Positive electrode active material for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary battery, and method for producing positive electrode active material for non-aqueous electrolyte secondary batteries

Abstract

This non-aqueous electrolyte secondary battery comprises a positive electrode active material which contains: a lithium transition metal composite oxide that satisfies 50 mol% ≤ Ni content ≤ 97 mol% and 0 mol% < Mn content < 50 mol%; and a modification compound that is present on the surfaces of primary particles of the lithium transition metal composite oxide or at grain boundaries between the primary particles. The proportion of metal elements other than Li that are present in a Li layer of a layered structure of the lithium transition metal composite oxide is 1.5-6 mol%. The modification compound contains an inorganic sulfate that contains Me (where Me is at least one element of alkali metals contained in the third period or later). The Me content in the modification compound satisfies 0 mol% < Me content ≤ 3 mol%, and the S content in the modification compound satisfies 0.1 mol% ≤ S content ≤ 3 mol%.

Description

Positive electrode active material for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary battery, and method for manufacturing positive electrode active material for non-aqueous electrolyte secondary batteries

[0001] This disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and more particularly to a positive electrode active material for a non-aqueous electrolyte secondary battery containing a high concentration of Ni, a non-aqueous electrolyte secondary battery, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002] In recent years, non-aqueous electrolyte secondary batteries, which consist of a positive electrode, a negative electrode, and a non-aqueous electrolyte, and charge and discharge by moving Li ions between the positive and negative electrodes, have been widely used as high-power, high-capacity secondary batteries. From the perspective of reducing battery resistance and increasing capacity, there is a need to improve the properties of the positive electrode active material contained in the positive electrode of the battery.

[0003] Patent Document 1 discloses a technique to reduce the adverse effects of residual Li by adding a sulfur-containing compound during the water washing process, thereby reducing residual Li and forming a coating layer of the Li and sulfur-containing compound on the surface of the positive electrode active material. Patent Document 2 also discloses a technique to suppress side reactions occurring between the electrolyte and the positive electrode active material by coating the surface of the positive electrode active material with a sulfur compound.

[0004] Japanese Patent Publication No. 2021-86834 Japanese Patent Publication No. 2018-129221

[0005] Incidentally, in lithium transition metal composite oxides with a Ni content of 50% or more, if the amount of Li extracted during charging increases, the surface state and layered structure of the lithium transition metal composite oxide become unstable, leading to deformation and collapse of the layered structure, and the discharge capacity tends to decrease. Existing technologies, such as those described in Patent Documents 1 and 2, still have room for improvement in terms of suppressing the decrease in initial discharge capacity.

[0006] The purpose of this disclosure is to provide a positive electrode active material that contributes to improving the initial discharge capacity.

[0007] A positive electrode active material for a non-aqueous electrolyte secondary battery, according to one aspect of the present disclosure, comprises a lithium transition metal composite oxide containing secondary particles formed by the aggregation of primary particles, and a modifying compound present on the surface of the primary particles or at the grain boundaries between primary particles, wherein the amount of Ni and the amount of Mn contained in the lithium transition metal composite oxide satisfy 50 mol% ≤ Ni amount ≤ 97 mol%, and 0 mol% < Mn amount < 50 mol%, respectively, with respect to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide, and the lithium transition metal composite oxide has a layered structure, and the proportion of metal elements other than Li present in the Li layer of the layered structure is Li The modified compound contains an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, the amount of Me contained in the modified compound satisfies 0 mol% < Me amount ≤ 3 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, and the amount of S contained in the modified compound satisfies 0.1 mol% ≤ S amount ≤ 3 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

[0008] One embodiment of the present disclosure of a non-aqueous electrolyte secondary battery is characterized by comprising a positive electrode containing the above-mentioned positive electrode active material for non-aqueous electrolyte secondary batteries, a negative electrode, and a non-aqueous electrolyte.

[0009] A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, according to one aspect of the present disclosure, is characterized by comprising: a mixing step of mixing a metal compound containing at least Ni and Mn with a Li compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; a washing step of washing and dewatering the fired product to obtain a cake-like composition; and an addition step of adding an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) to the cake-like composition or a powder obtained by drying the cake-like composition, and then performing a heat treatment.

[0010] According to a positive electrode active material for a non-aqueous electrolyte secondary battery, which is one aspect of this disclosure, the initial discharge capacity of the non-aqueous electrolyte secondary battery is improved.

[0011] This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. These are the S2p and O1s spectra obtained by X-ray photoelectron spectroscopy of the positive electrode active material prepared in Example 2-1. These are the S2p and O1s spectra obtained by X-ray photoelectron spectroscopy of the positive electrode active material prepared in Example 2-3. These are the S2p and O1s spectra obtained by X-ray photoelectron spectroscopy of the positive electrode active material prepared in Example 2-6. These are the S2p and O1s spectra obtained by X-ray photoelectron spectroscopy of the positive electrode active material prepared in Comparative Example 2-1. These are the S2p and O1s spectra obtained by X-ray photoelectron spectroscopy of the positive electrode active material prepared in Example 3-2.

[0012] Lithium transition metal composite oxides have a layered structure, and the charge-discharge reaction of a battery proceeds as Li ions reversibly enter and exit this layered structure. Generally, lithium transition metal composite oxides with a Ni content of 50% or more are known as high-capacity positive electrode active materials. However, when the amount of Li extracted during charging is large, lithium transition metal composite oxides with a Ni content of 50% or more tend to have an unstable surface state and layered structure, leading to deformation and collapse of the layered structure, and a decrease in initial discharge capacity.

[0013] Through our own investigations, we have found that existing technologies, such as those described in Patent Documents 1 and 2, are insufficient in suppressing the decrease in initial discharge capacity. As a result of our diligent research to solve the above problem, we have found that in a lithium transition metal composite oxide containing Ni and Mn, the initial discharge capacity can be improved by setting the proportion of metal elements other than Li present in the Li layer within a predetermined range, and by placing a modified compound containing an inorganic sulfate between the lithium transition metal composite oxides.

[0014] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail. In the following, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer casing will be given as an example, but the electrode body is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are stacked alternately one by one with separators in between. Furthermore, the outer casing is not limited to a cylindrical shape and may be, for example, rectangular, coin-shaped, etc., or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0015] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the secondary battery 10 comprises a wound electrode body 14, an electrolyte, and an outer casing 16 that houses the electrode body 14 and the electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is closed by a sealing body 17. In the following, for convenience of explanation, the side of the battery with the sealing body 17 will be referred to as the top, and the bottom side of the outer casing 16 as the bottom.

[0016] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular elongated bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape in the longitudinal direction. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the longitudinal and transverse directions than the positive electrode 11. The two separators 13 are formed to be at least slightly larger in dimensions than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the transverse direction of the positive electrode 11 and the negative electrode 12 is the axial direction. In other words, the end faces in the short direction of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode body 14.

[0017] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer casing 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0018] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has a grooved portion 22 formed on its side surface, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0019] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side, and functions as a safety valve. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0020] The following describes in detail the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte that constitute the secondary battery 10, with particular emphasis on the positive electrode 11.

