Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing the same, and nonaqueous electrolyte secondary battery

Abstract

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery comprises: lithium transition metal oxide particles; a metal compound containing a metal element M attached to the surface of the lithium transition metal oxide particles; and a lithium metal compound containing lithium (Li) and the metal element M attached to the surface of the lithium transition metal oxide particles. Here, the metal element M is at least one selected from aluminum (Al), titanium (Ti), manganese (Mn), gallium (Ga), molybdenum (Mo), tin (Sn), tungsten (W), and bismuth (Bi).

Description

[0001] The present application is a divisional application of an application filed on January 26, 2017, with application number 201780021349.5, and with the invention title “Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery”. Technical Field

[0002] The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery. Background Art

[0003] Lithium transition metal oxide particles, which constitute the positive electrode active material for non-aqueous electrolyte secondary batteries, can be synthesized by mixing a lithium compound and a transition metal oxide and calcining them. During calcination, some lithium is lost due to volatilization, so a stoichiometric amount of lithium is typically used relative to the target product. However, excess lithium on the surface of the lithium transition metal oxide particles increases gas generation during battery charging and storage, necessitating the calcination process to remove the excess lithium.

[0004] For example, Patent Document 1 discloses a positive electrode active material in which fine particles containing tungsten and lithium are attached to the surface of lithium transition metal oxide particles. Patent Document 1 discloses the steps of washing the lithium transition metal oxide particles with water, filtering, and drying.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-216105 Summary of the Invention

[0008] However, if the cleaning of the lithium transition metal oxide particles (calcined product) can be omitted, the filtration and drying steps are no longer necessary, and the manufacturing cost of the positive electrode active material and the environmental load can be reduced. The object of the present invention is to provide a positive electrode active material that can suppress the amount of gas generated by the battery during charging and storage, even without cleaning the lithium transition metal oxide particles. It should be noted that although the positive electrode active material of Patent Document 1 has undergone a cleaning step, the battery using it still generates a large amount of gas during charging and storage.

[0009] The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized in that it comprises: lithium transition metal oxide particles; a metal compound containing a metal element M attached to the surface of the lithium transition metal oxide particles; and a lithium metal compound containing lithium (Li) and a metal element M attached to the surface of the lithium transition metal oxide particles, wherein the metal element M is at least one selected from aluminum (Al), titanium (Ti), manganese (Mn), gallium (Ga), molybdenum (Mo), tin (Sn), tungsten (W) and bismuth (Bi).

[0010] The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is characterized in that it includes the following steps: a step of mixing a lithium compound and a transition metal oxide and calcining them to synthesize lithium transition metal oxide particles; and a step of mixing unwashed lithium transition metal oxide particles and a metal compound containing a metal element M and heat-treating them at a temperature lower than the aforementioned calcining temperature.

[0011] The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising a positive electrode containing the above-mentioned positive electrode active material, a negative electrode, and a nonaqueous electrolyte.

[0012] According to the present invention, a non-aqueous electrolyte secondary battery can be provided that generates less gas during charge storage, even without washing the lithium transition metal oxide particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION

[0014] As mentioned above, in order to suppress gas generation during non-aqueous electrolyte secondary batteries, such as during storage and charging, it is necessary to clean the lithium transition metal oxide particles and remove excess lithium on the particle surface. It is believed that when excess lithium exists on the surface of the lithium transition metal oxide particles, lithium carbonate is generated on the particle surface, which reacts with the electrolyte to generate gas.

[0015] The present inventors conducted intensive research to provide a battery that generates less gas during charge storage, even without washing lithium transition metal oxide particles. Furthermore, they successfully solved this problem by adding a compound containing a specific metal element to unwashed lithium transition metal oxide particles (hereinafter sometimes referred to as "unwashed particles").

