JP5522844B2 - Electrode for electrochemical element and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an electrode that can be used for an electrochemical element such as a battery or a capacitor, and a lithium ion secondary battery having the electrode.

In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries and capacitors having a small size and a high capacity have been required. Currently, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are generally used as positive electrode active materials for high-capacity secondary batteries and capacitors that can meet this requirement.

However, these positive electrode active materials have the following drawbacks. LiCoO ₂ has low thermal stability in the charged state. In addition, LiNiO ₂ has a higher capacity than LiCoO ₂ , but its thermal stability in a charged state is lower than LiCoO ₂ . Furthermore, LiMn ₂ O ₄ has high thermal stability in the charged state, but has a smaller capacity per volume than LiCoO ₂ .

In response to these circumstances, for example, in order to achieve both high capacity of thermal stability and LiNiO ₂ of LiMn ₂ O _4, while retaining the crystal structure of LiNiO ₂ layered, high thermal stability Mn Lithium-containing composite oxides in which a predetermined amount of Ni is substituted are proposed (Patent Documents 1 and 2).

JP 2003-221236 A International Publication No. 02/40404

  By the way, in order to increase the capacity of the secondary battery, in addition to selecting the type of the positive electrode active material, increasing the density of the positive electrode mixture layer containing the positive electrode active material and increasing the filling amount of the positive electrode active material. Conceivable.

  However, when the density of the positive electrode mixture layer is increased, voids in the positive electrode mixture layer are reduced, so that it is difficult for the nonaqueous electrolyte to permeate, and the nonaqueous electrolyte injection process during battery production takes time. As a result, battery productivity may be reduced. In addition, since the non-aqueous electrolyte does not easily penetrate into the positive electrode mixture layer, there is a possibility that the capacity of the battery may be reduced, and battery characteristics such as charge / discharge cycle characteristics may be deteriorated.

  The present invention has been made in view of the above circumstances, and an object thereof is an electrode for an electrochemical element having a high density and good nonaqueous electrolyte permeability, and a lithium ion secondary having the electrode. To provide a battery.

The electrode for an electrochemical element of the present invention that has achieved the above object is an electrode for an electrochemical element having an electrode mixture layer containing an active material on one side or both sides of a current collector. )
Li _x Ni _(1-yz) Co _y M _z O ₂ (1)
[In the general formula (1), M is at least one element of Mn and Al, 0.9 ≦ x ≦ 1.3, 0 <y <1, 0 <z <1, and y + z <. 1), and has two peak tops in the volume-based particle size distribution, and the peak top of the peak (A) on the small particle size side is in the range of 2 to 4 μm in particle size, And the peak top of the peak (B) on the large particle size side exists in the range of the particle size of 8.8 to 11 μm, the volume frequency of the particle size in the peak (A) is A, and the peak (B) When the volume frequency of the particle size is B, the lithium content satisfying the relationship of 0.18 ≦ A / (A + B) ≦ 0.45 and the particle size of the cumulative volume of 50% is 4.6 to 10.3 μm. Using the composite oxide as the active material, the pore distribution curve of the electrode mixture layer obtained by the mercury intrusion method is used. And the peak top of the peak (a) on the small pore diameter side exists in the pore diameter range of 140 to 220 nm, and the peak top of the peak (b) on the large pore diameter side is fine. The pore diameter is within a range of 330 to 910 nm, the peak top pore volume in the peak (a) is a (ml / g), and the peak top pore volume in the peak (b) is b (ml / ml). When g), the relationship 0.26 ≦ a / (a + b) ≦ 0.53 is satisfied.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode is an electrode for an electrochemical device of the present invention. .

  According to the present invention, it is possible to provide an electrode for an electrochemical element that has a high density and good non-aqueous electrolyte permeability, and a lithium ion secondary battery having the electrode.

It is a schematic diagram which shows an example of the electrochemical element (lithium ion secondary battery) of this invention, (a) Top view, (b) Cross-sectional view. FIG. 2 is a perspective view of FIG. 1.

  The electrode for an electrochemical element of the present invention (hereinafter sometimes simply referred to as “electrode”) is constituted by forming an electrode mixture layer containing an active material or the like on one side or both sides of a current collector. ing.

