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

Abstract

To provide a cathode active material in which a ratio of Ni against a total number mol of a metal element excluding Li is 85 mol% or more, and a ratio of Co is 10 mol% or less, and which contains a lithium composite oxide of which a reaction resistance of a battery is reduced.SOLUTION: A cathode active material for a non-aqueous electrolyte secondary battery, as an embodiment of the present disclosure, includes a layer structure containing a Li layer, and contains a lithium composite oxide containing at least Ni, Al, and Sr. α indicating a ratio of Ni against a total mol number of a metal element excluding Li in the lithium composite oxide is 0.85≤α≤0.95, β indicating a ratio of Al is 0<β≤0.08, and x indicating a ratio of Sr is 0<x≤0.015. A ratio of the metal element other than Li existed in the Li layer is within a range of 1 mol% or more and 2.5 mol% or less against a total mol amount of the metal element excluding Li in the lithium composite oxide.SELECTED DRAWING: None

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] In recent years, as a secondary battery with high output and high energy density, a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, which performs charge and discharge by moving lithium ions or the like between the positive electrode and the negative electrode, has been widely used. From the viewpoints of reducing the resistance of the battery and increasing the capacity, improvement of the characteristics of the positive electrode active material contained in the positive electrode of the battery has been demanded.

[0003] For example, Patent Document 1 discloses a lithium composite oxide having a layered structure and containing Mn, Ni, Co, Sr, and Mo. By setting the content of Mo to 0.1 mol% to 1.5 mol% and the ratio of the content of Mo / Sr to 0.5 to 2.0 in terms of molar ratio, a positive electrode active material that improves the charge-discharge cycle characteristics while coping with high capacity is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] By the way, in the lithium composite oxide contained in the positive electrode active material, a design of increasing the Ni content rate in order to obtain a high discharge capacity and decreasing the Co content rate in order to reduce the manufacturing cost can be considered. However, when the ratio of Ni is 85 mol% or more and the ratio of Co is 10 mol% or less with respect to the total molar number of metal elements excluding Li, the layered structure of the lithium composite oxide becomes unstable, and the reaction resistance of the battery may increase. The technology of Patent Document 1 does not consider the reaction resistance and still has room for improvement.

[0006] Therefore, an object of the present disclosure is to provide a positive electrode active material containing a lithium composite oxide in which the ratio of Ni is 85 mol% or more and the ratio of Co is 10 mol% or less with respect to the total molar amount of metal elements excluding Li, and the reaction resistance of the battery is reduced.

[0007] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure has a layered structure and has a general formula Li a Ni α Al β Co γ M δ Sr x O 2-w (where 0.95 < a < 1.05, 0.85 ≤ α ≤ 0.95, 0 < β ≤ 0.08, 0 ≤ γ ≤ 0.1, 0 ≤ δ ≤ 0.15, 0 < x ≤ 0.015, 0 ≤ w < 0.05, α + β + γ + δ = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn), and the layered structure includes a Li layer containing a metal element other than Li, and the ratio of the metal element other than Li present in the Li layer is in the range of 1 mol% or more and 2.5 mol% or less with respect to the total molar amount of metal elements excluding Li in the lithium composite oxide.

[0008] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode containing the above positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

[0009] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, a non-aqueous electrolyte secondary battery with low reaction resistance can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] The layered structure of the lithium composite oxide has a transition metal layer such as Ni, a Li layer, and an oxygen layer. The reversible ingress and egress of Li ions present in the Li layer enables the charge and discharge reactions of the battery to proceed. Here, in the lithium composite oxide contained in the positive electrode active material, when the proportion of Ni is 85 mol% or more and the proportion of Co is 10 mol% or less with respect to the total number of moles of metal elements excluding Li, a large number of Li ions are extracted from the Li layer during battery charging, causing the layered structure to become unstable and potentially increasing the reaction resistance of the battery. However, like the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, by containing a predetermined amount of Al and Sr and further containing a predetermined amount of metal elements other than Li in the Li layer, a synergistic effect between the addition of Al and the addition of Sr occurs, reducing the reaction resistance. Since the oxidation number of Al does not change during charge and discharge, it is presumed that the structure of the transition metal layer is stabilized by being contained in the transition metal layer. Sr is considered to exist as a compound within the layered structure or on the surface of the lithium composite oxide, and it is presumed that the resistance can be reduced because it changes the surface state of the lithium composite oxide through electronic interaction. Further, when a predetermined amount of metal elements is present in the Li layer, even if a large number of Li ions are extracted from the Li layer during battery charging, the Li layer is retained by the predetermined amount of metal elements present in the Li layer, stabilizing the layered structure and presumably suppressing a decrease in charge and discharge cycle characteristics. In the lithium composite oxide of the present disclosure, the metal element present in the Li layer of the layered structure is mainly Ni, but metal elements other than Ni contained in the lithium composite oxide may also be present in the Li layer.

[0012] 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 battery case will be exemplified, but the electrode body is not limited to the 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 battery case is not limited to a cylindrical shape and may be, for example, a rectangular shape, a coin shape, etc., or may be a battery case composed of a laminate sheet including a metal layer and a resin layer.

