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

Abstract

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a Ni-containing lithium transition metal oxide having a layered structure, the ratio of Ni in the lithium transition metal oxide being 91 mol% to 96 mol% relative to the total molar amount of metal elements other than Li, a transition metal being present in the Li layer of the layered structure in an amount of 1 mol% to 2.5 mol% relative to the total molar amount of transition metals in the Ni-containing lithium transition metal oxide, and the half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern of the Ni-containing lithium transition metal oxide based on X-ray diffraction satisfying 0.30° ≤ n ≤ 0.50°.

Description

[0001] This application is a divisional application of an application with an application date of December 17, 2018, an application number of 201880082341.4, and an invention title of "Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery and Non-Aqueous Electrolyte Secondary Battery". Technical Field

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

[0003] In recent years, as a secondary battery with high power and high energy density, a non-aqueous electrolyte secondary battery is widely used, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and lithium ions and the like move between the positive electrode and the negative electrode for charge and discharge.

[0004] As a positive electrode active material used in the positive electrode of a non-aqueous electrolyte secondary battery, the following positive electrode active materials are known, for example.

[0005] For example, Patent Document 1 discloses a positive electrode active material composed of a composite oxide represented by the compositional formula Li a Ni b Co c Mn d O2 (0.1 ≤ a ≤ 1.2, 0.40 ≤ b < 1.15, 0 < c < 0.60, 0 < d < 0.60, and having the relationship of 1.00 ≤ b + c + d ≤ 1.15, 0 < c + d ≤ 0.60), and the transition metal occupancy rate e of the Li layer is in the range of 0.006 ≤ e ≤ 0.150.

[0006] In addition, for example, in Patent Document 2, a positive electrode active material is disclosed, in which, in a hexagonal lithium nickel composite oxide represented by [Li] 3a [Ni 1-x- y Co x Al y 3b [O2] 6c (where the subscripts in [] represent sites, and x and y satisfy the conditions of 0 < x ≤ 0.20 and 0 < y ≤ 0.15), and the site occupancy rate of metal ions other than lithium at the 3a site obtained by Rietveld analysis of the X-ray diffraction pattern is 3% or less, and the average particle diameter of the primary particles is 0.1 μm or more, and a plurality of the primary particles aggregate to form secondary particles.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] ​Patent Document 1: Japanese Patent Laid-Open No. 2000-133262

[0010] Patent Document 2: Japanese Patent Laid-Open No. 2000-30693 Summary of the Invention

[0011] However, if a lithium transition metal oxide in which the ratio of Ni used is 91 mol% or more with respect to the total number of moles of metal elements other than Li is used as the positive electrode active material, high capacity of the non-aqueous electrolyte secondary battery can be achieved. On the contrary, there is a problem that the charge-discharge cycle characteristics are significantly reduced.

[0012] Therefore, an object of the present disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that can suppress a decrease in charge-discharge cycle characteristics of the non-aqueous electrolyte secondary battery when using a lithium transition metal oxide in which the ratio of Ni is 91 mol% or more with respect to the total number of moles of metal elements other than Li.

[0013] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a Ni-containing lithium transition metal oxide having a layered structure, the ratio of Ni in the lithium transition metal oxide being 91 mol% to 99 mol% with respect to the total number of moles of metal elements other than Li, and there being a transition metal in the Li layer of the layered structure in an amount of 1 mol% to 2.5 mol% with respect to the total number of moles of transition metals in the Ni-containing lithium transition metal oxide, and the half-value width n of the diffraction peak of the (208) plane of the X-ray diffraction pattern of the Ni-containing lithium transition metal oxide based on X-ray diffraction being 0.30° ≤ n ≤ 0.50°.

[0014] The non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a positive electrode having the above positive electrode active material for a non-aqueous electrolyte secondary battery.

[0015] According to one aspect of the present disclosure, a decrease in charge-discharge cycle characteristics can be suppressed. Detailed Embodiments

[0016] (Insight underlying the present disclosure)

[0017] As described above, when a lithium transition metal oxide in which the ratio of Ni used is 91 mol% or more relative to the total number of moles of metal elements other than Li is used as the positive electrode active material, the charge-discharge cycle characteristics are significantly reduced. Therefore, the present inventors conducted research and found that there is a close relationship between the amount of transition metal in the Li layer of the layered structure and the half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern and the charge-discharge cycle characteristics in a Ni-containing lithium transition metal oxide having a layered structure and a Ni ratio in the range of 91 mol% to 99 mol%. Thus, the positive electrode active material for a non-aqueous electrolyte secondary battery in the manner described below was conceived.

[0018] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is characterized by including a Ni-containing lithium transition metal oxide having a layered structure, wherein the ratio of Ni in the lithium transition metal oxide is 91 mol% to 99 mol% relative to the total number of moles of metal elements other than Li, and there is a transition metal in the Li layer of the layered structure in an amount of 1 mol% to 2.5 mol% relative to the total number of moles of the transition metal in the Ni-containing lithium transition metal oxide, and the half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern based on X-ray diffraction satisfies 0.30° ≤ n ≤ 0.50°.

