1.2Ｎｉ0.2Ｍｎ0.6Ｏ2の充放電曲線を示す。図１において、１はＬｉ1.05Ｎｉ0.35Ｍｎ0.45Ｏ2の放電曲線、２はＬｉ1.2Ｎｉ0.2Ｍｎ0.6Ｏ2の放電曲線である。３．３Ｖ以上の電位が高い領域では、２よりも１の方が、高エネルギー密度が得られることが分かる。したがって、上記層状固溶体と、かつ粒径の大きいスピネル構造を有するリチウムマンガン酸化物を混合させることで、下限電位を２．０Ｖまで下げなくても、高容量が得られ、電極密度を向上できる。その結果、体積エネルギー密度が向上する。また、３．３V以上で反応させることによって、ＬｉＭｎ2Ｏ4の劣化を抑制し、サイクル特性を維持できる。 The charge and discharge curves of Li 1.05 Ni 0.35 Mn 0.45 O 2 and Li 1.2 Ni 0.2 Mn 0.6 O 2 are shown in FIG. In FIG. 1, 1 is a discharge curve of Li 1.05 Ni 0.35 Mn 0.45 O 2 and 2 is a discharge curve of Li 1.2 Ni 0.2 Mn 0.6 O 2 . It can be seen that high energy density can be obtained with 1 rather than 2 in the region where the potential of 3.3 V or higher is high. Therefore, by mixing the layered solid solution and a lithium manganese oxide having a spinel structure with a large particle size, a high capacity can be obtained and the electrode density can be improved without lowering the lower limit potential to 2.0 V. As a result, volumetric energy density is improved. Moreover, by making it react at 3.3 V or more, deterioration of LiMn 2 O 4 can be suppressed and cycle characteristics can be maintained.
　また、ＬｉＭｎ2Ｏ4に代表されるスピネル構造を有するリチウムマンガン酸化物は、出力が高い。したがって、ＬｉＭｎ2Ｏ4の反応領域（３．９～４．１Ｖ）では、ＬｉＭｎ2Ｏ4も反応するため、電池の出力が向上する。 In addition, lithium manganese oxide having a spinel structure represented by LiMn 2 O 4 has high output. Accordingly, the reaction area of the LiMn 2 O 4 (3.9 ~ 4.1V ), because LiMn 2 O 4 also react, thus improving the cell output.
　本発明に係るリチウムイオン二次電池用正極材料は、第一の正極活物質と、第二の正極活物質を含み、第一の正極活物質は、組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．９５≦ｘ＜１．２、０．２＜ａ≦０．４、０．４≦ｂ＜０．６、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８、－１≦δ≦１、Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素）で表され、第二の正極活物質は、組成式ＬｉＭｎ2-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＭｎ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表されることを特徴とする。第一の正極活物質の組成式において、酸素の組成比を特定することは困難である。したがって、第一の正極活物質は、Ｌｉと、金属元素と、を含むリチウム遷移金属酸化物よりなり、金属元素として少なくともＮｉと、Ｍｎと、を含み、金属元素に対するＬｉの原子比が、１．１５＜Ｌｉ／金属元素＜１．５であり、Ｍｎに対するＮｉの原子比が、０．３３４＜Ｎｉ／Ｍｎ≦１であることを特徴とする。 The positive electrode material for a lithium ion secondary battery according to the present invention includes a first positive electrode active material and a second positive electrode active material, and the first positive electrode active material has a composition formula Li x Ni a Mn b M c O 2 + δ (0.95 ≦ x < 1.2,0.2 <a ≦ 0.4,0.4 ≦ b <0.6,0 ≦ c ≦ 0.02, a + b + c = 0.8, -1 ≦ δ ≦ 1, M is at least one element selected from Co, Al, V, Mo, W, Zr, Nb, Ti, and Fe), and the second positive electrode active material has a composition formula LiMn 2-y M ′ y O 4 (0 ≦ y ≦ 0.2, where M ′ is at least one of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti, and Cu) It is characterized by being. In the composition formula of the first positive electrode active material, it is difficult to specify the composition ratio of oxygen. Therefore, the first positive electrode active material is made of a lithium transition metal oxide containing Li and a metal element, contains at least Ni and Mn as the metal element, and the atomic ratio of Li to the metal element is 1 It is characterized in that 15 <Li / metal element <1.5, and the atomic ratio of Ni to Mn is 0.334 <Ni / Mn ≦ 1.
　第一の正極活物質において、金属元素に対するリチウム元素の割合（Ｌｉ／金属元素）が１．１５未満であると、反応に寄与するＬｉの量が減り高容量が得られない。一方、Ｌｉ／金属元素が１．５より大きいと、結晶格子が不安定になり放電容量が低下する。Ｎｉ／Ｍｎが０．３３４より低いと放電電位が低下し、放電末期の電位と第二の正極活物質の反応電位に大きな差が生じ、第二の正極活物質により、放電末期の抵抗を改善できない。Ｎｉ／Ｍｎが１より大きいと、酸素が関与した充放電反応がほとんど起こらず、容量が低下する。なお、第一の正極活物質に含まれる酸素量は、金属元素とリチウムの合計モル数と同等となることを基本として、金属の価数やＬｉの量により、層状固溶体構造を維持しながら保持される酸素量が適宜増減すると考えられるため、－１≦δ≦１とする。 In the first positive electrode active material, when the ratio of lithium element to metal element (Li / metal element) is less than 1.15, the amount of Li contributing to the reaction is reduced and high capacity can not be obtained. On the other hand, if Li / metal element is larger than 1.5, the crystal lattice becomes unstable and the discharge capacity is reduced. When Ni / Mn is lower than 0.334, the discharge potential decreases, and a large difference occurs between the reaction end potential and the reaction potential of the second positive electrode active material, and the second positive electrode active material improves the resistance at the discharge end Can not. When Ni / Mn is larger than 1, almost no charge / discharge reaction involving oxygen occurs, and the capacity decreases. The amount of oxygen contained in the first positive electrode active material is maintained while maintaining the layered solid solution structure by the valence of the metal and the amount of Li on the basis that the total molar number of the metal element and lithium is equivalent. Since it is considered that the amount of oxygen to be supplied is appropriately increased or decreased, -1.ltoreq..delta..ltoreq.1.