[0016] In the positive electrode active material of the present invention, a compound containing a specific metal element adheres to the surface of unwashed particles. Excess lithium present on the surface of the unwashed particles reacts with the compound to form a lithium metal compound, significantly reducing the amount of excess lithium that causes gas generation. Therefore, a non-aqueous electrolyte secondary battery can be provided that generates minimal gas even during storage and charging, even without washing the lithium transition metal oxide particles.

[0017] An example of an implementation method is described below in detail.

[0018] The accompanying drawings referred to in the description of the embodiments are schematically recorded, and the specific size ratios, etc. should be judged with reference to the following description. Below, an example is given of a cylindrical battery in which the electrode body 14 of the winding structure is housed in a cylindrical battery casing, but the structure of the electrode body is not limited to the winding structure, and can also be a stacked structure in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators. In addition, the battery casing is not limited to a cylindrical shape, and examples include square (square battery), coin-shaped (coin-shaped battery) and other metal shells, resin shells composed of resin films (laminated batteries), etc.

[0019] Figure 1 FIG is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 1 As shown, the nonaqueous electrolyte secondary battery 10 comprises an electrode assembly 14, a nonaqueous electrolyte (not shown), and a battery case that houses the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The battery case comprises a bottomed cylindrical shell body 15 and a sealing member 16 that closes the opening of the shell body.

[0020] The nonaqueous electrolyte secondary battery 10 includes insulating plates 17 and 18 disposed above and below the electrode body 14 , respectively. Figure 1 In the example shown, the positive electrode lead 19 attached to the positive electrode 11 extends through a through-hole in the insulating plate 17 to the side of the sealing body 16, while the negative electrode lead 20 attached to the negative electrode 12 extends through the outside of the insulating plate 18 to the bottom side of the case body 15. The positive electrode lead 19 is connected to the lower surface of a perforated metal plate 22, which serves as the bottom plate of the sealing body 16, by welding or the like. The lid 26, which serves as the top plate of the sealing body 16 and is electrically connected to the perforated metal plate 22, serves as the positive electrode terminal. The negative electrode lead 20 is connected to the inner surface of the bottom of the case body 15 by welding or the like, serving as the negative electrode terminal.

[0021] The case body 15 is, for example, a metal container with a bottomed cylindrical shape. A gasket 27 is provided between the case body 15 and the sealing member 16 to ensure the airtightness of the battery case interior. The case body 15 has, for example, a bulge 21 formed by pressing the side surface from the outside to support the sealing member 16. The bulge 21 is preferably formed in an annular shape along the circumference of the case body 15, and supports the sealing member 16 on its upper surface.

[0022] The sealing body 16 has a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25 and a lid 26 stacked in sequence from the electrode body 14 side. The components constituting the sealing body 16 have, for example, a disc shape or a ring shape and the components except the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and an insulating member 24 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat, for example, the lower valve body 23 breaks, whereby the upper valve body 25 expands toward the lid 26 side and separates from the lower valve body 23, thereby cutting off the electrical connection between the two. When the internal pressure further rises, the upper valve body 25 breaks, and the gas is discharged from the opening of the lid 26.

[0023] The components of the nonaqueous electrolyte secondary battery 10 , particularly the positive electrode active material, will be described in detail below.

[0024] [positive electrode]

[0025] The positive electrode comprises a positive electrode current collector and a positive electrode composite material layer formed on the positive electrode current collector. The positive electrode current collector may be made of a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a thin film having the metal disposed on the surface. The positive electrode composite material layer comprises a positive electrode active material, a conductive material, and a binder. The positive electrode is produced, for example, by coating a positive electrode composite material slurry comprising a positive electrode active material, a conductive material, a binder, etc. on the positive electrode current collector, drying the coating, and then rolling to form the positive electrode composite material layers on both sides of the current collector.