  The electrode of the present invention uses a lithium-containing composite oxide represented by the general formula (1) as an active material. The electrode of the present invention is used, for example, as a positive electrode of an electrochemical element. That is, the lithium-containing composite oxide acts as a positive electrode active material for an electrochemical element such as a lithium ion secondary battery, and contributes to increasing the capacity of the electrochemical element.

  Moreover, in order to increase the capacity of the electrochemical device, it is preferable to increase the density of the electrode mixture layer and increase the filling amount of the active material. However, as described above, the density of the electrode mixture layer related to the electrode makes it difficult for the nonaqueous electrolyte solution of the electrochemical element to penetrate well into the electrode mixture layer. Productivity will be reduced.

  Therefore, the electrode of the present invention has two peak tops in the pore distribution curve of the electrode mixture layer obtained by the mercury intrusion method, and the peak top of the peak (a) on the small pore diameter side has a pore diameter of 140 to 220 nm. And the peak top of the peak (b) on the large pore diameter side is in the range of the pore diameter of 330 to 910 nm, and the peak top pore volume in the peak (a) is defined as a (ml / G), where the peak top pore volume in the peak (b) is b (ml / g), the electrode mixture layer satisfies the relationship of 0.26 ≦ a / (a + b) ≦ 0.53 By controlling the pore distribution, it is possible to increase the permeability of the non-aqueous electrolyte while increasing the density of the electrode mixture layer.

  In this specification, the mercury intrusion method refers to the relationship between the pressure when the container containing the sample is evacuated, filled with mercury and filled, and the amount of mercury injected into the pores of the sample. From this, information such as pore distribution is obtained. The pore distribution curve referred to in this specification is a log differential pore volume (cc / g) obtained by differentiating the increase in pore volume per unit weight with the logarithm of pore diameter, with the logarithm of pore diameter as the horizontal axis. ) Is plotted on the vertical axis. Specifically, a 2 × 4 cm sample (electrode with current collector) was measured using a mercury porosimeter (“Poresizer 9310” manufactured by Micromeritic). It is obtained. Further, in this specification, “peak top” refers to a point where the coordinate value of the vertical axis takes the largest value in each peak of the pore distribution curve.

  That is, in the pore distribution curve of the electrode mixture layer, if the pore diameter at which the peak top of peak (a) or peak (b) appears is too small or the value of a / (a + b) is too large, the electrode mixture While the density of the layer increases, the permeability of the non-aqueous electrolyte decreases. On the other hand, in the pore distribution curve of the electrode mixture layer, if the pore diameter at which the peak top of peak (a) or peak (b) appears is too large, or the value of a / (a + b) is too small, the electrode mixture The layer density cannot be increased.

  The electrode of the present invention uses the lithium-containing composite oxide represented by the general formula (1) as an active material. In this lithium-containing composite oxide, Ni and Co contribute to the capacity of the lithium-containing composite oxide. It is an ingredient to do. Co also acts to improve the packing density in the electrode mixture layer. Therefore, in the general formula (1), y representing the amount of Co is set to be larger than 0, but y is preferably 0.1 or more from the viewpoint of better exhibiting the above-described action. In the general formula (1), y representing the amount of Co is smaller than 1. However, if the amount of Co is large, there is a risk of causing an increase in cost and a decrease in safety of the electrochemical device in which the electrode of the present invention is used. There is. Therefore, in the general formula (1), y representing the amount of Co is preferably 0.25 or less.

  The lithium-containing composite oxide represented by the general formula (1) contains an element M that is at least one of Mn and Al. When the lithium-containing composite oxide contains Mn as the element M, the thermal stability of the lithium-containing composite oxide is improved by the presence of Mn in the crystal lattice, so that the safety is higher. An electrochemical element can be configured.

  Further, when the lithium-containing composite oxide contains Mn, Co suppresses fluctuations in the valence of Mn associated with doping and dedoping of Li during charging and discharging of the electrochemical element, and the average valence of Mn is 4 It stabilizes to a value close to the valence, and suppresses Mn precipitation at the negative electrode peculiar to an electrochemical element using a lithium-containing composite oxide containing Mn, so that it is more charged than a normal lithium-containing composite oxide containing Mn. An electrochemical element having excellent discharge cycle characteristics can be configured.