　さらに高エネルギー密度を維持し、かつ放電末期の抵抗を低減するためには、第一の正極活物質が、組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．９５≦ｘ≦１．１、０．３＜ａ＜０．４、０．４＜ｂ＜０．５、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８、－１≦δ≦１、Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素）であることが好ましい。つまり、１．１５＜Ｌｉ／金属元素＜１．４、０．３３４＜Ｎｉ／Ｍｎ＜０．８をみたすことが好ましい。 In order to maintain the high energy density and reduce the resistance at the end of discharge, the first positive electrode active material is prepared by the composition formula Li x Ni a Mn b M c O 2 + δ (0.95 ≦ x ≦ 1 .1, 0.3 <a <0.4, 0.4 <b <0.5, 0 ≦ c ≦ 0.02, a + b + c = 0.8, −1 ≦ δ ≦ 1, M is Co, Al At least one of elements selected from V, Mo, W, Zr, Nb, Ti, and Fe). That is, it is preferable to satisfy 1.15 <Li / metal element <1.4 and 0.334 <Ni / Mn <0.8.
　また、金属元素は、さらに添加元素Ｍを含んでも良い。ただし、金属元素に対するＮｉ及びＭｎの原子比は、０．９７５≦（Ｎｉ＋Ｍｎ）／金属元素≦１．０であることが好ましい。添加元素Ｍは、本発明に影響のない範囲で加えられる添加物や不純物であり、Ｃｏ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｃｕ、Ａｌ、Ｆｅから選択される少なくともいずれかの元素である。 The metal element may further contain an additive element M. However, the atomic ratio of Ni and Mn to the metal element is preferably 0.975 ≦ (Ni + Mn) / metal element ≦ 1.0. The additive element M is an additive or an impurity added within a range not affecting the present invention, and at least one element selected from Co, V, Mo, W, Zr, Nb, Ti, Cu, Al, Fe It is.
　第二の正極活物質において、ｙは、Ｍ´の含有比率（物質量比率）を示す。Ｍ´は、適宜加えられる元素であり、添加量は本発明の効果が抑制されないように、０≦ｙ≦０．２の範囲までに抑える必要がある。 In the second positive electrode active material, y represents the content ratio (the mass ratio of substance) of M ′. M ′ is an element to be added appropriately, and the addition amount thereof needs to be suppressed to the range of 0 ≦ y ≦ 0.2 so that the effect of the present invention is not suppressed.
　第二の正極活物質の含有量は、正極材料に対し５質量％以上３０質量％未満であることが好ましい。第二の正極活物質の含有量が５質量％未満の場合、電極密度を向上させる効果が小さく、高い体積エネルギー密度が得られない。第二の正極活物質の含有量が３０質量％以上となると、高容量が得られる第一の正極活物質の割合が減るため、高いエネルギー密度が得られない。さらに、高い体積エネルギー密度を得るためには、第二の正極活物質の含有量が５質量％以上２０質量％以下であることが好ましい。 The content of the second positive electrode active material is preferably 5% by mass or more and less than 30% by mass with respect to the positive electrode material. When the content of the second positive electrode active material is less than 5% by mass, the effect of improving the electrode density is small, and a high volume energy density can not be obtained. When the content of the second positive electrode active material is 30% by mass or more, the proportion of the first positive electrode active material from which high capacity can be obtained decreases, so that high energy density can not be obtained. Furthermore, in order to obtain high volume energy density, the content of the second positive electrode active material is preferably 5% by mass or more and 20% by mass or less.
　第一の正極活物質の粒子径は、１００～４００ｎｍが好ましい。粒子径を小さくすることによって抵抗を低減できる。電極密度を向上させるためには、第二の正極活物質の粒子径は、５～１５μｍが好ましい。ＬｉＭｎ2Ｏ4に代表される第二の正極活物質は、粒子径が大きくても高い容量が得られる。 The particle diameter of the first positive electrode active material is preferably 100 to 400 nm. The resistance can be reduced by reducing the particle size. In order to improve the electrode density, the particle diameter of the second positive electrode active material is preferably 5 to 15 μm. The second positive electrode active material represented by LiMn 2 O 4 can obtain high capacity even if the particle size is large.
　本発明に係る正極材料は、本発明の属する技術分野において一般的に使用されている方法で作製することができる。 The positive electrode material according to the present invention can be produced by a method generally used in the technical field to which the present invention belongs.
　第一の正極活物質は、例えば、Ｌｉ、Ｎｉ、及びＭｎをそれぞれ含む化合物を適当な比率で混合し、焼成することにより作製することができる。混合する化合物の比率を変化させることにより、正極材料の組成を適宜調節することができる。Ｌｉを含有する化合物としては、例えば、酢酸リチウム、硝酸リチウム、炭酸リチウム、水酸化リチウム、酸化リチウム等を挙げることができる。Ｎｉを含有する化合物としては、例えば、酢酸ニッケル、硝酸ニッケル、炭酸ニッケル、硫酸ニッケル、水酸化ニッケル等を挙げることができる。Ｍｎを含有する化合物としては、例えば、酢酸マンガン、硝酸マンガン、炭酸マンガン、硫酸マンガン、酸化マンガン等を挙げることができる。 The first positive electrode active material can be produced, for example, by mixing and firing compounds containing Li, Ni, and Mn in appropriate proportions. The composition of the positive electrode material can be appropriately adjusted by changing the ratio of the compounds to be mixed. Examples of the compound containing Li include lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium oxide and the like. Examples of the compound containing Ni include nickel acetate, nickel nitrate, nickel carbonate, nickel sulfate, nickel hydroxide and the like. As a compound containing Mn, manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide etc. can be mentioned, for example.
　第二の正極活物質は、Ｌｉ、及びＭｎをそれぞれ含む化合物を適当な比率で混合し、焼成することにより作製することができる。Ｌｉを含有する化合物としては、例えば、酢酸リチウム、硝酸リチウム、炭酸リチウム、水酸化リチウム、酸化リチウム等を挙げることができる。Ｍｎを含有する化合物としては、例えば、酢酸マンガン、硝酸マンガン、炭酸マンガン、硫酸マンガン、酸化マンガン等を挙げることができる。 The second positive electrode active material can be produced by mixing and calcining compounds containing Li and Mn respectively in appropriate proportions. Examples of the compound containing Li include lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium oxide and the like. As a compound containing Mn, manganese acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide etc. can be mentioned, for example.