[0026] The positive electrode active material comprises: lithium transition metal oxide particles; a metal compound containing a metal element M (hereinafter referred to as "metal compound M1") attached to the surface of the lithium transition metal oxide particles; and a lithium metal compound containing lithium (Li) and the metal element M (hereinafter referred to as "lithium metal compound M2") attached to the surface of the lithium transition metal oxide particles. This positive electrode active material can be produced using unwashed lithium transition metal oxide particles. That is, in the production process of this positive electrode active material, there is no water washing step to remove excess Li after synthesizing the lithium transition metal oxide particles, and there is no filtration and drying step following the water washing step. Preferably, there is almost no excess Li on the surface of the lithium transition metal oxide particles to which the metal compound M1 and the lithium metal compound M2 are attached.

[0027] From the perspective of ensuring battery capacity, the content of lithium transition metal oxide particles in the positive electrode active material (the mass of lithium transition metal oxide particles in the positive electrode active material) is preferably 80% by mass or greater, more preferably 90% by mass or greater, and particularly preferably 95% by mass or greater. The metal compound M1 and the lithium metal compound M2 are fine particles with a smaller particle size than the lithium transition metal oxide particles and are dispersed on the surface of the lithium transition metal oxide particles. Therefore, the particle size of the positive electrode active material is determined by the particle size of the lithium transition metal oxide particles (particle size of the positive electrode active material ≈ particle size of the lithium transition metal oxide particles).

[0028] The average particle size of the lithium transition metal oxide particles is, for example, 2 to 30 μm, preferably 5 to 15 μm. The lithium transition metal oxide particles may be secondary particles formed by aggregation of primary particles ranging from 100 nm to 10 μm. The average particle size of the lithium transition metal oxide particles refers to the median diameter (D50) measured by laser diffraction, for example, using a laser diffraction scattering particle size distribution analyzer manufactured by HORIBA.

[0029] The lithium transition metal oxide constituting the lithium transition metal oxide particles contains, for example, at least one metal element selected from magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), tin (Sn), antimony (Sb), lead (Pb), and bismuth (Bi). Among these, it is preferred that the particles contain at least one metal element selected from Ni, Co, Mn, and Al.

[0030] Suitable lithium transition metal oxides are oxides in which the ratio of Ni to the total molar number of metal elements excluding Li is 30 mol% or more, more preferably 85 mol% or more. a Ni x M * (1-x) O2(0.95≤a≤1.2, 0.85≤x<1.0, M * The lithium transition metal oxide particles may be composed of a mixture of two or more lithium transition metal oxides having different compositions, but preferably contain at least 50% by mass, or 80% by mass, or substantially 100% by mass of the oxide represented by the above composition formula.

[0031] As described above, the metal compound M1 is a compound containing a metal element M and is attached to the surface of the lithium transition metal oxide particles. It should be noted that a portion of the metal compound M1 can also fall off from the surface of the lithium transition metal oxide particles and exist in the positive electrode composite material layer. By attaching the metal compound M1 to the surface of the unwashed lithium transition metal oxide particles, the remaining Li that causes gas generation when the battery is charged and stored can be rendered harmless. The metal compound M1 reacts with the Li present on the surface of the lithium transition metal oxide particles and changes into a lithium metal compound M2. That is, in the presence of the metal compound M1, it can be said that there is almost no remaining Li on the surface of the lithium transition metal oxide particles.

[0032] The amount of the excess Li compound on the surface of the lithium transition metal oxide particles is 0.2 to 4 mol%, preferably 0 to 4 mol%, relative to the lithium transition metal oxide. The amount of the excess Li compound on the surface of the lithium transition metal oxide particles can be detected, for example, by immersing the positive electrode active material powder in water, dissolving the excess Li compound, and titrating the resulting solution.

[0033] The metal element M contained in the metal compound M1 is at least one selected from aluminum (Al), titanium (Ti), manganese (Mn), gallium (Ga), molybdenum (Mo), tin (Sn), tungsten (W) and bismuth (Bi). Only when the metal element M is at least one of these, gas generation during charge storage and the like can be suppressed without causing defects such as reduced capacity. Among them, the metal element M is preferably selected from the group consisting of Al, Ga, Sn and W, the group consisting of Al, Ga and Sn, or at least one selected from the group consisting of Al and Ga.

