Method for producing positive electrode active material for secondary battery

Abstract

This method for producing a positive electrode active material for a secondary battery is characterized by comprising: a water washing step for washing a Ni-containing lithium transition metal oxide by stirring a slurry obtained by mixing the Ni-containing lithium transition metal oxide with water or an aqueous solution; a solid-liquid separation step for performing solid-liquid separation on the slurry to obtain a filter cake containing the Ni-containing lithium transition metal oxide; and a drying step in which the cake is dried, and in the washing step, a sulfonic acid compound represented by general formula (I) (in general formula (I), A is H, Li, or Na, and R is H or a hydrocarbon group) is added to the slurry. # imgabs0 #

Description

Technical Field

[0001] The present disclosure relates to a method for producing a positive electrode active material for a secondary battery. Background Art

[0002] From the perspective of achieving high battery capacity, the lithium transition metal oxide used as a positive electrode active material for a secondary battery preferably contains Ni, for example. However, if a lithium transition metal oxide containing Ni is used as a positive electrode active material for a secondary battery, the reaction resistance of the positive electrode may increase, thereby increasing the DC resistance of the battery.

[0003] Conventional technology has been known to improve battery characteristics, such as reducing DC resistance, by attaching sulfonic acid compounds to the surface of lithium transition metal oxide particles. For example, Patent Document 1 discloses a positive electrode active material comprising a lithium salt of an acid having a structure represented by the general formula: X1-R-X2 (where X1 and X2 may be sulfonic groups (-SO3H)) dispersed on the surface of lithium transition metal oxide particles.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-169286 Summary of the Invention

[0007] As described above, secondary battery positive electrode active materials having a sulfonic acid compound attached to the surface of lithium transition metal oxide particles are known, but methods for producing the same have not yet been established. Simply adding the sulfonic acid compound to the lithium transition metal oxide to attach the sulfonic acid compound to the surface of the lithium transition metal oxide particles does not result in a sufficient amount of the sulfonic acid compound attached to the surface of the lithium transition metal oxide particles.

[0008] Therefore, an object of the present disclosure is to provide a method for producing a positive electrode active material for a secondary battery, which can increase the amount of sulfonic acid compound attached to the surface of Ni-containing lithium transition metal oxide particles.

[0009] A method for producing a positive electrode active material for a secondary battery according to one embodiment of the present disclosure is characterized by comprising: a water washing step of stirring a slurry obtained by mixing a Ni-containing lithium transition metal oxide with water or an aqueous solution, thereby washing the Ni-containing lithium transition metal oxide with water; a solid-liquid separation step of performing solid-liquid separation on the slurry to obtain a filter cake containing the Ni-containing lithium transition metal oxide; and a drying step of drying the filter cake, wherein in the water washing step, a sulfonic acid compound represented by the following general formula (I) is added to the slurry:

[0010] [Chemical Formula 1]

[0011]

[0012] (In the general formula (I), A is H, Li or Na, and R is H or a hydrocarbon group).

[0013] According to one embodiment of the present disclosure, the amount of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles can be increased. DETAILED DESCRIPTION

[0014] The method for producing a positive electrode active material for a secondary battery according to this embodiment comprises: a water washing step in which a slurry obtained by mixing a Ni-containing lithium transition metal oxide with water or an aqueous solution is stirred to wash the Ni-containing lithium transition metal oxide; a solid-liquid separation step in which the slurry is subjected to solid-liquid separation to obtain a filter cake containing the Ni-containing lithium transition metal oxide; and a drying step in which the filter cake is dried. The method for producing a positive electrode active material for a secondary battery according to this embodiment is described in detail below, step by step.

[0015] (Washing process)

[0016] The water washing step involves stirring a slurry obtained by mixing the Ni-containing lithium transition metal oxide with water or an aqueous solution to wash the Ni-containing lithium transition metal oxide. Furthermore, during the water washing step, a sulfonic acid compound, described below, is added to the slurry. This allows the sulfonic acid compound to adhere to the surface of the Ni-containing lithium transition metal oxide particles.

[0017] Sometimes, lithium compounds (e.g., lithium carbonate, etc.) used during synthesis remain in an unreacted state on the surface of the Ni-containing lithium transition metal oxide particles before the water washing step. However, by implementing the water washing step, the unreacted lithium compounds and the like remaining on the surface of the Ni-containing lithium transition metal oxide particles can be removed. As a result, the number of pores on the surface of the Ni-containing lithium transition metal oxide particles and the surface area of the particles increase, thereby promoting the adhesion of the sulfonic acid compound to the surface of the Ni-containing lithium transition metal oxide particles. Therefore, by adding the sulfonic acid compound in the water washing step, the amount of sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles can be increased. For example, sulfonic acid compounds of more than 80% by mass of the total amount of sulfonic acid compounds added to the slurry can be attached to the surface of the Ni-containing lithium transition metal oxide particles.

