Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

The purpose of the present disclosure is to provide a positive electrode active material for nonaqueous electrolyte secondary batteries, said positive electrode active material contributing to the achievement of a good balance between the battery capacity and the cycle characteristics. A positive electrode active material for nonaqueous electrolyte secondary batteries according to one embodiment of the present disclosure contains a lithium transition metal composite oxide which is represented by general formula LiaNibCocAldXeOf (wherein 0.9 ≤ a ≤ 1.2; 0.88 ≤ b ≤ 0.96; 0 ≤ c ≤ 0.12; 0 ≤ d ≤ 0.12; 0 ≤ e ≤ 0.1; 1.9 ≤ f ≤ 2.1; (b + c + d) = 1; and X represents at least one element that is selected from among Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W and B); and the lithium transition metal composite oxide has a pore volume of pores having a pore diameter of 0.3 μm or less of from 6 × 10-4 mL / g to 50 × 10-4 mL / g, while having a particle fracture strength of 120 MPa or more at the volume average particle diameter.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

Background Art

[0002] For high-capacity batteries, lithium nickelate-based positive electrode active materials are widely used. Patent Document 1 discloses a technique for improving the cycle characteristics and output characteristics of a battery by adjusting the contact area between an electrolytic solution and a positive electrode active material within a certain range by using a lithium nickelate-based positive electrode active material having an average crushing strength (particle crushing strength) of 15 to 100 MPa.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, from the viewpoint of increasing the capacity, the Ni content in lithium nickelate has been increasing. As a result of investigations by the present inventors, it has been found that in a lithium nickelate system with a high Ni content, even a positive electrode active material having the physical properties disclosed in Patent Document 1 may have a decrease in battery capacity and cycle characteristics. Patent Document 1 still has room for improvement in terms of achieving both high battery capacity and good cycle characteristics.

[0005] Therefore, an object of the present disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that contributes to achieving both high battery capacity and good cycle characteristics.

Means for Solving the Problems

[0006] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure has the general formula Li a Ni b Coc Al d X e O f (wherein 0.9 ≦ a ≦ 1.2, 0.88 ≦ b ≦ 0.96, 0 ≦ c ≦ 0.12, 0 ≦ d ≦ 0.12, 0 ≦ e ≦ 0.1, 1.9 ≦ f ≦ 2.1, b + c + d = 1, and X is at least one element selected from Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W, and B) and contains a lithium transition metal composite oxide, and the lithium transition metal composite oxide has a pore volume of 6 × 10 -4 ~50 × 10 -4 mL / g with a particle breakage strength of 120 MPa or more at the average volume particle diameter.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

Advantages of the Invention

[0008] According to one aspect of the present disclosure, a secondary battery in which both battery capacity and cycle characteristics are achieved can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer case will be exemplified, but the electrode body is not limited to a wound type, and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one with a separator interposed therebetween. Further, the outer case is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, etc., or may be a pouch type composed of a laminate sheet including a metal layer and a resin layer.

[0011] FIG. 1 is a longitudinal sectional view of a cylindrical secondary battery 10 which is an example of an embodiment. In the secondary battery 10 shown in FIG. 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an exterior body 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Hereinafter, for convenience of explanation, the side of the sealing body 16 will be referred to as "upper" and the bottom side of the exterior body 15 will be referred to as "lower".

[0012] The opening end of the exterior body 15 is closed by a sealing body 16, so that the inside of the secondary battery 10 is sealed. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through the through hole of the insulating plate 17 and is welded to the lower surface of a filter 22 which is the bottom plate of the sealing body 16. In the secondary battery 10, a cap 26 which is the top plate of the sealing body 16 and is electrically connected to the filter 22 serves as a positive electrode terminal. On the other hand, the negative electrode lead 20 extends through the through hole of the insulating plate 18 to the bottom side of the exterior body 15 and is welded to the inner surface of the bottom of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as a negative electrode terminal. When the negative electrode lead 20 is installed at the end portion, the negative electrode lead 20 extends to the bottom side of the exterior body 15 through the outside of the insulating plate 18 and is welded to the inner surface of the bottom of the exterior body 15.