　正極材料の組成は、例えば誘導結合プラズマ法（ＩＣＰ）等による元素分析により決定することができる。 The composition of the positive electrode material can be determined, for example, by elemental analysis using inductively coupled plasma (ICP) or the like.
　＜リチウムイオン二次電池＞
　本発明に係るリチウムイオン二次電池は、上記の正極材料を含むことを特徴とする。上記の正極材料を正極に使用することにより、高い体積エネルギー密度、かつ高出力を達成できる。 <Lithium ion secondary battery>
The lithium ion secondary battery according to the present invention is characterized by containing the above-mentioned positive electrode material. By using the above-described positive electrode material for the positive electrode, high volume energy density and high output can be achieved.
　また、ＬｉＭｎ2Ｏ4に代表される第二の正極活物質は３．２Ｖ以下で使用すると、サイクル特性が低下するおそれがある。したがって、使用の際は、下限電位をＬｉ金属基準で３．３Ｖ以上とすることで、第二の正極活物質の劣化を抑制し、高いサイクル特性を維持できる。本発明に係るリチウムイオン二次電池は、電気自動車に対して好ましく使用することができる。 In addition, when the second positive electrode active material typified by LiMn 2 O 4 is used at 3.2 V or less, the cycle characteristics may be degraded. Therefore, in use, by setting the lower limit potential to 3.3 V or more based on Li metal, deterioration of the second positive electrode active material can be suppressed, and high cycle characteristics can be maintained. The lithium ion secondary battery according to the present invention can be preferably used for an electric vehicle.
　正極活物質は、充放電により、リチウムイオンを吸蔵放出する。正極活物質から放出されたリチウムイオンはすべて正極に戻るわけではないため、充放電後における正極活物質の組成は、充放電前とは異なると予想される。 The positive electrode active material occludes and releases lithium ions by charge and discharge. Since not all lithium ions released from the positive electrode active material return to the positive electrode, the composition of the positive electrode active material after charge and discharge is expected to be different from that before charge and discharge.
　例えば、ＬｉＭＯ2で表される層状化合物の正極活物質は、Ｌｉ金属基準で２．０～４．３Ｖの電位範囲で使用したときに、満放電状態（２．０Ｖ）でＬｉの組成比が０．７５程度となることが分かっている。層状化合物と同様に考えると、層状固溶体の充放電後のＬｉの物質量も、充放電前と比較して満放電状態で２割程度減少していると推測される。したがって、本発明に係る正極材料を用いてリチウム二次電池を作製し、充放電した場合、満放電状態では、第一の正極活物質は、組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．７５≦ｘ＜１．２、０．２＜ａ≦０．４、０．４≦ｂ＜０．６、０≦ｃ≦０．０２、－１≦δ≦１）となる。つまり、第一の正極活物質中のＬｉ以外の金属元素に対するＬｉの原子比は、０．９０＜Ｌｉ／金属元素＜１．５の関係をみたす。 For example, the positive electrode active material of a layered compound represented by LiMO 2 has a composition ratio of Li in a full discharge state (2.0 V) when used in a potential range of 2.0 to 4.3 V based on Li metal. It is known to be about 0.75. In the same way as in the case of the layered compound, it is presumed that the substance mass of Li after charging and discharging of the layered solid solution is also reduced by about 20% in the fully discharged state compared to before charging and discharging. Therefore, when a lithium secondary battery is manufactured using the positive electrode material according to the present invention and charged and discharged, the first positive electrode active material is represented by the composition formula Li x Ni a Mn b M c O 2 + in a full discharge state. δ (0.75 ≦ x <1.2, 0.2 <a ≦ 0.4, 0.4 ≦ b <0.6, 0 ≦ c ≦ 0.02, -1 ≦ δ ≦ 1). That is, the atomic ratio of Li to metal elements other than Li in the first positive electrode active material satisfies the relationship 0.90 <Li / metal element <1.5.
　リチウムイオン二次電池は、正極材料を含む正極、負極材料を含む負極、セパレータ、電解液、電解質等から構成される。 The lithium ion secondary battery is composed of a positive electrode containing a positive electrode material, a negative electrode containing a negative electrode material, a separator, an electrolytic solution, an electrolyte and the like.
　負極材料は、リチウムイオンを吸蔵放出することができる物質であれば特に限定されない。リチウムイオン二次電池において一般的に使用されている物質を負極材料として使用することができる。例えば、黒鉛、リチウム合金等を例示することができる。 The negative electrode material is not particularly limited as long as it is a substance capable of inserting and extracting lithium ions. Materials generally used in lithium ion secondary batteries can be used as the negative electrode material. For example, graphite, lithium alloy and the like can be exemplified.
　セパレータとしては、リチウムイオン二次電池において一般的に使用されているものを使用することができる。例えば、ポリプロピレン、ポリエチレン、プロピレンとエチレンとの共重合体等のポリオレフィン製の微孔性フィルムや不織布等を例示することができる。 As a separator, those generally used in lithium ion secondary batteries can be used. For example, a microporous film or non-woven fabric made of polyolefin such as polypropylene, polyethylene, and a copolymer of propylene and ethylene can be exemplified.
　電解液及び電解質としては、リチウムイオン二次電池において一般的に使用されているものを使用することができる。例えば、電解液として、ジエチルカーボネート、ジメチルカーボネート、エチレンカーボネート、プロピレンカーボネート、ビニレンカーボネート、メチルアセテート、エチルメチルカーボネート、メチルプロピルカーボネート、ジメトキシエタン等を例示することができる。また、電解質として、ＬｉＣｌＯ4、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＳｂＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＣ4Ｆ9ＳＯ3、ＬｉＣＦ3ＣＯ2、Ｌｉ2Ｃ2Ｆ4（ＳＯ3）2、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＣ（ＣＦ3ＳＯ2）3等を例示することができる。 As the electrolytic solution and the electrolyte, those generally used in lithium ion secondary batteries can be used. For example, as the electrolytic solution, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, methyl acetate, ethyl methyl carbonate, methyl propyl carbonate, dimethoxyethane and the like can be exemplified. Further, as the electrolyte, LiClO 4, LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) can be exemplified 3 or the like.