  Further, in the lithium-containing composite oxide, if Al is present in the crystal lattice, the crystal structure of the lithium-containing composite oxide can be stabilized and the thermal stability thereof can be improved. Thus, it is possible to configure a safer electrochemical device. In addition, Al is present at the grain boundaries and surfaces of the lithium-containing composite oxide particles, so that the stability over time and side reactions with the non-aqueous electrolyte can be suppressed, and a longer-lifetime electrochemical device is constructed. It becomes possible to do.

  In the lithium-containing composite oxide, from the viewpoint of securing the above-described action by including the element M, z representing the amount of the element M in the general formula (1) is set to be larger than 0. From the viewpoint of achieving good results, z is preferably 0.05 or more. In the general formula (1), z representing the amount of the element M is smaller than 1, but for example, since Al cannot participate in the charge / discharge capacity, the content in the lithium-containing composite oxide is increased. As a result, the effect of increasing the capacity may be reduced. Therefore, in the general formula (1), z representing the amount of the element M is preferably 0.35 or less.

  Further, as described above, in the lithium-containing composite oxide represented by the general formula (1), the total y + z of y representing the amount of Co and z representing the amount of the element M is smaller than 1, but the lithium In the composite oxide containing Ni, since Ni is a component that contributes to an increase in capacity, if the amount of Co and element M is too large, the amount of Ni may decrease and the effect of increasing the capacity may be reduced. Therefore, in the general formula (1), the total y + z of y representing the amount of Co and z representing the amount of the element M is preferably 0.5 or less.

The lithium-containing composite oxide having the above composition has a large true density of 4.55 to 4.95 g / cm ³ and is a material having a high volume energy density. For example, the true density of the lithium-containing composite oxide containing Mn in a certain range varies greatly depending on the composition, but the structure is stabilized and the uniformity can be improved in the narrow composition range as described above. For example, it is considered to be a large value close to the true density of LiCoO ₂ . Moreover, the capacity | capacitance per mass of lithium containing complex oxide can be enlarged, and it can be set as the material excellent in reversibility.

  The lithium-containing composite oxide has a higher true density especially when the composition is close to the stoichiometric ratio. Specifically, in the general composition formula (1), x representing the amount of Li is It is preferable to set it to 0.9 or more and 1.3 or less, and true density and reversibility can be improved by adjusting the value of x in this way.

  The lithium-containing composite oxide represented by the general formula (1) includes Li-containing compounds (such as lithium hydroxide), Ni-containing compounds (such as nickel sulfate), Co-containing compounds (such as cobalt sulfate), and Mn-containing compounds (sulfuric acid). Manganese and the like) and an Al-containing compound (such as aluminum sulfate) can be mixed and fired. In addition, in order to synthesize the lithium-containing composite oxide with higher purity, a composite compound (hydroxide, oxide, etc.) containing elements related to Ni, Co and element M and a Li-containing compound are mixed and fired. It is preferable to do.

  Firing conditions can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.) and maintained at that temperature, preheating is performed. After that, it is preferable to raise the temperature to the firing temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  In the electrode of the present invention, the pore distribution curve of the electrode mixture layer determined by the mercury intrusion method has two peak tops, and the peak top of the peak (a) on the small pore diameter side is within the pore diameter range of 140 to 220 nm. And the peak top of the peak (b) on the large pore diameter side exists in the range of the pore diameter of 330 to 910 nm, and the pore volume of the peak top in the peak (a) is expressed as a (ml / g ), Where the peak top pore volume in the peak (b) is b (ml / g), the relationship 0.26 ≦ a / (a + b) ≦ 0.53 is satisfied. In order to control the pore distribution of the layer in this manner, a method of using the lithium-containing composite oxide having a specific form or adjusting the conditions of calendar treatment (details will be described later) during electrode production Is mentioned .

That is, in the electrode of the present invention, the lithium-containing composite oxide has two peak tops in a volume-based particle size distribution, and the peak top of the small particle size side (A) has a particle size of 2 to 2. The peak top of the peak (B) on the large particle size side exists within the range of 4 μm and the peak top (B) has a particle size within the range of 8.8 to 11 μm. A, where B represents the volume frequency of the peak top in the peak (B), the relationship 0.18 ≦ A / (A + B) ≦ 0.45 is satisfied, and the particle size (D ₅₀ ) has a cumulative volume of 50%. Having a diameter of 4.6 to 10.3 μm. As a result, the pore distribution of the electrode mixture layer can be easily controlled as described above, and the pore distribution of the electrode mixture layer is controlled as described above, and the lithium-containing composite oxide has the above-described control. By using a material having a particle size distribution of, it is possible to obtain an electrode having an electrode mixture layer having a high density and a high permeability of the non-aqueous electrolyte.