[0019] The charge-discharge reaction of the battery proceeds in the layered structure of the Ni-containing lithium transition metal oxide by the presence of a transition metal layer such as Ni, a Li layer, and an oxygen layer, and the reversible entry and exit of Li ions present in the Li layer. Here, in the Ni-containing lithium transition metal oxide in the range of 91 mol% to 99 mol% of the Ni ratio, a large amount of Li ions are taken from the Li layer during battery discharge, and thus the layered structure becomes unstable and the charge-discharge cycle characteristics are reduced. However, when there is a transition metal in the Li layer of the layered structure in the specified amount as in the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, it is presumed that even if a large amount of Li ions are taken from the Li layer during battery discharge, the Li layer is maintained by the specified amount of transition metal present in the Li layer, and thus stabilization of the layered structure can be achieved and a reduction in the charge-discharge cycle characteristics can be suppressed. It should be noted that in the Ni-containing lithium transition metal oxide of the present disclosure, the transition metal present in the Li layer of the layered structure is mainly Ni, but there may sometimes be a transition metal other than Ni contained in the Ni-containing lithium transition metal oxide in the Li layer.

[0020] In addition, the half-value width of the diffraction peak of the (208) plane in the X-ray diffraction pattern based on X-ray diffraction is an index indicating the fluctuation of the arrangement between the Li layer and the transition metal layer of the layered structure. Moreover, if the half-value width is too small, the fluctuation of the arrangement between the Li layer and the transition metal layer is small, and the Li ions in the Li layer are strongly bound, resulting in a reduction in charge-discharge cycle characteristics. However, as in the case of the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, when the half-value width of the diffraction peak of the (208) plane is within the above-specified range, it is considered that an appropriate fluctuation occurs in the arrangement between the Li layer and the transition metal layer of the layered structure, and the binding of the Li ions in the Li layer is alleviated to some extent. Therefore, during the charge-discharge reaction, the entry and exit of the Li ions in the Li layer become smooth, and the reduction in charge-discharge cycle characteristics is suppressed.

[0021] Hereinafter, an example of a non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure will be described.

[0022] The non-aqueous electrolyte secondary battery as an example of the embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Preferably, a separator is provided between the positive electrode and the negative electrode. Specifically, it has a wound electrode body in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and a structure in which the non-aqueous electrolyte is housed in a housing. The electrode body is not limited to the wound electrode body, and other forms of electrode bodies such as a laminated electrode body in which the positive electrode and the negative electrode are laminated with a separator interposed therebetween can also be applied. In addition, the form of the non-aqueous electrolyte secondary battery is not particularly limited, and examples include a cylindrical type, a square type, a coin type, a button type, a laminated type, and the like.

[0023] Hereinafter, the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator used in the non-aqueous electrolyte secondary battery as an example of the embodiment will be described in detail.

[0024] <Positive electrode>

[0025] The positive electrode is composed of, for example, a positive electrode current collector such as a metal foil, and a positive electrode active material layer formed on the positive electrode current collector. As the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode such as aluminum, a thin film having the metal disposed on the surface layer, or the like can be used. The positive electrode active material layer contains, for example, a positive electrode active material, a binder material, a conductive material, and the like.

[0026] The positive electrode can be obtained, for example, by coating a positive electrode composite paste containing a positive electrode active material, a binder material, a conductive material, etc. on the positive electrode current collector and drying it to form a positive electrode active material layer on the positive electrode current collector, and then calendering the positive electrode active material layer.

[0027] The positive electrode active material contains a Ni-containing lithium transition metal oxide having a layered structure. In terms of aspects such as increasing the capacity of the battery and suppressing the reduction of charge-discharge cycle characteristics, the ratio of Ni to the total molar amount of metal elements other than lithium in the lithium transition metal oxide is in the range of 91 mol% to 99 mol%, preferably in the range of 91 mol% to 96 mol%. If the ratio of Ni exceeds 99 mol%, even if the amount of transition metal in the Li layer of the layered structure and the half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern based on X-ray diffraction have a specific range described later, it is impossible to sufficiently suppress the reduction of charge-discharge cycle characteristics. It should be noted that if the ratio of Ni is less than 91 mol%, it is difficult to achieve a high capacity of the battery in the first place.

[0028] Examples of the layered structure of the Ni-containing lithium transition metal oxide include a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. Among them, in terms of aspects such as increasing the capacity and the stability of the crystal structure, a layered structure belonging to the space group R-3m is preferred.

[0029] In terms of aspects such as suppressing the reduction of charge-discharge cycle characteristics, the Ni-containing lithium transition metal oxide preferably contains Al. For example, Al can be uniformly dispersed in the layered structure of the Ni-containing lithium transition metal oxide, or can be present in a part of the layered structure. In addition, at the manufacturing stage of the Ni-containing lithium transition metal oxide, a part of the Al contained in the layered structure sometimes precipitates on the surface of the particles of the Ni-containing lithium transition metal oxide, but the precipitated Al is also the Al contained in the Ni-containing lithium transition metal oxide.

[0030] The Ni-containing lithium transition metal oxide can contain elements other than Al and is represented by the following general formula, for example.

[0031] Li z Ni x M 1-x-y Al y O2(1)

[0032] In the above formula, x representing the ratio of Ni in the Ni-containing lithium transition metal oxide only needs to satisfy 0.91 ≤ x ≤ 0.99. As described above, in terms of aspects such as increasing the capacity of the battery and suppressing the reduction of charge-discharge cycle characteristics, it preferably satisfies 0.91 ≤ x ≤ 0.96.