[0018] The Ni-containing lithium transition metal oxide can be obtained using a known technique. For example, it can be obtained by mixing a Ni composite hydroxide obtained by coprecipitating (crystallizing) metal elements other than lithium constituting the Ni-containing lithium transition metal oxide, or a Ni composite oxide obtained by further heat-treating the Ni composite hydroxide, with a lithium compound, and then calcining the resulting lithium mixture. Examples of the lithium compound include lithium carbonate and lithium hydroxide.

[0019] The lithium transition metal oxide containing Ni may contain other elements in addition to Ni and Li. Examples of other elements include Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Examples of lithium transition metal oxides containing Ni include the general formula: Li b Ni 1-x M x O 2＋β (wherein, 0≤x≤0.35, 0.95≤b≤1.20, 0≤β≤0.5, and M is at least one element selected from Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W).

[0020] The sulfonic acid compound is represented by the following general formula (I).

[0021] [Chemical Formula 2]

[0022]

[0023] In general formula (I), A is H, Li, or Na. R is H or a hydrocarbon group. The hydrocarbon group is preferably a hydrocarbon having 1 to 24 carbon atoms. Examples of the hydrocarbon group include alkyl groups, alkenyl groups, and aryl groups. Examples of alkyl groups include methyl, ethyl, propyl (including n-propyl and isopropyl), butyl (including n-butyl, tert-butyl, isobutyl, and sec-butyl), and hexyl (including branched and linear isomers thereof). Examples of alkenyl groups include vinyl, allyl, and hexenyl (including branched and linear isomers thereof). Examples of aryl groups include phenyl, tolyl, xylyl, naphthyl, and benzyl.

[0024] The sulfonic acid compound can be added as a powder or as a solution containing the sulfonic acid compound. The solution containing the sulfonic acid compound is not particularly limited as long as it contains the sulfonic acid compound. Preferably, it is a solution in which the sulfonic acid compound is dissolved in an aqueous alkaline solution such as lithium hydroxide or sodium hydroxide. The concentration of the sulfonic acid compound in the solution containing the sulfonic acid compound is, for example, 0.5 mol / L to 15 mol / L. The pH of the solution containing the sulfonic acid compound can be, for example, in the range of 0.1 to 12, preferably in the range of 7 to 11.

[0025] Water washing can be performed by a known method. For example, a Ni-containing lithium transition metal oxide and water or an aqueous solution are added to a reaction tank equipped with a stirrer and stirred. Furthermore, at a predetermined timing, a sulfonic acid compound powder or a solution containing the sulfonic acid compound is added to the reaction tank and stirred.

[0026] The sulfonic acid compound can be added immediately after the water washing step begins. However, in order to further increase the amount of sulfonic acid compound attached to the surface of the lithium transition metal oxide particles, it is preferably added after the water washing step begins, after the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles reaches 1.5 or less. As the water washing step progresses, the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles decreases. Therefore, in this embodiment, for example, the slurry is periodically collected during the water washing process, the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles is measured, and the sulfonic acid compound is added to the slurry when the atomic concentration ratio of Li / Ni reaches 1.5 or less. Alternatively, the elapsed time of the water washing step and the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles can be measured in a preliminary experiment to determine the time when the molar ratio of Li / Ni reaches 1.5 or less. The atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles can be measured by X-ray photoelectron spectroscopy (XPS).

[0027] For example, the amount of the sulfonic acid compound added is preferably adjusted so that the mass ratio of the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide is 0.05% by mass or greater. If the amount of the sulfonic acid compound added is too small, the coverage of the Ni-containing lithium transition metal oxide particle surface by the sulfonic acid compound is low, and the effect of improving battery characteristics may be reduced.

[0028] In the water washing process, for example, the slurry concentration of the slurry is preferably 500 g / L or more, more preferably 500 g / L or more and 2000 g / L or less. The slurry concentration (g / L) refers to the mass (g) of the Ni-containing lithium transition metal oxide mixed with 1 L of water or aqueous solution. When the slurry concentration is less than 500 g / L, there is a risk that lithium may be washed away excessively from the Ni-containing lithium transition metal oxide, which may sometimes affect the battery characteristics.