  The volume-based particle size distribution of the lithium-containing composite oxide referred to in the present specification is measured by a laser diffraction / scattering particle size distribution measuring apparatus, for example, “Microtrack HRA” manufactured by Nikkiso Co., Ltd.

  In addition to the active material, the electrode mixture layer according to the electrode of the present invention usually contains a binder and a conductive additive. Examples of the binder used in the electrode mixture layer according to the electrode of the present invention include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), and styrene butadiene rubber. , Tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer Polymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride- Interfluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoro Methyl vinyl ether-tetrafluoroethylene copolymer, or ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, and copolymers thereof Na ion crosslinked body etc. of these are mentioned, These may be used individually by 1 type and may use 2 or more types together. Among these, considering the stability in the electrochemical element and the characteristics of the electrochemical element, PVDF, PTFE, and PHFP are preferable. In addition, a copolymer formed of these monomers can be used together. It may be used.

  The conductive additive used in the electrode mixture layer according to the electrode of the present invention may be any one that is chemically stable in the electrochemical element. For example, graphite such as natural graphite and artificial graphite, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metallic powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

  The electrode of the present invention can be produced by forming an electrode mixture layer containing the lithium-containing composite oxide as an active material on one side or both sides of a current collector.

  The electrode mixture layer is prepared by, for example, preparing a paste-like or slurry-like electrode mixture-containing composition by adding the lithium-containing composite oxide, a binder, a conductive auxiliary agent, or the like to a solvent, and applying it to various coatings. It can be formed by applying to the surface of the current collector by a method, drying, and adjusting the thickness of the electrode mixture layer by calendering. Also, the pore distribution of the electrode mixture layer can be adjusted by adjusting the conditions in the calendar process. For example, even if the particle size distribution of the lithium-containing composite oxide used for the electrode is slightly deviated from the preferred value, the pore distribution of the electrode mixture layer can be determined by selecting the calendering conditions during electrode preparation. It can be adjusted as described above.

  Examples of the coating method for applying the electrode mixture-containing composition to the surface of the current collector include a substrate lifting method using a doctor blade; a coater method using a die coater, comma coater, knife coater, etc .; screen printing, letterpress Printing methods such as printing can be adopted.

  In the electrode mixture layer, the lithium-containing composite oxide may be 80 to 99 mass%, the binder may be 0.5 to 10 mass%, and the conductive additive may be 0.5 to 10 mass%. preferable.

Moreover, it is preferable that the thickness of an electrode mixture layer is 15-200 micrometers per single side | surface of a collector after a calendar process. Furthermore, in order to control the pore distribution of the electrode mixture layer, as a condition for the calendar treatment, for example, the linear pressure is preferably set to 10 to 15 kN / cm. Then, for example, a particle size in the presence of the peak (B) at D ₅₀ and particle size distribution curve of the lithium-containing composite oxide used for the electrode mixture layer, when a relatively large among the range of the It is preferable to increase the linear pressure. On the other hand, when the particle size at which the peak (A) in the particle size distribution curve of the lithium-containing composite oxide used in the electrode mixture layer is relatively small within the above range, the linear pressure is lowered. It is preferable to do.

  The material of the electrode current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed electrochemical device. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. As the current collector of the electrode, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  In addition, the electrode of this invention is not limited to what was manufactured by the said manufacturing method, The electrode manufactured by the other manufacturing method may be used.

  Moreover, you may form in the electrode of this invention according to a conventional method the lead body for electrically connecting with the other member in an electrochemical element as needed.

  By using the electrode for an electrochemical element of the present invention as a positive electrode, an electrochemical element such as a battery (a lithium ion primary battery or a lithium ion secondary battery) or a capacitor can be configured.

  That is, the lithium ion secondary battery of the present invention may include a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and may have the electrochemical element electrode of the present invention as the positive electrode. There is no restriction | limiting in particular about a structure, The structure and structure employ | adopted by the lithium ion secondary battery known conventionally can be applied.