[0013] The exterior body 15 is, for example, a bottomed cylindrical metal exterior can. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the sealing property inside the secondary battery 10. The exterior body 15 has, for example, a groove portion 21 for supporting the sealing body 16 which is formed by pressing the side surface from the outside. The groove portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and supports the sealing body 16 via the gasket 27 on its upper surface.

[0014] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are laminated in order from the side of the electrode body 14. Each member constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each member except the insulating member 24 is 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 the insulating member 24 is interposed between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 breaks, whereby the upper valve body 25 bulges toward the cap 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 gas is discharged from the opening 26a of the cap 26.

[0015] Hereinafter, the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the secondary battery 10 will be described in detail, particularly the positive electrode active material contained in the positive electrode mixture layer constituting the positive electrode 11.

[0016] [Positive Electrode] The positive electrode has a positive electrode core body and a positive electrode mixture layer formed on the positive electrode core body. For the positive electrode core body, a foil of a metal stable within the potential range of the positive electrode such as aluminum, a film having the metal disposed on the surface layer, or the like can be used. The positive electrode mixture layer contains, for example, a positive electrode active material, a binder, a conductive agent, and the like. The positive electrode mixture layer can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. onto the positive electrode core body, drying to form a coating film, and then compressing this coating film.

[0017] The porosity of the positive electrode mixture layer is preferably 25% by volume or less, more preferably 22% by volume or less. If the porosity of the positive electrode mixture layer is 25% by volume or less, the effects of the present embodiment become more remarkable. The lower limit value of the porosity of the positive electrode mixture layer can be, for example, 16% by volume. The porosity of the positive electrode mixture layer is calculated according to the following formula from the bulk density of the positive electrode mixture layer and the true densities and contents (the ratios of the masses of the respective components to the total mass of the positive electrode mixture layer) of the respective components such as the positive electrode active material, conductive agent, and binder contained in the positive electrode mixture layer. By adjusting the compression ratio of the positive electrode mixture layer, the bulk density of the positive electrode mixture layer can be changed, so that the porosity of the positive electrode mixture layer can be changed. Porosity of the positive electrode active material layer = 1 - (sum of (content / true density) of each component × bulk density of the positive electrode active material layer)

[0018] Examples of the conductive agent contained in the positive electrode active material layer include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more kinds.

[0019] Examples of the binder contained in the positive electrode active material layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, and polyolefin-based resins. These may be used alone or in combination of two or more kinds.

[0020] The positive electrode active material contained in the positive electrode active material layer is represented by the general formula Li a Ni b Co c Al d X e O f (wherein 0.9 ≦ a ≦ 1.2, 0.88 ≦ b ≦ 0.96, 0 ≦ c ≦ 0.12, 0 ≦ d ≦ 0.12, 0 ≦ e ≦ 0.1, 1.9 ≦ f ≦ 2.1, b + c + d = 1, and X is at least one element selected from Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W, and B). The molar fraction of the metal element contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma atomic emission spectrometry (ICP-AES). Note that the positive electrode active material may contain a lithium transition metal composite oxide other than that represented by the above general formula or other compounds as long as the object of the present disclosure is not impaired.

[0021] The a indicating the proportion of Li in the lithium transition metal composite oxide satisfies 0.9 ≤ a ≤ 1.2, and preferably satisfies 0.95 ≤ α ≤ 1.05. When α is less than 0.9, the battery capacity may decrease compared with the case where α satisfies the above range. When α exceeds 1.2, it may lead to a decrease in charge-discharge cycle characteristics compared with the case where α satisfies the above range.

[0022] The b indicating the proportion of Ni to the total molar number of metal elements excluding Li and X in the lithium transition metal composite oxide satisfies 0.88 ≤ b ≤ 0.96, and preferably satisfies 0.88 ≤ b ≤ 0.92. By setting b to 0.88 or more, a high-capacity battery can be obtained. Also, by setting a to 0.96 or less, an appropriate amount of other elements such as Co and Al can be included.

