Positive electrode active material for nonaqueous electrolyte secondary batteries, nonaqueous electrolyte secondary battery, and method for producing positive electrode active material for nonaqueous electrolyte secondary batteries

Abstract

A positive electrode active material for nonaqueous electrolyte secondary batteries according to an embodiment contains a lithium transition metal composite oxide, a sulfonic acid compound, and a P compound that contains P. The lithium transition metal composite oxide has a layered structure, has a Ni content of 65 mol% or more, and is composed of secondary particles formed by aggregation of primary particles. The sulfonic acid compound is present on the surfaces of the secondary particles. The P compound is present at least at the interface between the primary particles. The Gini coefficient of PO3- in the secondary particles is 0.6 or less.

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 with a high Ni content, a non-aqueous electrolyte secondary battery containing this active material, and a method for producing this active material.

[0002] Lithium transition metal composite oxides with a high Ni content are known as positive electrode active materials for high-capacity non-aqueous electrolyte secondary batteries. However, lithium transition metal composite oxides with a Ni content of 65% or more have highly reactive Ni on the surface when the charge level is high. ４＋ Because of the large amount of these substances present, side reactions with non-aqueous electrolytes are likely to occur. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery that uses a lithium transition metal composite oxide with low-solubility Li salts scattered on its surface as the positive electrode active material, with the aim of reducing reaction resistance when stored at high temperatures.

[0003] Japanese Patent Publication No. 2019-169286

[0004] In recent years, there has been an increasing demand for higher capacity non-aqueous electrolyte secondary batteries. While battery capacity can be increased by charging at high voltages, such high-voltage charge-discharge cycles tend to result in a lower capacity retention rate than normal voltage charge-discharge cycles. Patent Document 1 does not address suppressing the decrease in battery capacity due to high-voltage charge-discharge cycles, and the technology described in Patent Document 1 still has room for improvement.

[0005] The purpose of this disclosure is to reduce the reaction resistance and suppress the decrease in battery capacity due to high-voltage charge-discharge cycles in a positive electrode active material containing a lithium transition metal composite oxide with a high Ni content.

[0006] The positive electrode active material for a non-aqueous electrolyte secondary battery according to this disclosure comprises a lithium transition metal composite oxide, a sulfonic acid compound represented by the following general formula I, and a P compound containing P, wherein the lithium transition metal composite oxide has a layered structure and the general formula Li ｘ Ni ａ Coｂ Mn ｃ Me ｄ O ２－ｙ (wherein the formula, 0.95≦x≦1.15, 0.65≦a≦0.98, 0≦b≦0.15, 0≦c≦0.35, 0≦d≦0.10, 0≦y<0.05, a+b+c+d=1, Me is represented by at least one element selected from the group consisting of Nb, Zr, Ti, W, Mo, Si and Al), and is a secondary particle formed by the aggregation of primary particles, the sulfonic acid compound is present on the surface of the secondary particle, the P compound is present at least at the interface between primary particles, and in the elemental concentration distribution of the secondary particle cross-section using time-of-flight secondary ion mass spectrometry, PO is present inside the secondary particle ３－ It is characterized by having a Gini coefficient of 0.6 or less. (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0007] The non-aqueous electrolyte secondary battery according to this disclosure is characterized by comprising a positive electrode containing the positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

[0008] The present disclosure relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a firing step of mixing a Ni metal compound containing 65 mol% or more of Ni relative to the total molar amount of metal elements with a Li compound and firing to obtain a fired product; a washing step of washing and dewatering the fired product to obtain a cake-like composition; and a drying step of heating and drying the cake-like composition, wherein an aqueous solution containing a P compound in an amount of 0.0003% to 0.35% by mass relative to the mass of lithium transition metal composite oxide, in terms of P element, is added during the washing step, and at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition in the washing step.

[0009] The positive electrode active material for non-aqueous electrolyte secondary batteries according to this disclosure can reduce reaction resistance while suppressing the decrease in battery capacity due to high-voltage charge-discharge cycles.

[0010] This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment.

[0011] High-voltage charge-discharge cycles increase the battery capacity, but the capacity retention rate tends to be lower than that of normal-voltage charge-discharge cycles. In particular, lithium transition metal composite oxides with a high Ni content are prone to side reactions with non-aqueous electrolytes in a high state of charge, so this tendency is prominent.

[0012] The inventors have intensively studied and found that the positive electrode active material contains a high-capacity lithium transition metal composite oxide with a high Ni content, a sulfonic acid compound present on the surface of the secondary particles of the composite oxide, and a P compound present at the interface between at least primary particles of the composite oxide. By having a PO ３－ dini coefficient of 0.6 or less inside the secondary particles, the reaction resistance can be reduced and the decrease in battery capacity due to high-voltage charge-discharge cycles can be suppressed. It is considered that while the sulfonic acid compound protects the surface of the secondary particles, the P compound is present relatively uniformly inside the secondary particles, so that side reactions between the lithium transition metal composite oxide and the non-aqueous electrolyte are more significantly suppressed, and the above effects are specifically manifested.