[0021] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. Preferably, the positive electrode mixture layer is formed on both sides of the positive electrode current collector. The positive electrode current collector can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The thickness of the positive electrode current collector is, for example, 10 μm or more and 30 μm or less.

[0022] The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, conductive agent, etc., to the surface of the positive electrode current collector, drying the coating film, and then rolling it to form the positive electrode mixture layer on both sides of the positive electrode current collector.

[0023] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB), carbon black (CB) such as Ketjenblack, carbon nanotubes (CNT), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types. The content of the conductive agent in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer.

[0024] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more. The binder content in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer.

[0025] The positive electrode mixture layer contains a positive electrode active material (hereinafter sometimes referred to as lithium composite oxide (Z)) comprising a lithium transition metal composite oxide and a modified compound. The positive electrode mixture layer may also contain positive electrode active materials other than lithium composite oxide (Z). In the positive electrode mixture layer, the content of lithium composite oxide (Z) is, for example, 90% by mass or more of the total mass of the positive electrode active material. Furthermore, the positive electrode mixture layer may contain only lithium composite oxide (Z) as the positive electrode active material.

[0026] Lithium transition metal composite oxides contain at least Ni and Mn. By ensuring that the Ni and Mn content satisfies the range described below, it is possible to achieve both high capacity and structural stability through synergistic effects with the modified compounds described later.

[0027] The amount of Ni contained in the lithium transition metal composite oxide satisfies the condition of 50 mol% ≤ Ni amount ≤ 97 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Preferably, the Ni amount is 60 mol% ≤ Ni amount ≤ 94 mol%, and more preferably 60 mol% ≤ Ni amount ≤ 92 moles.

[0028] The amount of Mn contained in the lithium transition metal composite oxide satisfies the condition that 0 mol% < Mn amount < 50 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Preferably, the Mn amount is 1 mol% ≤ Mn amount ≤ 30 mol%, and more preferably 3 mol% ≤ Mn amount ≤ 20 mol%.

[0029] The lithium transition metal composite oxide may further contain M1 (where M1 is at least one element selected from the group consisting of B, Al, Si, Ti, Fe, Co, Zr, Nb, Mo, Sn, W, and Bi). The amount of M1 contained in the lithium transition metal composite oxide satisfies 0 mol% ≤ M1 amount < 50 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. Preferably, the amount of M1 is 0 mol% ≤ M1 amount ≤ 30 mol%.

[0030] Lithium transition metal composite oxides include, for example, those with the general formula Li ａ Ni ｘ Mn ｙ M1 ｚ O ２－ｂ(where 0.8 ≤ a ≤ 1.2, 0.50 ≤ x ≤ 0.97, 0 < y < 0.50, 0 ≤ z < 0.50, 0 ≤ b ≤ 0.05, x + y + z = 1, and M1 is at least one element selected from the group consisting of B, Al, Si, Ti, Fe, Co, Zr, Nb, Mo, Sn, W, and Bi) is a composite oxide. The lithium transition metal composite oxide has the general formula Li ａ Ni ｘ Mn ｙ Co ｚ Al ｗ M2 ｖ O ２－ｂ (where 0.8 ≤ a ≤ 1.2, 0.50 ≤ x ≤ 0.97, 0.01 ≤ y ≤ 0.30, 0 ≤ z ≤ 0.20, 0 ≤ w ≤ 0.10, 0 ≤ v ≤ 0.10, 0 ≤ b ≤ 0.05, x + y + z + w + v = 1, and M2 is at least one element selected from the group consisting of B, Si, Ti, Fe, Zr, Nb, Mo, Sn, W, and Bi) may be a composite oxide. The ratio of the metal elements contained in the lithium transition metal composite oxide can be measured, for example, by an inductively coupled plasma optical emission spectrometer (ICP-AES).

[0031] The lithium transition metal composite oxide has a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, and the like. From the viewpoints of high capacity and stability of the crystal structure, it is preferable that the lithium transition metal composite oxide has a layered structure belonging to the space group R-3m. The layered structure of the lithium transition metal composite oxide includes, for example, a transition metal layer and a Li layer. The charge-discharge reaction of the battery proceeds by the reversible entry and exit of Li ions present in the Li layer.

[0032] In the layered structure of lithium transition metal composite oxides, the proportion of metal elements other than Li present in the Li layer is between 1.5 mol% and 6 mol% of the total number of moles of metal elements other than Li in the lithium transition metal composite oxide. If the proportion of metal elements other than Li in the Li layer is less than 1.5 mol%, the stability of the layered structure when Li ions are extracted from the Li layer decreases, the structure may break down, and the battery capacity may decrease. Also, if the proportion of metal elements other than Li in the Li layer exceeds 6 mol%, the diffusivity of Li ions in the Li layer decreases, and the battery capacity may decrease. The metal elements other than Li present in the Li layer are mainly Ni, but other metal elements may also be included.

[0033] The proportion of metal elements other than Li present in the layered Li layer can be obtained from the Rietveld analysis results of the X-ray diffraction pattern obtained by the above-mentioned powder X-ray diffraction measurement of lithium transition metal composite oxide. For the Rietveld analysis of the X-ray diffraction pattern, for example, Rietveld analysis software such as SmartLab Studio II (Rigaku Corporation) can be used.

[0034] Lithium transition metal composite oxides contain secondary particles formed by the aggregation of primary particles. The particle size of the primary particles is, for example, between 0.02 μm and 2 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The average particle diameter of the secondary particles is, for example, between 2 μm and 30 μm. Here, the average particle diameter refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of secondary particles can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0035] The modifying compound exists on the surface of the primary particles of the lithium transition metal composite oxide, or at the grain boundaries between the primary particles of the lithium transition metal composite oxide. The modifying compound may be uniformly dispersed or present only in a portion of the material. Here, the surface of the primary particles of the lithium transition metal composite oxide includes the surface of the secondary particles of the lithium transition metal composite oxide. In other words, the surface of the primary particles of the lithium transition metal composite oxide includes the surface of the primary particles located inside the lithium transition metal composite oxide and the surface of the primary particles exposed to the surface of the lithium transition metal composite oxide. Furthermore, the surface of the primary particles of the lithium transition metal composite oxide means the particle surface of the primary particle and its vicinity, for example, the near-surface region within 30 nm from the particle surface. The presence of the modifying compound on the surface of the primary particles of the lithium transition metal composite oxide, or at the grain boundaries between the primary particles of the lithium transition metal composite oxide, can be confirmed by energy-dispersive X-ray spectroscopy (TEM-EDX).

[0036] The modified compound contains an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals). By placing the modified compound between the lithium transition metal composite oxides, the surface state and layered structure of the lithium transition metal composite oxides can be stabilized, and the initial discharge capacity can be improved. Me is, for example, Na or K.