[0023] The c indicating the proportion of Co to the total molar number of metal elements excluding Li and X in the lithium transition metal composite oxide satisfies 0 ≤ c ≤ 0.12, and preferably satisfies 0.01 ≤ b ≤ 0.07.

[0024] The d indicating the proportion of Al to the total molar number of metal elements excluding Li and X in the lithium transition metal composite oxide satisfies 0 ≤ d ≤ 0.12, and more preferably satisfies 0.01 ≤ c ≤ 0.09. Since Al does not cause a change in oxidation number even during charge and discharge, it is considered that the structure of the transition metal layer is stabilized by being contained in the transition metal layer.

[0025] The lithium transition metal composite oxide preferably contains Ni, Co, and Al. By using a Ni-Co-Al-based lithium transition metal composite oxide, it is possible to suppress cation mixing in which Ni enters the Li site while increasing the battery capacity.

[0026] The e indicating the proportion of X (X is at least one element selected from Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W, B) in the lithium transition metal composite oxide preferably satisfies 0 ≤ e ≤ 0.1, and more preferably satisfies 0.0001 ≤ e ≤ 0.01.

[0027] The lithium transition metal composite oxide is secondary particles formed by aggregation of primary particles. The average volume particle diameter of the lithium transition metal composite oxide is preferably 3 μm to 30 μm, more preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. The average volume particle diameter means the particle diameter (D50) at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smaller particle diameter, and is also called the median diameter. The particle size distribution of the secondary particles of the lithium transition metal composite oxide can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bell Corporation) with water as the dispersion medium. Further, the particle diameter of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle diameter of the primary particles can be measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM).

[0028] X (X is at least one element selected from Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W, B) may adhere to the surface of the secondary particles or the surface of the primary particles in the lithium transition metal composite oxide. X may exist in the state of a compound containing X on the surface of the secondary particles or the surface of the primary particles. Note that a part of X may be dissolved in the lithium transition metal composite oxide.

[0029] The lithium transition metal composite oxide has a pore volume of 6×10 -4 ~50×10 -4 mL / g for pores with a pore diameter of 0.3 μm or less. Outside this range, it is impossible to achieve both battery capacity and cycle characteristics. The pore volume can be measured by a mercury intrusion method using a mercury porosimeter (for example, AutoPore IV9510 type manufactured by Micromeritics). It is calculated by integrating the volume of pores with a pore diameter of 0 to 0.3 μm in the obtained pore distribution.

[0030] The lithium transition metal composite oxide has a particle fracture strength at the average volume particle diameter of 120 MPa or more. If the particle fracture strength is less than 120 MPa, it is impossible to achieve both battery capacity and cycle characteristics. The upper limit value of the particle fracture strength can be, for example, 300 MPa. The particle fracture strength can be calculated using a micro compression tester (for example, MCT-211 manufactured by Shimadzu Corporation). For one lithium transition metal composite oxide with an average volume particle diameter, a load is applied with an upper pressure indenter having a tip of φ50 μm at a loading rate of 2.7 mN / second, and the fracture load when the lithium transition metal composite oxide is fractured is measured. The fracture loads of 10 lithium transition metal composite oxides with an average volume particle diameter are measured in the same manner, and the average value is taken as the particle fracture strength.

[0031] Next, an example of a method for manufacturing a lithium transition metal composite oxide will be described.

[0032] The method for manufacturing a positive electrode active material includes a first step of obtaining a composite oxide containing Ni and an arbitrary metal element, and a second step of mixing and firing the composite oxide obtained in the first step with other raw materials to obtain a lithium transition metal composite oxide.

[0033] In the first step, while stirring a solution of a metal salt containing Ni and an arbitrary metal element (such as Co, Al), an alkaline solution such as sodium hydroxide is dropped, and the pH is adjusted to the alkaline side (for example, 8.5 to 12.5) to precipitate (co-precipitate) a composite hydroxide containing Ni and an arbitrary metal element, and by calcining the composite hydroxide temporarily, a composite oxide containing Ni and an arbitrary metal element can be obtained. In the temporary calcination, by lowering the temperature and shortening the time, the pore volume with a pore diameter of 0.3 μm or less tends to increase.