[0033] In the above formula, y representing the ratio of Al in the Ni-containing lithium transition metal oxide preferably satisfies 0.04 ≤ y ≤ 0.09, more preferably 0.04 ≤ y ≤ 0.06, in terms of suppressing the deterioration of charge-discharge cycle characteristics and the like. If y is less than 0.04, the charge-discharge cycle characteristics may deteriorate compared to the case where y satisfies the above range. When y exceeds 0.09, the ratio of Ni decreases compared to the case where y satisfies the above range, and the capacity of the non-aqueous electrolyte secondary battery may decrease.

[0034] M in the above formula is not particularly limited as long as it is an element other than Li, Ni, and Al. For example, at least one element selected from Co, Mn, Fe, Mg, Ti, Cr, Cu, Sn, Zr, Nb, Mo, Ta, W, Na, K, Ba, Sr, Bi, Be, Zn, Ca, and B can be cited. Among them, in terms of suppressing the deterioration of charge-discharge cycle characteristics, M in the above formula is preferably at least one element selected from Co, W, Nb, Mg, Ti, Mn, Zr, and Mo.

[0035] (1 - x - y) representing the ratio of M in the Ni-containing lithium transition metal oxide in the above formula satisfies 0 ≤ (1 - x - y).

[0036] z representing the ratio of Li in the Ni-containing lithium transition metal oxide in the above formula preferably satisfies 0.95 ≤ z ≤ 1.10, more preferably 0.97 ≤ z ≤ 1.03. When z is less than 0.97, the capacity may decrease compared to the case where z satisfies the above range. When z exceeds 1.03, more Li compound is added compared to the case where z satisfies the above range, and thus it may be uneconomical from the viewpoint of production cost.

[0037] The contents of the elements constituting the Ni-containing lithium transition metal oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), electron probe microanalysis (EPMA), energy dispersive X-ray analyzer (EDX), or the like.

[0038] For Ni-containing lithium transition metal oxides, transition metals exist in the Li layer of the layered structure. Moreover, in terms of suppressing the degradation of charge-discharge cycle characteristics, the amount of transition metals in the Li layer of the layered structure is 1 mol% to 2.5 mol%, preferably 1 mol% to 2 mol%, relative to the total molar amount of transition metals in the layered structure. When the amount of transition metals in the Li layer of the layered structure is less than 1 mol%, compared with the case where the above range is satisfied, the stability of the layered structure in the state where Li ions in the Li layer are taken away is reduced, and the charge-discharge cycle characteristics are reduced. In addition, when the amount of transition metals in the Li layer of the layered structure exceeds 2.5 mol%, compared with the case where the above range is satisfied, the diffusivity of Li ions in the Li layer is reduced, and it becomes easy to cause polarization degradation due to a decrease in battery capacity and an increase in resistance. The transition metals present in the Li layer of the layered structure are mainly Ni, preferably Ni, Co, Mn, etc.

[0039] The amount of transition metals in the Li layer of the layered structure can be obtained from the Rietveld analysis results of the X-ray diffraction pattern of the Ni-containing lithium transition metal oxide based on X-ray diffraction measurement.

[0040] The X-ray diffraction pattern is obtained by powder X-ray diffraction method based on the following conditions using a powder X-ray diffractometer (manufactured by Rigaku Corporation, trade name "RINT-TTR", radiation source Cu-Kα).

[0041] Measurement range: 15 - 120°

[0042] Scanning speed: 4° / min

[0043] Analysis range: 30 - 120°

[0044] Background: B-spline curve

[0045] Profile function: Split-type fitting Voigt function

[0046] Constraint condition: Li(3a) + Ni(3a) = 1

[0047] Ni(3a) + Ni(3b) = x

[0048] ICSD No.: 98 - 009 - 4814

[0049] In addition, in the Rietveld analysis of the X-ray diffraction pattern, PDXL2 (Rigaku Corporation) is used as the Rietveld analysis software.

[0050] In the Ni-containing lithium transition metal oxide, in terms of suppressing charge and discharge cycle characteristics, the half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern based on X-ray diffraction is 0.30° ≤ n ≤ 0.50°, preferably 0.30° ≤ n ≤ 0.45°. When the half-value width n of the diffraction peak of the (208) plane is less than 0.30°, compared with the case where the above range is satisfied, the binding of Li ions in the Li layer is strong, and the charge and discharge cycle characteristics are reduced. In addition, when the half-value width n of the diffraction peak of the (208) plane exceeds 0.50°, compared with the case where the above range is satisfied, the crystallinity of the Ni-containing Li transition metal oxide is reduced, the framework of the crystal structure becomes brittle, and it becomes impossible to maintain a crystal structure such as space group R-3m. Therefore, the cycle characteristics are reduced.