[0037] Inorganic sulfates are sulfates that do not contain carbon. Furthermore, in this specification, sulfates refer to sulfates in the broad sense that contain sulfur and oxygen. Inorganic sulfates are, for example, at least one compound selected from the group consisting of sulfites, disulfites, peroxodisulfates, and sulfates in the narrow sense, and more preferably at least one compound selected from the group consisting of sulfites, disulfites, peroxodisulfates. Sulfites are defined as sulfate ions (SO4). ３ ２－ A salt consisting of ) and Me, for example, Na ２ SO ３ _K ２ SO ３ Examples include the disulfite ion (S). Disulfites are disulfite ions (S) ２ O ５ ２－A salt consisting of ) and Me, for example, Na ２ SO ５ _K ２ SO ５ Examples include disulfate salts, which are composed of disulfate ions (S ２ O ７ ２－ A salt consisting of ) and Me, for example, Na ２ S ２ O ７ _K ２ S ２ O ７ Examples include the peroxodisulfate, which is a peroxodisulfate ion (S ２ O ８ ２－ A salt consisting of ) and Me, for example, Na ２ S ２ O ８ _K ２ S ２ O ８ These are some examples. Sulfates in the narrow sense refer to sulfate ions (SO4). ４ ２－ It is a salt composed of ) and Me, and Na ２ SO ４ _K ２ SO ４ These are some examples.

[0038] As described above, inorganic sulfates contain Me, and therefore modified compounds also contain Me. The amount of Me contained in the modified compound satisfies 0 mol% < Me amount ≤ 3 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. The lower limit of the Me amount is, for example, 0.1 mol%.

[0039] As described above, inorganic sulfates contain sulfur (S), and therefore modified compounds also contain S. The amount of S contained in the modified compound satisfies the condition of 0.1 mol% ≤ S amount ≤ 3 mol% relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

[0040] The amounts of Me and S contained in the modified compound can be measured, for example, by an inductively coupled plasma atomic emission spectrometer (ICP-AES). While ICP-AES may sometimes quantify S originating from components in the complex hydroxide, if the S amount is 0.1 mol% or more, it can be said that the S originating from the inorganic sulfate has been quantified.

[0041] The modified compound may further contain at least one of Ca and Sr. The modified compound includes, for example, an inorganic sulfate and a compound containing at least one of Ca and Sr. The inorganic sulfate and the compound containing at least one of Ca and Sr may exist separately or in a mixed state. The compound containing at least one of Ca and Sr may be, for example, an oxide or a carbonate compound.

[0042] The amounts of Ca and Sr contained in the modified compound may satisfy the condition 0 mol% < Ca amount + Sr amount ≤ 2 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. The lower limit of Ca amount + Sr amount is, for example, 0.1 mol%. Furthermore, it is preferable that Ca amount ≥ Sr amount.

[0043] The amounts of Ca and Sr contained in the modified compound can be confirmed, for example, by energy-dispersive X-ray spectroscopy (TEM-EDX).

[0044] The crystallite size s of the lithium composite oxide (Z), calculated by Scherrer's formula from the full width at half maximum of the diffraction peak of the (10⁴) plane in the X-ray diffraction pattern obtained by X-ray diffraction, is, for example, in the range of 300 Å to 700 Å.

[0045] The X-ray diffraction pattern is obtained by powder X-ray diffraction using a powder X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation, Cu-Kα source) under the following conditions: Measurement range: 15–120° Scan rate: 4° / min Analysis range: 30–120° Background: B-spline profile Function: Split-type pseudo-Voigt function Constraints: Li(3a) + Ni(3a) = 1 Ni(3a) + Ni(3b) = α (α is the respective Ni content)

[0046] Scherrer's equation is expressed as follows: In the equation below, s is the crystallite size, λ is the wavelength of the X-ray, B is the full width at half maximum 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 set to 0.9. s = Kλ / Bcosθ

[0047] The BET specific surface area of ​​lithium composite oxide (Z) is, for example, 2.2 m². ２ The value is less than or equal to / g. The BET specific surface area of ​​the composite oxide is measured according to the BET method (nitrogen adsorption method) described in JIS R1626.

[0048] The lithium composite oxide (Z) may have a first peak with a peak at 170 ± 2 eV and a second peak with a peak at 167 ± 2 eV in the S2p spectrum obtained by X-ray photoelectron spectroscopy. The first peak is SO ４ ２－ The second peak is estimated to belong to SO ３ ２－ It is estimated that this peak belongs to SO. For example, in the method for producing the positive electrode active material described later, if a compound containing S is added during water washing, SO will be released from the positive electrode active material. ４ ２－ A first peak is obtained that is attributed to SO ３ ２－ A second peak attributable to the first peak cannot be obtained. For example, as described later, by adding a compound containing S to a cake-like composition or a powder obtained by drying the cake-like composition, a modified compound containing S can be made present on the surface of the primary particles of the lithium transition metal composite oxide or at the grain boundaries between the primary particles of the lithium transition metal composite oxide, and both the first and second peaks can be obtained from the positive electrode active material.

[0049] The first and second peaks are obtained, for example, by separating the primary data of the S2p spectrum obtained by X-ray photoelectron spectroscopy into two peaks with peaks at 170±2 eV and 167±2 eV. After setting the peak positions of the two peaks to 170±2 eV and 167±2 eV respectively, peak fitting is performed by varying the peak width and peak height, so that each peak has a shape with a Gauss-Lorentz distribution.

[0050] In the lithium composite oxide (Z), the peak of the third peak, which has a peak at 531±1 eV, may be higher than the peak of the fourth peak, which has a peak at 529±1 eV, in the O1s spectrum obtained by X-ray photoelectron spectroscopy. The third peak is presumed to be a peak attributed to oxygen contained in the compound present on the surface of the lithium composite oxide (Z), and the fourth peak is presumed to be a peak attributed to oxygen contained in the lithium transition metal composite oxide. By having the peak of the third peak higher than the peak of the fourth peak, the protective effect of the modifying compound on the surface of the lithium transition metal composite oxide can be ensured, and the surface state and layered structure of the lithium transition metal composite oxide can be further stabilized. The third and fourth peaks can be confirmed in the primary data of the O1s spectrum obtained by X-ray photoelectron spectroscopy.

[0051] The S2p and O1s spectra were obtained by X-ray photoelectron spectroscopy using an X-ray photoelectron spectrometer (PHI 5000 VersaProbe, ULVAC PHI, Inc.) under the following conditions: X-rays used: Monochrome Al-Kα rays (45W, 17kV) Analysis area: Approximately 200 μmφ

[0052] Next, an example of a method for producing a positive electrode active material according to this embodiment will be described. The method for producing a positive electrode active material includes, for example, a mixing step of mixing a metal compound containing at least Ni and Mn with a Li compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; a washing step of washing and dewatering the fired product to obtain a cake-like composition; and an addition step of adding an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) to the cake-like composition or a powder obtained by drying the cake-like composition, and then performing a heat treatment.

[0053] Examples of metal compounds containing Ni and Mn include NiMn-containing metal hydroxides, NiMn-containing metal oxides, and NiMn-containing metal carbonate compounds. While not particularly limited, for example, a complex hydroxide can be precipitated (coprecipitation) to obtain a NiMn-containing metal hydroxide by separately adding a solution of a metal salt containing Ni, Mn, Co, Al, etc., and an alkaline solution such as sodium hydroxide dropwise to a reaction vessel where a pH-adjusted solution is being stirred, thereby adjusting the pH to the alkaline side (e.g., 8.5 to 12.5). Alternatively, a NiMn-containing metal oxide can be produced by calcining the NiMn-containing metal hydroxide. The calcination temperature is not particularly limited, but is, for example, in the range of 250°C to 600°C.