　本発明に係るリチウムイオン二次電池の構造の一実施形態を、図２を用いて説明する。リチウムイオン二次電池１２は、集電体の両面に正極材料を塗布した正極３と、集電体の両面に負極材料を塗布した負極４と、セパレータ５とを有する電極群を備える。正極３及び負極４は、セパレータ５を介して捲回され、捲回体の電極群を形成している。この捲回体は電池缶６に挿入される。 One embodiment of a structure of a lithium ion secondary battery according to the present invention will be described with reference to FIG. The lithium ion secondary battery 12 includes an electrode group including a positive electrode 3 having a positive electrode material coated on both sides of a current collector, a negative electrode 4 having a negative electrode material coated on both sides of the current collector, and a separator 5. The positive electrode 3 and the negative electrode 4 are wound via the separator 5 to form a wound electrode group. The wound body is inserted into the battery can 6.
　負極４は、負極リード片８を介して、電池缶６に電気的に接続される。電池缶６には、パッキン１０を介して、密閉蓋９が取り付けられる。正極３は、正極リード片７を介して、密閉蓋９に電気的に接続される。捲回体は、絶縁板１１によって絶縁される。 The negative electrode 4 is electrically connected to the battery can 6 via the negative electrode lead piece 8. A sealing lid 9 is attached to the battery can 6 via a packing 10. The positive electrode 3 is electrically connected to the sealing lid 9 through the positive electrode lead piece 7. The wound body is insulated by the insulating plate 11.
　なお、電極群は、図２に示す捲回体でなくてもよく、セパレータ５を介して正極３と負極４とを積層した積層体でもよい。 The electrode group may not be a wound body shown in FIG. 2, and may be a laminate in which the positive electrode 3 and the negative electrode 4 are stacked via the separator 5.
　以下、実施例及び比較例を用いて本発明をより詳細に説明するが、本発明の技術的範囲はこれに限定されるものではない。 Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples, but the technical scope of the present invention is not limited thereto.
　＜正極材料の作製＞
　第一の正極活物質を以下の方法で作製した。炭酸リチウム、炭酸ニッケル、及び炭酸マンガンをボールミルで混合し、前駆体を得た。得られた前駆体を大気中において５００℃で１２時間焼成し、リチウム遷移金属酸化物を得た。得られたリチウム遷移金属酸化物をペレット化した後、大気中において８５０～１０５０℃で１２時間焼成した。焼成したペレットをメノウ乳鉢で粉砕し、組成式ＬｉxＮｉaＭｎbＭcＯ2+δで表される第一の正極活物質を得た。 <Production of positive electrode material>
The first positive electrode active material was produced by the following method. Lithium carbonate, nickel carbonate and manganese carbonate were mixed in a ball mill to obtain a precursor. The obtained precursor was calcined at 500 ° C. for 12 hours in the air to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then fired at 850 to 1050 ° C. for 12 hours in the air. The fired pellet was ground in an agate mortar to obtain a first positive electrode active material represented by the composition formula Li x Ni a Mn b M c O 2 + δ .
　第二の正極活物質を以下の方法で作製した。水酸化リチウム、酸化マンガンをボールミルで混合し、前駆体を得た。得られた前駆体を大気中において５００℃で１２時間焼成し、リチウム遷移金属酸化物を得た。得られたリチウム遷移金属酸化物をペレット化した後、大気中において８００℃で１２時間焼成した。焼成したペレットをメノウ乳鉢で粉砕し、ＬｉＭｎ2Ｏ4を得た。これを第二の正極活物質とした。 The second positive electrode active material was produced by the following method. Lithium hydroxide and manganese oxide were mixed in a ball mill to obtain a precursor. The obtained precursor was calcined at 500 ° C. for 12 hours in the air to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then fired at 800 ° C. for 12 hours in the air. The fired pellet was crushed in an agate mortar to obtain LiMn 2 O 4 . This was used as a second positive electrode active material.
　第一の正極活物質と、第二の正極活物質とを混合し、正極材料とした。作製した正極材料における、第一の正極活物質の組成と、第二の正極活物質の含有量を、表１に示す。 The first positive electrode active material and the second positive electrode active material were mixed to obtain a positive electrode material. The composition of the first positive electrode active material and the content of the second positive electrode active material in the manufactured positive electrode material are shown in Table 1.
　＜試作電池の作製＞
　上述の正極材料を用いて正極を作製し、実施例１～１２、比較例１～６の試作電池を作製した。試作電池に用いた電池
　正極材料と、導電剤とバインダとを均一に混合して正極スラリーを作製した。正極スラリーを厚み２０μｍのアルミ集電体箔上に塗布し、１２０℃で乾燥した。乾燥後、４０ＭＰａの圧力でプレスして電極板を得た。その後、電極板を直径１５ｍｍの円盤状に打ち抜き、正極を作製した。 <Production of a prototype battery>
A positive electrode was produced using the above-mentioned positive electrode material, and trial batteries of Examples 1 to 12 and Comparative Examples 1 to 6 were produced. A positive electrode slurry was prepared by uniformly mixing the positive electrode material of the battery used in the trial battery, the conductive agent, and the binder. The positive electrode slurry was applied onto a 20 μm thick aluminum current collector foil and dried at 120 ° C. After drying, it was pressed at a pressure of 40 MPa to obtain an electrode plate. Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.
　負極は金属リチウムを用いて作製した。非水電解液としては、体積比１：２のエチレンカーボネートとジメチルカーボネートとの混合溶媒に、ＬｉＰＦ6を１．０ｍｏｌ／Ｌの濃度で溶解させたものを用いた。 The negative electrode was produced using metallic lithium. As a non-aqueous electrolytic solution, one in which LiPF 6 was dissolved at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 2 was used.