[0034] In the second step, first, the composite oxide obtained in the first step, a Li raw material, and an X raw material are mixed to obtain a mixture. The mixing ratio of the composite oxide, the Li raw material, and the X raw material may be appropriately determined so that each element in the finally obtained Li-transition metal oxide has a desired ratio. Examples of the Li raw material include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, LiF, etc. Examples of the X raw material include oxides, hydroxides, sulfates, nitrates, etc. containing X. Next, the mixture is sintered in an oxygen atmosphere to obtain the lithium-transition metal composite oxide according to the present embodiment. In this sintering, the particle destruction strength tends to increase by raising the temperature and lengthening the time. Note that X may be attached to the lithium-transition metal composite oxide in which the X raw material was not mixed in the second step by a wet method or a dry method. Further, the lithium-transition metal composite oxide powder obtained in the second step may be washed with water.

[0035] [Negative electrode] The negative electrode includes, for example, a negative electrode core body such as a metal foil, and a negative electrode mixture layer formed on the negative electrode core body. For the negative electrode core body, a foil of a metal stable within the potential range of the negative electrode such as copper, a film having the metal disposed on the surface layer, etc. can be used. The negative electrode mixture layer preferably contains a negative electrode active material and, in addition, a thickening agent, a binder, etc. The negative electrode mixture layer can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a thickening agent, a binder, etc. on the negative electrode core body, drying to form a coating film, and then compressing this coating film.

[0036] As the negative electrode active material, a carbon material capable of occluding and releasing lithium ions can be used. In addition to graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke, carbon black, etc. can be used. Further, as non-carbon-based materials, silicon, tin, and alloys or oxides mainly composed of these can be used.

[0037] As the binder, PTFE or the like can be used as in the case of the positive electrode, or styrene-butadiene copolymer (SBR) or its modified product or the like can also be used. As the thickener, carboxymethyl cellulose (CMC) or the like can be used.

[0038] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulation properties or the like is used. Specific examples of the porous sheet include a microporous membrane, a woven fabric, a non-woven fabric, etc. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Also, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, or a separator 13 with a material such as an aramid resin or ceramic coated on its surface may be used.

[0039] [Non-aqueous electrolyte] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (electrolyte solution), and a solid electrolyte using a gel-like polymer or the like may also be used. For the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine.

[0040] Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc., chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, etc., cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, etc., and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, etc.

[0041] Examples of the above 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, crown ether, etc., and chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl 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.

[0042] As the above halogenated compounds, it is preferable to use fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP), etc.

[0043] 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, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 1 or more}, and the like. The lithium salt may be used alone or in combination of multiple kinds. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the solvent.

Examples

[0044] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0045] <Example 1> [Preparation of positive electrode active material] The composite hydroxide represented by [Ni 0.91 Co 0.04 Al 0.05 (OH)2 obtained by the coprecipitation method is calcined preliminarily to obtain a composite oxide (Ni 0.91 Co 0.04 Al 0.05Oxygen (O₂) was obtained (first step). Lithium hydroxide (LiOH) was mixed so that the molar ratio of the total amount of Ni, Co, and Al in the composite oxide to Li was 1:1.02, and the mixture was sintered in an oxygen atmosphere to obtain the positive electrode active material of Example 1 (second step). In the following Examples and Comparative Examples, the temperatures of the preliminary sintering and the main sintering are based on the conditions of the preliminary sintering and the main sintering of Example 1. Assuming the conditions of Example 1 as 0, they are represented by relative evaluations of "+1", "0 (reference)", "-1", "-2", "-3" in descending order of temperature. Also, the times of the preliminary sintering and the main sintering are based on the conditions of the preliminary sintering and the main sintering of Example 1. Assuming the conditions of Example 1 as 0, they are represented by relative evaluations of "+2", "+1", "0 (reference)", "-1", "-2" in descending order of time.