  The negative electrode has, for example, a structure in which a negative electrode mixture layer composed of a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive additive is included on one or both sides of the current collector. Can be used.

  Examples of the negative electrode active material include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and metals that can be alloyed with lithium (Si , Sn, etc.) or alloys thereof. Moreover, the same thing as what was illustrated previously as what can be used for the electrode of this invention can be used for a binder and a conductive support agent.

  The material of the current collector of the negative electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. For the current collector of the negative electrode, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials can be used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  The negative electrode is, for example, a paste-like or slurry-like negative electrode mixture-containing composition (binder) in which a negative electrode active material and a binder, and further, if necessary, a negative electrode mixture containing a conductive additive are dispersed in a solvent. May be dissolved in a solvent) on one or both sides of the current collector and dried to form a negative electrode mixture layer. The negative electrode is not limited to the one obtained by the above production method, and may be one produced by another method. The thickness of the negative electrode mixture layer is preferably 10 to 300 μm per one side of the current collector.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 100-140 degreeC. Therefore, the separator has a melting point, that is, a thermoplastic resin having a melting temperature measured using a differential scanning calorimeter (DSC) of 100 to 140 ° C. in accordance with JIS K 7121 as a component. Preferably, it is a single layer porous film mainly composed of polyethylene or a laminated porous film comprising a porous film such as a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated. Is preferred. When a resin having a melting point higher than that of polyethylene such as polyethylene and polypropylene is used by mixing or laminating, it is desirable that polyethylene is 30% by mass or more, and 50% by mass or more as a resin constituting the porous membrane. More desirable.

  As such a resin porous membrane, for example, a porous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known non-aqueous secondary battery or the like, that is, a solvent extraction method, a dry type Alternatively, an ion-permeable porous film manufactured by a wet stretching method or the like can be used.

  The average pore size of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

Moreover, as a characteristic of the separator, a Gurley value represented by the number of seconds in which 100 ml of air permeates the membrane under a pressure of 0.879 g / mm ² is 10 to 500 sec. It is desirable to be. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  Even when the inside of the lithium ion secondary battery is 150 ° C. or higher, the lithium-containing composite oxide according to the electrode of the present invention is excellent in thermal stability, and thus safety can be maintained.

  As the non-aqueous electrolyte, a solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone, etc. Aprotic organic solvents, and the like, may be used these alone, or in combination of two or more of these. Also, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can be used. Among these, a mixed solvent of EC, MEC, and DEC is preferable. In this case, it is more preferable to include DEC in an amount of 15% by volume to 80% by volume with respect to the total volume of the mixed solvent. This is because such a mixed solvent can enhance the stability of the solvent during high-voltage charging while maintaining the low temperature characteristics and charge / discharge cycle characteristics of the battery high.

As the electrolyte salt related to the non-aqueous electrolyte, a salt of a fluorine-containing compound such as lithium perchlorate, lithium organic boron, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, 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 ) 3, LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ [where Rf Represents a fluoroalkyl group. These may be used alone or in combination of two or more thereof. Among these, LiPF ₆ and LiBF ₄ are more preferable because of good charge / discharge characteristics. This is because these fluorine-containing organic lithium salts have a large anionic property and are easily ion-separated, so that they are easily dissolved in the solvent. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 to 1.7 mol / L.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, and fluorobenzene are used for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of the non-aqueous electrolyte. An additive such as t-butylbenzene may be added as appropriate. In addition, when the said lithium containing complex oxide contains Mn, since the surface activity can be stabilized, it is especially preferable to add the additive containing a sulfur element.

  The lithium ion secondary battery of the present invention includes, for example, an electrode laminate in which the electrode of the present invention and the negative electrode are laminated via the separator, and an electrode wound body obtained by winding the electrode laminate in a spiral shape. The electrode body and the non-aqueous electrolyte are prepared and sealed in an exterior body according to a conventional method. As the form of the battery, similarly to the conventionally known lithium ion secondary battery, a cylindrical battery using a cylindrical (cylindrical or rectangular) outer can, or a flat shape (circular in plan view) A flat battery using a rectangular flat-shaped outer can, a soft package battery using a metal-deposited laminated film as an outer package, and the like. The outer can can be made of steel or aluminum.