[0034] Specific examples of the metal compound M1 include oxides of the metal element M1, such as aluminum oxide, gallium oxide, tin oxide, and tungsten oxide; nitrides of the metal element M1, such as aluminum nitride and gallium nitride; and hydroxides of the metal element M1, such as aluminum hydroxide and gallium hydroxide. The metal compound M1 may be used alone or in combination of two or more. Preferably, one or more oxides are used.

[0035] The content of the metal compound M1 in the positive electrode active material is, for example, less than 4 mol %, preferably less than 0.2 mol % relative to the mass of the positive electrode active material. The content of the metal compound M1 is preferably less than the content of the lithium metal compound M2.

[0036] As described above, the particle size of the metal compound M1 is smaller than the particle size of the lithium transition metal oxide particles. The average particle size of the metal compound M1 attached to the surface of the lithium transition metal oxide particles can be measured using a scanning electron microscope (SEM) (the same applies to the lithium metal compound M2). Specifically, based on the SEM image of the lithium transition metal oxide particles (positive electrode active material) with the metal compound M1 attached to the surface, 100 particles of the metal compound M1 are randomly selected, the longest diameter of each particle is measured, and the average value of the measured values ​​is calculated as the average particle size. The average particle size of the metal compound M1 measured by this method is, for example, 50 nm to 3 μm, preferably 100 nm to 1 μm.

[0037] As described above, the lithium metal compound M2 is an oxide containing Li and a metal element M, and is attached to the surface of the lithium transition metal oxide particles. It should be noted that a portion of the lithium metal compound M2 may also fall off from the surface of the lithium transition metal oxide particles and exist in the positive electrode composite material layer. The lithium metal compound M2 is generated by the reaction of the remaining Li compound present on the surface of the lithium transition metal oxide particles with the metal compound M1. The lithium metal compound M2 has low reactivity with the electrolyte and will not become a substance that causes gas generation in situations such as during charging and storage.

[0038] Specific examples of the lithium metal compound M2 include composite oxides of Li and the metal element M1, such as lithium aluminate, lithium gallate, lithium stannate, and lithium tungstate; and composite nitrides of Li and the metal element M1, such as lithium aluminum nitride and lithium gallium nitride. The lithium metal compound M2 may be present in two or more forms, but preferably includes one or more oxides.

[0039] The lithium metal compound M2 adheres to the surface of the lithium transition metal oxide particles in greater amounts than the metal compound M1. The content of the lithium metal compound M2 in the positive electrode active material is, for example, 0.2 to 4 mol % relative to the mass of the positive electrode active material.

[0040] As described above, the particle size of the lithium metal compound M2 is smaller than that of the lithium transition metal oxide particles. The average particle size of the lithium metal compound M2 attached to the surface of the lithium transition metal oxide particles is, for example, 50 nm to 3 μm, preferably 100 nm to 1 μm. The average particle size of the lithium metal compound M2 is approximately the same as that of the metal compound M1.

[0041] The positive electrode active material is obtained, for example, by a manufacturing process comprising the following steps: a step of mixing a lithium compound and a transition metal oxide and calcining to synthesize lithium transition metal oxide particles (hereinafter referred to as "step (1)"); and a step of mixing unwashed lithium transition metal oxide particles and a metal compound M1 and heat-treating them at a temperature lower than the calcination temperature of step (1) (hereinafter referred to as "step (2)"). Although there are residual Li compounds on the surface of the unwashed lithium transition metal oxide particles (unwashed particles), by adding the metal compound M1 and performing the heat treatment, the metal compound M1 reacts with the residual Li compounds to form a lithium metal compound M2, thereby significantly reducing the residual Li compounds that cause gas generation. According to this manufacturing process, washing of the lithium transition metal oxide particles is unnecessary, and filtering and drying steps following the water washing step are also unnecessary. Therefore, it is possible to achieve a reduction in the manufacturing cost of the positive electrode active material and a reduction in the environmental load.