[0046] As a result of analysis by an ICP emission spectroscopic analyzer (manufactured by Thermo Fisher Scientific, trade name "iCAP6300"), the composition of the positive electrode active material of Example 1 was LiNi 0.91 Co 0.04 Al 0.05 O₂. Also, the positive electrode active material of Example 1 was secondary particles with an average volume particle diameter of 11 μm, the pore volume with a pore diameter of 0.3 μm or less was 33×10 -4 mL / g, and the particle destruction strength at the average volume particle diameter was 120 MPa.

[0047] [Fabrication of Positive Electrode] 100 parts by mass of the above positive electrode active material, 1 part by mass of acetylene black (AB) as a conductive agent, and 0.9 part by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil. After drying the coating film, the coating film was compressed using a roller so that the porosity of the positive electrode mixture layer was 25%. Then, it was cut to a predetermined electrode size to obtain a positive electrode having positive electrode mixture layers formed on both sides of the positive electrode core. Note that an exposed portion where the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0048] [Fabrication of Negative Electrode] 90 parts by mass of graphite powder as the negative electrode active material, 5 parts by mass of silicon oxide, 3 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and 2 parts by mass of styrene-butadiene rubber (SBR) as a binder were mixed, and an appropriate amount of water was further added to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a negative electrode core made of a copper foil. After drying the coating film, the coating film was compressed using a roller and cut into a predetermined electrode size to obtain a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode core. Note that an exposed portion where the surface of the negative electrode core was exposed was provided in a part of the negative electrode.

[0049] [Preparation of Non-aqueous Electrolyte] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70. Lithium hexafluorophosphate (LiPF6) was added to the mixed solvent so that the concentration became 1 mol / liter to prepare a non-aqueous electrolyte.

[0050] [Fabrication of Battery] An aluminum lead was attached to the exposed portion of the positive electrode, and a nickel lead was attached to the exposed portion of the negative electrode. The positive electrode and the negative electrode were wound in a spiral shape through a separator made of a microporous polyethylene film to fabricate a wound electrode body. This electrode body was housed in a cylindrical exterior body with a diameter of φ21 mm and a height of 70 mm. After injecting the non-aqueous electrolyte, the opening of the exterior body was sealed with a sealing body to fabricate a cylindrical battery.

[0051] [Evaluation of Specific Capacity of Positive Electrode Active Material] The above battery was charged at a constant current of 0.3C until the battery voltage reached 4.2V in a temperature environment of 25°C, and then charged at a constant voltage of 4.2V until the current value reached 0.02C. Then, it was discharged at a constant current of 0.3C until the battery voltage reached 2.5V, and further discharged at a constant current of 0.02C until the battery voltage reached 2.5V. This charge-discharge cycle was carried out 2 cycles, and the value calculated by dividing the discharge capacity of the second cycle by the mass of the positive electrode active material was taken as the specific capacity of the positive electrode active material.

[0052] [Evaluation of Capacity Retention Rate] For the above-mentioned battery, the following cycle test was conducted. The discharge capacity at the first cycle of the cycle test and the discharge capacity at the 300th cycle were determined, and the capacity retention rate was calculated by the following formula. Capacity retention rate (%) = (Discharge capacity at the 300th cycle ÷ Discharge capacity at the first cycle) × 100 <Cycle test> The battery was charged at a constant current of 0.3C until the battery voltage reached 4.2V in a temperature environment of 25°C, and then charged at a constant voltage of 4.2V until the current value reached 0.02C. Thereafter, it was discharged at a constant current of 0.3C until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 300 times.

[0053] <Examples 2 to 5, Comparative Examples 1 to 8> In the production of the positive electrode active material, except that the conditions (temperature, time) of the preliminary firing and the final firing were set to the conditions shown in Table 1, and in the production of the positive electrode, the porosity of the positive electrode mixture layer was set to the value shown in Table 1, the battery was produced and evaluated in the same manner as in Example 1. In any of Examples 2 to 5 and Comparative Examples 1 to 8, the average volume particle diameter of the positive electrode active material was 11 μm, the same as in Example 1. Also, as a result of analysis by an ICP emission spectroscopic analyzer, the composition of the positive electrode active materials in Examples 2 to 5 and Comparative Examples 1 to 8 was the same as in Example 1, LiNi 0.91 Co 0.04 Al 0.05 O2.