[0054] Next, a mixture is obtained by mixing a metal compound containing at least Ni and Mn with a Li compound. Examples of Li compounds include Li ２ CO ３ LiOH, Li ２ O ２ Li ２ O, LiNO ３ LiNO ２ Li ２ SO ４ LiOH H ２ Examples include O, LiH, and LiF.

[0055] During mixing, at least one of the Ca compound and the Sr compound may be mixed. The Ca compound may be Ca(OH) ２ CaHPO ４ Ca(H ２ PO４ ) ２ , Ca ３ (PO ４ ) ２ , CaO, CaCO ３ , CaSO ４ , Ca(NO ３ ) ２、 CaCl ２ , CaAlO ４ etc. Examples of Sr compounds include Sr(OH)<00OO083>, SrHPO ４ , Sr(H ２ PO ４ ) ２ , Sr ３ (PO ４ ) ２ , SrO, SrCO ３ , SrSO ４ , Sr(NO ３ ) ２、 SrCl ２ , SrAlO ４ etc.

[0056] When mixing, M2 compounds may be mixed. Examples of M2 compounds include ZrO ２ , Nb ２ O ５ , Nb ２ O ５ ·nH ２ O, TiO ２ , Ti(OH) ４ , SiO, SiO ２ , Li ２ MoO ４ , MoO ３ , H ２ MoO ４ , WO ３ , Li ２ WO ４ , Fe(OH) ２ , Fe ２ O ３ , SnO ２ , Bi(OH) ３ , Bi ２ O ３ , H ３ BO ３ , B ２ O ３ , Sb ２ O ３ etc.

[0057] A calcined product is obtained by calcining the mixture. For example, the mixture is processed in an oxygen stream with an oxygen concentration of 60% or higher, and the flow rate of the oxygen stream is set to 10 cm in the calcination furnace. ３ The mixture is fired at a rate of 0.1 L / min to 4 L / min per unit area, or at a rate of 1 L / min or more per kg of mixture. In the firing conditions, the first set temperature is set to 450°C or lower, the holding time at the first set temperature is in the range of 0 hours to 8 hours, and the heating rate below 450°C is in the range of more than 1.5°C / min and 6.0°C / min or lower. The second set temperature is set to 450°C to 680°C, the holding time at the second set temperature is in the range of 0 hours to 8 hours, and the heating rate above 450°C to 680°C is in the range of more than 1.0°C / min and 4.5°C / min or lower. The maximum temperature reached is in the range of 690°C to 900°C. The heating rate from above 680°C to the maximum temperature reached may be, for example, 0.1°C / min to 3.5°C / min. The holding time at the maximum temperature reached may be 1 hour to 10 hours or lower. Furthermore, this firing step may be a multi-stage firing process, and multiple settings may be set for each temperature range, as long as they are within the range specified above.

[0058] A cake-like composition is obtained by washing and dewatering the calcined material. The washing step is carried out, for example, using a 3 L reaction vessel, under conditions such as a solid-liquid ratio of 300 g / L to 2000 g / L, a washing time of 1 minute to 1 hour, and a stirring speed of 100 rpm or more. If the size of the reaction vessel is changed, the washing time and stirring speed may be changed. The water content of the cake-like composition obtained by dewatering is, for example, 10% or less, but may also be 8% or less.

[0059] A positive electrode active material can be obtained by adding an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) to a cake-like composition or a powder obtained by drying a cake-like composition, and then performing heat treatment. The drying of the cake-like composition is carried out, for example, under conditions that include oxygen, nitrogen, air, etc., under conditions ranging from reduced pressure to increased pressure. For example, a reduced pressure atmosphere, particularly a vacuum atmosphere, is preferred, and the drying is carried out under conditions such as a pressure of 1 kPa or less, a temperature of 120°C to 300°C, and a time of 1 hour to 10 hours.

[0060] The heat treatment of the cake-like composition after the addition of Me, or the powder obtained by drying the cake-like composition, is carried out at a temperature of, for example, 150°C to 500°C. The atmosphere during the heat treatment may be a vacuum, an oxygen stream, or air. Also, during the heat treatment, for example, tungsten oxide (WO) may be used. ３ ), lithium tungstate (Li ２ WO ４ Li ４ WO ５ Li ６ W ２ O ９ ), boric acid (H ３ BO ３ ), lithium borate (Li ２ B ４ O ７ Li ３ BO ３ LiB ３ O ５ LiBO ２ ), lithium phosphate (Li ３－ｘ H ｘ PO ４ Additions such as (0 ≤ x ≤ 3) may also be added.

[0061] The inorganic sulfate to be added is, for example, at least one compound selected from the group consisting of sulfites, disulfites, disulfates, peroxodisulfates, and sulfates in the narrow sense, and more preferably at least one compound selected from the group consisting of sulfites, disulfites, disulfates, and peroxodisulfates. Examples of inorganic sulfates to be added include Na ２ SO ３ _K ２ SO ３ Na ２ SO ５ _K ２ SO ５ Na ２ S ２ O ７ _K ２ S ２ O ７ Na ２ S ２ O ８ _K ２ S ２ O ８ Na２ SO ４ _K ２ SO ４ These are some examples. By adding inorganic sulfate after the firing step, inorganic sulfate can be made present on the surface of the primary particles of the lithium transition metal composite oxide or at the grain boundaries between the primary particles of the lithium transition metal composite oxide.

[0062] [Negative Electrode] The negative electrode 12 may, for example, have a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode current collector, and lithium metal may be deposited on the surface of the negative electrode current collector by charging. When the negative electrode 12 has a negative electrode mixture layer, it is preferable that the negative electrode mixture layer is formed on both sides of the negative electrode current collector. For the negative electrode current collector, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on the surface layer, can be used. The thickness of the negative electrode current collector is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., to the surface of a negative electrode current collector, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0063] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads. In addition, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, or lithium titanium composite oxides may be used as the negative electrode active material. Furthermore, materials with a carbon coating may also be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0064] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0065] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. In addition, a heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0066] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by coating the surface of the positive electrode 11, the negative electrode 12, or the separator 13 with a slurry containing the filler.

[0067] [Non-aqueous electrolytes] Non-aqueous electrolytes, for example, have lithium ion conductivity. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0068] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0069] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0070] Examples of the above ethers include 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, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl 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, and tetraethylene glycol dimethyl ether.

[0071] The electrolyte salt is preferably a lithium salt. A suitable lithium salt is LiClO ４ LiBF ４ LiPF ６ LiAlCl ４ LiSbF ６ , LiSCN, LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiB １０ Cl １０ Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO4). ２ F ２Examples include lithium difluorobis(oxalato)phosphate (LiDFOBP), lithium tetrafluoro(oxalato)phosphate, etc. Examples of borates include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), etc. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ ) etc. are used. Of these, LiPF is used from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ It is preferable to use the following. The concentration of the lithium salt may be, for example, 4 moles or less per liter of non-aqueous solvent, or 3 moles or less, preferably 1.8 moles or less, and more preferably 0.8 moles or more and 1.8 moles or less.