[0013] FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. As illustrated in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes an electrode body 14, a non-aqueous electrolyte (not shown), and a battery case 15 that houses the electrode body 14 and the non-aqueous electrolyte. 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. The battery case 15 is composed of a bottomed cylindrical outer can 16 and a sealing body 17 that closes the opening of the outer can 16.

[0014] The electrode body 14 is composed of a long positive electrode 11, a long negative electrode 12, two long separators 13, a positive electrode tab 20 joined to the positive electrode 11, and a negative electrode tab 21 joined to the negative electrode 12. The negative electrode 12 is formed with a size slightly larger than that of the positive electrode 11 in order to prevent precipitation of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (short side direction). The two separators 13 are formed with a size at least slightly larger than that of the positive electrode 11 and are arranged, for example, so as to sandwich the positive electrode 11.

[0015] The non-aqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 respectively arranged above and below the electrode body 14. In the example shown in FIG. 1, the positive electrode tab 20 attached to the positive electrode 11 extends toward the sealing body 17 through the through hole of the insulating plate 18, and the negative electrode tab 21 attached to the negative electrode 12 extends toward the bottom side of the outer can 16 through the outside of the insulating plate 19. The positive electrode tab 20 is connected to the lower surface of the bottom plate 23 of the sealing body 17 by welding or the like, and the cap 27 of the sealing body 17 electrically connected to the bottom plate 23 serves as a positive electrode terminal. The negative electrode tab 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0016] The outer can 16 is, for example, a metal container having a bottomed cylindrical shape. A gasket 28 is provided between the outer can 16 and the sealing body 17, and the internal space of the battery case 15 is sealed. The outer can 16 has, for example, a groove portion 22 formed by pressing the side surface portion from the outside to support the sealing body 17. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16 and supports the sealing body 17 on its upper surface.

[0017] The sealing body 17 has a structure in which a bottom plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in this order from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at the central portions thereof, and the insulating member 25 is interposed between the peripheral portions thereof. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is interrupted. When the internal pressure further rises, the upper valve body 26 is broken, and gas is discharged from the opening of the cap 27.

[0018] Hereinafter, the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte constituting the non-aqueous electrolyte secondary battery 10 will be described in detail, and in particular, the positive electrode active material contained in the positive electrode active material layer 31 constituting the positive electrode 11 will be described in detail.

[0019] [Positive Electrode] The positive electrode 11 has a positive electrode current collector 30 and positive electrode active material layers 31 formed on both surfaces of the positive electrode current collector 30. As the positive electrode current collector 30, a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film having the metal disposed on the surface layer can be used. The positive electrode active material layer 31 contains a positive electrode active material, a conductive material, and a binder. The thickness of the positive electrode active material layer 31 is, for example, 10 μm to 150 μm on one side of the positive electrode current collector 30. The positive electrode 11 can be manufactured by applying a positive electrode slurry containing a positive electrode active material, a conductive material, a binder, etc. to the surface of the positive electrode current collector 30, drying the coating film, and then compressing it to form the positive electrode active material layer 31 on both surfaces of the positive electrode current collector 30.

[0020] Examples of the conductive material contained in the positive electrode active material layer 31 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode active material layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc.

[0021] The positive electrode active material has a layered structure and is represented by the general formula Li a Ni α Al β Co γ M δ Sr x O 2-w (where 0.95 < a < 1.05, 0.85 ≤ α ≤ 0.95, 0 < β ≤ 0.08, 0 ≤ γ ≤ 0.1, 0 ≤ δ ≤ 0.15, 0 < x ≤ 0.015, 0 ≤ w < 0.05, α + β + γ + δ = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn) and contains a lithium composite oxide.

[0022] Examples of the layered structure of the lithium composite oxide include a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. Among these, a layered structure belonging to the space group R-3m is preferable in terms of high capacity and stability of the crystal structure.

[0023] The a indicating the ratio of Li in the lithium composite oxide satisfies 0.95 ≤ a < 1.05, and more preferably satisfies 0.97 ≤ a ≤ 1.03. When a is less than 0.95, the battery capacity may decrease compared to the case where a satisfies the above range. When a is 1.05 or more, more lithium compounds need to be added compared to the case where a satisfies the above range, which may not be economical from the perspective of production cost.

[0024] α, which represents the ratio of Ni to the total molar number of metal elements excluding Li in the lithium composite oxide, satisfies 0.85 ≦ α ≦ 0.95 in order to increase the battery capacity and add other metal elements.

[0025] β, which represents the ratio of Al to the total molar number of metal elements excluding Li in the lithium composite oxide, satisfies 0 < β ≦ 0.08. Since the oxidation number of Al does not change 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. On the other hand, when the content rate of Al exceeds 8 mol%, Al impurities are generated and the battery capacity decreases. Al may be uniformly dispersed in the layered structure of the lithium composite oxide, for example, or may be present in a part of the layered structure.

[0026] Co and M (M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn) are optional components. γ and δ, which represent the ratios of Co and M to the total molar number of metal elements excluding Li in the lithium composite oxide, satisfy 0 ≦ γ ≦ 0.1 and 0 ≦ δ ≦ 0.15, respectively. Since Co is expensive, it is desirable to suppress the content rate of Co from the viewpoint of manufacturing cost.