  The lithium ion secondary battery of the present invention can be applied to power tools, automobiles, bicycles, power storage applications, etc., as well as power supplies for various electronic devices such as portable electronic devices such as mobile phones and laptop computers. be able to.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Synthesis of lithium-containing composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, cobalt sulfate and manganese sulfate were each added to 2.4 mol / dm ^3. , 0.8 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.8 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The solution was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Co, and Mn (spherical coprecipitation compound). At this time, the temperature of the reaction solution is kept at 50 ° C., and a sodium hydroxide aqueous solution having a concentration of 6.4 mol / dm ³ is dropped at the same time so that the pH of the reaction solution is maintained around 12. Further, nitrogen gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co and Mn in a molar ratio of 6: 2: 2. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is put in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, further heated to 900 ° C. and heated to 12 ° C. The lithium-containing composite oxide was synthesized by firing for a period of time.

  The obtained lithium-containing composite oxide was washed with water, heat-treated at 850 ° C. for 12 hours in the air (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. At that time, the pulverization force and time were adjusted, and two pulverization steps were performed to obtain two types of powders having different particle diameters, and then mixed. The lithium-containing composite oxide after mixing was stored in a desiccator.

When the particle size distribution of the obtained mixed powder of lithium-containing composite oxide was measured using “Microtrac HRA” manufactured by Nikkiso Co., Ltd., D ₅₀ = 8.1 μm, small particle size in the volume-based particle size distribution curve The particle size of the peak top of the peak (A) on the side is 3.2 μm, the particle size of the peak top of the peak (B) on the large particle size side is 10.2 μm, and the value of A / (A + B) is 0.40. It has been found.

Further, the composition analysis of the mixed powder of the lithium-containing composite oxide was performed as follows using an ICP (Inductively Coupled Plasma) method. First, 0.2 g of the lithium-containing composite oxide was placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were sequentially added and dissolved by heating. After cooling, the solution was further diluted 25 times and analyzed by ICP (“ICP-757” manufactured by JARREL ASH) ( Calibration curve method). From the obtained results, the composition of the lithium-containing composite oxide was derived and found to be a composition represented by Li _1.02 Ni _0.6 Co _0.2 Mn _0.2 O ₂ .

<Preparation of positive electrode>
96 parts by mass of the lithium-containing composite oxide, 20 parts by mass of N-methyl-2-pyrrolidone (NMP) solution containing PVDF as a binder at a concentration of 10% by mass, 1 part by mass of artificial graphite as a conductive auxiliary agent, and 1 part by mass of ketjen black was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  The positive electrode mixture-containing paste is applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, dried to form a positive electrode mixture layer, and then subjected to a calendar treatment at a linear pressure of 13 kN / cm. Then, the thickness of the positive electrode mixture layer and the pore distribution were adjusted, and an aluminum lead body was welded to the exposed portion of the aluminum foil, and was cut to a predetermined width and length to produce a strip-shaped positive electrode .

  The positive electrode mixture layer in the obtained positive electrode had a thickness of 65 μm per one side. Further, in the volume-based pore distribution curve of the positive electrode mixture layer obtained by mercury porosimetry, the peak top of peak (a) is at a position where the pore diameter is 188 nm, and the peak top of peak (b) is at a position where the pore diameter is 442 nm, The value of a / (a + b) was 0.41.

<Production of negative electrode>
Water was added to 97.5 parts by mass of natural graphite having a number average particle diameter of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener. And mixed to prepare a negative electrode mixture-containing paste. The negative electrode mixture-containing paste was applied to both sides of a copper foil having a thickness of 8 μm and dried to form a negative electrode mixture layer, and then calendering was performed to adjust the thickness of the negative electrode mixture layer. A nickel lead body was welded to the exposed portion and cut to a predetermined width and length to produce a strip-shaped negative electrode. The total thickness of the obtained negative electrode was 128 μm.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent having a volume ratio of EC: MEC: DEC of 2: 3: 1 to prepare a non-aqueous electrolyte.