[0072] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0073] Examples of unsaturated cyclic carbonate esters include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0074] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0075] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0076] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0077] The present disclosure will be further explained below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0078] <Example 1-1> [Preparation of positive electrode active material] [Ni obtained by coprecipitation method ０．６０ Co ０．２０ Mn ０．２０ ] (OH) ２The composite hydroxide represented by was calcined at 400°C for 8 hours to obtain a metal compound containing Ni, Co, and Mn. Next, the above metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, and Mn was 0.1 mol%, the molar ratio of Zr was 0.1 mol%, and the molar ratio of Ti was 0.3 mol%. ２ And, ZrO ２ And, TiO ２ Mix the following, and further, add lithium hydroxide monohydrate (LiOH·H) so that the molar ratio of Li to the total number of moles of Ni, Co, Mn, Ca, Zr, and Ti is 103 mol%. ２ O) was mixed to obtain a mixture. This mixture was heated under an oxygen stream with an oxygen concentration of 95% (flow rate of 3 L / min per 1 kg of mixture) at a heating rate of 4°C / min from room temperature to 400°C, and then heated from 400°C to 650°C at a heating rate of 2°C / min. After that, the temperature was heated from 650°C to 850°C at a heating rate of 1°C / min and held for 10 hours to obtain a calcined product. To this calcined product, the product was added to water in a 3 L reaction vessel so that the solid-liquid ratio was 500 g / L, washed with water at a stirring speed of 300 rpm for 10 minutes, and then dehydrated to obtain a cake-like composition. Furthermore, 0.1 mol% sodium disulfite (Na) relative to the total number of moles of Ni, Co, and Mn was added to this cake-like composition. ２ S ２ O ５ ) was added. After this, heat treatment was performed for 2 hours in a vacuum atmosphere at a temperature of 200°C and a pressure of 10 Pa to obtain the positive electrode active material of Example 1-1.

[0079] Measurements of the obtained cathode active material using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy-dispersive X-ray spectroscopy (TEM-EDX) confirmed the presence of the elements shown in Table 4 below. Furthermore, TEM-EDX measurements confirmed the presence of Ca and inorganic sulfates on the primary particle surface or at the grain boundaries between primary particles of the lithium transition metal composite oxide. X-ray diffraction measurements revealed that the proportion of non-Li metal elements in the Li layer relative to the total molar amount of non-Li metal elements in the lithium transition metal composite oxide was 2.1 mol%. Additionally, the cathode active material exhibited both a first peak with a peak at 170±2 eV and a second peak with a peak at 167±2 eV in its S2p ​​spectrum obtained by X-ray photoelectron spectroscopy. Furthermore, in the O1s spectrum obtained by X-ray photoelectron spectroscopy, the peak P3 of the third peak at 531±1 eV was higher than the peak P2 of the fourth peak at 529±1 eV.

[0080] [Preparation of the positive electrode] 95 parts by mass of the above positive electrode active material, 3 parts by mass of acetylene black (AB), and 2 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after the coating film was dried, the coating film was rolled out with a rolling mill and cut to a predetermined electrode size to produce the positive electrode. An exposed portion was provided on a part of the positive electrode in which the surface of the positive electrode current collector was exposed.

[0081] [Fabrication of the negative electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution in a solid content mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and after the coating film was dried, the coating film was rolled using a rolling mill and cut to a predetermined electrode size to produce the negative electrode. An exposed portion was provided on a part of the negative electrode in which the surface of the negative electrode current collector was exposed.

[0082] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 1.2 mol / liter.

[0083] [Preparation of Test Cell] A positive electrode lead was attached to the exposed portion of the positive electrode, and a negative electrode lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were wound in a spiral shape via a polyolefin separator, and then press-molded radially to produce a flat, wound electrode body. This electrode body was housed in an outer casing made of aluminum laminate sheet, the non-aqueous electrolyte was injected, and the opening of the outer casing was sealed to obtain a test cell.

[0084] [Evaluation of Initial Discharge Capacity] Under conditions of 25°C, the test cell was charged with a constant current of 0.2C to 4.2V, and then charged with a constant voltage of 0.01C at 4.2V. Subsequently, it was discharged with a constant current of 0.2C to 2.5V, and the discharge capacity at this time was defined as the initial discharge capacity.

[0085] <Comparative Example 1-1> In the preparation of the positive electrode active material, ZrO2 is used so that the molar ratio of Zr is 0.3 mol% and the molar ratio of Ca is 0.5 mol%. ２ and Ca(OH) ２ Change the mixing ratio of TiO ２ and Na ２ S ２ O ５Except for the absence of additives, a test cell was prepared and evaluated in the same manner as in Example 1-1. Measurement of the obtained positive electrode active material by ICP-AES and TEM-EDX confirmed the elements shown in Table 4 below. Furthermore, TEM-EDX measurements confirmed the presence of Ca on the primary particle surface or at the grain boundaries between primary particles of the lithium transition metal composite oxide, but the absence of inorganic sulfates. X-ray diffraction measurements revealed that the proportion of metal elements other than Li in the Li layer relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide was 2.1 mol%. Although inorganic sulfates were not added, 0.07 mol% of S was quantified, originating from components in the composite hydroxide.

[0086] Table 1 shows the conditions for preparing the positive electrode active material for Example 1-1 and Comparative Example 1-1. Table 2 shows the evaluation results of the test cells for Example 1-1 and Comparative Example 1-1. In Table 2, the initial discharge capacity of the test cell for Example 1-1 is expressed relatively, with the initial discharge capacity of the test cell for Comparative Example 1-1 set to 100. As shown in Table 2, the initial discharge capacity of the test cell for Example 1-1 was greater than that of the test cell for Comparative Example 1-1.

[0087]

[0088]

[0089] <Example 2-1> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９０ Mn ０．１０ ] (OH) ２ The composite hydroxide represented by was calcined at 500°C for 10 hours to obtain a metal compound containing Ni and Mn. (2) In the calcination step, the metal compound LiOH·H ２ Mix only O and lithium hydroxide monohydrate (LiOH·H) so that the molar ratio of Li to the total number of moles of Ni and Mn is 105 mol%. ２(O) was mixed to obtain a mixture. (3) The temperature was raised from room temperature to 400°C at a heating rate of 3°C / min, then the temperature was raised from 400°C to 650°C at a heating rate of 2°C / min and held at 650°C for 3 hours. After that, the temperature was raised from 650°C to 780°C at a heating rate of 1°C / min and held for 5 hours to obtain a calcined product. (4) In the addition step, 0.1 mol% potassium disulfite (K) relative to the total number of moles of Ni and Mn was added to the cake-like composition. ２ S ２ O ５ The following was added, and the heat treatment temperature was changed to 150°C.

[0090] <Example 2-2> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni and Mn was 0.1 mol%, and the molar ratio of Ti was 0.1 mol%. ２ And, TiO ２ (2) Mix the following: (2) In the addition step, 0.1 mol% sodium sulfite (Na) relative to the total number of moles of Ni and Mn is added to the cake composition. ２ SO ３ The following was done: ) was added, and the atmosphere and temperature of the heat treatment were changed to an oxygen atmosphere and 450°C, respectively.