[0029] The water washing temperature is, for example, 10°C or more and 40°C or less. In addition, the water washing time is, for example, 5 minutes or more and 60 minutes or less. There is no particular limitation on the water or aqueous solution used. From the viewpoint of removing unreacted lithium compounds remaining on the particle surface of the Ni-containing lithium transition metal oxide, for example, water with a conductivity less than 10 μS / cm in conductivity measurement is preferred, and water with 1 μS / cm or less is more preferred. In addition, when washing with an aqueous solution other than water, water can be further used for washing afterwards to reduce the amount of impurities contained in the aqueous solution.

[0030] (Solid-liquid separation process)

[0031] The solid-liquid separation process is a process of performing solid-liquid separation on the slurry to obtain a filter cake containing the Ni-containing lithium transition metal oxide. The method of solid-liquid separation is not particularly limited and is carried out using commonly used devices and methods. For example, a suction filter, a centrifuge, a filter press, etc. are used. The water content of the filter cake obtained by solid-liquid separation is, for example, 2.0 mass% or more and 10 mass% or less.

[0032] (Drying process)

[0033] The drying process is a process of drying the filter cake containing the Ni-containing lithium transition metal oxide obtained through the solid-liquid separation process. In the drying process, for example, from the aspect of suppressing the deterioration of battery characteristics when used as a positive electrode active material for a secondary battery, it is preferred to dry the filter cake containing the Ni-containing lithium transition metal oxide until the water content of the filter cake becomes 1.0 mass% or less. The drying treatment conditions are, for example, preferably drying at a temperature of 100°C or more and 250°C or less in an oxygen atmosphere or a vacuum atmosphere. The drying time is, for example, preferably set to 0.5 hours or more.

[0034] For the positive electrode active material obtained by such a manufacturing method, it is preferred to perform a screening treatment for removing coarse particles as needed. Thereby, a positive electrode active material adjusted to a specified particle size can be obtained. As the device used in the screening treatment, for example, a vibrating screen, a centrifugal classification device, etc. can be cited. In addition, the positive electrode active material before the screening treatment can be crushed using a roll mill or the like as needed. Crushing means dispersing or loosening (Japanese: 解きほぐす) the aggregated particles.

[0035] Secondary batteries using the positive electrode active material produced using the above-described manufacturing method are obtained by, for example, stacking or winding electrodes (positive and negative electrodes) and a separator, creating an electrode assembly, housed together with an electrolyte in a container such as a battery can or laminate. The positive electrode, negative electrode, separator, and electrolyte are described below.

[0036] The electrolyte has, for example, ion conductivity (eg, lithium ion conductivity) and may be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0037] The liquid electrolyte (electrolyte) comprises, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents thereof. The non-aqueous solvent may contain a halogen-substituted product (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6.

[0038] In addition, as a solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. The polymer electrolyte, for example, contains a lithium salt and a matrix polymer, or contains 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 to undergo gelation is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc. As an inorganic solid electrolyte, for example, well-known materials in 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. It should be noted that the electrolytes exemplified above are non-aqueous electrolytes, but the electrolyte is not limited to non-aqueous electrolytes and may also be aqueous electrolytes.

[0039] The positive electrode has a positive electrode collector and a positive electrode mixture layer formed on the positive electrode collector. The positive electrode mixture layer is preferably formed on both sides of the positive electrode collector. The positive electrode collector can use a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, a film in which the metal is arranged on the surface, etc. The positive electrode mixture layer contains a positive electrode active material produced by the above-mentioned manufacturing method. In addition, the positive electrode mixture layer may contain a binder, a conductive agent, etc. The positive electrode can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. on the positive electrode collector, drying the coating film, and then rolling it to form a positive electrode mixture layer on the positive electrode collector.

[0040] Examples of the conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, and graphite, etc. These may be used alone or in combination of two or more.

[0041] As binders, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO) can be used in combination. These can be used alone or in combination of two or more.

[0042] The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The negative electrode current collector can use a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode, or a film in which the metal is arranged on the surface. The negative electrode mixture layer contains, for example, a negative electrode active material, a binder, etc. The negative electrode can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on the negative electrode current collector, drying the coating, and then rolling it to form a negative electrode mixture layer on the negative electrode current collector.