<Battery assembly>
The belt-like positive electrode is stacked on the belt-like negative electrode through a microporous polyethylene separator (porosity: 41%) having a thickness of 16 μm, wound in a spiral shape, and then pressed so as to be flat. An electrode winding body having a flat winding structure was formed, and the electrode winding body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a prismatic battery case made of aluminum alloy having an outer dimension of thickness 5.0 mm, width 42 mm, and height 61 mm, the lead body is welded, and an aluminum alloy lid The plate was welded to the open end of the battery case. Subsequently, a non-aqueous electrolyte was injected from an inlet provided in the cover plate, and then the inlet was sealed, so that a lithium ion secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG. 2 was obtained. Moreover, the time-dependent change of the impedance of the battery immediately after injection of the non-aqueous electrolyte was measured, and the time when the impedance was stabilized was evaluated as the time required for impregnation with the non-aqueous electrolyte.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 and then pressed into a flat shape to form a flat electrode winding body 6 in a rectangular (square tube) battery case 4 together with a non-aqueous electrolyte. Contained. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, and the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. An insulator 5 made of a polyethylene sheet is arranged at the bottom of the battery case 4, and is connected to one end of each of the positive electrode 1 and the negative electrode 2 from the flat electrode winding body 6 made of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the lid plate 9, and the non-aqueous electrolyte inlet 14 is welded by, for example, laser welding with a sealing member inserted. The battery is sealed to ensure the hermeticity of the battery (therefore, in the battery of FIGS. 1 and 2, the nonaqueous electrolyte inlet 14 is actually a nonaqueous electrolyte inlet and a sealing member. , For ease of explanation, shown as non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of this Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Examples 2, 3 and Comparative Examples 1-8
From the lithium-containing composite oxide synthesized in the same manner as in Example 1, the pulverization force and time were changed to adjust the two types of particle diameters obtained and the amount of mixture thereof, and D ₅₀ , peak (A ) And a peak top particle size of peak (B), and a mixed powder of lithium-containing composite oxide having a value of A / (A + B). A positive electrode was prepared in the same manner as in Example 1 except that a mixed powder of these lithium-containing composite oxides was used as the positive electrode active material, and the linear pressure of the calendar treatment at the time of positive electrode preparation was as shown in Table 1. A lithium ion secondary battery was produced in the same manner as in Example 1 except that these positive electrodes were used.

  For the batteries of the examples and comparative examples, Table 1 shows the values related to the particle size distribution of the positive electrode active material (lithium-containing composite oxide) used for the positive electrode. Table 2 shows the respective values concerning the pore distribution.

  Moreover, about the positive electrode which concerns on the battery of an Example and a comparative example, the density of the positive mix layer was measured with the following method. The positive electrode was cut into a size of 10 cm × 10 cm, the mass was measured using an electronic balance with a minimum scale of 0.1 mg, and the mass of the current collector was subtracted to calculate the mass of the positive electrode mixture layer. On the other hand, the total thickness of the positive electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the positive electrode mixture layer was calculated from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. did. Then, the density of the positive electrode mixture layer was calculated by dividing the mass of the positive electrode mixture layer by the volume.

  Furthermore, for each battery of the example and the comparative example, the non-aqueous electrolyte impregnation time is fixed to 84 minutes, and constant current charging is performed until the charging voltage reaches 4.2 V at a current rate of 0.2 C; The battery was fully charged by constant voltage charging performed at a constant voltage of 2 V until the current density decreased to 1/10. Thereafter, the battery was discharged at a discharge rate of 2.5 V at a current rate of 0.2 C, and the capacity was measured. In addition, the impregnation time of the non-aqueous electrolyte of each battery was fixed to 84 minutes by starting constant current charge after 84 minutes passed immediately after injection | pouring of non-aqueous electrolyte.

  In the battery of the example and the comparative example, the time required for impregnation of the nonaqueous electrolyte measured at the time of assembling the battery of the example and the comparative example, the density of the positive electrode mixture layer related to the positive electrode used in the battery of the example and the comparative example The battery capacity when the impregnation time of the non-aqueous electrolyte is fixed at 84 minutes is shown in Table 3 (in Table 3, the battery capacity is simply described as “battery capacity”).

  As is clear from Table 3, in the batteries of Examples 1 to 3, in which the lithium-containing composite oxide having an appropriate particle size distribution was used as the active material and the positive electrode having the proper pore distribution of the positive electrode mixture layer was used, The density of the agent layer is high, and the capacity when the impregnation time of the nonaqueous electrolyte is fixed is large. In addition, the batteries of Examples 1 to 3 are said to have good productivity because the time required for impregnation with the non-aqueous electrolyte during assembly is short.