[0027] x, which represents the ratio of Sr to the total molar number of metal elements excluding Li in the lithium composite oxide, satisfies 0 < x ≦ 0.015. By containing Sr, it is considered that the surface state of the lithium composite oxide can be changed by electron interaction, so that the resistance can be reduced. Sr exists as a compound in the layered structure or on the surface of the lithium composite oxide, and in either form, it can change the surface state of the lithium composite oxide.

[0028] The content rates of the elements constituting the lithium composite oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0029] The lithium composite oxide has a metal element other than Li present in the Li layer of the layered structure. And the proportion of the metal element other than Li present in the Li layer of the layered structure is in the range of 1 mol% or more and 2.5 mol% or less, preferably 1 mol% or more and 2 mol% or less, with respect to the total molar amount of the metal elements excluding Li in the lithium composite oxide, in order to reduce the reaction resistance of the battery. When the proportion of the metal element other than Li in the Li layer of the layered structure is less than 1 mol%, compared with the case of satisfying the above range, the stability of the layered structure in the state where Li ions in the Li layer are extracted decreases, and the reaction resistance of the battery increases. Also, when the proportion of the metal element other than Li in the Li layer of the layered structure exceeds 2.5 mol%, compared with the case of satisfying the above range, the diffusibility of Li ions in the Li layer decreases, and the reaction resistance of the battery increases along with the decrease in battery capacity. The metal element present in the Li layer of the layered structure is mainly Ni, but other metal elements may be included.

[0030] The proportion of the metal element other than Li in the Li layer of the layered structure is obtained from the Rietveld analysis result of the X-ray diffraction pattern by X-ray diffraction measurement of the lithium composite oxide.

[0031] The X-ray diffraction pattern is obtained by the powder X-ray diffraction method under the following conditions using a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name "RINT-TTR", radiation source Cu-Kα). Measurement range: 15 - 120° Scan speed: 4° / min Analysis range: 30 - 120° Background: B-spline Profile function: Split pseudo-Voigt function Constraint condition: Li(3a) + Ni(3a) = 1 Ni(3a) + Ni(3b) = α (α is the Ni content ratio of each) ICSD No.: 98 - 009 - 4814 Also, for the Rietveld analysis of the X-ray diffraction pattern, PDXL2 (Rigaku Corporation), which is Rietveld analysis software, is used.

[0032] The lithium composite oxide preferably has a lattice constant a indicating the length of the a-axis of the crystal structure obtained from the results of the X-ray diffraction pattern by the above X-ray diffraction in the range of 2.870 Å < a < 2.877 Å, and a lattice constant c indicating the length of the c-axis in the range of 14.18 Å < c < 14.21 Å. When the lattice constant a is 2.870 Å or less, compared with the case where the above range is satisfied, the interatomic distance in the crystal structure becomes narrow and unstable, and the reaction resistance of the battery may increase. When the lattice constant a is 2.877 Å or more, the interatomic distance in the crystal structure becomes wide and unstable, and the output characteristics of the battery may deteriorate compared with the case where the above range is satisfied. When the lattice constant c is 14.18 Å or less, the interatomic distance in the crystal structure becomes narrow and unstable, and the reaction resistance of the battery may increase compared with the case where the above range is satisfied. When the lattice constant c is 14.21 Å or more, the interatomic distance in the crystal structure becomes wide and unstable, and the output characteristics of the battery may deteriorate compared with the case where the above range is satisfied.

[0033] The lithium composite oxide preferably has a crystallite size s calculated by the Scherrer equation from the half-width of the diffraction peak of the (104) plane of the X-ray diffraction pattern by the above X-ray diffraction in the range of 400 Å ≤ s ≤ 800 Å. When the crystallite size s of the lithium composite oxide is smaller than 400 Å, compared with the case where the above range is satisfied, the crystallinity decreases and the reaction resistance of the battery may increase. When the crystallite size s of the lithium composite oxide exceeds 800 Å, compared with the case where the above range is satisfied, the diffusivity of Li deteriorates and the output characteristics of the battery may deteriorate. The Scherrer equation is represented by the following formula.

[0034] s = Kλ / Bcosθ In the above formula, s is the crystallite size, λ is the wavelength of the X-ray, B is the half-width of the diffraction peak of the (104) plane, θ is the diffraction angle (rad), and K is the Scherrer constant. In this embodiment, K is 0.9.

[0035] The content ratio of the lithium composite oxide in the positive electrode active material is preferably 90% by mass or more, more preferably 99% by mass or more, based on the total mass of the positive electrode active material, in terms of, for example, improving the capacity of the battery and effectively suppressing the deterioration of charge-discharge cycle characteristics.

[0036] In addition, the positive electrode active material of the present embodiment may contain other lithium composite oxides in addition to the lithium composite oxide of the present embodiment. Examples of the other lithium composite oxides include lithium composite oxides having a Ni content of 0 mol% or more and less than 85 mol%.

[0037] Next, an example of a method for manufacturing a lithium composite oxide will be described.

[0038] The method for manufacturing a lithium composite oxide includes, for example, a first step of obtaining a composite oxide containing Ni, Al, and an optional metal element, a second step of mixing the composite oxide obtained in the first step with a lithium compound to obtain a mixture, and a third step of firing the mixture. The ratios of metal elements other than Li in the Li layer of the layered structure of the finally obtained lithium composite oxide, the lattice constant a, the lattice constant c, and the crystallite size s are adjusted, for example, by controlling the mixing ratio of raw materials in the second step, the firing temperature and time in the third step, and the like.