[0013] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical exterior body will be exemplified. However, the electrode body is not limited to a wound type, and may be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one through a separator. Further, the exterior body is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, etc., or may be a battery case composed of a laminate sheet including a metal layer and a resin layer.

[0014] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 which is an example of an embodiment. As shown in FIG. 1, the secondary battery 10 includes a wound electrode body 14, an electrolytic solution, and an exterior body 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 through the separator 13. The exterior body 16 is a bottomed cylindrical metal container with an open end on one side in the axial direction, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the side of the battery with the sealing body 17 is taken as the top, and the bottom side of the exterior body 16 is taken as the bottom.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] [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.

[0021] The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is the main component of the positive electrode mixture layer. Here, the main component means the component with the highest mass ratio among the constituent components of the positive electrode mixture layer. The positive electrode mixture layer preferably contains 80% by mass or more of the positive electrode active material, and more preferably 90% by mass or more of the positive electrode active material, relative to the total mass of the positive electrode mixture layer.

[0022] 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 a positive electrode active material, a conductive agent, etc., to the surface of the positive electrode current collector, drying the coating film, and then rolling it to form a 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 active material comprises a lithium transition metal composite oxide, a sulfonic acid compound, and a P-containing P compound. The synergistic effect of the sulfonic acid compound and the P-compound specifically reduces reaction resistance while suppressing the decrease in battery capacity due to high-voltage charge-discharge cycles.

[0026] Lithium transition metal composite oxides have a layered structure and have the general formula Li ｘ Ni ａ Co ｂ Mn ｃ Me ｄ O ２－ｙ This is a composite oxide represented by the formula (wherein 0.95≦x≦1.15, 0.65≦a≦0.98, 0≦b≦0.15, 0≦c≦0.35, 0≦d≦0.10, 0≦y<0.05, a+b+c+d=1, and Me is at least one element selected from the group consisting of Nb, Zr, Ti, W, Mo, Si, and Al). The proportion of metal elements contained in the lithium transition metal composite oxide can be measured, for example, by an inductively coupled plasma atomic emission spectrometer (ICP-AES). Specific examples of the layered structure include a layered structure belonging to space group R-3m, or a layered crystalline structure belonging to space group C2 / m.

[0027] As described above, lithium transition metal composite oxides contain 65 mol% or more of Ni relative to the total number of moles of metal elements excluding Li. By setting the Ni content (a in the general formula above) to 65 mol% or more, high-capacity batteries can be obtained. The upper limit of the Ni content is 98 mol%. If the Ni content exceeds 98 mol%, it becomes difficult to ensure the stability of the layered structure of the lithium transition metal composite oxide, and battery performance such as cycle characteristics may deteriorate. Examples of a suitable range for the Ni content are 75 mol% to 95 mol%, 80 mol% to 95 mol%, or 85 mol% to 95 mol%.

[0028] The value of x, which represents the proportion of Li in the lithium transition metal composite oxide, is preferably 0.95 ≤ x ≤ 1.15, and more preferably 0.97 ≤ a ≤ 1.03. If x is less than 0.95, the capacity may decrease compared to when x satisfies the above range. If x is greater than 1.10, more Li compounds will need to be added compared to when x satisfies the above range, which may not be economical from a manufacturing cost standpoint.

[0029] When Co is contained in a lithium transition metal composite oxide, the Co content (b in the general formula above) is 15 mol% or less relative to the total number of moles of metal elements excluding Li. Since Co is an expensive element, it is preferable to keep the Co content low when considering manufacturing costs.

[0030] When Mn is contained in a lithium transition metal composite oxide, the Mn content (c in the general formula above) is 35 mol% or less relative to the total number of moles of metal elements excluding Li. If the Mn content exceeds 35 mol%, the battery capacity and high-temperature cycle characteristics may decrease. An example of a suitable range for Mn content is 5 mol% to 30 mol%.

[0031] When a lithium transition metal composite oxide contains Me (where Me is at least one element selected from the group consisting of Nb, Zr, Ti, W, Mo, Si, and Al), the Me content (d in the above general formula) is 10 mol% or less relative to the total number of moles of metal elements excluding Li.

[0032] Lithium transition metal composite oxides are secondary particles formed by the aggregation of multiple primary particles. The particle size of the primary particles is, for example, between 0.05 μm and 1 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 volume-based median diameter (D50) of the secondary particles is, for example, between 3 μm and 30 μm, preferably between 5 μm and 25 μm. 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 the composite oxide (Z) can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0033] The sulfonic acid compounds contained in the positive electrode active material are present on the surface of the lithium transition metal composite oxide and are represented by the following general formula I. (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0034] In the general formula I above, A is preferably a Group 1 element, and more preferably Li. This allows for a lower DC resistance. When A is a Group 1 element, n = 1.