[0054] The evaluation results of the batteries in Examples 1 to 5 and Comparative Examples 1 to 8 are shown in Table 1. In Table 1, the results of the examples and comparative examples are shown as relative values when the specific capacity and capacity retention rate of the positive electrode active material of the battery in Comparative Example 1 are set to 100. In addition to the above-mentioned conditions of the preliminary firing and the final firing, and the porosity of the positive electrode mixture layer, Table 1 also shows the pore volume with a pore diameter of 0.3 μm or less and the particle fracture strength in terms of the average volume particle diameter.

[0055]

Table 1

[0056] From the results of Examples 1 to 5, when a positive electrode active material having a pore volume of pores with a pore diameter of 0.3 μm or less of 6×10 -4 ~50×10 -4 mL / g and a particle destruction strength at the average volume particle diameter of 120 MPa or more is used, it can be seen that a battery with both high battery capacity and good cycle characteristics can be obtained. On the other hand, in the batteries of Comparative Examples 1 to 8 that do not satisfy the above conditions, the battery capacity and cycle characteristics were not compatible.

[0057] <Example 6> In the second step of preparing the positive electrode active material, the composite oxide and Ca(OH)2 were mixed so that the Ca content was 0.2 mol% with respect to the total amount of Ni, Co, and Al in the composite oxide. Further, a battery was fabricated and evaluated in the same manner as in Example 1, except that lithium hydroxide (LiOH) was mixed so that the molar ratio of the total amount of Ni, Co, Al, and Ca to Li was 1:1.02. The average volume particle diameter of the positive electrode active material was 11 μm, the same as in Example 1. Also, as a result of analysis by an ICP emission spectroscopic analyzer, the composition of the positive electrode active material was LiNi 0.91 Co 0.04 Al 0.05 Ca 0.002 O2. Further, as a result of observation by a transmission electron microscope (TEM), it was confirmed that Ca was attached to the surface of the secondary particles or primary particles of the positive electrode active material.

[0058] <Examples 7 to 10> In the second step of preparing the positive electrode active material, TiO2, WO3, Nb2O5, and B2O3 were each mixed so that the content of Ti, W, Nb, and B was 0.2 mol% instead of Ca(OH)2. A battery was fabricated and evaluated in the same manner as in Example 6. In any of Examples 7 to 10, the average volume particle diameter of the positive electrode active material was 11 μm, the same as in Example 6. Also, as a result of analysis by an ICP emission spectroscopic analyzer, the compositions of the positive electrode active materials in Examples 7 to 10 were LiNi 0.91 Co 0.04 Al 0.05 Ti 0.002 O2, LiNi 0.91 Co 0.04 Al0.05 W 0.002 O2, LiNi 0.91 Co 0.04 Al 0.05 Nb 0.002 O2, LiNi 0.91 Co 0.04 Al 0.05 B 0.002 It was O2. Further, as a result of SEM observation, it was confirmed that Ti, W, Nb, and B were each adhered to the surface of the secondary particles or primary particles of the positive electrode active material in Examples 7 to 10.

[0059] <Comparative Example 9> In the second step of preparing the positive electrode active material, except that the composite oxide and Ca(OH)2 were mixed so that the content of Ca was 0.2 mol% with respect to the total amount of Ni, Co, and Al of the composite oxide, and further, lithium hydroxide (LiOH) was mixed so that the molar ratio of the total amount of Ni, Co, Al, and Ca to Li was 1:1.02, a battery was produced and evaluated in the same manner as in Comparative Example 1. The average volume particle diameter of the positive electrode active material was 11 μm as in Comparative Example 1. Further, as a result of analysis by an ICP emission spectroscopic analyzer, the composition of the positive electrode active material was the same as in Example 6, LiNi 0.91 Co 0.04 Al 0.05 Ca 0.002 It was O2. Further, as a result of SEM observation, it was confirmed that Ca was adhered to the surface of the secondary particles or primary particles of the positive electrode active material.