[0039] In the first step, for example, while stirring a solution of a metal salt containing Ni, Al, and an optional metal element (such as Co, Mn, Fe), an alkaline solution such as sodium hydroxide is dropped to adjust the pH to the alkaline side (for example, 8.5 to 12.5), thereby precipitating (co-precipitating) a composite hydroxide containing Ni, Al, and an optional metal element, and firing the composite hydroxide to obtain a composite oxide containing Ni, Al, and an optional metal element. The firing temperature is not particularly limited, but is, for example, in the range of 300°C to 600°C.

[0040] In the second step, the composite oxide obtained in the first step is mixed with a lithium compound and a strontium compound to obtain a mixture. Examples of the lithium compound include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, LiF, etc. Examples of the strontium compound include Sr(OH)2, SrO, SrCo3, SrSO4, Sr(NO3)2, etc. The mixing ratio of the composite oxide obtained in the first step and the lithium compound is preferably, for example, a ratio such that the molar ratio of the metal element excluding Li to Li is in the range of 1:0.98 to 1:1.1 in terms of facilitating the adjustment of the above parameters to the specified ranges. In the second step, when mixing the composite oxide obtained in the first step with the lithium compound and the strontium compound, other metal raw materials may be added as necessary. The other metal raw materials are oxides or the like containing metal elements other than the metal elements constituting the composite oxide obtained in the first step.

[0041] In the third step, the mixture obtained in the second step is fired at a predetermined temperature and for a predetermined time to obtain the lithium composite oxide according to this embodiment. The firing of the mixture in the third step includes, for example, a first firing step of firing in a firing furnace under an oxygen stream at a first heating rate to a first set temperature of 450°C or higher and 680°C or lower, and a second firing step of firing the fired product obtained in the first firing step in the firing furnace under an oxygen stream at a second heating rate to a second set temperature of higher than 680°C and 800°C or lower. Here, the first heating rate is in the range of 1.5°C / min or higher and 5.5°C / min or lower, and the second heating rate is slower than the first heating rate and is in the range of 0.1°C / min or higher and 3.5°C / min or lower. By such multi-step firing, in the finally obtained lithium transition metal oxide of this embodiment, the ratio of metal elements other than Li present in the Li layer of the layered structure, lattice constant a, lattice constant c, crystallite size s, and other parameters can be adjusted to the ranges specified above. Note that the first heating rate and the second heating rate may be set in plural for each temperature region as long as they are within the ranges specified above. The holding time of the first set temperature in the first firing step is preferably 0 hours or more and 5 hours or less, more preferably 0 hours or more and 3 hours or less, in terms of adjusting the above parameters of the lithium transition metal oxide to the ranges specified above. The holding time of the first set temperature is the time for maintaining the first set temperature after reaching the first set temperature. The holding time of the second set temperature in the second firing step is preferably 1 hour or more and 10 hours or less, more preferably 1 hour or more and 5 hours or less, in terms of adjusting the above parameters of the lithium transition metal oxide to the ranges specified above. The holding time of the second set temperature is the time for maintaining the second set temperature after reaching the second set temperature. When firing the mixture, in terms of adjusting the above parameters to the ranges specified above, for example, it is carried out in an oxygen stream with an oxygen concentration of 60% or higher, and the flow rate of the oxygen stream can be in the range of 0.2 mL / min to 4 mL / min per 10 cm of the firing furnace 3 and can be 0.3 L / min or more per 1 kg of the mixture.

[0042] [Negative electrode] The negative electrode 12 has a negative electrode current collector 40 and negative electrode active material layers 41 formed on both surfaces of the negative electrode current collector 40. As the negative electrode current collector 40, a foil of a metal stable within the potential range of the negative electrode 12 such as copper or a copper alloy, a film having such a metal disposed on the surface layer, or the like can be used. The negative electrode active material layer 41 contains a negative electrode active material and a binder. The thickness of the negative electrode active material layer 41 is, for example, 10 μm to 150 μm on one side of the negative electrode current collector 40. The negative electrode 12 can be manufactured by applying a negative electrode slurry containing a negative electrode active material, a binder, etc. to the surface of the negative electrode current collector 40, drying the coating film, and then rolling to form the negative electrode active material layer 41 on both surfaces of the negative electrode current collector 40.

[0043] The negative electrode active material contained in the negative electrode active material layer 41 is not particularly limited as long as it can reversibly occlude and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Further, as the negative electrode active material, a metal that alloyizes with Li such as Si or Sn, a metal compound containing Si, Sn, etc., a lithium titanium composite oxide, or the like may be used. Further, those provided with a carbon coating may be used. For example, a Si-containing compound represented by SiO y (0.5 ≦ y ≦ 1.6), or Li 2z SiO (2+z) A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0 < z < 2) may be used in combination with graphite.

[0044] As the binder contained in the negative electrode active material layer 41, a fluorine-containing resin such as PTFE or PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) is used. Further, the negative electrode active material layer 41 may contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc.