[0043] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and carbon-based active materials such as graphite are generally used. Graphite can be any of natural graphites such as flaky graphite, block graphite, and earthy graphite, block artificial graphite, and artificial graphites such as graphitized mesophase carbon microbeads. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. can also be used. As negative electrode active materials other than carbon-based active materials, silicon-based active materials are preferred. As silicon-based active materials, for example, SiO x (0.5≤x≤1.6) Si-containing compound, or Li 2y SiO （2＋y） A Si-containing compound represented by (0<y<2) in which Si fine particles are dispersed in a lithium silicate phase. The content of the silicon-based active material in the negative electrode mixture layer is, for example, preferably 1% by mass to 15% by mass, and more preferably 5% by mass to 10% by mass, relative to the total mass of the negative electrode active material.

[0044] The binder contained in the negative electrode mixture layer may be the same binder as that for the positive electrode. Furthermore, the negative electrode mixture layer may contain a conductive agent. The conductive agent may be the same as that for the positive electrode.

[0045] The separator can be, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. Suitable materials for the separator include olefin resins such as polyethylene and polypropylene, and cellulose. The separator can be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, it can be a multilayer separator comprising a polyethylene layer and a polypropylene layer, or a separator coated with materials such as an aramid resin and ceramics on the surface of the separator.

[0046] Example

[0047] Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.

[0048] <Example 1>

[0049] The Ni-containing lithium transition metal oxide (LiNi 0.9 Co 0.05 Mn 0.05 A slurry (slurry concentration of 1000 g / L) obtained by mixing 100 g of lithium hydroxide (LiOH) with 100 mL of pure water was stirred and a water washing process was performed for 30 minutes. The Ni-containing lithium transition metal oxide was obtained by mixing an oxide with Ni as the main component with lithium hydroxide and then firing it. 15 minutes after the start of the water washing process, a solution containing a sulfonic acid compound was added. The solution containing the sulfonic acid compound was prepared by adding 100 g of methanesulfonic acid to a LiOH neutralized solution obtained by dissolving 44 g of lithium hydroxide monohydrate in 200 g of pure water. Moreover, the atomic concentration ratio of Li / Ni on the particle surface of the Ni-containing lithium transition metal oxide when the solution containing the sulfonic acid compound was added was 1.0. In addition, the solution containing the sulfonic acid compound was added to the slurry so that the ratio of the mass of the sulfonic acid compound in the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide became 0.75% by mass.

[0050] The washed slurry was subjected to solid-liquid separation to obtain a filter cake containing Ni-containing lithium transition metal oxide. The obtained filter cake was heated to 200°C in a vacuum dryer and dried for 5 hours. The moisture content of the dried filter cake was 0.05% by mass.

[0051] The dried filter cake was crushed using a roll mill or the like, and then passed through a sieve with a mesh size of 100 μm to remove coarse particles, thereby obtaining a positive electrode active material.

[0052] The amount (yield) of the sulfonic acid compound adhering to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 1 was measured and found to be 82%. This amount (yield) of the sulfonic acid compound adhering to the positive electrode active material was calculated using the formula: "amount of sulfonic acid compound adhering to the positive electrode active material / amount of sulfonic acid compound added." The amount of sulfonic acid compound adhering to the positive electrode active material was analyzed using high-frequency inductively coupled plasma (ICP).

[0053] [Production of positive electrode]

[0054] A positive electrode mixture slurry with a solid content of 70% was prepared by mixing the positive electrode active material, acetylene black (a conductive material), and polyvinylidene fluoride (a binder) in a mass ratio of 98:1:1. This slurry was applied to both sides of a 15μm-thick aluminum foil. After drying, the coated film was rolled using a calendar roll to produce a positive electrode with a positive electrode active material layer formed on both sides of the positive electrode current collector.

[0055] [Production of negative electrode]

[0056] Graphite powder (negative electrode active material), carboxymethyl cellulose (CMC) (binder), and styrene butadiene rubber (SBR) were mixed at a mass ratio of 98:1:1. An appropriate amount of water was added to this mixture to prepare a negative electrode mixture slurry. This slurry was applied to both sides of an 8μm-thick copper foil. After drying, the coated film was rolled using a calendar roll to produce a negative electrode with negative electrode active material layers formed on both sides of the negative electrode current collector.

[0057] [Preparation of non-aqueous electrolyte]

[0058] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:3 by volume ratio), and dissolving LiPF6 at a concentration of 1 mol / L.

[0059] [Fabrication of non-aqueous electrolyte secondary batteries]

[0060] After attaching leads to the positive and negative electrodes, the electrodes are wound with a separator between them to create a wound electrode assembly. This electrode assembly is then inserted into the casing body, and the negative electrode lead is welded to the bottom surface of the casing body. Next, the positive electrode lead is welded to the sealing member. A non-aqueous electrolyte is then injected into the casing body, and the open end of the casing body is sealed with the sealing member via a gasket, creating a non-aqueous electrolyte secondary battery.