[0091] <Example 2-3> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９０ Co ０．０３ Mn ０．０７ ] (OH) ２ Using the composite hydroxide represented by , a metal compound containing Ni, Co, and Mn was obtained by calcining at 300°C for 10 hours. (2) In the calcination step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, and Mn was 0.5 mol%, the molar ratio of Sr was 0.1 mol%, and the molar ratio of Nb was 0.5 mol%. ２ And, Sr(OH) ２ And, Nb ２ O ５ -nH ２O was mixed with the other. The maximum temperature to be reached was also changed to 750°C. (3) In the addition step, 0.1 mol% of Na relative to the total number of moles of Ni, Co and Mn was added to the cake-like composition. ２ S ２ O ５ The substance was added, and the heat treatment atmosphere and temperature were changed to an oxygen atmosphere and 450°C, respectively.

[0092] <Example 2-4> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) A metal compound containing Ni, Co, and Mn was obtained in the same manner as in Example 2-3. (2) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, and Mn was 0.5 mol%, and the molar ratio of Nb was 0.5 mol%. ２ And, Nb ２ O ５ The two were mixed. The maximum temperature to be reached and the holding time were changed to 720°C and 7 hours, respectively. (3) In the addition step, 1.0 mol% of Na relative to the total number of moles of Ni, Co, and Mn was added to the cake composition. ２ S ２ O ５ The substance was added, and the heat treatment atmosphere and temperature were changed to an air atmosphere and 300°C, respectively.

[0093] <Example 2-5> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) A metal compound containing Ni, Co, and Mn was obtained in the same manner as in Example 2-3. (2) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, and Mn was 0.5 mol%, and the molar ratio of Fe was 0.3 mol%. ２ And, Fe ２ O ３ The two were mixed. The maximum temperature to be reached and the holding time were changed to 720°C and 7 hours, respectively. (3) In the addition step, 0.1 mol% of Na relative to the total number of moles of Ni, Co, and Mn was added to the powder obtained by drying the cake-like composition. ２ S ２ O ５The following were added, and the atmosphere and temperature of the heat treatment were changed to an air atmosphere and 300°C, respectively. The powder obtained by drying the cake-like composition was obtained by drying the cake-like composition in a vacuum atmosphere at a temperature of 200°C and a pressure of 10 Pa for 4 hours.

[0094] <Example 2-6> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９０ Co ０．０４ Al ０．０１ Mn ０．０５ ] (OH) ２ The composite hydroxide represented by was calcined at 300°C for 4 hours to obtain a metal compound containing Ni, Co, Al, and Mn. (2) In the calcination step, the metal compound and Ca(OH) were mixed such that the molar ratio of Ca to the total number of moles of Ni, Co, Al, and Mn was 0.3 mol%, and the molar ratio of Sr was 0.1 mol%. ２ And, Sr(OH) ２ (3) The mixture was heated from room temperature to 500°C at a heating rate of 3°C / min, then heated from 400°C to 650°C at a heating rate of 2°C / min, and then heated from 650°C to 730°C at a heating rate of 1°C / min, and held for 7 hours to obtain a calcined product. (4) In the addition step, 0.3 mol% of Na relative to the total number of moles of Ni, Co, Al, and Mn was added to the dried powder of the cake-like composition. ２ S ２ O ５ and 0.3 mol% boric acid (H ３ BO ３ The following were added, and the heat treatment atmosphere and temperature were changed to an oxygen atmosphere and 300°C, respectively. The powder obtained by drying the cake-like composition was obtained in the same manner as in Examples 2-5.

[0095] <Example 2-7> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) A metal compound containing Ni, Co, Al, and Mn was obtained in the same manner as in Example 2-6. (2) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, Al, and Mn was 0.3 mol%, the molar ratio of Sr was 0.1 mol%, and the molar ratio of Nb was 0.1 mol%.２ And, Sr(OH) ２ And, Nb ２ O ５ -nH ２ O was mixed with the other. The maximum temperature to be reached and the holding time were changed to 700°C and 10 hours, respectively. (3) In the addition step, 0.3 mol% of K relative to the total number of moles of Ni, Co, Al, and Mn was added to the dried powder of the cake composition. ２ S ２ O ５ The following were added, and the heat treatment atmosphere and temperature were changed to an oxygen atmosphere and 200°C, respectively. The powder obtained by drying the cake-like composition was obtained in the same manner as in Examples 2-5.

[0096] <Comparative Example 2-1> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows. Although no inorganic sulfate was added, 0.06 mol% of S was quantified from the components contained in the composite hydroxide. (1) In the firing step, the molar ratio of Ca to the total number of moles of Ni and Mn was 0.5 mol%, the molar ratio of Zr was 0.3 mol%, and the molar ratio of Nb was 0.1 mol%, so that the metal compound and Ca(OH) ２ And, ZrO ２ And, Nb ２ O ５ The two were mixed together. Also, the maximum temperature to be reached was changed to 750°C. (2) In the addition step, K ２ S ２ O ５ It was not added.

[0097] <Comparative Example 2-2> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni and Mn was 0.5 mol%, the molar ratio of Zr was 0.3 mol%, and the molar ratio of Nb was 0.1 mol%. ２ And, ZrO ２ And, Nb ２ O ５The two were mixed. The maximum temperature to be reached and the holding time were changed to 750°C and 7 hours, respectively. (2) In the addition step, 0.75 mol% sodium lauryl sulfate (NaC) relative to the total number of moles of Ni and Mn was added to the powder obtained by drying the cake-like composition. １２ H ２５ SO ４ The following were added, and the atmosphere and temperature of the heat treatment were changed to an oxygen atmosphere and 300°C, respectively. The powder obtained by drying the cake-like composition was obtained in the same manner as in Examples 2-5.

[0098] <Comparative Example 2-3> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) In the firing step, the metal compound and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni and Mn was 0.5 mol%, the molar ratio of Zr was 0.5 mol%, and the molar ratio of Fe was 0.1 mol%. ２ And, ZrO ２ And, Fe ２ O ３ The two were mixed. The maximum temperature to be reached was also changed to 720°C. (2) In the addition step, 0.3 mol% of Na relative to the total number of moles of Ni and Mn was added to the cake-like composition. ２ S ２ O ５ The substance was added, and the heat treatment temperature was changed to 120°C.

[0099] <Comparative Example 2-4> A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９０ Co ０．０５ Al ０．０５ ] (OH) ２ A composite hydroxide represented by was used to obtain a metal compound containing Ni, Co, and Al. (2) In the calcination step, the metal compound and LiOH·H ２ A mixture was prepared by mixing only O. (3) In the addition step, 0.3 mol% of S was added to the cake-like composition relative to the total number of moles of Ni, Co, and Al, and Na ２ S ２ O ５ The substance was added, and the heat treatment atmosphere and temperature were changed to an oxygen atmosphere and 700°C, respectively.