[0051] Preferably, for the Ni-containing lithium transition metal oxide, the lattice constant a representing the a-axis length of the crystal structure obtained from the results of the X-ray diffraction pattern based on X-ray diffraction is in the range, and the lattice constant c representing the c-axis length is in the range. When the above lattice constant a is below, compared with the case where the above range is satisfied, the interatomic distance in the crystal structure is narrow and becomes an unstable structure, and the charge and discharge cycle characteristics of the battery sometimes decrease. In addition, when the above lattice constant a is above, the interatomic distance in the crystal structure is wide and becomes an unstable structure, and the power characteristics of the battery sometimes decrease compared with the case where the above range is satisfied. In addition, when the above lattice constant c is below, the interatomic distance in the crystal structure is narrow and becomes an unstable structure, and the charge and discharge cycle characteristics of the battery sometimes decrease compared with the case where the above range is satisfied. In addition, when the above lattice constant c is above, the interatomic distance in the crystal structure is wide and becomes an unstable structure, and the charge and discharge cycle characteristics of the battery sometimes decrease compared with the case where the above range is satisfied.

[0052] Preferably, for the Ni-containing lithium transition metal oxide, the crystallite size s calculated from the half-value width of the diffraction peak of the (104) plane in the X-ray diffraction pattern based on X-ray diffraction according to the Scherrer formula (Scherrer equation) is When the crystallite size s of the Ni-containing lithium transition metal oxide is less than , compared with the case where the above range is satisfied, the crystallinity is reduced, and the charge and discharge cycle characteristics of the battery sometimes decrease. In addition, when the crystallite size s of the Ni-containing lithium transition metal oxide exceeds In such a case, compared with the case where the above range is satisfied, the diffusivity of Li deteriorates, and the power characteristics of the battery sometimes decrease. The Scherrer formula is represented by the following formula (2).

[0053] s = Kλ / Bcosθ (2)

[0054] In formula (2), s is the crystallite size, λ is the wavelength of X-rays, B is the half-value width of the diffraction peak of the (104) plane, θ is the diffraction angle (rad), and K is the Scherrer constant. In the present embodiment, K is set to 0.9.

[0055] Regarding the content of the Ni-containing lithium transition metal oxide, for example, in terms of improving the capacity of the battery and effectively suppressing the deterioration of the charge-discharge cycle characteristics, etc., it 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 for a non-aqueous electrolyte secondary battery.

[0056] In addition, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment may further contain other lithium transition metal oxides in addition to the Ni-containing lithium transition metal oxide. As other lithium transition metal oxides, for example, a lithium transition metal oxide having a Ni content of 0 mol% or more and less than 91 mol% can be cited.

[0057] An example of the manufacturing method of the Ni-containing lithium transition metal oxide will be described.

[0058] The manufacturing method of the Ni-containing lithium transition metal oxide, for example, includes the following steps: a first step of obtaining a composite oxide containing Ni and an arbitrary metal element; a second step of mixing the composite oxide obtained in the first step with a Li compound; and a third step of calcining the mixture. Each parameter such as the amount of transition metal in the Li layer of the layered structure of the finally obtained Ni-containing lithium transition metal oxide, the half-value width n of the diffraction peak of the (208) plane, the lattice constant a, the lattice constant c, and the crystallite size s is adjusted by controlling, for example, the mixing ratio of the raw materials in the second step, the calcination temperature and time in the third step, etc.

[0059] In the first step, for example, while stirring a solution of a metal salt containing Ni and an arbitrary metal element (Co, Al, Mn, etc.), an alkali solution such as sodium hydroxide is added dropwise, and the pH is adjusted to the alkaline side (for example, 8.5 to 11.5) to precipitate (co-precipitate) a composite hydroxide containing Ni and an arbitrary metal element, and the composite hydroxide is calcined to obtain a composite oxide containing Ni and an arbitrary metal element. The mixing ratio of Ni and the arbitrary metal element can be appropriately determined so that the ratio of Ni is in the range of 91 mol% to 99 mol%. The calcination temperature is not particularly limited, and is, for example, in the range of 500°C to 600°C.

[0060] In the second step, the composite oxide obtained in the first step is mixed with a Li compound to obtain a mixture. Regarding the mixing ratio of the composite oxide obtained in the first step and the Li compound, in terms of easily adjusting the above parameters to the above-defined ranges, for example, it is preferably set such that the molar ratio of the metal element other than Li to Li is in the range of 1:0.98 to 1:1.15. When mixing the composite oxide obtained in the first step and the Li compound in the second step, other metal raw materials may be added as needed. The other metal raw materials are oxides and the like containing metal elements other than the metal elements constituting the composite oxide obtained in the first step and Li.

[0061] In the third step, the mixture obtained in the second step is calcined at a specified temperature and time to obtain the Ni-containing lithium transition metal oxide of the present embodiment. In terms of easily adjusting the above parameters to the above-defined ranges, the calcination of the mixture in the third step is preferably a two-stage calcination. The calcination temperature in the first stage is preferably in the range of 450°C to 680°C, for example. In addition, the calcination temperature in the second stage is preferably set to a temperature higher than that in the first stage, for example, preferably in the range of 700°C to 800°C. The calcination time in the first stage and the second stage is preferably 3 to 10 hours, for example. The calcination of the mixture obtained in the second step is preferably carried out in an oxygen stream.

[0062] Regarding the calcination time in the third step, the time at a temperature higher than that in the first stage is preferably 10 hours or less. The time at a temperature higher than that in the first stage includes: after the end of the calcination in the first stage, from the start of the temperature rise to the calcination temperature in the second stage until the end of the calcination in the second stage, and the time at a temperature lower than that in the first stage. The difference between the calcination temperature in the first stage and the calcination temperature in the second stage is preferably 40°C or more and 300°C or less.