[0061] <Example 2>

[0062] A positive electrode active material was produced in the same manner as in Example 1, except that a slurry (slurry concentration of 1500 g / L) prepared by mixing 150 g of Ni-containing lithium transition metal oxide and 100 mL of pure water was stirred during the water washing step. The atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles when the solution containing the sulfonic acid compound was added was 1.1. Furthermore, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 2 was 88%. A non-aqueous electrolyte secondary battery was produced using this positive electrode active material in the same manner as in Example 1.

[0063] <Example 3>

[0064] As a Ni-containing lithium transition metal oxide obtained by mixing an oxide containing Ni as a main component with lithium hydroxide and then firing, LiNi 0.9 Co 0.05 Al 0.05 A positive electrode active material was prepared in the same manner as in Example 1, except that the solution containing the sulfonic acid compound was added. It should be noted that the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles was 1.1 when the solution containing the sulfonic acid compound was added. Furthermore, in the positive electrode active material obtained in Example 3, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles was 82%. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1.

[0065] <Example 4>

[0066] As a Ni-containing lithium transition metal oxide obtained by mixing an oxide containing Ni as a main component with lithium hydroxide and then firing, LiNi 0.9 Co 0.05 Al 0.05 A positive electrode active material was prepared in the same manner as in Example 1, except that a slurry (slurry concentration of 1500 g / L) prepared by mixing 150 g of Ni-containing lithium transition metal oxide with 100 mL of pure water was stirred in the water washing step. It should be noted that the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles when the solution containing the sulfonic acid compound was added was 1.2. Furthermore, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 4 was 86%. A non-aqueous electrolyte secondary battery was prepared using this positive electrode active material in the same manner as in Example 1.

[0067] <Example 5>

[0068] A positive electrode active material was produced in the same manner as in Example 1, except that a slurry (slurry concentration of 500 g / L) prepared by mixing 50 g of Ni-containing lithium transition metal oxide with 100 mL of pure water was stirred during the water washing step. The atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles when the solution containing the sulfonic acid compound was added was 1.2. Furthermore, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 5 was 59%. A non-aqueous electrolyte secondary battery was produced using this positive electrode active material in the same manner as in Example 1.

[0069] <Example 6>

[0070] A positive electrode active material was produced in the same manner as in Example 1, except that a solution containing a sulfonic acid compound was added 2 minutes after the start of the water washing step. The atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles at the time of addition of the solution containing the sulfonic acid compound was 2.0. Furthermore, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 6 was 25%. A non-aqueous electrolyte secondary battery was produced using this positive electrode active material in the same manner as in Example 1.

[0071] <Example 7>

[0072] A positive electrode active material was produced in the same manner as in Example 2, except that sulfonic acid compound powder was added to the slurry during the water washing step. The atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles when the sulfonic acid compound powder was added was 1.1. Furthermore, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in the positive electrode active material obtained in Example 7 was 85%. A non-aqueous electrolyte secondary battery was produced using this positive electrode active material in the same manner as in Example 1.

[0073] <Comparative Example 1>

[0074] Ni-containing lithium transition metal oxide (LiNi) is obtained by mixing an oxide containing Ni as the main component with lithium hydroxide and then firing the mixture. 0.9 Co 0.05 Mn 0.05A solution containing a sulfonic acid compound was added to the solution (O2). That is, the solution containing the sulfonic acid compound was added without a water washing step. The solution was then passed through a 100 μm sieve to remove coarse particles, yielding a positive electrode active material. In the positive electrode active material obtained in Comparative Example 1, the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles was 11%. Using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0075] Comparative Example 2

[0076] The Ni-containing lithium transition metal oxide (LiNi) is obtained by mixing an oxide containing Ni as the main component with lithium hydroxide and then firing it. 0.9 Co 0.05 Mn 0.05 O2) was used as the positive electrode active material of Comparative Example 2. That is, no sulfonic acid compound was added in Comparative Example 2. Using this positive electrode active material, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0077] [Charge and discharge test]

[0078] The nonaqueous electrolyte secondary batteries of each Example and Comparative Example were charged at a constant current of 0.5 C at a temperature of 25°C until the battery voltage reached 4.2 V. They were then discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. The charge and discharge capacities at these times were measured, and the charge and discharge efficiency was calculated using the following formula.