  On the other hand, in the pore distribution curve of the positive electrode mixture layer, Comparative Example 1 using a positive electrode in which the peak top pore diameter of peak (a) and peak (b) is too small and the a / (a + b) value is too large. The battery of Comparative Example 4 in which the lithium-containing composite oxide in which the peak top particle size of the peak (A) is too small in the volume-based particle size distribution is used as the positive electrode active material, and A / (A + B in the volume-based particle size distribution ) The battery of Comparative Example 5 using a lithium-containing composite oxide having an excessively large value as the positive electrode active material, and using the positive electrode having a too large a / (a + b) value in the pore distribution curve of the positive electrode mixture layer, and the positive electrode mixture In the battery of Comparative Example 7 using the positive electrode in which the pore diameter at the peak top of the peak (a) is too small in the pore distribution curve of the layer, the time required for impregnation with the nonaqueous electrolyte during assembly is long, and the productivity is poor. In addition, although the density of the positive electrode mixture layer is high, the capacity when the impregnation time of the nonaqueous electrolyte solution is fixed is small, and the positive electrode mixture can be obtained even in the impregnation time that can ensure good discharge characteristics in the battery of the example. It is considered that the non-aqueous electrolyte does not penetrate uniformly throughout the entire agent layer.

Further, a lithium-containing composite oxide D ₅₀ is too large in the positive electrode active material in the particle size distribution on the volume basis, in a pore distribution curve of the positive electrode mixture layer, the peak top of the peak (a) and peak (b) fine pore size is too large, a / (a + b) value of Comparative example 2 using too small cathode battery, the volume-based particle size distribution, D ₅₀ is too large, the particle size of the peak top of the peak (B) is too large The battery of Comparative Example 3 using a lithium-containing composite oxide as a positive electrode active material, and using a lithium-containing composite oxide whose A / (A + B) value is too small in the volume-based particle size distribution as the positive electrode active material, The peak top pore diameter of peak (b) is large in the battery of Comparative Example 6 using a positive electrode in which the a / (a + b) value is too small in the pore distribution curve, and in the pore distribution curve of the positive electrode mixture layer. That the battery of Comparative Example 8 using the cathode, reduce the density of the positive electrode mixture layer, the capacity at the time of fixing the impregnation time of the nonaqueous electrolyte solution is smaller than the battery of Example.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (2)

An electrode for an electrochemical element having an electrode mixture layer containing an active material on one side or both sides of a current collector,
The following general formula (1)
Li _x Ni _(1-yz) Co _y M _z O ₂ (1)
[In the general formula (1), M is at least one element of Mn and Al, and 0.9 ≦ x ≦ 1.3, 0.1 ≦ y ≦ 0.25 , 0.05 ≦ z ≦ 0.35 and y + z ≦ 0.5 ], and has two peak tops in the volume-based particle size distribution, and the peak top of the peak (A) on the small particle size side is the particle size It exists in the range of 2-4 μm, and the peak top of the peak (B) on the large particle size side exists in the range of particle size 8.8-11 μm, and the volume of the particle size in the peak (A) When the frequency is A and the volume frequency of the particle size at the peak (B) is B, the relationship 0.18 ≦ A / (A + B) ≦ 0.45 is satisfied, and the particle size with a cumulative volume of 50% is 4 .6-10.3 μm of lithium-containing composite oxide is used as an active material,
The pore distribution curve of the electrode mixture layer obtained by the mercury intrusion method has two peak tops, and the peak top of the peak (a) on the small pore diameter side is within the pore diameter range of 140 to 220 nm. And the peak top of the peak (b) on the large pore diameter side is in the range of the pore diameter of 330 to 910 nm, the pore volume of the peak top in the peak (a) is a (ml / g), the peak An electrode for an electrochemical element, wherein the relationship of 0.26 ≦ a / (a + b) ≦ 0.53 is satisfied, where b (ml / g) is the peak top pore volume in (b). A lithium ion secondary battery having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The lithium ion secondary battery, wherein the positive electrode is the electrode for an electrochemical element according to claim 1.