[0035] In general formula I, R is preferably an alkyl group. More preferably, R is an alkyl group having 5 or fewer carbon atoms, even more preferably an alkyl group having 3 or fewer carbon atoms, and particularly preferably a methyl group. In addition, some of the hydrogen atoms bonded to carbon in R may be substituted with fluorine. However, not all of the hydrogen atoms bonded to carbon in R may be substituted with fluorine. A smaller molecular weight of R can reduce the DC resistance.

[0036] Examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate.

[0037] The mass of the sulfonic acid compound contained in the positive electrode active material is preferably 0.05% by mass or more and 1.5% by mass or less, more preferably 0.1% by mass or more and 1.0% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the mass of the lithium transition metal composite oxide.

[0038] The presence of sulfonic acid compounds in the positive electrode active material can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the positive electrode 11 has an absorption of 1238 cm⁻¹. －１ , 1175cm －１ , 1065cm －１ 785cm －１ It may have at least one absorption peak in the vicinity.

[0039] In the infrared absorption spectrum obtained by FT-IR, for example, a positive electrode active material containing lithium methanesulfonate shows an absorption of 1238 cm⁻¹. －１ , 1175cm －１ , 1065cm －１ 785cm －１ There is an absorption peak in the vicinity. 1238 cm －１ , 1175cm －１ , 1065cm －１ The nearby peak is an absorption peak caused by SO stretching vibrations originating from lithium methanesulfonate. 785 cm －１ The nearby peaks are absorption peaks caused by CS stretching vibrations originating from lithium methanesulfonate.

[0040] Even in cathode active materials containing sulfonic acid compounds other than lithium methanesulfonate, absorption peaks originating from sulfonic acid compounds can be identified, similar to those in cathode active materials containing lithium methanesulfonate. Furthermore, the presence of sulfonic acid compounds in cathode active materials can be confirmed by ICP, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), synchrotron radiation XRD measurement, TOF-SIMS, H-NMR, etc.

[0041] P compounds are present at least at the interfaces between primary particles. P compounds may also be present on the surface of secondary particles and at the interfaces between primary particles. In the elemental concentration distribution of the cross-section of a secondary particle using time-of-flight secondary ion mass spectrometry, PO is present inside the secondary particle. ３－ The Gini coefficient is 0.6 or less. By having a sulfonic acid compound on the surface of the secondary particles of the lithium transition metal composite oxide while relatively uniformly distributing the P compound inside the secondary particles, the side reaction between the lithium transition metal composite oxide and the non-aqueous electrolyte is more significantly suppressed, and the decrease in battery capacity due to high-voltage charge-discharge cycles can be suppressed while specifically reducing the reaction resistance.

[0042] The P compound is not particularly limited in its form, as long as it is present at least at the interfaces between primary particles. The P compound may be adhering to the surface of secondary particles, adhering to the surface of primary particles, or existing detached from the surface of primary particles. The presence of the P compound can be confirmed by measuring the cross-section of the secondary particles using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). The P compound may be scattered near the surface of the primary particles, including the surface of the secondary particles, or it may exist in a layered manner, broadly covering the surface of the primary particles.

[0043] PO ３－ Since it is detected due to the P compound, PO inside the secondary particle ３－ A smaller Gini coefficient indicates that the P compound is uniformly dispersed within the secondary particles. ３－ The Gini coefficient is, for example, 0.1 or greater.

[0044] PO inside secondary particles ３－ The Gini coefficient is the PO inside the secondary particle. ３－ Normalized strength I ＰＯ３－＿ＩＮ Regarding this, it is the value obtained by doubling the area enclosed between the diagonal and the Lorentz curve when the cumulative rate is expressed in order of intensity. The Gini coefficient is 0 when the uniformity is perfect and its value increases as the uniformity decreases. Note that in this specification, PO inside secondary particles ３－ The Gini coefficient is calculated by arbitrarily selecting 50 secondary particles and determining the PO inside the secondary particles. ３－This refers to the value obtained by measuring the Gini coefficient using the method described below and taking the arithmetic mean of those measurements.

[0045] PO ３－ Normalized strength I ＰＯ３－ This is obtained by measurement using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5, IONTOF Corporation) under the following conditions: Primary ion: Bi ３ ＋ Ion voltage: 30 kV; Ion current: 0.03 pA @ 100 us; Observation range: 50 μm × 50 μm; Mass range: 60 us (~310 amu); Detection: 4 frames / scan, 150 scans

[0046] Ni and PO obtained from the above measurements ３－ The image showing the density distribution of Ni and PO was divided into 256 x 256 pixels, and for each pixel, Ni and PO ３－ The detection intensity of each is calculated. Furthermore, the detection intensity of Ni is calculated. ３－ The ratio of detection intensities is PO ３－ Normalized strength I ＰＯ３－ It is calculated as follows.