[0063] Hereinafter, other materials contained in the positive electrode active material layer will be described.

[0064] As the conductive material contained in the positive electrode active material layer, for example, carbon powders such as carbon black, acetylene black, Ketjen black, and graphite can be cited. They can be used alone or in combination of two or more.

[0065] As the binder material contained in the positive electrode active material layer, for example, fluorine-based polymers, rubber-based polymers, etc. can be cited. As the fluorine-based polymer, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or their modified products, etc. can be cited. As the rubber-based polymer, for example, ethylene-propylene-isoprene copolymer, ethylene-propylene-butadiene copolymer, etc. can be cited. They can be used alone or in combination of two or more.

[0066] <Negative electrode>

[0067] The negative electrode includes, for example, a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector. For the negative electrode current collector, a foil of a metal stable within the potential range of the negative electrode such as copper, or a thin film of the metal disposed on the surface layer can be used. The negative electrode active material layer includes, for example, a negative electrode active material, a binder material, a thickening material, and the like.

[0068] The negative electrode can be obtained, for example, as follows: A negative electrode composite material slurry containing a negative electrode active material, a thickening material, and a binder material is coated on the negative electrode current collector and dried, thereby forming a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer is calendered, whereby it can be obtained.

[0069] There is no particular limitation on the negative electrode active material contained in the negative electrode active material layer as long as it is a material capable of storing / releasing lithium ions. For example, carbon materials, metals capable of forming an alloy with lithium, or alloy compounds containing such metals can be cited. As the carbon materials, graphitic materials such as natural graphite, non-graphitizable carbon, artificial graphite, and coke can be used. As the alloy compounds, compounds containing at least one metal capable of forming an alloy with lithium can be cited. As the elements capable of forming an alloy with lithium, silicon and tin are preferred, and silicon oxide, tin oxide, etc. formed by bonding them with oxygen can also be used. In addition, those obtained by mixing the above carbon materials with compounds of silicon and tin can be used. In addition to the above, lithium titanate or the like having a potential for charge and discharge with respect to metallic lithium higher than that of carbon materials can also be used.

[0070] As the binder material contained in the negative electrode active material layer, for example, fluorine-based polymers, rubber-based polymers, etc. can also be used in the same manner as in the case of the positive electrode, and styrene-butadiene copolymer (SBR) or its modified products can also be used. As the binder material contained in the negative electrode active material layer, fluorine-based resins, PAN, polyimide-based resins, acrylic resins, polyolefin-based resins, etc. can be used in the same manner as in the case of the positive electrode. When preparing the negative electrode composite material slurry using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid (PAA) or its salts (which can be PAA-Na, PAA-K, etc., and partially neutralized salts), polyvinyl alcohol (PVA), etc. are preferably used.

[0071] As the thickening material contained in the negative electrode active material layer, for example, carboxymethyl cellulose (CMC), polyethylene oxide (PEO), etc. can be cited. They can be used alone or in combination of two or more.

[0072] <Non-aqueous electrolyte>

[0073] 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 (non-aqueous electrolytic solution), and may also be a solid electrolyte using a gel-like polymer or the like. In 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 them can be used. The non-aqueous solvent may also contain a halogen-substituted body obtained by substituting at least a part of the hydrogen of these solvents with a halogen atom such as fluorine.

[0074] 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), chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, γ-butyrolactone, etc.

[0075] 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-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, 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.

[0076] As the above halogen-substituted body, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP), etc. are preferably used.

[0077] 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-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borates such as Li2B4O7, Li(B(C2O4)F2), LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l and m are integers of 0 or more}, etc., imide salts, etc. These lithium salts can be used alone or in combination of multiple kinds. Among them, from the viewpoints of ionic conductivity, electrochemical stability, etc., LiPF6 is preferably used. The concentration of the lithium salt is preferably set to 0.8 to 1.8 mol per 1 L of the non-aqueous solvent.

[0078] <Separator>

[0079] A separator can use a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the separator, olefin-based resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator can be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin, and those obtained by coating an aromatic polyamide resin, etc. on the surface of the separator can also be used. At the interface between the separator and at least one of the positive electrode and the negative electrode, a filler layer containing an inorganic filler can be formed. As the inorganic filler, for example, oxides containing at least one of titanium (Ti), aluminum (Al), silicon (Si), and magnesium (Mg), phosphate compounds, and those obtained by treating the surface with hydroxides, etc. can be cited. The filler layer can be formed, for example, by coating a slurry containing the filler on the surface of the positive electrode, negative electrode, or separator.

[0080] Examples

[0081] Hereinafter, the present invention will be further described based on examples, but the present invention is not limited to these examples.

[0082] <Example 1>

[0083] [Production of positive electrode active material]

[0084] The composite hydroxide represented by [Ni 0.955 Al 0.045 (OH)2 obtained by the coprecipitation method was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni and Al (Ni 0.955 Al 0.045O2). LiOH was mixed with a composite oxide containing Ni and Al such that the molar ratio of Li to the total amount of Ni and Al was 0.98:1. The mixture was calcined in an oxygen stream at 670 °C for 5 hours and then at 710 °C for 3 hours. Impurities were removed by washing with water to obtain a Ni-containing lithium transition metal oxide. The time from the start of heating to the second-stage calcination temperature until the end of the second-stage calcination and reaching the first-stage calcination temperature after the end of the first-stage calcination was about 4 hours. Using an ICP atomic emission spectrometry apparatus (manufactured by Thermo Fisher Scientific, trade name "iCAP6300"), the composition of the obtained Ni-containing lithium transition metal oxide was measured, and the result was Li 0.97 Ni 0.955 Al 0.045 O2. This was used as the positive electrode active material of Example 1.