[0042] Examples of the lithium compound used in step (1) include lithium hydroxide, lithium carbonate, and lithium nitrate. Examples of the transition metal oxide include composite oxides containing at least one selected from Ni, Co, Mn, and Al (e.g., nickel-cobalt-aluminum oxide and nickel-cobalt-manganese oxide). As described above, since some Li is lost due to volatilization during calcination, a greater amount of Li (lithium compound) than the stoichiometric ratio of the target product is used. Consequently, excess Li exists on the particle surface of the calcined product (lithium transition metal oxide particles).

[0043] The calcination temperature in step (1) is preferably higher than 700° C. The suitable range of the calcination temperature is 720 to 900° C., more preferably 730 to 800° C. Calcination is preferably performed in an oxygen gas flow.

[0044] In step (2), the lithium transition metal oxide particles obtained in step (1) are used in an unwashed state. A metal compound M1 is mixed with the unwashed particles at a ratio of, for example, 20 to 600 μmol / g, so that fine particles of the metal compound M1 adhere to the surface of the unwashed particles. Next, the mixture is heat-treated so that the Li present on the surface of the unwashed particles reacts with the metal compound M1 to form a lithium metal compound M2. Thus, a positive electrode active material can be obtained in which fine particles of the metal compound M1 and the lithium metal compound M2 adhere to the surface of the lithium transition metal oxide particles.

[0045] As a method for attaching the metal compound M1 to the surface of the unwashed particles, a method of mechanically mixing the unwashed particles and the metal compound M1 can be exemplified. Alternatively, the metal compound M1 can be attached to the surface of the unwashed particles by preparing an aqueous dispersion in which the metal compound M1 is dispersed in water and spraying or dropping the dispersion onto the unwashed particles. In this case, the metal compound M1 easily and uniformly adheres to the surface of the unwashed particles, and the metal compound M1 reacts easily with Li.

[0046] The heat treatment temperature in step (2) is lower than the calcination temperature in step (1), and is preferably 200 to 700° C., more preferably 300 to 500° C. When the heat treatment temperature is within this range, sufficient reactivity between the metal compound M1 and the remaining Li can be ensured, while the reaction between the metal compound M1 and Li in the lithium transition metal oxide crystals can be suppressed.

[0047] As the conductive material contained in the positive electrode composite material layer, examples include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. As the binding material, examples include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyolefins such as ethylene-propylene-isobutylene copolymer and ethylene-propylene-butadiene copolymer, polyacrylonitrile (PAN), polyimide, acrylic resin, etc. In addition, carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. can also be used in combination with these resins. They can be used alone or in combination of two or more.

[0048] [negative electrode]

[0049] The negative electrode comprises a negative electrode current collector and a negative electrode composite material layer formed on the current collector. The negative electrode current collector may be made of a metal foil such as copper that is stable within the potential range of the negative electrode, or a thin film formed by disposing the metal on the surface. The negative electrode composite material layer comprises a negative electrode active material and a binding material. The negative electrode can be produced, for example, by coating a negative electrode composite material slurry comprising a negative electrode active material, a binding material, etc. onto the negative electrode current collector, drying the coating, and then rolling the coating to form the negative electrode composite material layers on both sides of the current collector.

[0050] The negative electrode active material is not particularly limited as long as it can reversibly adsorb and release lithium ions. Examples include carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn) that alloy with lithium; and oxides containing metal elements such as Si and Sn. The negative electrode active material may be used alone or in combination of two or more.

[0051] As the binder, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc. can be used in the same manner as in the case of the positive electrode. When an aqueous solvent is used to prepare the composite material slurry, preferably used are: CMC or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, etc.

[0052] [Separator]

[0053] As separators, porous sheets with ion permeability and insulating properties can be used. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Suitable materials for separators include olefin resins such as polyethylene and polypropylene, and cellulose. Separators can have either a single-layer structure or a laminated structure.

[0054] [Non-aqueous electrolyte]

[0055] The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more thereof. The non-aqueous solvent may also contain a halogen-substituted substance in which at least a portion of the hydrogen atoms of these solvents are replaced by a halogen atom such as fluorine. In addition, the non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution) but may also be a solid electrolyte using a gel-like polymer or the like.