[0100] Table 3 shows the conditions for preparing the positive electrode active materials for Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-4. Table 4 shows the evaluation results of the test cells for Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-4. In Table 4, the initial discharge capacity of the test cells other than Comparative Example 2-1 is expressed relatively, with the initial discharge capacity of the test cell of Comparative Example 2-1 set to 100. In addition to the evaluation results, Table 4 also shows the following information: (1) The amount of elements contained in the lithium transition metal composite oxide and modified compound calculated from the measurement results of ICP-AES and TEM-EDX (2) The presence or absence of inorganic sulfates and Ca or Sr on the primary particle surface or grain boundaries between primary particles of the lithium transition metal composite oxide (3) The proportion of metal elements other than Li present in the Li layer of the layered structure

[0101] As shown in Table 4, the initial discharge capacities of the test cells in Examples 2-1 to 2-7 were greater than those of the test cells in Comparative Examples 2-1 to 2-4. In particular, the initial discharge capacities of the test cells in Examples 2-2 to 2-7, which contained at least one of Ca and Sr in the modified compound, were greater than those of the test cell in Example 2-1, which did not contain either Ca or Sr in the modified compound. Note that the sodium lauryl sulfate used in Comparative Example 2-2 was an organic sulfate, and therefore did not show any effect on improving the initial discharge capacity. As shown in Figures 2 to 4, Examples 2-1, 2-3, and 2-6 all had both a first peak with a peak at 170 ± 2 eV and a second peak with a peak at 167 ± 2 eV in the S2p spectrum, and the peak P3 of the third peak in the O1s spectrum was higher than the peak P4 of the fourth peak. Similar results were obtained in Examples 2-2, 2-4, 2-5, and 2-7. On the other hand, as shown in Figure 5, in Comparative Example 2-1, the S2p spectrum obtained by X-ray photoelectron spectroscopy did not show a second peak, and the O1s spectrum showed that the third peak was lower than the fourth peak.

[0102]

[0103]

[0104] <Example 3-1> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９２ Mn ０．０８ ] (OH) ２ The composite hydroxide represented by was calcined at 400°C for 5 hours to obtain a metal compound containing Ni and Mn. (2) In the calcination step, the metal compound and Sr(OH) were mixed so that the molar ratio of Sr to the total number of moles of Ni and Mn was 0.1 mol%. ２ (3) The mixture was heated from room temperature to 300°C at a heating rate of 3°C / min, then heated from room temperature to 450°C at a heating rate of 3°C / min, then heated from 450°C to 650°C at a heating rate of 2°C / min, and then heated from 650°C to 750°C at a heating rate of 1°C / min, and held for 3 hours to obtain a calcined product. (4) In the addition step, 1.0 mol% of Na relative to the total number of moles of Ni and Mn was added to the powder obtained by drying the cake-like composition. ２ S ２ O ５ The following were added, and the heat treatment atmosphere and temperature were changed to an oxygen atmosphere and 300°C, respectively. The powder obtained by drying the cake-like composition was obtained in the same manner as in Examples 2-5.

[0105] <Example 3-2> A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９２ Co ０．０３ Al ０．０２ Mn ０．０３ ] (OH) ２ A metal compound containing Ni, Co, Al, and Mn was obtained using a composite hydroxide represented by . (2) In the calcination step, the metal compound and WO were mixed so that the molar ratio of W to the total number of moles of Ni, Co, Al, and Mn was 0.1 mol%. ３ The following were mixed. The maximum temperature to be reached and the holding time were changed to 720°C and 7 hours, respectively. (3) In the addition step, 0.3 mol% of Na relative to the total number of moles of Ni, Co, Al, and Mn was added to the dried powder of the cake composition. ２ SO ４The substance was added, and the heat treatment atmosphere and temperature were changed to an air atmosphere and 200°C, respectively.

[0106] <Comparative Example 3-1> A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the positive electrode active material was prepared as follows. Although no inorganic sulfate was added, 0.06 mol% of S was quantified from the components contained in the composite hydroxide. (1) In the firing step, the molar ratio of Zr to the total number of moles of Ni and Mn was 0.1 mol%, and the molar ratio of Ti was 0.1 mol%, so that the metal compound and Ca(OH) ２ And, Sr(OH) ２ And, ZrO ２ And, TiO ２ The two were mixed. Also, the holding time was changed to 7 hours. (2) In the addition step, Na ２ S ２ O ５ Without adding the substance, the heat treatment atmosphere and temperature were changed to an air atmosphere and 200°C, respectively.

[0107] <Comparative Example 3-2> A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the positive electrode active material was prepared as follows: (1) In the firing step, the molar ratio of Ti to the total number of moles of Ni and Mn was 0.1 mol%, and the metal compound and TiO ２ The following was mixed. The holding time was also changed to 5 hours. (2) In the addition step, during the washing of the calcined product, 0.3 mol% of Na relative to the total number of moles of Ni and Mn was added. ２ S ２ O ５ The substance was added, and the heat treatment atmosphere and temperature were changed to a vacuum atmosphere and 120°C, respectively.

[0108] <Comparative Example 3-3> A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the positive electrode active material was prepared as follows: (1) In the firing step, the metal compound and LiOH·H ２ A mixture was prepared by mixing only O. The maximum temperature to be reached was also changed to 730°C. (2) In the addition step, 0.1 mol% of Li relative to the total number of moles of Ni and Mn was added to the powder obtained by drying the cake-like composition. ２ SO４ The substance was added, and the heat treatment temperature was changed to 500°C.

[0109] <Comparative Example 3-4> A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the positive electrode active material was prepared as follows. Although no inorganic sulfate was added, 0.06 mol% of S was quantified from the components contained in the composite hydroxide. (1) In the firing step, the molar ratio of Ca to the total number of moles of Ni and Mn was 0.1 mol%, and the molar ratio of Ti was 1.0 mol%, so that the metal compound and Ca(OH) ２ And, TiO ２ The two were mixed. Also, the maximum temperature to be reached was changed to 730°C. (2) In the addition step, during the washing of the calcined product with water, sodium ascorbate (C) was added so as to be 0.3 mol% of Na relative to the total number of moles of Ni and Mn. ６ H ７ O ６ Sodium (Na) was added, and the heat treatment temperature was changed to 200°C.

[0110] Table 5 shows the conditions for preparing the positive electrode active materials for Examples 3-1 to 3-2 and Comparative Examples 3-1 to 3-4. Table 6 shows the evaluation results of the test cells for Examples 3-1 to 3-2 and Comparative Examples 3-1 to 3-4. In Table 6, the initial discharge capacity of the test cells other than Comparative Example 3-1 is expressed relatively, with the initial discharge capacity of the test cell of Comparative Example 3-1 set to 100. In addition to the evaluation results, Table 6 also shows the following information: (1) The amount of elements contained in the lithium transition metal composite oxide and modified compound calculated from the measurement results of ICP-AES and TEM-EDX (2) The presence or absence of inorganic sulfates and Ca or Sr on the primary particle surface or grain boundaries between primary particles of the lithium transition metal composite oxide (3) The proportion of metal elements other than Li present in the Li layer of the layered structure

[0111] As shown in Table 6, the initial discharge capacities of the test cells in Examples 3-1 to 3-2 were greater than those of the test cells in Comparative Examples 3-1 to 3-4. In particular, the initial discharge capacity of the test cell in Example 3-1, which contained Sr in the modified compound, was greater than that of the test cell in Example 3-2, which did not contain either Ca or Sr in the modified compound. As shown in Figure 6, Example 3-2 had both a first peak with a peak at 170±2 eV and a second peak with a peak at 167±2 eV in the S2p spectrum, and the peak P3 of the third peak in the O1s spectrum was higher than the peak P4 of the fourth peak. Similar results were obtained in Example 3-1.