[0045] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, and the like. As the material of the separator, polyolefins such as polyethylene and polypropylene, cellulose, and the like are suitable. The separator 13 may have a single-layer structure or a laminated structure. Further, a resin layer having high heat resistance such as an aramid resin or a filler layer containing a filler of an inorganic compound may be provided on the surface of the separator 13.

[0046] [Non-aqueous electrolyte] The non-aqueous electrolyte includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As 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. Examples of the halogen-substituted product include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0047] Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, cyclic carboxylic acid esters such as γ-butyrolactone (GBL), γ-valerolactone (GVL), and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0048] 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.

[0049] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-m (C n F 2n+1 ) m (1 < m < 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), etc., LiN(SO2CF3)2, LiN(C1F 2p+1 SO2)(C q F 2q+1Examples of imide salts include those such as {p, q are integers of 0 or more} SO2). The lithium salts may be used alone or in combination of two or more. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent. Further, vinylene carbonate or a propane sultone-based additive may be added.

Examples

[0050] Hereinafter, the present disclosure will be further described by way of examples and comparative examples, but the present disclosure is not limited to the following examples. For ease of comparison, comparative examples in which the total molar amount of metal elements excluding Li in the lithium composite oxide does not become 1 are also included.

[0051] [Preparation of Positive Electrode Active Material] <Example 1-1> The composite hydroxide represented by [Ni 0.86 Al 0.03 Co 0.03 Mn 0.08 (OH)2 obtained by the coprecipitation method was calcined at 500 ° C for 8 hours to obtain a composite oxide (Ni 0.86 Al 0.03 Co 0.03 Mn 0.08 O2). LiOH, Sr(OH)2, Ti(OH)4 and the above composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, Mn, Ti and Sr became 1.03: 1 to obtain a mixture. Under an oxygen stream with an oxygen concentration of 95% (flow rates of 2 mL / min per 10 cm 3 and 5 L / min per 1 kg of the mixture), the mixture was calcined from room temperature to 650 ° C at a heating rate of 2.0 ° C / min, and then from 650 ° C to 780 ° C at a heating rate of 0.5 ° C / min. This calcined product was washed with water to remove impurities, and a lithium composite oxide was obtained. As a result of measuring the composition of the obtained lithium composite oxide using an ICP emission spectroscopic analyzer (manufactured by Thermo Fisher Scientific, trade name "iCAP6300"), the composition was LiNi 0.85 Al 0.03 Co0.03 Mn 0.08 Ti 0.01 Sr 0.001 It was O₂. This was used as the positive electrode active material of Example 1-1.

[0052] <Comparative Example 1-1> LiOH, Ti(OH)₄ and a composite oxide (Ni 0.86 Al 0.03 Co 0.03 Mn 0.08 O₂) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, Mn, and Ti was 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 1-1. The composition of the obtained lithium composite oxide was LiNi 0.85 Al 0.03 Co 0.03 Mn 0.08 Ti 0.01 O₂. This was used as the positive electrode active material of Comparative Example 1-1.

[0053] <Comparative Example 1-2> [Ni 0.85 Co 0.05 Mn 0.1 (OH)₂ - represented composite hydroxide was used, and LiOH and a composite oxide (Ni 0.85 Co 0.05 Mn 0.1 O₂) were mixed so that the molar ratio of Li to the total amount of Ni, Co, and Mn was 1.1:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 1-1. The composition of the obtained lithium composite oxide was LiNi 0.85 Co 0.05 Mn 0.1 O₂. This was used as the positive electrode active material of Comparative Example 1-2.

[0054] <Comparative Example 1-3> [Ni 0.85 Co 0.05 Mn 0.1 (OH)₂ - represented composite hydroxide was used, and LiOH, Sr(OH)₂ and a composite oxide (Ni 0.85 Co 0.05 Mn 0.1O2) was mixed with Li so that the molar ratio of Li to the total amount of Ni, Co, Mn, and Sr was 1.08:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 1-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.85 Co 0.05 Mn 0.1 Sr 0.01 O2. This was used as the positive electrode active material of Comparative Example 1-3.

[0055] <Comparative Example 1-4> [Ni 0.88 Al 0.09 Co 0.03 (OH)2 complex hydroxide was used, and LiOH and the complex oxide (Ni 0.88 Al 0.09 Co 0.03 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, and Co was 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 1-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.88 Al 0.09 Co 0.03 O2. This was used as the positive electrode active material of Comparative Example 1-4.

[0056] <Comparative Example 1-5> [Ni 0.88 Al 0.09 Co 0.03 (OH)2 complex hydroxide was used, and LiOH, Sr(OH)2, and the complex oxide (Ni 0.88 Al 0.09 Co 0.03 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 1-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.88 Al 0.09 Co 0.03 Sr 0.01 O2. This was used as the positive electrode active material of Comparative Example 1-5.

[0057] <Example 2-1> [Ni 0.94 Al0.05 Co 0.01 (OH)2 was used to obtain a composite hydroxide, which was calcined at 500 °C for 8 hours to obtain a composite oxide (Ni 0.94 Al 0.05 Co 0.01 O2). LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.03:1 to obtain a mixture. Under an oxygen stream with an oxygen concentration of 95% (flow rate of 2 mL / min per 10 cm 3 and 5 L / min per 1 kg of the mixture), the mixture was calcined from room temperature to 650 °C at a heating rate of 3.0 °C / min, and then from 650 °C to 700 °C at a heating rate of 0.5 °C / min. This calcined product was washed with water to remove impurities, obtaining a lithium composite oxide. The composition of the obtained lithium composite oxide was LiNi 0.94 Al 0.05 Co 0.01 Sr 0.001 O2. This was used as the positive electrode active material in Example 2-1.