　＜充放電試験＞
　実施例１～１２、比較例１～６の試作電池に対して、充放電試験を行った。実施例１～１１、比較例１～６の試作電池は、０．０５Ｃ相当の電流で上限電圧を４．６Ｖ、放電は０．５Ｃ相当の電流で下限電圧を３．３Ｖとした充放電試験を行い、２サイクル目の放電容量を定格容量とした。高出力が得られる４．６～３．３Ｖの領域における放電容量を表１に示す。 <Charge / discharge test>
The charge and discharge test was performed on the trial batteries of Examples 1 to 12 and Comparative Examples 1 to 6. The test batteries of Examples 1 to 11 and Comparative Examples 1 to 6 are charge / discharge tests with an upper limit voltage of 4.6 V at a current of 0.05 C equivalent and a lower limit voltage of 3.3 V at a current of 0.5 C equivalent for discharge. And the discharge capacity at the second cycle was taken as the rated capacity. The discharge capacities in the region of 4.6 to 3.3 V where high output can be obtained are shown in Table 1.
　実施例１２の試作電池は、充放電の上限電圧を４．６Ｖ、下限電圧を２．０Ｖとしたこと以外、実施例１と同様にして放電容量を測定した。測定した放電容量を表１に示す。 The experimental battery of Example 12 measured the discharge capacity in the same manner as in Example 1 except that the upper limit voltage for charge and discharge was 4.6 V and the lower limit voltage was 2.0 V. The measured discharge capacities are shown in Table 1.
　＜直流抵抗の測定＞
　各実施例及び比較例の試作電池に対して、ＳＯＣ５０％のときの直流抵抗を求めた。 <Measurement of DC resistance>
The direct current resistance at SOC 50% was determined for the test batteries of each example and comparative example.
　実施例１～１１、比較例１～６の試作電池に対し、充電は０．０５Ｃ相当の電流で上限電圧を４．６Ｖ、放電は０．０５Ｃ相当の電流で下限電圧を３．３Ｖとした充放電試験を行い、２サイクル目の放電容量を定格容量とした。２サイクル後の試作電池を４．６Ｖまで充電し、その後、定格容量の５０％の容量まで放電した。その後、１．２ｍＡの電流を１０秒間印加し、直流抵抗を測定した。電流印加前と電流を１０秒間印加した後の電位差を、印加した電流値（１．２ｍＡ）で割った値を直流抵抗値と定義した。 For the prototype batteries of Examples 1 to 11 and Comparative Examples 1 to 6, the upper limit voltage is 4.6 V at a current of 0.05 C equivalent and the lower limit voltage is 3.3 V at a current of 0.05 C equivalent for discharging. A charge and discharge test was conducted, and the discharge capacity at the second cycle was taken as the rated capacity. The prototype battery after two cycles was charged to 4.6 V and then discharged to a capacity of 50% of the rated capacity. Thereafter, a current of 1.2 mA was applied for 10 seconds to measure the direct current resistance. The value obtained by dividing the potential difference before and after applying the current for 10 seconds by the applied current value (1.2 mA) was defined as the DC resistance value.
　実施例１２の試作電池は、充放電の上限電圧を４．６Ｖ、下限電圧を２．０Ｖとしたこと以外、実施例１と同様にして直流抵抗を測定した。測定した直流抵抗値を表１に示す。
＜容量維持率の測定＞
　各実施例及び比較例の試作電池に対して、１００サイクル後の容量維持率を求めた。 The experimental battery of Example 12 measured DC resistance in the same manner as in Example 1 except that the upper limit voltage for charging and discharging was set to 4.6 V and the lower limit voltage was set to 2.0 V. The measured DC resistance values are shown in Table 1.
<Measurement of capacity retention rate>
The capacity retention rate after 100 cycles was determined for the trial batteries of each example and comparative example.
　実施例１～１１、比較例１～６の試作電池に対し、充電は０．０５Ｃ相当の電流で上限電圧を４．６Ｖ、放電は０．０５Ｃ相当の電流で下限電圧を３．３Ｖとした充放電試験を行い、２サイクル目の放電容量を定格容量とした。その後、充電１C、放電１Cで９９サイクルさせた後、０．０５Cで充放電し、１００サイクル後の容量を測定した。１００サイクル後の放電容量を、定格容量で除した値を容量維持率と定義した。 For the prototype batteries of Examples 1 to 11 and Comparative Examples 1 to 6, the upper limit voltage is 4.6 V at a current of 0.05 C equivalent and the lower limit voltage is 3.3 V at a current of 0.05 C equivalent for discharging. A charge and discharge test was conducted, and the discharge capacity at the second cycle was taken as the rated capacity. Thereafter, after 99 cycles of charge 1 C and discharge 1 C, charge and discharge were carried out at 0.05 C, and the capacity after 100 cycles was measured. A value obtained by dividing the discharge capacity after 100 cycles by the rated capacity was defined as a capacity retention rate.
　実施例１２の正極材料を用いて作製した試作電池は、充放電の上限電圧を４．６Ｖ、下限電圧を２．０Ｖとしたこと以外、実施例１と同様にして容量維持率を測定した。 The capacity retention ratio of the prototype battery manufactured using the positive electrode material of Example 12 was measured in the same manner as in Example 1 except that the upper limit voltage for charging and discharging was set to 4.6 V and the lower limit voltage was set to 2.0 V.
　容量維持率の値を表１に示す。 The values of capacity retention rates are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　図３に、実施例１と比較例１の放電曲線を示す。図３において、１３は実施例１の放電曲線、１４は比較例１の放電曲線である。図３より、３．３Ｖ以上の電位範囲において、実施例１は比較例１よりも高容量であることが分かる。また、実施例１は比較例１よりも電位が高い。したがって、実施例１は比較例１よりも高いエネルギー密度が得られる。実施例２～１２の放電曲線についても、実施例１と同様な結果が得られた。したがって、実施例１～１２は、比較例に比べ高いエネルギー密度が得られる。 The discharge curves of Example 1 and Comparative Example 1 are shown in FIG. In FIG. 3, 13 is a discharge curve of Example 1, and 14 is a discharge curve of Comparative Example 1. It can be seen from FIG. 3 that Example 1 has a higher capacity than Comparative Example 1 in the potential range of 3.3 V or more. In addition, Example 1 has a higher potential than Comparative Example 1. Therefore, Example 1 can obtain higher energy density than Comparative Example 1. The same results as in Example 1 were obtained for the discharge curves of Examples 2 to 12. Therefore, Examples 1 to 12 can obtain higher energy density as compared to the Comparative Example.