[0060] <Comparative Examples 10 to 13> In the second step of preparing the positive electrode active material, except that TiO2, WO3, Nb2O5, and B2O3 were each mixed so that the content of each of Ti, W, Nb, and B was 0.2 mol% instead of Ca(OH)2, a battery was produced and evaluated in the same manner as in Comparative Example 9. In any of Comparative Examples 10 to 13, the average volume particle diameter of the positive electrode active material was 11 μm as in Comparative Example 9. Further, as a result of analysis by an ICP emission spectroscopic analyzer, the composition of the positive electrode active material in Comparative Examples 10 to 13 was the same as in Examples 7 to 10, LiNi 0.91 Co 0.04 Al 0.05 Ti 0.002O2, LiNi 0.91 Co 0.04 Al 0.05 W 0.002 O2, LiNi 0.91 Co 0.04 Al 0.05 Nb 0.002 O2, LiNi 0.91 Co 0.04 Al 0.05 B 0.002 It was O2. Further, as a result of SEM observation, it was confirmed that Ti, W, Nb, and B were each attached to the surface of the secondary particles or primary particles of the positive electrode active material of Comparative Examples 10 to 13.

[0061] Table 2 shows the evaluation results of each battery of Examples 6 to 10 and Comparative Examples 9 to 13, and the evaluation results of Example 1 and Comparative Example 1 for comparison. In Table 1, the results of Examples 6 to 10 are shown as relative values when the specific capacity and capacity retention rate of the positive electrode active material of each battery of Comparative Examples 9 to 13 containing the same X are set to 100. Table 2 also shows the pore volume of pores with a pore diameter of 0.3 μm or less, the particle fracture strength at the average volume particle diameter, and the porosity of the positive electrode binder layer.

[0062]

Table 2

[0063] The positive electrode active materials of Examples 6 to 10 in which X (Ca, Ti, W, Nb, B) was attached to the surface were able to greatly improve the specific capacity and capacity retention rate of the positive electrode active material compared to the positive electrode active materials of the corresponding Comparative Examples 9 to 13. On the other hand, although Example 1 in which X was not attached to the surface was also able to improve the specific capacity and capacity retention rate of the positive electrode active material compared to Comparative Example 1, the improvement rate was lower than that of Examples 6 to 10. Therefore, it can be seen that the positive electrode active material with X attached to the surface can achieve a higher effect of this embodiment compared to the positive electrode active material with X attached to the surface.

Explanation of Reference Numerals

[0064] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Exterior body, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Groove-in part, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket

Claims

1. General formula Li ａ Ni ｂ Co ｃ Al ｄ X ｅ O ｆ (wherein, 0.9 ≦ a ≦ 1.2, 0.88 ≦ b ≦ 0.96, 0 ≦ c ≦ 0.12, 0 ≦ d ≦ 0.12, 0 ≦ e ≦ 0.1, 1.9 ≦ f ≦ 2.1, b + c + d = 1, X is at least one element selected from Mn, Mg, Ca, Sr, Ba, Ti, Zr, V, Nb, Ta, Mo, W, B) and contains a lithium transition metal composite oxide represented by The lithium transition metal composite oxide contains secondary particles formed by aggregation of primary particles, and has a pore volume with a pore diameter of 0.3 μm or less of 6 × 10 －４ to 50 × 10 －４ mL / g, and a particle fracture strength at the average volume particle diameter of 120 MPa or more, which is a positive electrode active material for a non-aqueous electrolyte secondary battery.

2. The X is a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which is attached to the surface of the secondary particles or the surface of the primary particles.

3. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, a negative electrode, and a non-aqueous electrolyte.

4. The positive electrode has a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core. The non-aqueous electrolyte secondary battery according to claim 3, wherein the porosity of the positive electrode mixture layer is 25% by volume or less.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the porosity of the positive electrode mixture layer is 22% by volume or less.

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