[0058] <Example 2-2> [Ni 0.94 Co 0.05 Mn 0.005 (OH)2 was used to obtain a composite hydroxide. A mixture was obtained by mixing LiOH, Nb2O5, Sr(OH)2, and the composite oxide (Ni 0.94 Co 0.05 Mn 0.005 O2) so that the molar ratio of Li to the total amount of Ni, Co, Mn, Nb, and Sr was 1.03:1. A lithium composite oxide was obtained in the same manner as in Example 2-1 except that the mixture was calcined from room temperature to 650 °C at a heating rate of 1.5 °C / min and then from 650 °C to 700 °C at a heating rate of 1.0 °C / min. The composition of the obtained lithium composite oxide was LiNi 0.94 Al 0.05 Mn 0.005 Nb 0.005 Sr 0.01 O2. This was used as the positive electrode active material in Example 2-2.

[0059] <Comparative Example 2-1> LiOH and a composite oxide (Ni 0.94 Al 0.05 Co 0.01 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, and Co was 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 2-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.94 Al 0.05 Co 0.01 O2. This was used as the positive electrode active material of Comparative Example 2-1.

[0060] <Comparative Example 2-2> LiOH, Sr(OH)2, and a composite oxide (Ni 0.94 Al 0.05 Co 0.01 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.13:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 2-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.94 Al 0.05 Co 0.01 Sr 0.01 O2. This was used as the positive electrode active material of Comparative Example 2-2.

[0061] <Comparative Example 2-3> A lithium composite oxide was obtained in the same manner as in Example 2-1 except that it was calcined from room temperature to 650°C at a heating rate of 6.0°C / min and then from 650°C to 750°C at a heating rate of 5.0°C / min. The composition of the obtained lithium composite oxide was LiNi 0.94 Al 0.05 Co 0.01 Sr 0.01 O2. This was used as the positive electrode active material of Comparative Example 2-3.

[0062] <Example 3-1> [Ni 0.91 Al 0.04 Co 0.05 (OH)2 represented by the composite hydroxide was used and calcined at 500°C for 8 hours to obtain a composite oxide (Ni 0.91 Al 0.04 Co 0.05Oxygen (O2) was obtained. LiOH, Sr(OH)2, and the above complex oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.03:1 to obtain a mixture. Under an oxygen stream with an oxygen concentration of 95% (flow rate of about 2 mL / min per 10 cm 3 and 5 L / min per 1 kg of the mixture), the mixture was calcined from room temperature to 650 °C at a heating rate of 2.0 °C / min, and then from 650 °C to 720 °C at a heating rate of 0.5 °C / min. The calcined product was washed with water to remove impurities, and a lithium complex oxide was obtained. The composition of the obtained lithium complex oxide was LiNi 0.91 Al 0.04 Co 0.05 Sr 0.0005 O2. This was used as the positive electrode active material in Example 3-1.

[0063] <Example 3-2> A lithium complex oxide was obtained in the same manner as in Example 3-1, except that LiOH, Sr(OH)2, and the complex oxide (Ni 0.91 Al 0.04 Co 0.05 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.01:1 to obtain a mixture. The composition of the obtained lithium complex oxide was LiNi 0.91 Al 0.04 Co 0.05 Sr 0.013 O2. This was used as the positive electrode active material in Example 3-2.

[0064] <Example 3-3> [Ni 0.915 Al 0.04 Co 0.045 (OH)2 complex hydroxide was used, and a lithium complex oxide was obtained in the same manner as in Example 3-1, except that LiOH, Sr(OH)2, SiO, and the complex oxide (Ni 0.91 Al 0.04 Co 0.045 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, Si, and Sr was 1.03:1 to obtain a mixture. The composition of the obtained lithium complex oxide was LiNi 0.91 Al 0.04 Co 0.045Si 0.005 Sr 0.001 It was O2. This was used as the positive electrode active material in Example 3-3.

[0065] <Comparative Example 3-1> LiOH and composite oxide (Ni 0.91 Al 0.04 Co 0.05 O2) were mixed in such a way that the molar ratio of Li to the total amount of Ni, Al, and Co was 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 3-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.91 Al 0.04 Co 0.05 O2. This was used as the positive electrode active material in Comparative Example 3-1.

[0066] <Comparative Example 3-2> LiOH, Sr(OH)2, and composite oxide (Ni 0.91 Al 0.04 Co 0.05 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Sr was 1.03:1, and after firing from room temperature to 650 °C at a heating rate of 3.0 °C / min and then from 650 °C to 750 °C at a heating rate of 1.0 °C / min, a lithium composite oxide was obtained in the same manner as in Example 3-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.91 Al 0.04 Co 0.05 Sr 0.02 O2. This was used as the positive electrode active material in Comparative Example 3-2.