[0047] The surface of the secondary particle is defined as the area from the surface of the secondary particle recognized in the image above up to 0.5 μm inward. The area inside this secondary particle surface is defined as the interior of the secondary particle, and the pixels contained within the interior of the secondary particle (hereinafter referred to as interior pixels) are defined. I corresponding to each interior pixel ＰＯ３－ The set is I ＰＯ３－＿ＩＮ And so, I ＰＯ３－＿ＩＮ Therefore, PO inside secondary particles ３－ The Gini coefficient is calculated. The sample to be observed in cross-section may be a sample in which the positive electrode active material is embedded in resin or the like, or a positive electrode mixture layer containing the positive electrode active material.

[0048] The mass of the P compound contained in the positive electrode active material is, for example, 0.0003% by mass or more and 0.35% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide.

[0049] The P compound is, for example, a Li-P compound. The Li-P compound may be an oxide. The Li-P compound is a compound containing Li and P, for example, Li ３ PO４ , P ２ O ５ Li ３－ｘ H ｘ PO ４ Examples include (0 < x < 3).

[0050] The positive electrode mixture layer may contain positive electrode active materials other than the positive electrode active material containing the lithium transition metal composite oxide, sulfonic acid compound, and P compound described above. For example, the positive electrode mixture layer may contain positive electrode active materials that do not contain sulfonic acid compound or P compound. The proportion of the positive electrode active material containing the lithium transition metal composite oxide, sulfonic acid compound, and P compound described above in the positive electrode active material is preferably 70% by mass or more, and may be substantially 100% by mass.

[0051] The following describes an example of a method for producing the positive electrode active material described above.

[0052] The manufacturing process for the positive electrode active material includes, for example, a firing step in which a Ni metal compound containing 65 mol% or more Ni is mixed with a Li compound and the mixture is fired; a washing step in which the fired product is washed with water and dehydrated to obtain a cake-like composition; and a drying step in which the cake-like composition is dried.

[0053] In the calcination step, a Ni metal compound containing 65 mol% or more Ni is mixed with a Li compound. Examples of Ni metal compounds include Ni-containing metal hydroxides, Ni-containing metal oxides, and Ni-containing metal carbonate compounds. Ni metal compounds can be obtained, for example, by adding an alkaline solution such as sodium hydroxide dropwise to a solution of a metal salt containing Ni and an arbitrary metal element (Co, Mn, etc.) while stirring, thereby adjusting the pH to the alkaline side (e.g., 8.5 or higher and 12.5 or lower), which precipitates (coprecipitation) a composite hydroxide containing Ni and an arbitrary metal element, and then heat-treating the composite hydroxide. The heat treatment temperature is not particularly limited, but for example, it is in the range of 250°C or higher and 600°C or lower. An example of a Li compound is Li ２ CO ３ LiOH, Li ２ O ２ Li ２ O, LiNO ３ LiNO ２Li ２ SO ４ LiOH H ２ Examples include O, LiH, and LiF.

[0054] In the calcination step, a Ni metal compound containing 65 mol% or more of Ni, a Li compound, and a compound containing the element Me (Me is at least one element selected from the group consisting of Zr, Nb, Ti, W, Mo, Si, and Al) may be further mixed. The compound containing the element Me is a compound containing at least one of the phosphate, sulfate, oxide, hydroxide, sulfide, and chloride containing the element Me. An example of such a compound is ZrO ２ ZrSiO ４ , Zr(SO ４ ) ２ , Zr(WO ４ ) ２ , ZrCl ３ Nb2O ５ Nb2O ５・ nH2O, TiO ２ WO ３ WS ２ Al ２ (WO ４ ) ３ MoO ２ MoO ３ MoS ２ Al ２ O ３ Al(OH) ３ NaAl(OH) ４ AlPO ４ These are some examples. These compounds may be used individually or in combination of two or more. As described above, when the lithium transition metal composite oxide contains the element Me, the effect of suppressing the decrease in battery capacity due to high-voltage charge-discharge cycles may be more pronounced.

[0055] The mixing ratio of the Ni metal compound, the Li compound, and the compound containing the element Me is preferably such that the molar ratio of the total amount of metal elements in the compound containing the Ni metal compound and the element Me to Li is in the range of 1:0.8 to 1:1.2, and is particularly preferably 1:0.98 to 1:1.12.