[0079] Charge and discharge efficiency = (discharge capacity / charge capacity) × 100

[0080] Table 1 summarizes the production conditions for the positive electrode active material in each Example and Comparative Example. Table 2 summarizes the results of the amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles and the charge-discharge efficiency for each Example and Comparative Example. Note that the charge-discharge efficiency is reported relative to the value of Comparative Example 1 (1.00).

[0081] [Table 1]

[0082]

[0083] [Table 2]

[0084]

[0085] The amount (yield) of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles in Examples 1 to 7 was higher than that in Comparative Example 1. This suggests that adding the sulfonic acid compound during the water-washing step of the Ni-containing lithium transition metal oxide can increase the amount of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles. Furthermore, when comparing Examples 1 to 7, the amount of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles was higher in Examples 1 to 5, in which the sulfonic acid compound was added after the Li / Ni atomic concentration ratio on the surface of the Ni-containing lithium transition metal oxide reached 1.5 or less, compared to Example 6, in which the sulfonic acid compound was added before the Li / Ni atomic concentration ratio reached 1.5 or less.

[0086] From the viewpoint of battery characteristics, Examples 1 to 6 in which the amount of the sulfonic acid compound attached to the surface of the Ni-containing lithium transition metal oxide particles was high showed higher charge and discharge efficiency than Comparative Examples 1 and 2.

[0087] [Note] (1)

[0089] A method for producing a positive electrode active material for a secondary battery, comprising:

[0090] A water washing step of stirring a slurry obtained by mixing the Ni-containing lithium transition metal oxide with water or an aqueous solution to wash the Ni-containing lithium transition metal oxide with water;

[0091] a solid-liquid separation step of performing solid-liquid separation on the slurry to obtain a filter cake containing the Ni-containing lithium transition metal oxide; and

[0092] Drying process, drying the filter cake,

[0093] In the water washing step, a sulfonic acid compound represented by the following general formula (I) is added to the slurry.

[0094] [Chemical Formula 3]

[0095]

[0096] (In the general formula (I), A is H, Li or Na, and R is H or a hydrocarbon group). (2)

[0098] The method for producing a positive electrode active material for a secondary battery according to (1), wherein the sulfonic acid compound is added to the slurry after the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide becomes 1.5 or less in the water washing step. (3)

[0100] The method for producing a cathode active material for a secondary battery according to (1) or (2), wherein the slurry concentration is 500 g / L or more. (4)

[0102] The method for producing a positive electrode active material for a secondary battery according to any one of (1) to (3), wherein in the drying step, the filter cake is dried until the water content of the filter cake becomes 0.05% by mass or less. (5)

[0104] The method for producing a positive electrode active material for a secondary battery according to any one of (1) to (4), wherein 80% by mass or more of the sulfonic acid compound based on the total amount of the sulfonic acid compound added to the slurry is adhered to the surface of the Ni-containing lithium transition metal oxide.

Claims

1. A method for producing a positive electrode active material for a secondary battery, comprising: a water washing step of stirring a slurry obtained by mixing the Ni-containing lithium transition metal oxide with water or an aqueous solution, thereby washing the Ni-containing lithium transition metal oxide with water; a solid-liquid separation step of performing solid-liquid separation on the slurry to obtain a filter cake containing the Ni-containing lithium transition metal oxide; as well as Drying process, drying the filter cake, In the water washing step, a sulfonic acid compound represented by the following general formula (I) is added to the slurry. (*Please consider the subtle difference between adding solution or powder.) In the general formula (I), A is H, Li or Na, and R is H or a hydrocarbon group.

2. The method for producing a positive electrode active material for a secondary battery according to claim 1, wherein: In the water washing step, the sulfonic acid compound is added to the slurry after the atomic concentration ratio of Li / Ni on the surface of the Ni-containing lithium transition metal oxide particles becomes 2.0 or less.

3. The method for producing a positive electrode active material for a secondary battery according to claim 1 or 2, wherein: The slurry concentration of the slurry is 500 g / L or more.

4. The method for producing a positive electrode active material for a secondary battery according to claim 1 or 2, wherein: In the drying step, the filter cake is dried until the moisture content of the filter cake becomes 0.05% by mass or less.

5. The method for producing a positive electrode active material for a secondary battery according to claim 1 or 2, wherein: 80 mass % or more of the sulfonic acid compound based on the total amount of the sulfonic acid compound added to the slurry adheres to the surface of the particles of the Ni-containing lithium transition metal oxide.

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