[0067] <Comparative Example 3-3> [Ni 0.92 Al 0.04 Co 0.04 (OH)2 composite hydroxide was used, and LiOH, Mg(OH)2, and composite oxide (Ni 0.92 Al 0.04 Co 0.04O2) was mixed with Li and the total amount of Ni, Al, Co, and Mg so that the molar ratio became 1.03:1 to obtain a mixture, and then a lithium composite oxide was obtained in the same manner as in Example 3-1 except for this. The composition of the obtained lithium composite oxide was LiNi 0.91 Al 0.04 Co 0.04 Mg 0.01 O2. This was used as the positive electrode active material of Comparative Example 3-3.

[0068] <Comparative Example 3-4> [Ni 0.92 Al 0.04 Co 0.04 (OH)2 was used, and a lithium composite oxide was obtained in the same manner as in Example 1-1 except that LiOH, Ba(OH)2, and the composite oxide (Ni 0.92 Al 0.04 Co 0.04 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, and Ba became 1.03:1 to obtain a mixture. The composition of the obtained lithium composite oxide was LiNi 0.91 Al 0.04 Co 0.04 Ba 0.01 O2. This was used as the positive electrode active material of Comparative Example 3-4.

[0069] <Example 4-1> [Ni 0.88 Al 0.03 Co 0.08 Fe 0.01 (OH)2 was used, calcined at 400 °C for 8 hours, and a composite oxide (Ni 0.88 Al 0.03 Co 0.03 Fe 0.01 O2) was obtained. LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, Co, Fe, and Sr became 1.03:1 to obtain a mixture. The mixture was under an oxygen stream with an oxygen concentration of 95% (10 cm 3At a flow rate of 2 mL / min per unit area and 5 L / min per 1 kg of the mixture, the mixture was fired from room temperature to 670 °C at a heating rate of 2.0 °C / min, and then fired from 670 °C to 760 °C at a heating rate of 0.5 °C / min. The fired product was washed with water to remove impurities, and a lithium composite oxide was obtained. The composition of the obtained lithium composite oxide was LiNi 0.88 Al 0.03 Co 0.08 Fe 0.01 Sr 0.0008 O2. This was used as the positive electrode active material in Example 4-1.

[0070] <Comparative Example 4-1> LiOH and a composite oxide (Ni 0.88 Al 0.03 Co 0.08 Fe 0.01 O2) were mixed in the same manner as in Example 4-1 except that the molar ratio of Li to the total amount of Ni, Al, Co, and Fe was 1.03:1 to obtain a lithium composite oxide. The composition of the obtained lithium composite oxide was LiNi 0.88 Al 0.03 Co 0.08 Fe 0.01 O2. This was used as the positive electrode active material in Comparative Example 4-1.

[0071] Powder X-ray diffraction measurements were performed on the lithium composite oxides (positive electrode active materials) of the examples and comparative examples under the above-mentioned conditions to obtain X-ray diffraction patterns. Diffraction lines indicating a layered structure were confirmed from all the X-ray diffraction patterns of the examples and comparative examples.

[0072] From the X-ray diffraction patterns of each example and each comparative example, the ratios of metal elements other than Li, the lattice constant a, the lattice constant c, and the crystallite size s were determined. The results are summarized in Table 1. The measurement method is as described above.

[0073]

Table 1

[0074] Using the lithium composite oxides (cathode active materials) of the examples and comparative examples, test cells were fabricated as follows.

[0075] [Fabrication of Cathode] 91 parts by mass of the cathode active material of Example 1-1, 7 parts by mass of acetylene black as a conductive material, and 2 parts by mass of polyvinylidene fluoride as a binder were mixed, and this was mixed with N-methyl-2-pyrrolidone (NMP) to prepare a cathode slurry. Next, the slurry was applied to a cathode current collector made of an aluminum foil with a thickness of 15 μm, and after drying the coating film, the coating film was rolled by a rolling roller to fabricate a cathode. The cathodes of the other examples and comparative examples were fabricated in the same manner.

[0076] [Preparation of Non-aqueous Electrolyte] Ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:3:4. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent at a concentration of 1.2 mol / liter to prepare a non-aqueous electrolyte.

[0077] [Fabrication of Test Cell] The cathode of Example 1-1 and the anode made of a lithium metal foil were laminated so as to face each other with a separator interposed therebetween, and this was wound to fabricate an electrode body (about 66 mAh). Next, the electrode body and the above non-aqueous electrolyte were inserted into an aluminum exterior body to fabricate a test cell. The cathodes of the other examples and comparative examples were fabricated in the same manner.

[0078] [Measurement of Reaction Resistance] For the above test cell, under the temperature condition of 25°C, constant current charging was carried out at 13.2 mA until the cell voltage reached 4.3 V, and then constant voltage charging was carried out at 4.3 V until the current value reached 0.66 mA. Subsequently, constant current discharging was carried out at 13.2 mA until the cell voltage reached 2.5 V. Then, again under the temperature condition of 25°C, constant current charging was carried out at 13.2 mA until the cell voltage reached 4.3 V, and then constant voltage charging was carried out at 4.3 V until the current value reached 0.66 mA. Next, the test cell was used to measure the AC impedance from 20 kHz to 0.01 Hz using an AC impedance measuring instrument, a Nyquist plot was drawn from the measurement data, and the reaction resistance was obtained from the size of the arc between 10 Hz and 0.1 Hz.