[0085] <Example 2>

[0086] LiOH was mixed with the composite oxide containing Ni and Al of Example 1 such that the molar ratio of Li to the total amount of Ni and Al was 1:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.955 Al 0.045 O2. This was used as the positive electrode active material of Example 2.

[0087] <Example 3>

[0088] LiOH was mixed with the composite oxide containing Ni and Al of Example 1 such that the molar ratio of Li to the total amount of Ni and Al was 1.03:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.955 Al 0.045 O2. This was used as the positive electrode active material of Example 3.

[0089] <Example 4>

[0090] The composite hydroxide represented by [Ni 0.955 Al 0.045 (OH)2 obtained by the coprecipitation method was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni and Al (Ni 0.955 Al 0.045O2). LiOH was mixed with the above-mentioned composite oxide containing Ni and Al and SiO in such an amount that the molar ratio of Li to the total amount of Ni, Al, and Si was 1.05:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.952 Al 0.045 Si 0.003 O2. This was used as the positive electrode active material of Example 4.

[0091] <Example 5>

[0092] The composite hydroxide represented by [Ni 0.94 Co 0.015 Al 0.045 (OH)2 obtained by the coprecipitation method was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.94 Co 0.015 Al 0.045 O2). LiOH was mixed with the above-mentioned composite oxide containing Ni, Co, and Al in such an amount that the molar ratio of Li to the total amount of Ni, Co, and Al was 0.98:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.97 Ni 0.94 Co 0.015 Al 0.045 O2. This was used as the positive electrode active material of Example 5.

[0093] <Example 6>

[0094] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 5 in such a way that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.94 Co 0.015 Al 0.045 O2. This was used as the positive electrode active material of Example 6.

[0095] <Example 7>

[0096] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 5 in such a way that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.03:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li0.99 Ni 0.94 Co 0.015 Al 0.045 O2. This is used as the positive electrode active material of Example 7.

[0097] <Example 8>

[0098] The composite hydroxide represented by [Ni 0.94 Co 0.015 Al 0.045 (OH)2 obtained by the coprecipitation method is calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.94 Co 0.015 Al 0.045 O2). LiOH is mixed with the above composite oxide containing Ni, Co, and Al and SiO in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Si is 1.05:1. Except as described above, a Ni-containing lithium transition metal oxide is produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide is Li 0.98 Ni 0.937 Co 0.015 Al 0.045 Si 0.003 O2. This is used as the positive electrode active material of Example 8.

[0099] <Example 9>

[0100] The composite hydroxide represented by [Ni 0.94 Co 0.015 Al 0.045 (OH)2 obtained by the coprecipitation method is calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.94 Co 0.015 Al 0.045 O2). LiOH is mixed with the above composite oxide containing Ni, Co, and Al and Ti(OH)2·α type in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Ti is 1.03:1. Except as described above, a Ni-containing lithium transition metal oxide is produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide is Li 0.98 Ni 0.935 Co 0.015 Al 0.045 Ti 0.005 O2. This is used as the positive electrode active material of Example 9.

[0101] <Example 10>

[0102] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 9 and Ti(OH)2·α type in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Ti was 1.05:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.935 Co 0.015 Al 0.045 Ti 0.005 O2. This was used as the positive electrode active material of Example 10.

[0103] <Example 11>

[0104] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 9 and Li3MoO4 in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Mo was 1.075:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.935 Co 0.015 Al 0.045 Mo 0.005 O2. This was used as the positive electrode active material of Example 11.

[0105] <Example 12>

[0106] The composite hydroxide represented by [Ni 0.94 Co 0.015 Al 0.045 (OH)2 obtained by the coprecipitation method was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.94 Co 0.015 Al 0.045 O2). LiOH was mixed with the above composite oxide containing Ni, Co, and Al and MnO2 in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Mn was 1.05:1. Except for the above, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.93 Co 0.015 Al 0.045 Mn 0.01 O2. This was used as the positive electrode active material of Example 12.

[0107] <Example 13>

[0108] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 12 and MnO₂ in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Mn was 1.08:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.93 Co 0.015 Al 0.045 Mn 0.01 O₂. This was used as the positive electrode active material of Example 13.

[0109] <Example 14>

[0110] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 12 and LiNbO₃ in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Nb was 1.08:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.93 Co 0.015 Al 0.045 Nb 0.01 O₂. This was used as the positive electrode active material of Example 14.

[0111] <Example 15>

[0112] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 12 and LiNbO₃ in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Nb was 1.10:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.93 Co 0.015 Al 0.045 Nb 0.01 O₂. This was used as the positive electrode active material of Example 15.