[0112]

[0113]

[0114] The positive electrode active materials in Examples 1-1, 2-1 to 2-7, and 3-1 to 3-2 all have a BET specific surface area of ​​2.2 m². ２ It was confirmed that the amount was less than or equal to / g. Furthermore, it was confirmed that the crystallite size of the lithium transition metal composite oxide of the positive electrode active material in all of these examples, calculated by Scherrer's formula from the full width at half maximum of the diffraction peak of the (10⁴) plane of the X-ray diffraction pattern obtained by X-ray diffraction, was in the range of 300 Å to 700 Å.

[0115] This disclosure is further illustrated by the following embodiments. Configuration 1: A positive electrode active material for a non-aqueous electrolyte secondary battery comprising: a lithium transition metal composite oxide containing secondary particles formed by the aggregation of primary particles; and a modifying compound present on the surface of the primary particles or at the grain boundaries between the primary particles, wherein the amount of Ni and the amount of Mn contained in the lithium transition metal composite oxide satisfy 50 mol% ≤ Ni amount ≤ 97 mol%, and 0 mol% < Mn amount < 50 mol%, respectively, with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide; the lithium transition metal composite oxide has a layered structure, and the proportion of metal elements other than Li present in the Li layer of the layered structure is 1.5 mol% or more and 6 mol% or less, with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide; and the modifying compound contains an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals). The amount of Me contained in the modified compound satisfies 0 mol% < amount of Me ≤ 3 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, and the amount of S contained in the modified compound satisfies 0.1 mol% ≤ amount of S ≤ 3 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to configuration 1: The modified compound further contains at least one of Ca and Sr, and the amounts of Ca and Sr contained in the modified compound satisfy 0 mol% < amount of Ca + amount of Sr ≤ 2 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to configuration 1, wherein the amount of Ca ≥ amount of Sr, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery according to configuration 2, wherein the amount of Ca ≥ amount of Sr Configuration 4: The lithium transition metal composite oxide further contains M1 (M1 is at least one element selected from the group consisting of B, Al, Si, Ti, Fe, Co, Zr, Nb, Mo, Sn, W, and Bi), and the amount of M1 contained in the lithium transition metal composite oxide satisfies 0 mol% < amount of M1 < 50 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery is as described in any one of Configurations 1 to 3.Configuration 5: The BET specific surface area is 2.2 m². ２ A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 4, wherein the amount is less than or equal to / g. Configuration 6: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 5, wherein the crystallite size of the lithium transition metal composite oxide, calculated by Scherrer's formula from the full width at half maximum of the diffraction peak of the (104) plane of the X-ray diffraction pattern obtained by X-ray diffraction, is in the range of 300 Å to 700 Å. Configuration 7: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 6, having two peaks in the S2p spectrum obtained by X-ray photoelectron spectroscopy that are attributed to 170 ± 2 eV and 167 ± 2 eV. Configuration 8: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 7, wherein in the O1s spectrum obtained by X-ray photoelectron spectroscopy, the peak of the third peak having a peak at 531 ± 1 eV is higher than the peak of the fourth peak having a peak at 529 ± 1 eV. Configuration 9: A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery described in any one of Configurations 1 to 8, a negative electrode, and a non-aqueous electrolyte. Configuration 10: A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a mixing step of mixing a metal compound containing at least Ni and Mn with a Li compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; a washing step of washing and dewatering the fired product to obtain a cake-like composition; and an addition step of adding an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) to the cake-like composition or a powder obtained by drying the cake-like composition, and performing a heat treatment. Configuration 11: The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 10, wherein the heat treatment is performed at a temperature of 150°C or higher and 500°C or lower. Configuration 12: The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 10 or 11, wherein the inorganic sulfate is at least one compound selected from the group consisting of sulfites, disulfites, disulfates, and peroxodisulfates. Configuration 13: The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 10 to 12, wherein in the mixing step, at least one of a Ca compound and an Sr compound is further added and mixed to obtain the mixture.

[0116] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a lithium transition metal composite oxide containing secondary particles formed by the aggregation of primary particles; and a modifying compound present on the surface of the primary particles or at the grain boundaries between the primary particles, wherein the amount of Ni and Mn contained in the lithium transition metal composite oxide satisfies 50 mol% ≤ Ni amount ≤ 97 mol%, and 0 mol% < Mn amount < 50 mol%, respectively, with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide; the lithium transition metal composite oxide has a layered structure, and the proportion of metal elements other than Li present in the Li layer of the layered structure is 1.5 mol% or more and 6 mol% or less, with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide; and the modifying compound contains an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals). The amount of Me contained in the modified compound satisfies 0 mol% < Me amount ≤ 3 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, and the amount of S contained in the modified compound satisfies 0.1 mol% ≤ S amount ≤ 3 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, wherein this is a positive electrode active material for a non-aqueous electrolyte secondary battery.

2. The modified compound further contains at least one of Ca and Sr, and the amount of Ca and Sr contained in the modified compound satisfies 0 mol% < Ca amount + Sr amount ≤ 2 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, as described in claim 1.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the amount of Ca ≥ the amount of Sr.

4. The lithium transition metal composite oxide further contains M1 (M1 is at least one element selected from the group consisting of B, Al, Si, Ti, Fe, Co, Zr, Nb, Mo, Sn, W, and Bi), and the amount of M1 contained in the lithium transition metal composite oxide satisfies 0 mol% < amount of M1 < 50 mol% with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, as described in claim 1.

5. The BET specific surface area is 2.2 m². ２ The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the amount is less than or equal to / g.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the crystallite size of the lithium transition metal composite oxide, calculated by Scherrer's formula from the full width at half maximum of the diffraction peak of the (10⁴) plane of the X-ray diffraction pattern obtained by X-ray diffraction, is in the range of 300 Å or more and 700 Å or less.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, having two peaks in the S2p spectrum obtained by X-ray photoelectron spectroscopy, which are attributed to 170±2 eV and 167±2 eV.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, in the O1s spectrum obtained by X-ray photoelectron spectroscopy, the peak of the third peak having a peak at 531 ± 1 eV is higher than the peak of the fourth peak having a peak at 529 ± 1 eV.

9. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery described in any one of claims 1 to 8, a negative electrode, and a non-aqueous electrolyte.

10. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a mixing step of mixing a metal compound containing at least Ni and Mn with a Li compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; a washing step of washing and dewatering the fired product to obtain a cake-like composition; and an addition step of adding an inorganic sulfate containing Me (Me is at least one element included in the third period or later of alkali metals) to the cake-like composition or a powder obtained by drying the cake-like composition, and performing a heat treatment.

11. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein the heat treatment is performed at a temperature of 150°C or higher and 500°C or lower.

12. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein the inorganic sulfate is at least one compound selected from the group consisting of sulfites, disulfites, disulfates, and peroxodisulfates.

13. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein in the mixing step, at least one of a Ca compound and an Sr compound is further added and mixed to obtain the mixture.

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