　表１に示すように、実施例１～１２では、比較例１～６に比して、単位体積あたりの放電容量が高い。さらに、実施例１～１２では、第二の正極活物質を含まない比較例２に比して、直流抵抗が同等以下である。 As shown in Table 1, in Examples 1 to 12, the discharge capacity per unit volume is higher than in Comparative Examples 1 to 6. Furthermore, in Examples 1 to 12, the direct current resistance is equal to or less than Comparative Example 2 in which the second positive electrode active material is not contained.
　一方、比較例２～６では、高容量と低抵抗を両立することはできなかった。比較例１は第一の正極活物質のＬｉ／（Ｎｉ＋Ｍｎ）が１．５と高く、Ｎｉ／Ｍｎが０．３３と小さいために、４．６～３．３Ｖの領域において単位体積当たりの放電容量が低い。比較例２では、電極密度の低い第一の正極活物質のみから構成されているため、単位体積あたりの放電容量が低い。比較例３では、容量の低い第二の正極活物質のみから構成されているため、単位体積あたりの放電容量が低い。比較例４では、容量の低い第二の正極活物質の含有率が３０％と多いため、単位体積あたりの放電容量が低い。比較例５では，第一の正極活物質のＬｉ／（Ｎｉ＋Ｍｎ）が１．１２５と低いため、放電容量が低く、単位体積当たりの放電容量が低い。比較例６では第一の正極活物質のＬｉ／（Ｎｉ＋Ｍｎ）が１．５０と高いため、放電容量が低く、単位体積当たりの放電容量が低い。 On the other hand, in Comparative Examples 2 to 6, it was not possible to simultaneously achieve high capacity and low resistance. In Comparative Example 1, since Li / (Ni + Mn) of the first positive electrode active material is as high as 1.5 and Ni / Mn is as small as 0.33, discharge per unit volume in the region of 4.6 to 3.3 V Capacity is low. In Comparative Example 2, since only the first positive electrode active material with low electrode density is formed, the discharge capacity per unit volume is low. In Comparative Example 3, the discharge capacity per unit volume is low because only the second positive electrode active material with low capacity is used. In Comparative Example 4, since the content of the second positive electrode active material having a low capacity is as large as 30%, the discharge capacity per unit volume is low. In Comparative Example 5, since Li / (Ni + Mn) of the first positive electrode active material is as low as 1.125, the discharge capacity is low and the discharge capacity per unit volume is low. In Comparative Example 6, since Li / (Ni + Mn) of the first positive electrode active material is as high as 1.50, the discharge capacity is low and the discharge capacity per unit volume is low.
　したがって、Ｌｉ、Ｎｉ、Ｍｎの原子量比が １．１５＜Ｌｉ／（Ｎｉ＋Ｍｎ）＜１．５および０．３３４＜Ｎｉ／Ｍｎ≦１の関係を満たす第一の正極活物質と、組成式ＬｉＭｎ2-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＦｅ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表される第二の正極活物質を含み、正極材料に対する第二の正極活物質の含有量が５質量％以上３０質量％未満である正極材料を用いることにより、リチウムイオン二次電池の、単位体積当たりの放電容量が向上し、かつ、抵抗が低減する。その結果、体積エネルギー密度が高く、かつ、出力の高いリチウムイオン二次電池を提供できる。 Therefore, the first positive electrode active material satisfying the relationship of atomic weight ratios of Li, Ni, and Mn of 1.15 <Li / (Ni + Mn) <1.5 and 0.334 <Ni / Mn ≦ 1, and the composition formula LiMn 2 -y M ' y O 4 (0 y y 0.2 0.2, M' is represented by Fe, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti, Cu, or any other element) Per unit volume of a lithium ion secondary battery by using a positive electrode material containing a second positive electrode active material and having a content of the second positive electrode active material to the positive electrode material of 5% by mass or more and less than 30% by mass. Discharge capacity is improved and resistance is reduced. As a result, it is possible to provide a lithium ion secondary battery having a high volumetric energy density and a high output.
　また、実施例１～３、１１を比較すると、第一の正極活物質の組成が０．３３４＜Ｎｉ／Ｍｎ＜０．８を満たすことによって、単位体積当たりの放電容量が向上する。 Further, comparing Examples 1 to 3 and 11, when the composition of the first positive electrode active material satisfies 0.334 <Ni / Mn <0.8, the discharge capacity per unit volume is improved.
　実施例１と実施例１２を比較すると、実施例１は実施例１２よりも容量維持率が高い。これは、充放電の下限電位が異なるためである。実施例１２は、充放電の下限電位が２．0Ｖと低いため、サイクルを繰り返すと第二の正極活物質が劣化し、容量維持率が低下した。一方、実施例１では、充放電の下限電位を３．３Vとすることによって、第二の正極活物質の劣化を抑制し、高い容量維持率とすることができた。 Comparing Example 1 with Example 12, Example 1 has a higher capacity retention rate than Example 12. This is because the lower limit potentials of charge and discharge are different. In Example 12, since the lower limit potential of charge and discharge was as low as 2.0 V, when the cycle was repeated, the second positive electrode active material was deteriorated, and the capacity retention rate was lowered. On the other hand, in Example 1, by setting the lower limit potential of charge and discharge to 3.3 V, deterioration of the second positive electrode active material was suppressed, and a high capacity retention rate could be achieved.
　以上の結果から、Ｌｉと、少なくともＮｉ及びＭｎを含む金属元素を有するリチウム遷移金属酸化物のＬｉ／（Ｎｉ＋Ｍｎ）およびＮｉ／Ｍｎを最適化した第一の正極活物質と、組成式ＬｉＭｎ1-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＭｎ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表される第二の正極活物質を混合し、第二の正極活物質が劣化しない電位領域で使用することで、高い体積エネルギー密度、高出力、優れたサイクル特性を達成できる。 From the above results, it is apparent that Li / (Ni + Mn) and Ni / Mn of the lithium transition metal oxide having a metal element containing at least Ni and at least Ni and Mn are optimized, and the composition formula LiMn 1− y M ′ y O 4 (0 ≦ y ≦ 0.2, M ′ is represented by at least one element of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti and Cu) By mixing the second positive electrode active material and using it in a potential region where the second positive electrode active material is not deteriorated, high volume energy density, high output, and excellent cycle characteristics can be achieved.