[0113] <Example 16>

[0114] The composite hydroxide represented by [Ni 0.91 Co 0.045 Al 0.045 (OH)₂ obtained by the coprecipitation method was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.91 Co 0.045 Al 0.045O2). LiOH was mixed with the above complex oxide containing Ni, Co, and Al in such an amount that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.03:1. Except as described above, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 1.03 Ni 0.91 Co 0.045 Al 0.045 O2. This was used as the positive electrode active material of Example 16.

[0115] <Example 17>

[0116] LiOH was mixed with the complex oxide containing Ni, Co, and Al of Example 12 and Ti(OH)2·α type in such an amount that the molar ratio of Li to the total amount of Ni, Co, Al, and Ti was 1.10:1. Except as described above, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 1. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.91 Co 0.015 Al 0.045 Ti 0.03 O2. This was used as the positive electrode active material of Example 17.

[0117] <Comparative Example 1>

[0118] LiOH was mixed with NiO in such an amount that the molar ratio of Li to Ni was 1.03:1. The mixture was calcined in an oxygen stream at 670 °C for 5 hours and then at 750 °C for 3 hours, and impurities were removed by washing with water to obtain a Ni-containing lithium transition metal oxide. The time from the start of heating to the second-stage calcination temperature until the end of the second-stage calcination and reaching the first-stage calcination temperature after the end of the first-stage calcination was about 5 hours. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 1.0 O2. This was used as the positive electrode active material of Comparative Example 1.

[0119] <Comparative Example 2>

[0120] LiOH was mixed with the complex oxide containing Ni, Co, and Al of Example 5 in such an amount that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.03:1. The mixture was calcined in an oxygen stream at 670 °C for 5 hours and then at 750 °C for 3 hours to obtain a Ni-containing lithium transition metal oxide. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.94 Co 0.015 Al 0.045O2. This is used as the positive electrode active material for Comparative Example 2.

[0121] <Comparative Example 3>

[0122] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 12 and MnO2 in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Mn was 1.1:1. After calcining this mixture in an oxygen stream at 670 °C for 5 hours and then at 800 °C for 3 hours, a Ni-containing lithium transition metal oxide was obtained. The time from the start of heating to the second-stage calcination temperature after the end of the first-stage calcination until the end of the second-stage calcination and reaching the first-stage calcination temperature was about 6 hours. The composition of the Ni-containing lithium transition metal oxide obtained above was Li 0.98 Ni 0.93 Co 0.015 Al 0.045 Mn 0.01 O2. This is used as the positive electrode active material for Comparative Example 3.

[0123] <Comparative Example 4>

[0124] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 9 and Ti(OH)2·α-type in an amount such that the molar ratio of Li to the total amount of Ni, Co, Al, and Ti was 1.1:1. After calcining this mixture in an oxygen stream at 670 °C for 5 hours and then at 710 °C for 3 hours, a Ni-containing lithium transition metal oxide was obtained. The composition of the Ni-containing lithium transition metal oxide obtained above was Li 0.99 Ni 0.935 Co 0.015 Al 0.045 Ti 0.005 O2. This is used as the positive electrode active material for Comparative Example 4.

[0125] <Comparative Example 5>

[0126] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Example 5 in an amount such that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.05:1. After calcining this mixture in an oxygen stream at 670 °C for 5 hours and then at 710 °C for 3 hours, a Ni-containing lithium transition metal oxide was obtained. The composition of the Ni-containing lithium transition metal oxide obtained above was Li 0.98 Ni 0.94 Co 0.015 Al 0.045 O2. This is used as the positive electrode active material for Comparative Example 5.

[0127] <Comparative Example 6>

[0128] The composite hydroxide shown as [Ni 0.88 Co 0.09 Al 0.03 (OH)2 was calcined at 500 °C for 2 hours to obtain a composite oxide containing Ni, Co, and Al (Ni 0.88 Co 0.09 Al 0.03 O2). LiOH was mixed with the above composite oxide containing Ni, Co, and Al in an amount such that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.03:1. The mixture was calcined in an oxygen stream at 670 °C for 5 hours and then at 750 °C for 3 hours, and impurities were removed by washing with water to obtain a Ni-containing lithium transition metal oxide. After the end of the first-stage calcination, from the start of the temperature rise to the second-stage calcination temperature until the end of the second-stage calcination, the time to reach the first-stage calcination temperature was about 5 hours. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.98 Ni 0.88 Co 0.09 Al 0.03 O2. This was used as the positive electrode active material of Comparative Example 6.

[0129] <Comparative Example 7>

[0130] LiOH was mixed with the composite oxide containing Ni, Co, and Al of Comparative Example 6 in an amount such that the molar ratio of Li to the total amount of Ni, Co, and Al was 1.05:1. Except for this, a Ni-containing lithium transition metal oxide was produced in the same manner as in Example 6. The composition of the obtained Ni-containing lithium transition metal oxide was Li 0.99 Ni 0.88 Co 0.09 Al 0.03 O2. This was used as the positive electrode active material of Comparative Example 7.

[0131] For the Ni-containing lithium transition metal oxides (positive electrode active materials) of Examples 1 to 17 and Comparative Examples 1 to 7, powder X-ray diffraction measurements were carried out under existing 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.

[0132] The amount of transition metal in the Li layer, the half-value width of the diffraction peak of the (208) plane, the lattice constant a, the lattice constant c, and the crystallite size s were determined from the X-ray diffraction patterns of each example and each comparative example. The results are summarized in Tables 1 and 2. The measurement method was as described.