[0056] Examples of the above-mentioned esters include: cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), methylpropyl carbonate, ethylpropyl carbonate, and methyl isopropyl carbonate; cyclic carboxylates such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); chain carboxylates such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate; and the like.

[0057] Examples of the ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ethers; 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, and the like; Chain ethers such as methyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0058] As the halogen-substituted product, preferably used are fluorinated cyclic carbonates such as fluorinated ethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as fluorinated methyl propionate (FMP), and the like.

[0059] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1<x<6, n is 1 or 2), LiB 10 Cl 10 、LiCl、LiBr、LiI、lithium chloroborane、lower aliphatic carboxylic acid lithium、Li2B4O7、Li(B(C2O4)F2) and other borates、LiN(SO2CF3)2、LiN(C l F 2l+1 SO2)(C m F 2m+1 SO2) {l, m is an integer greater than or equal to 1} and other imide salts. The lithium salt may be used alone or in combination. Among them, LiPF6 is preferred from the perspectives of ion conductivity and electrochemical stability. The lithium salt concentration is preferably 0.8 to 1.8 mol per liter of the non-aqueous solvent.

[0060] Example

[0061] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0062] <Example 1>

[0063] [Preparation of positive electrode active material]

[0064] LiNi was mixed in a molar ratio of 1:1.03 0.91 Co 0.06 Al 0.03 Nickel cobalt aluminum oxide represented by O2 and lithium hydroxide (LiOH) were calcined at 745°C for 20 hours in an oxygen gas stream. Tungsten oxide (WO3) was added to the unwashed calcined product at a ratio of 161 μmol per 1 g of the calcined product and mixed, and then heat-treated at 400°C for 3 hours in an oxygen gas stream to obtain a positive electrode active material.

[0065] [Production of positive electrode]

[0066] The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 100:1.25:1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to adjust the viscosity to prepare a positive electrode composite material slurry. This positive electrode composite material slurry was then applied to one side of a positive electrode current collector made of aluminum foil, and the coating was dried on a hot plate at 80°C. The coated current collector was compressed using a roller to a density of 3 g / cc (positive electrode composite material layer), and then cut into the specified electrode size to produce a positive electrode plate with positive electrode composite material layers formed on both sides of the positive electrode current collector.

[0067] [Production of negative electrode]

[0068] Graphite powder, styrene-butadiene rubber (SBR), and carboxymethyl cellulose were mixed in a mass ratio of 100:1:1, and an appropriate amount of water was added to adjust the viscosity to prepare a negative electrode composite material slurry. This negative electrode composite material slurry was then applied to one side of a negative electrode current collector made of copper foil, and the coating was dried on an 80°C hot plate. The coated current collector was compressed using a roller and then cut into the specified electrode size, producing a negative electrode plate with the negative electrode composite material layer formed on both sides of the negative electrode current collector.

[0069] [Preparation of non-aqueous electrolyte]

[0070] Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 3:7. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of 1 mol / L to prepare a non-aqueous electrolyte.

[0071] [Battery Production]

[0072] The positive electrode plate attached to an aluminum lead and the negative electrode plate attached to a nickel lead were spirally wound with a polyethylene separator interposed therebetween to produce a wound electrode assembly. This electrode assembly was inserted into an outer casing made of aluminum laminate and dried at 105°C in a vacuum for 2 hours. The nonaqueous electrolyte was then injected into the outer casing. The outer casing containing the electrode assembly and nonaqueous electrolyte was sealed to produce Battery A1.

[0073] Battery A1 was subjected to a charge and discharge test and a storage test, and the evaluation results are shown in Tables 1 and 2, respectively (the same applies to the following Examples and Comparative Examples).