[0056] The firing step is a multi-step firing process that includes, for example, a first firing step of firing at 450°C or higher and 680°C or lower under an oxygen stream, and a second firing step of firing the fired product obtained in the first firing step at a temperature exceeding 680°C under an oxygen stream. In the first firing step, the temperature is raised to a first set temperature of 680°C or lower at a first heating rate of 0.2°C / min or higher and 5.5°C / min or lower. In the second firing step, the temperature is raised to a second set temperature of 900°C or lower at a second heating rate of 0.1°C / min or higher and 3.5°C / min or lower, and the second heating rate is slower than the first heating rate. Note that the first and second heating rates may be set in a plurality for each predetermined temperature range within the above range.

[0057] The holding time of the first set temperature in the first firing step is preferably 5 hours or less, more preferably 3 hours or less. The holding time of the first set temperature is the time for maintaining the first set temperature after reaching the first set temperature, and the holding time may be zero. The holding time of the second set temperature in the second firing step is preferably 1 hour or more and 10 hours or less, more preferably 1 hour or more and 5 hours or less. The holding time of the second set temperature is the time for maintaining the second set temperature after reaching the second set temperature. The firing of the mixture is carried out, for example, in an oxygen stream with an oxygen concentration of 60% or more, and the flow rate of the oxygen stream is 0.2 mL / min or more and 4 mL / min or less per 10 cm of the firing furnace, and 0.3 L / min or more per 1 kg of the mixture. ３ per, 0.2 mL / min or more and 4 mL / min or less, and 0.3 L / min or more per 1 kg of the mixture.

[0058] In the water washing step, the fired product obtained in the firing step is washed with water to remove impurities while adding a P compound. The water washing step is carried out, for example, using a reaction vessel of 1 L to 10 L, under conditions where the solid-liquid ratio is 300 g / L or more and 2000 g / L or less, the water washing time is 1 minute or more and 1 hour or less, and the stirring speed is 100 rpm or more. When the solid-liquid ratio is 300 g / L or more and 2000 g / L or less, when a phosphorus-containing compound is added during water washing as described later, the coefficient of phosphorus (PO ３－ ) in the secondary particles is likely to be 0.6 or less. Thereafter, a cake-like composition is obtained by dehydrating the washed fired product.

[0059] In the washing step, by adding a raw material containing P (hereinafter referred to as P raw material) during washing or after dehydration, P can be relatively uniformly dispersed inside the secondary particles of the lithium transition metal composite oxide. Therefore, the Dini coefficient of PO ３－ inside the secondary particles can be made 0.6 or less. Particularly, from the viewpoint of easily uniformly dispersing P inside the secondary particles, it is preferable to add the P raw material during washing. Examples of the P raw material include, for example, Li ３ PO ４ , P ２ O ５ , Li ３－ｘ H ｘ PO ４ (0 < x < 3), etc.

[0060] In the washing step, an aqueous phosphoric acid solution as the P raw material may be added. In this case, separately from the water used for washing, the aqueous phosphoric acid solution as the P raw material may be added during washing. By adding the aqueous phosphoric acid solution as the P raw material separately from the water used for washing during washing, the P compound can be uniformly dispersed inside the secondary particles, and the Dini coefficient of PO ３－ inside the secondary particles can be made 0.6 or less. The concentration of the aqueous phosphoric acid solution is, for example, 0.01% by mass or more and 85% by mass or less, preferably 0.01% by mass or more and 30% by mass or less from the viewpoint of dispersibility, and more preferably 0.01% by mass or more and 10% by mass or less. By adding the P raw material as an aqueous phosphoric acid solution, P can be more uniformly dispersed inside the secondary particles. For example, by adding an aqueous phosphoric acid solution containing 0.0008% by mass or more and 2.0% by mass or less of H ３ PO ４ with respect to the mass of the lithium transition metal composite oxide, the mass of the P compound contained in the positive electrode active material can be made 0.0003% by mass or more and 0.35% by mass or less in terms of P element. The total amount of the aqueous phosphoric acid solution as the P raw material added during the washing step is not particularly limited, but for example, it is 150% by mass or less, preferably 50% by mass or less, and more preferably 10% by mass or less with respect to the mass of the lithium transition metal composite oxide. The concentration of the aqueous phosphoric acid solution can be adjusted according to the amount of the P raw material added.

[0061] By adding, for example, at least one of a sulfonic acid compound and a sulfonic acid solution to the dehydrated cake-like composition in the water washing step, the sulfonic acid compound can be attached to the surface of the secondary particles of the lithium transition metal composite oxide. Alternatively, at least one of a sulfonic acid compound and a sulfonic acid solution may be added to the dehydrated cake-like composition. The sulfonic acid compound may be in powder or solution form. The sulfonic acid solution is, for example, a methanesulfonic acid solution obtained by dissolving methanesulfonic acid in water. A Li compound or Li compound solution may be added to the cake-like composition together with the sulfonic acid solution, or a mixed solution of the sulfonic acid solution and the Li compound or Li compound solution may be added to the cake-like composition. The Li compound is, for example, LiOH, and the Li compound solution is, for example, a LiOH solution obtained by dissolving LiOH in water. The amount of Li compound and sulfonic acid solution added to the cake-like composition preferably satisfies the relationship 0 ≤ Li compound / sulfonic acid ≤ 1.3 in molar ratio. The amount of sulfonic acid compound or sulfonic acid added is preferably 0.1% by mass or more and 2% by mass or less relative to the mass of the lithium transition metal composite oxide. The concentration of the sulfonic acid solution and the sulfonic acid compound solution is, for example, 0.5% by mass or more and 40% by mass or less. In addition, P raw material may be added to the cake-like composition after dehydration. In this case, P raw material may be added simultaneously with at least one of the sulfonic acid compound and the sulfonic acid solution.