[0133] [Table 1]

[0134]

[0135] [Table 2]

[0136]

[0137] Using the Ni-containing lithium composite oxides (positive electrode active materials) of Examples 1 to 17 and Comparative Examples 1 to 7, test batteries were fabricated as follows.

[0138] [Fabrication of Positive Electrode]

[0139] The positive electrode active material of Example 1 was mixed at a ratio of 91 parts by mass, acetylene black as a conductive material at a ratio of 7 parts by mass, and polyvinylidene fluoride as a binder at a ratio of 2 parts by mass. Using a kneader (T.K. HIVISMIX, manufactured by Primix Co., Ltd.), the mixture was kneaded to prepare a positive electrode composite material slurry. Subsequently, the positive electrode composite material slurry was coated on an aluminum foil with a thickness of 15 μm, and the coating film was dried to form a positive electrode active material layer on the aluminum foil. This was used as the positive electrode of Example 1. The positive electrodes of the other examples and comparative examples were fabricated in the same manner.

[0140] [Preparation of Non-aqueous Electrolyte]

[0141] Ethylene carbonate (EC), ethyl methyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:3:4. For this mixed solvent, lithium hexafluorophosphate (LiPF6) was dissolved to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0142] [Fabrication of Test Battery]

[0143] The positive electrode of Example 1 and the negative electrode formed of a lithium metal foil were laminated with a separator interposed therebetween in a facing manner, and then wound to fabricate an electrode body. Subsequently, the electrode body and the above non-aqueous electrolyte were inserted into an aluminum outer casing to fabricate a test battery. The test batteries of the other examples and comparative examples were fabricated in the same manner.

[0144] [Measurement of Capacity Retention Rate in Charge-Discharge Cycle Characteristics]

[0145] At an ambient temperature of 25°C, for the test batteries of each example and each comparative example, constant current charging was performed at a constant current of 0.2C until the battery voltage reached 4.3V, then constant voltage charging was performed at 4.3V until the current value reached 0.05 mA, and constant current discharging was performed at a constant current of 0.2C until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 20 times, and the capacity retention rate in the charge-discharge cycle of the test batteries of each example and each comparative example was calculated according to the following formula. The higher this value, the more the decrease in charge-discharge cycle characteristics is suppressed.

[0146] Capacity retention rate = (discharge capacity of the 20th cycle / discharge capacity of the 1st cycle) × 100

[0147] The results of the capacity retention rate in the charge and discharge cycles of the test batteries of each example and each comparative example are shown in Tables 3 and 4.

[0148] [Table 3]

[0149]

[0150] [Table 4]

[0151]

[0152] The positive electrode active materials of Examples 1 to 17 and Comparative Examples 1 to 5 all include a Ni-containing lithium transition metal oxide having a layered structure, and the ratio of Ni in the lithium transition metal oxide is 91 mol% or more relative to the total molar amount of metal elements other than Li. Among them, for Examples 1 to 17 in which the ratio of Ni in the lithium transition metal oxide is 91 mol% to 99 mol%, there is a transition metal in the Li layer relative to the total molar amount of the transition metals in the Ni-containing lithium transition metal oxide of 1 to 2.5 mol% (that is, the amount of transition metal in the Li layer is 1 to 2.5 mol%), and the half-value width n of the diffraction peak of the (208) plane of the X-ray diffraction pattern of the lithium transition metal oxide based on X-ray diffraction satisfies 0.30° ≤ n ≤ 0.50°. Compared with Comparative Examples 1 to 5 in which any of the ratio of Ni, the amount of transition metal in the Li layer, and the half-value width n of the diffraction peak of the (208) plane does not satisfy the above range, the capacity retention rate is high, and the reduction of the charge and discharge cycle characteristics is suppressed. It should be noted that for Comparative Examples 6 and 7 in which the ratio of Ni in the lithium transition metal oxide is less than 91 mol% relative to the total molar amount of metal elements other than Li, the capacity retention rate is high, but the battery capacity is originally low, and it is not preferred as a positive electrode active material for a non-aqueous electrolyte secondary battery that can be expected to have a high capacity.

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a Ni-containing lithium transition metal oxide having a layered structure. The ratio of Ni in the lithium transition metal oxide is 91 mol% to 99 mol% relative to the total molar amount of metal elements other than Li. The lithium transition metal oxide contains Ti and Al. In the Li layer of the layered structure, there is a transition metal present in an amount of 1 to 2.5 mol% relative to the total molar amount of the transition metals in the Ni-containing lithium transition metal oxide. The half-value width n of the diffraction peak of the (208) plane in the X-ray diffraction pattern of the lithium transition metal oxide based on X-ray diffraction is 0.30° ≤ n ≤ 0.50°.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, For the lithium transition metal oxide, the lattice constant a representing the length of the a-axis and the lattice constant c representing the length of the c-axis of the crystal structure obtained from the analysis result of the X-ray diffraction pattern based on X-ray diffraction are in the range of.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein For the lithium transition metal oxide, the crystallite size s calculated from the half-value width of the diffraction peak of the (104) plane in the X-ray diffraction pattern based on X-ray diffraction is in the range of.

4. A non-aqueous electrolyte secondary battery, which comprises 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.

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