[0074] [Charge and discharge test]

[0075] After constant current charging at 0.1C to 4.2V, constant voltage charging was performed at 4.2V until the current value reached 0.01C, completing the charging. After a 10-minute pause, the battery was discharged at a constant current of 0.1C to 2.5V. After a 5-minute pause, the battery was discharged at a constant current of 0.05C to 2.5V. After a further 5-minute pause, the battery was discharged at a constant current of 0.01C to 2.5V, completing the discharge. The pause time between cycles was 10 minutes.

[0076] [Save Test]

[0077] After performing the above charge and discharge cycles twice, the volume of Battery A1, which had only undergone one charge cycle, was measured using the buoyancy method (Archimedes method). A storage test was then performed in a thermostat at 85°C for 3 hours. After the storage test, Battery A1 was cooled to room temperature and its volume was measured again using the buoyancy method. The difference between the volume before and after the storage test was used as the gas generation amount, which was standardized per 1g of positive electrode active material.

[0078] <Example 2>

[0079] Battery A2 was produced in the same manner as in Example 1 except that WO 3 was replaced with molybdenum oxide (MoO 3 ) when producing the positive electrode active material.

[0080] <Example 3>

[0081] Battery A3 was produced in the same manner as in Example 1 except that WO 3 was replaced with alumina (Al 2 O 3 ) when producing the positive electrode active material and the amount thereof added was set to 242 μmol per 1 g of the calcined product.

[0082] <Comparative Example 1>

[0083] Battery B1 was produced in the same manner as in Example 1 except that WO 3 was not added and the calcined product produced in Example 1 was used as the positive electrode active material.

[0084] Comparative Example 2

[0085] Battery B2 was produced in the same manner as in Example 3 except that Al 2 O 3 was replaced with niobium oxide (Nb 2 O 5 ) when producing the positive electrode active material.

[0086] <Comparative Example 3>

[0087] Battery B3 was produced in the same manner as in Example 1 except that WO 3 was replaced with boron oxide (B 2 O 3 ) in the production of the positive electrode active material and the amount thereof added was set to 484 μmol per 1 g of the calcined product.

[0088] [Table 1]

[0089] Metal compound M1 <![CDATA[Additive amount *1 > Battery <![CDATA[Gas generation amount *2 > Comparative Example 1 none - B1 0.874 Example 1 <![CDATA[WO3]]> 161 A1 0.683 Example 2 <![CDATA[MoO3]]> 161 A2 0.759 Example 3 <![CDATA[Al2O3]]> 242 A3 0.742 Comparative Example 2 <![CDATA[Nb2O5]]> 242 B2 1.179 Comparative Example 3 <![CDATA[B2O3]]> 484 B3 1.169

[0090] *1: Addition amount per 1g of positive electrode active material (μmol / g)

[0091] *2: Gas generation per 1g of positive electrode active material (cc / g)

[0092] As shown in Table 1, batteries A1 to A3 of the examples all exhibited lower gas generation during the storage test than battery B1 of Comparative Example 1. This suggests that the addition of WO₃, MoO₃, and Al₂O₃ is effective in suppressing gas generation during the storage test. On the other hand, the addition of Nb₂O₅ and B₂Ox (Comparative Examples 2 and 3) resulted in an increase in gas generation. It should be noted that the use of compounds containing Ga, which is in the same group as Al, is expected to produce the same effect as the use of compounds containing Al, such as Al₂O₃.

[0093] <Example 4>

[0094] Battery A4 was produced in the same manner as in Example 1, except that WO3 was replaced with bismuth oxide (Bi2O3) in the preparation of the positive electrode active material, the amount of which added was set to 484 μmol per 1 g of the calcined product, and the following substance was used as the non-aqueous electrolyte. A storage test of Battery A4 was also conducted in the same manner as in Example 1, and the evaluation results are shown in Table 2 (the same applies to the following Examples and Comparative Examples).

[0095] [Preparation of non-aqueous electrolyte]

[0096] EC, MEC, and dimethyl carbonate (DMC) were mixed at a volume ratio of 20:5:75. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of 1.4 mol / L, and 4% by mass of vinylene carbonate was added relative to the mass of the mixed solvent to prepare a non-aqueous electrolyte.