　１　Ｌｉ1.05Ｎｉ0.35Ｍｎ0.45Ｏ2の放電曲線
　２　Ｌｉ1.2Ｎｉ0.2Ｍｎ0.6Ｏ2の放電曲線
　３　正極
　４　負極
　５　セパレータ
　６　電池缶
　７　正極リード片
　８　負極リード片
　９　密閉蓋
　１０　パッキン
　１１　絶縁板
　１２　リチウムイオン二次電池
　１３　実施例１の放電曲線
　１４　比較例１の放電曲線 DESCRIPTION OF SYMBOLS 1 Li 1.05 Ni 0.35 Mn 0.45 O 2 discharge curve 2 Li 1.2 Ni 0.2 Mn 0.6 O 2 discharge curve 3 positive electrode 4 negative electrode 5 separator 6 battery can 7 positive electrode lead piece 8 negative electrode lead piece 9 sealing lid 10 packing 11 insulating plate 12 Lithium Ion Secondary Battery 13 Discharge Curve of Example 1 14 Discharge Curve of Comparative Example 1

Claims (14)

  1. 　リチウムイオンを吸蔵、放出する正極活物質を含むリチウムイオン二次電池用正極材料であって、
    　Ｌｉと、金属元素と、を含むリチウム遷移金属酸化物よりなり、前記金属元素として少なくともＮｉと、Ｍｎと、を含み、前記金属元素に対する前記Ｌｉの原子比が、１．１５＜Ｌｉ／金属元素＜１．５であり、前記Ｍｎに対する前記Ｎｉの原子比が、０．３３４＜Ｎｉ／Ｍｎ≦１である第一の正極活物質と、
    　組成式ＬｉＭｎ2-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＭｎ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表される第二の正極活物質を含み、
    　前記第二の正極活物質の含有量は、前記正極材料に対し５質量％以上３０質量％未満であることを特徴とするリチウムイオン二次電池用正極材料。     A positive electrode material for a lithium ion secondary battery, comprising a positive electrode active material that absorbs and releases lithium ions,
    It is made of a lithium transition metal oxide containing Li and a metal element, containing at least Ni and Mn as the metal element, and the atomic ratio of Li to the metal element is 1.15 <Li / metal element A first positive electrode active material, wherein an atomic ratio of the Ni to the Mn is 0.334 <Ni / Mn ≦ 1.
    Composition formula LiMn 2-y M ′ y O 4 (0 ≦ y ≦ 0.2, where M ′ is at least one element of Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, Ti, and Cu) Containing the second positive electrode active material represented by
    Content of said 2nd positive electrode active material is 5 mass% or more and less than 30 mass% with respect to said positive electrode material, The positive electrode material for lithium ion secondary batteries characterized by the above-mentioned.
  2. 　請求項１に記載のリチウムイオン二次電池用正極材料であって、
    　前記第一の正極活物質は、前記金属元素として、添加元素Ｍを含み、
    　前記Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素であり、
    　前記金属元素に対する前記Ｍｎ及び前記Ｎｉの原子比が、０．９７５≦（Ｎｉ＋Ｍｎ）／金属元素≦１であることを特徴とするリチウムイオン二次電池用正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 1, wherein
    The first positive electrode active material contains an additive element M as the metal element,
    The M is at least one element selected from Co, Al, V, Mo, W, Zr, Nb, Ti, and Fe,
    A positive electrode material for a lithium ion secondary battery, wherein an atomic ratio of the Mn and the Ni to the metal element is 0.975 ≦ (Ni + Mn) / metal element ≦ 1.
  3. 　請求項１に記載のリチウムイオン二次電池用正極材料であって、
    　前記第一の正極活物質の粒子径は、前記第二の正極活物質の粒子径よりも小さいことを特徴とするリチウムイオン二次電池用正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 1, wherein
    A particle diameter of the first positive electrode active material is smaller than a particle diameter of the second positive electrode active material, and a positive electrode material for a lithium ion secondary battery.
  4. 　請求項１に記載のリチウムイオン二次電池用正極材料であって、
    　前記第一の正極活物質の前記Ｍｎに対する前記Ｎｉの原子比は、０．３３４＜Ｎｉ／Ｍｎ＜０．８であることを特徴とするリチウムイオン二次電池用正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 1, wherein
    An atomic ratio of the Ni to the Mn of the first positive electrode active material is 0.334 <Ni / Mn <0.8. A positive electrode material for a lithium ion secondary battery.
  5. 　請求項１に記載のリチウムイオン二次電池用正極材料であって、
    　前記第一の正極活物質は、組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．９５≦ｘ＜１．２、０．２＜ａ≦０．４、０．４≦ｂ＜０．６、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８、－１≦δ≦１、Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素）で表されることを特徴とするリチウムイオン二次電池用正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 1, wherein
    The first positive electrode active material has a composition formula Li x Ni a Mn b M c O 2 + δ (0.95 ≦ x <1.2, 0.2 <a ≦ 0.4, 0.4 ≦ b < 0.6, 0 ≦ c ≦ 0.02, a + b + c = 0.8, −1 ≦ δ ≦ 1, M is at least one selected from Co, Al, V, Mo, W, Zr, Nb, Ti, Fe The positive electrode material for lithium ion secondary batteries characterized by being represented by any element).
  6. 　請求項５に記載のリチウムイオン二次電池用正極材料であって、
    　組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．９５≦ｘ≦１．１、０．３＜ａ＜０．４、０．４＜ｂ＜０．５、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８、－１≦δ≦１、Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素）で表されることを特徴とするリチウムイオン二次電池用正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 5, wherein
    Compositional formula Li x Ni a Mn b M c O 2 + δ (0.95 ≦ x ≦ 1.1, 0.3 <a <0.4, 0.4 <b <0.5, 0 ≦ c ≦ 0 .02, a + b + c = 0.8, -1 ≦ δ ≦ 1, M is represented by Co, Al, V, Mo, W, Zr, Nb, Ti, Fe, and at least one of the elements) What is claimed is: 1. A positive electrode material for a lithium ion secondary battery characterized by:
  7. 　請求項１から６のいずれかに記載のリチウムイオン二次電池用正極材料を含むことを特徴とするリチウムイオン二次電池用正極。 A positive electrode for a lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 6.