[0079] The reaction resistances of the test cells in the examples and comparative examples are shown separately in Tables 2 to 5. The reaction resistance of the test cell of Example 1-1 shown in Table 2 is relatively represented with the reaction resistance of the test cell of Comparative Example 1-1 as 100. Similarly, the reaction resistance of the test cell of Comparative Example 1-3 is relatively represented with the reaction resistance of the test cell of Comparative Example 1-2 as 100, and the reaction resistance of the test cell of Comparative Example 1-5 is relatively represented with the reaction resistance of the test cell of Comparative Example 1-4 as 100.

[0080] The reaction resistances of the test cells of Examples 2-1 to 2-2 and Comparative Examples 2-2 to 2-3 shown in Table 3 are relatively represented with the reaction resistance of the test cell of Comparative Example 2-1 as 100.

[0081] The reaction resistances of the test cells of Examples 3-1 to 3-3 and Comparative Examples 3-2 to 3-4 shown in Table 4 are relatively represented with the reaction resistance of the test cell of Comparative Example 3-1 as 100.

[0082] The reaction resistance of the test cell of Example 4-1 shown in Table 5 is relatively represented with the reaction resistance of the test cell of Comparative Example 4-1 as 100.

[0083]

Table 2

[0084]

Table 3

[0085]

Table 4

[0086]

Table 5

[0087] In Table 2, Example 1-1 containing 0.1 mol% of Sr had a lower reaction resistance than Comparative Example 1-1 containing no Sr, indicating the effect of Sr content. Also, in Comparative Examples 1-2 to 1-5, since the Al content was 0 mol% or 9 mol% and not in the range of 0 < β ≤ 0.08, the reaction resistance did not change with the presence or absence of Sr. Also, from Example 1-1, it is presumed that the lithium composite oxide (cathode active material) may contain Mn and Ti.

[0088] In Table 3, Example 2-1 with a proportion of metal elements other than Li in the Li layer of 1.2 had a lower reaction resistance than Comparative Example 2-1 due to the effect of Sr content. However, Comparative Examples 2-2 and 2-3 with proportions of metal elements other than Li in the Li layer of 0.4 and 3.0, respectively, contained Sr but had a higher reaction resistance than Comparative Example 2-1. Also, from Example 2-2, it is presumed that the lithium composite oxide (cathode active material) may contain Mn and Nb.

[0089] In Table 4, Examples 3-1 to 3-3 had a lower reaction resistance than Comparative Example 3-1 due to the effect of Sr content. On the other hand, Comparative Example 3-2 contained a large amount of Sr at 2 mol%, so it had a higher reaction resistance than Comparative Example 3-1. Also, Comparative Examples 3-3 and 3-4 contained Mg and Ba, respectively, instead of Sr, but the reaction resistance was substantially unchanged from Comparative Example 3-1. Also, from Example 3-3, it is presumed that the lithium composite oxide (cathode active material) may contain Si.

[0090] Also in Table 5, Example 4-1 containing 0.08 mol% of Sr had a lower reaction resistance than Comparative Example 4-1 containing no Sr, indicating the effect of Sr content. Further, it is presumed from Example 4-1 that the lithium composite oxide (positive electrode active material) may contain Fe.

Description of Reference Numerals

[0091] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Exterior can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Grooved portion, 23 Bottom plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 31 Positive electrode active material layer, 40 Negative electrode current collector, 41 Negative electrode active material layer

Claims

1. comprising a lithium composite oxide having a layered structure and containing at least Ni, Al, and Sr, where α, which represents the ratio of Ni to the total number of moles of metal elements excluding Li in the lithium composite oxide, satisfies 0.85 ≤ α ≤ 0.95, β, which represents the ratio of Al to the total number of moles of metal elements excluding Li in the lithium composite oxide, satisfies 0 < β ≤ 0.08, x, which represents the ratio of Sr to the total number of moles of metal elements excluding Li in the lithium composite oxide, satisfies 0 < x ≤ 0.015, the layered structure includes a Li layer containing a metal element other than Li, and the ratio of the metal element other than Li present in the Li layer is in the range of 1 mol% or more and 2.5 mol% or less with respect to the total molar amount of the metal elements excluding Li in the lithium composite oxide, a positive electrode active material for a non-aqueous electrolyte secondary battery.

2. the lithium composite oxide has a lattice constant a representing the a-axis length and a lattice constant c representing the c-axis length of the crystal structure obtained from the analysis result of the X-ray diffraction pattern by X-ray diffraction in the ranges of 2.870 Å < a < 2.877 Å and 14.18 Å < c < 14.21 Å, the positive electrode active material for a non-aqueous electrolyte secondary battery according to Claim 1.

3. the lithium composite oxide has a crystallite size s calculated by the Scherrer equation from the half-value width of the diffraction peak of the (104) plane in the X-ray diffraction pattern by X-ray diffraction in the range of 400 Å ≤ s ≤ 800 Å, the positive electrode active material for a non-aqueous electrolyte secondary battery according to Claim 1 or 2.

4. 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 any one of Claims 1 to 3, a negative electrode, and a non-aqueous electrolyte.

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