[0097] <Example 5>

[0098] Battery A5 was produced in the same manner as in Example 4 except that Bi 2 O 3 was replaced with tin oxide (SnO 2 ) when producing the positive electrode active material.

[0099] <Example 6>

[0100] Battery A6 was produced in the same manner as in Example 4 except that Bi 2 O 3 was replaced with manganese oxide (MnO) when producing the positive electrode active material.

[0101] <Example 7>

[0102] Battery A7 was produced in the same manner as in Example 4 except that Bi 2 O 3 was replaced with titanium oxide (TiO 2 ) when producing the positive electrode active material.

[0103] <Comparative Example 4>

[0104] Battery B4 was produced in the same manner as in Example 4 except that Bi 2 O 3 was not added and the calcined product produced in Example 1 was used as the positive electrode active material.

[0105] <Comparative Example 5>

[0106] Battery B5 was produced in the same manner as in Example 4 except that Bi 2 O 3 was replaced with copper hydroxide (Cu(OH) 2 ) when producing the positive electrode active material.

[0107] [Table 2]

[0108] Metal compounds <![CDATA[Addition amount *1 > Battery <![CDATA[Gas generation amount *2 > Comparative Example 4 none - B4 1.45 Example 4 <![CDATA[Bi2O3]]> 484 A4 1.13 Example 5 <![CDATA[SnO2]]> 484 A5 0.85 Example 6 MnO 484 A6 0.99 Example 7 <![CDATA[TiO2]]> 484 A7 0.94 Comparative Example 5 <![CDATA[Cu(OH)2]]> 484 B5 1.79

[0109] *1: Addition amount per 1g of positive electrode active material (μmol / g)

[0110] *2: Gas generation per 1g of positive electrode active material (cc / g)

[0111] As shown in Table 2, batteries A4 to A7 of the examples all exhibited lower gas generation during the storage test than battery B4 of Comparative Example 4. This suggests that the addition of Bi2O3, SnO2, MnO, and TiO2 was effective in suppressing gas generation during the storage test. On the other hand, the addition of Cu(OH)2 (Comparative Example 5) resulted in an increase in gas generation.

[0112] Industrial applicability

[0113] The present invention can be used for a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

[0114] Description of Reference Numerals

[0115] 10 Non-aqueous electrolyte secondary batteries

[0116] 11. Positive electrode

[0117] 12 negative electrode

[0118] 13 Dividers

[0119] 14 Electrode body

[0120] 15 Shell body

[0121] 16 Sealing body

[0122] 17, 18 insulation board

[0123] 19 Positive lead

[0124] 20 Negative lead

[0125] 21 bulge

[0126] 22 Perforated Metal Sheet

[0127] 23 Lower valve body

[0128] 24 Insulation components

[0129] 25 Upper valve body

[0130] 26 lid

[0131] 27 gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: lithium transition metal oxide particles; A metal compound containing a metal element M and not containing lithium (Li) attached to the surface of the lithium transition metal oxide particles; and A lithium metal compound containing lithium (Li) and a metal element M attached to the surface of the lithium transition metal oxide particles, The metal element M is at least one selected from aluminum (Al), titanium (Ti), manganese (Mn), gallium (Ga), molybdenum (Mo), tin (Sn), tungsten (W), and bismuth (Bi). The average particle size of the metal compound containing the metal element M and not containing lithium (Li) is 50 nm to 3 μm, and the average particle size of the lithium metal compound containing lithium (Li) and the metal element M is 50 nm to 3 μm, The amount of residual Li compound on the surface of the lithium transition metal oxide particles is 0 to 4 mol% relative to the lithium transition metal oxide. in, The lithium metal compound is attached to the surface of the lithium transition metal oxide particles in greater amounts than the metal compound. By performing the heat treatment, the metal compound reacts with lithium present on the surface of the unwashed lithium transition metal oxide particles to form the lithium metal compound.

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