  8. 　正極材料を備える正極と、負極材料とを備える負極と、を備えるリチウムイオン二次電池であって、
    　前記正極材料は、第一の正極活物質と第二の正極活物質とを含み、
    　前記第一の正極活物質は、Ｌｉと、金属元素と、を含むリチウム遷移金属酸化物よりなり、前記金属元素として少なくともＮｉと、Ｍｎと、を含み、前記金属元素に対する前記Ｌｉの原子比は、０．９０＜Ｌｉ／金属元素＜１．５であり、前記Ｍｎに対する前記Ｎｉの原子比は、０．３３４＜Ｎｉ／Ｍｎ≦１であり、
    　前記第二の正極活物質は、組成式ＬｉＭｎ2-yＭ´yＯ4（０≦ｙ≦０．２、Ｍ´はＭｎ、Ｃｏ、Ｎｉ、Ｖ、Ｍｇ、Ｍｏ、Ｗ、Ａｌ、Ｎｂ、Ｔｉ、Ｃｕの少なくともいずれかの元素）で表され、
    　前記第二の正極活物質の含有量は、前記正極材料に対し５質量％以上３０質量％未満であることを特徴とするリチウムイオン二次電池。     A lithium ion secondary battery comprising a positive electrode comprising a positive electrode material and a negative electrode comprising a negative electrode material,
    The positive electrode material includes a first positive electrode active material and a second positive electrode active material,
    The first positive electrode active material is made of a lithium transition metal oxide containing Li and a metal element, contains at least Ni and Mn as the metal element, and the atomic ratio of Li to the metal element is And 0.90 <Li / metal element <1.5, and the atomic ratio of the Ni to the Mn is 0.334 <Ni / Mn ≦ 1;
    The second positive electrode active material has a composition formula LiMn 2 -y M ′ y O 4 (0 ≦ y ≦ 0.2, where M ′ is Mn, Co, Ni, V, Mg, Mo, W, Al, Nb, And at least one element of Ti and Cu),
    Content of said 2nd positive electrode active material is 5 mass% or more and less than 30 mass% with respect to the said positive electrode material, The lithium ion secondary battery characterized by the above-mentioned.
  9. 　請求項８に記載のリチウムイオン二次電池であって、
    　前記第一の正極活物質は、前記金属元素として、添加元素Ｍを含み、
    　前記Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素であり、
    　前記金属元素に対する前記Ｍｎ及び前記Ｎｉの原子比が、０．９７５≦（Ｎｉ＋Ｍｎ）／金属元素≦１であることを特徴とするリチウムイオン二次電池。     A lithium ion secondary battery according to claim 8, wherein
    The first positive electrode active material contains an additive element M as the metal element,
    The M is at least one element selected from Co, Al, V, Mo, W, Zr, Nb, Ti, and Fe,
    The atomic ratio of said Mn and said Ni with respect to the said metallic element is 0.975 <= (Ni + Mn) / metallic element <= 1, The lithium ion secondary battery characterized by the above-mentioned.
  10. 　請求項８に記載のリチウムイオン二次電池用正極材料であって、
    　前記第一の正極活物質の粒子径は、前記第二の正極活物質の粒子径よりも小さいことを特徴とするリチウムイオン二次電池用正極材料。     It is a positive electrode material for lithium ion secondary batteries of Claim 8, Comprising:
    A particle diameter of the first positive electrode active material is smaller than a particle diameter of the second positive electrode active material, and a positive electrode material for a lithium ion secondary battery.
  11. 　請求項８に記載のリチウムイオン二次電池であって、
    　前記第一の正極活物質の前記Ｍｎに対する前記Ｎｉの原子比は、０．３３４＜Ｎｉ／Ｍｎ＜０．８であることを特徴とするリチウムイオン二次電池。     A lithium ion secondary battery according to claim 8, wherein
    The atomic ratio of the Ni to the Mn of the first positive electrode active material is 0.334 <Ni / Mn <0.8.
  12. 　請求項８に記載のリチウムイオン二次電池であって、
    　前記第一の正極活物質は、組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．７５≦ｘ＜１．２、０．２＜ａ≦０．４、０．４≦ｂ＜０．６、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８、－１≦δ≦１、Ｍは、Ｃｏ、Ａｌ、Ｖ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ｆｅから選択される少なくともいずれかの元素）で表されることを特徴とするリチウムイオン二次電池。     A lithium ion secondary battery according to claim 8, wherein
    The first positive electrode active material has a composition formula Li x Ni a Mn b M c O 2+ δ (0.75 ≦ x <1.2, 0.2 <a ≦ 0.4, 0.4 ≦ b < 0.6, 0 ≦ c ≦ 0.02, a + b + c = 0.8, −1 ≦ δ ≦ 1, M is at least one selected from Co, Al, V, Mo, W, Zr, Nb, Ti, Fe A lithium ion secondary battery characterized by being represented by any element).
  13. 　請求項１２に記載のリチウムイオン二次電池であって、
    　組成式ＬｉxＮｉaＭｎbＭcＯ2+δ（０．７５≦ｘ≦１．１、０．３＜ａ＜０．４、０．４＜ｂ＜０．５、０≦ｃ≦０．０２、ａ＋ｂ＋ｃ＝０．８－１≦δ≦１）で表されることを特徴とするリチウムイオン二次電池。     13. The lithium ion secondary battery according to claim 12, wherein
    Compositional formula Li x Ni a Mn b M c O 2+ δ (0.75 ≦ x ≦ 1.1, 0.3 <a <0.4, 0.4 <b <0.5, 0 ≦ c ≦ 0 . 02, a + b + c = 0.8-1 ≦ δ ≦ 1), and a lithium ion secondary battery.
  14. 　請求項８ないし１４のいずれかに記載のリチウムイオン二次電池であって、
    　使用される際の下限電位がＬｉ金属基準で３．３Ｖ以上であることを特徴とするリチウムイオン二次電池。     A lithium ion secondary battery according to any one of claims 8 to 14, wherein
    The lower limit electric potential at the time of being used is 3.3V or more in Li metal standard, The lithium ion secondary battery characterized by the above-mentioned.
PCT/JP2014/055216 2014-03-03 2014-03-03 Positive electrode material for lithium ion secondary batteries, and lithium ion secondary battery WO2015132844A1 (en)

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