[0062] In the drying step, the cake-like composition obtained in the washing step is dried. If necessary, the positive electrode active material is crushed, classified, etc., to adjust the D50 of the positive electrode active material to the desired range. This drying may be carried out at a temperature of less than 100°C. An example of a suitable drying temperature is 150°C to 250°C. The drying process may be carried out under vacuum or under air. An example of a drying process time is 1 hour to 5 hours.

[0063] [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.

[0064] 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.

[0065] 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.

[0066] [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.

[0067] 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.

[0068] [Non-aqueous electrolytes] Non-aqueous electrolytes, for example, have lithium ion conductivity. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0069] 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).

[0070] 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).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0076] 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.

[0077] 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.

[0078] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0079] <Example 1-1> [Preparation of positive electrode active material] Ni obtained by coprecipitation method ０．９０ Co ０．０５ Mn ０．０５ (OH) ２The composite hydroxide represented by was calcined at 500°C for 8 hours to obtain a Ni-containing metal oxide containing Ni, Co, and Mn. The above Ni-containing metal oxide was mixed with lithium hydroxide monohydrate (LiOH·H ２ O) was mixed so that the molar ratio of Li to the total number of moles of Ni, Co, and Mn was 103 mol%, 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 1000 g / L, and washed with water at a stirring speed of 200 rpm for 10 minutes. At this time, an aqueous phosphoric acid solution with a concentration of 0.5 mass% was prepared as a phosphorus raw material, and 0.043 mass% of H was added relative to the mass of the lithium transition metal composite oxide. ３ PO ４ An aqueous phosphoric acid solution containing the required amount was added dropwise. The mixture was then dehydrated using a filter press to obtain a cake-like composition. A methanesulfonic acid solution was then added to the obtained cake-like composition. The concentration of the methanesulfonic acid solution was 10% by mass, and the amount of methanesulfonic acid added was 0.3% by mass relative to the total mass of the lithium transition metal composite oxide (water washing step). Subsequently, a drying step was performed at 180°C for 2 hours under a vacuum atmosphere to obtain the positive electrode active material of Example 1-1. The content of element P in the positive electrode active material was measured using an ICP emission spectrometer (ICP-AES), and the result was 0.014% by mass relative to the total mass of the positive electrode active material.

[0080] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) confirmed the presence of P compounds on the surface of secondary particles and at the interfaces between primary particles. ３－ The Gini coefficient was 0.3. Furthermore, Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of lithium methanesulfonate on the surface of the secondary particles.

[0081] [Preparation of the positive electrode] The above positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, 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.

[0082] [Fabrication of the negative electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), and lithium methanesulfonate were mixed in an aqueous solution in a solid content mass ratio of 100:1:1:0.08 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, and after the coating film was dried, the coating film was rolled using a rolling mill, cut to a predetermined electrode size, and the negative electrode was manufactured. An exposed portion was provided on a part of the negative electrode in which the surface of the negative electrode core was exposed.

[0083] [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.

[0084] [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.

[0085] [Measurement of Reaction Resistance] The test cell was charged at a constant current of 0.1C at a temperature of 25°C until the cell voltage reached 4.3V, and then charged at a constant voltage of 4.3V until the current value was 0.01C. After that, it was again charged at a constant current of 0.1C at a temperature of 25°C until the cell voltage reached 4.3V, and then charged at a constant voltage of 4.3V until the current value was 0.01C. Next, after 2 hours at a temperature of 25°C, the AC impedance of the test cell was measured using a Solartron 1255B (manufactured by Solartron Corporation) with an applied voltage of 10mV and a measurement frequency range of 0.01Hz to 200kHz. A Nyquist plot was drawn from the measurement data, and the reaction resistance was determined from the size of the arc between 10Hz and 0.1Hz.

[0086] [Measurement of Capacity Retention Rate in High-Voltage Cycles] The test cell was charged to 4.3V with a constant current of 0.2C at a temperature of 25°C, and then charged again at a constant voltage of 4.3V until the current value was 0.01C. After a rest period of 1 hour, it was discharged again at a temperature of 25°C with a constant current of 0.2C until it reached 2.5V. This charge-discharge cycle was considered one cycle, and the cycle was repeated 50 times. The capacity retention rate was calculated using the following formula: Capacity Retention Rate = Discharge Capacity at Cycle 50 / Discharge Capacity at Cycle 1

[0087] <Example 1-2> In the preparation of the positive electrode active material, the amount of phosphoric acid aqueous solution added was changed to 0.0043% by mass of H relative to the mass of the lithium transition metal composite oxide. ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that an amount of phosphoric acid aqueous solution containing the compound was added. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.6.

[0088] <Examples 1-3> In the preparation of the positive electrode active material, the amount of phosphoric acid aqueous solution added was changed to 0.43% by mass of H relative to the mass of the lithium transition metal composite oxide. ３ PO ４A test cell was prepared and evaluated in the same manner as in Example 1-1, except that an amount of phosphoric acid aqueous solution containing the compound was added. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.6.

[0089] <Example 1-4> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1-1, except that the concentration of the phosphoric acid aqueous solution was changed to 0.1% by mass. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0090] <Example 1-5> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1-1, except that the concentration of the phosphoric acid aqueous solution was changed to 10% by mass. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.5.

[0091] <Example 1-6> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1-1, except that the concentration of the phosphoric acid aqueous solution was changed to 60% by mass. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.6.

[0092] <Comparative Example 1-1> In the preparation of the positive electrode active material, Ni-containing metal oxide and LiOH·H ２ When mixing with O, add 0.035% by mass of P relative to the mass of the lithium transition metal composite oxide. ２ O ５A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the P compound was added and mixed, and no phosphoric acid aqueous solution was added during washing with water. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.8.

[0093] <Comparative Example 1-2> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that an aqueous phosphoric acid solution was not added in the preparation of the positive electrode active material. It was confirmed that lithium methanesulfonate was present on the surface of the secondary particles in the prepared positive electrode active material.

[0094] <Comparative Example 1-3> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that lithium methanesulfonate was not added in the preparation of the positive electrode active material. It was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles in the prepared positive electrode active material. PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0095] <Example 2-1> In the preparation of the positive electrode active material, [Ni ０．８０ Co ０．１０ Mn ０．０５ Al ０．０５ ] (OH) ２ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.2.

[0096] <Comparative Example 2-1> In the preparation of the positive electrode active material, Ni-containing metal oxide and LiOH·H ２ When mixing with O, add 0.035% by mass of P relative to the mass of the lithium transition metal composite oxide. ２ O ５A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the P compound was added and mixed, and no phosphoric acid aqueous solution was added during washing with water. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.8.

[0097] <Example 3-1> In the preparation of the positive electrode active material, [Ni ０．９２ Co ０．０４ Al ０．０４ ] (OH) ２ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0098] <Comparative Example 3-1> In the preparation of the positive electrode active material, Ni-containing metal oxide and LiOH·H ２ When mixing with O, add 0.035% by mass of P relative to the mass of the lithium transition metal composite oxide. ２ O ５ A test cell was prepared and evaluated in the same manner as in Example 3-1, except that the P compound was added and mixed, and no phosphoric acid aqueous solution was added during washing with water. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interface between the primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.9.

[0099] <Example 4-1> In the preparation of the positive electrode active material, [Ni ０．７０ Co ０．０５ Mn ０．２５ ] (OH) ２A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. In the prepared positive electrode active material, it was confirmed that P compounds were present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0100] <Comparative Example 4-1> In the preparation of a positive electrode active material, Ni-containing metal oxide and LiOH·H ２ When mixing with O, add 0.035% by mass of P relative to the mass of the lithium transition metal composite oxide. ２ O ５ A test cell was prepared and evaluated in the same manner as in Example 4-1, except that the P compound was added and mixed, and no phosphoric acid aqueous solution was added during washing with water. In the prepared positive electrode active material, it was confirmed that the P compound was present on the surface of the secondary particles and at the interfaces between primary particles, and that lithium methanesulfonate was present on the surface of the secondary particles. PO inside the secondary particles ３－ The Gini coefficient was 0.8.

[0101] The evaluation results of the test cells for the examples and comparative examples are shown in Tables 1 to 4. In Table 1, the reaction resistance and capacity retention rates of the test cells for the examples and comparative examples 1-2 to 1-3 are expressed relatively, with the reaction resistance and capacity retention rates of the test cell for comparative example 1-1 each set to 100. In Tables 2 to 4, the reaction resistance and capacity retention rates of the test cells for the examples are expressed relatively, with the reaction resistance and capacity retention rates of the test cells for the comparative examples each set to 100.

[0102]

[0103]

[0104]

[0105]

[0106] As shown in Tables 1 to 4, the test cells in the examples all achieve both suppression of reaction resistance and improvement of capacity retention. On the other hand, the test cells in the comparative examples do not sufficiently achieve either suppression of reaction resistance or improvement of capacity retention. The positive electrode active materials in Comparative Examples 1-2 and 1-3 lack at least one of the P compound or the sulfonic acid compound, and it can be seen that the presence of both the P compound and the sulfonic acid compound is necessary to reduce reaction resistance while suppressing the decrease in battery capacity due to high-voltage charge-discharge cycles. Furthermore, in Comparative Examples 1-1, 2-1, 3-1, and 4-1, by adding the P compound during calcination rather than during washing, the distribution of P inside the secondary particles becomes uneven, and PO ３－ The Gini coefficient exceeded 0.6, meaning that it was not possible to achieve both suppression of reaction resistance and improvement of capacity retention.

[0107] This disclosure is further illustrated by the following embodiments. Configuration 1: A lithium transition metal composite oxide, and a sulfonic acid compound represented by the following general formula I, (wherein A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.) A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a P compound containing P, wherein the lithium transition metal composite oxide has a layered structure and the general formula is Li ｘ Ni ａ Co ｂ Mn ｃ Me ｄ O ２－ｙ (wherein the formula, 0.95≦x≦1.15, 0.65≦a≦0.98, 0≦b≦0.15, 0≦c≦0.35, 0≦d≦0.10, 0≦y<0.05, a+b+c+d=1, Me is at least one element selected from the group consisting of Nb, Zr, Ti, W, Mo, Si and Al), and is a secondary particle formed by the aggregation of primary particles, the sulfonic acid compound is present on the surface of the secondary particle, the P compound is present at least at the interface between the primary particles, and in the elemental concentration distribution of the cross-section of the secondary particle using time-of-flight secondary ion mass spectrometry, PO inside the secondary particle ３－A positive electrode active material for a non-aqueous electrolyte secondary battery having a Gini coefficient of 0.6 or less. Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein A is a Group 1 element. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein A is Li. Configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein R is an alkyl group. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein R is a methyl group. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the mass of the sulfonic acid compound is 0.05% by mass or more and 1.5% by mass or less, relative to the mass of the lithium transition metal composite oxide. Configuration 7: In the infrared absorption spectrum, 1238 cm⁻¹ －１ , 1175cm －１ , 1065cm －１ 785cm －１ A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 6, having an absorption peak in at least one location in the vicinity. Configuration 8: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 7, wherein the mass of the P compound is 0.0003% by mass or more and 0.35% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide. Configuration 9: A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to 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 firing step of mixing a Ni metal compound containing 65 mol% or more of Ni relative to the total molar amount of metal elements with a Li compound and 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 a drying step of heating and drying the cake-like composition, wherein an aqueous solution containing a P compound in an amount of 0.0008% by mass or more and 2.0% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide is added to the washing step, and at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition in the washing step.

[0108] 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 lithium transition metal composite oxide and a sulfonic acid compound represented by the following general formula I, (wherein A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.) A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a P compound containing P, wherein the lithium transition metal composite oxide has a layered structure and the general formula is Li ｘ Ni ａ Co ｂ Mn ｃ Me ｄ O ２－ｙ (wherein the formula, 0.95≦x≦1.15, 0.65≦a≦0.98, 0≦b≦0.15, 0≦c≦0.35, 0≦d≦0.10, 0≦y<0.05, a+b+c+d=1, Me is at least one element selected from the group consisting of Nb, Zr, Ti, W, Mo, Si and Al), and is a secondary particle formed by the aggregation of primary particles, the sulfonic acid compound is present on the surface of the secondary particle, the P compound is present at least at the interface between the primary particles, and in the elemental concentration distribution of the cross-section of the secondary particle using time-of-flight secondary ion mass spectrometry, PO inside the secondary particle ３－ A positive electrode active material for non-aqueous electrolyte secondary batteries, having a Gini coefficient of 0.6 or less.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein A is a Group 1 element.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein A is Li.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein R is an alkyl group.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein R is a methyl group.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the mass of the sulfonic acid compound is 0.05% by mass or more and 1.5% by mass or less, relative to the mass of the lithium transition metal composite oxide.

7. In the infrared absorption spectrum, at least one absorption peak is present at or around 1238 cm －１ , 1175 cm －１ , 1065 cm －１ , 785 cm －１ The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which has an absorption peak at at least one place around it.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the mass of the P compound is 0.0003% by mass or more and 0.35% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide.

9. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material 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 firing step of mixing a Ni metal compound containing 65 mol% or more Ni relative to the total molar amount of metal elements with a Li compound and 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 a drying step of heating and drying the cake-like composition, wherein an aqueous solution containing a P compound in an amount of 0.0008% by mass or more and 2.0% by mass or less relative to the mass of lithium transition metal composite oxide, and at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition in the washing step.

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