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 stirring a slurry obtained by mixing a 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; an addition step for adding a solution containing a sulfonic acid compound to the filter cake; a mixing step in which the filter cake and the solution containing the sulfonic acid compound are mixed; and a drying step for drying a mixture containing the filter cake and the solution containing the sulfonic acid compound, the water content of the filter cake obtained by the solid-liquid separation step being 3 mass% or more, and the sulfonic acid compound being represented by general formula (I) [Chemical Formula 1] # imgabs0 # (in general formula (I), A is H, Li, or Na, and R is H or a hydrocarbon group).

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 mentioned above, secondary battery positive electrode active materials with sulfonic acid compounds attached to the surface of lithium transition metal oxide particles are known, but methods for their production have not yet been established. Therefore, even when using positive electrode active materials with sulfonic acid compounds attached to the surface of lithium transition metal oxide particles, the discharge capacity and charge-discharge efficiency of the battery are sometimes reduced. This is believed to be because when manufacturing positive electrode active materials with sulfonic acid compounds attached to the surface of lithium transition metal oxide particles, the sulfonic acid compounds cannot be dispersed and attached to the entire lithium transition metal oxide, and the sulfonic acid compounds are concentrated in a portion of the lithium transition metal oxide.

[0008] Therefore, the object of the present disclosure is to provide a method for producing a positive electrode active material for a secondary battery, wherein a sulfonic acid compound is attached to the surface of lithium transition metal oxide particles, thereby obtaining a positive electrode active material for a secondary battery that can suppress the reduction in the discharge capacity and charge-discharge efficiency of the battery.

[0009] A method for manufacturing 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 to wash the Ni-containing lithium transition metal oxide; 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; an addition step of adding a solution containing a sulfonic acid compound to the filter cake; a mixing step of mixing the filter cake with the solution containing the sulfonic acid compound; and a drying step of drying a mixture containing the filter cake and the solution containing the sulfonic acid compound. The water content of the filter cake obtained through the solid-liquid separation step is 3% by mass or more, and the sulfonic acid compound is represented by the following general formula (I),

[0010] [Chemical formula 1]

[0011]

[0012] (In 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, a positive electrode active material for a secondary battery capable of suppressing a decrease in discharge capacity and charge-discharge efficiency of the battery can be obtained. Detailed Embodiments

[0014] The method for manufacturing a positive electrode active material for a secondary battery of the present embodiment comprises: a water washing step of stirring a slurry obtained by mixing a Ni-containing lithium transition metal oxide with water or an aqueous solution to wash the Ni-containing lithium transition metal oxide; 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; an addition step of adding a solution containing a sulfonic acid compound to the filter cake; a mixing step of mixing the filter cake with the solution containing the sulfonic acid compound; and a drying step of drying a mixture containing the filter cake and the solution containing the sulfonic acid compound. Hereinafter, each step of the method for manufacturing a positive electrode active material for a secondary battery of the present embodiment will be described in detail.

[0015] (Water Washing Step)

[0016] The water washing step is a step of stirring a slurry obtained by mixing a Ni-containing lithium transition metal oxide with water or an aqueous solution to wash the Ni-containing lithium transition metal oxide.

[0017] Sometimes, lithium compounds (such as lithium carbonate, etc.) used in synthesis remain on the particle surface of Ni-containing lithium transition metal oxides in an unreacted state before the water washing process. However, by performing the water washing process, the unreacted lithium compounds remaining on the particle surface of the Ni-containing lithium transition metal oxides can be removed. As a result, the number of pores on the particle surface of the Ni-containing lithium transition metal oxides and the surface area of the particles increase. Therefore, in the subsequent addition process of adding a solution containing a sulfonic acid compound, the attachment of the sulfonic acid compound to the particle surface of the Ni-containing lithium transition metal oxides can be promoted.

[0018] The Ni-containing lithium transition metal oxides can be substances obtained by using known techniques. For example, they can be obtained as follows: After mixing a Ni composite hydroxide obtained by co-precipitating (crystallizing) metal elements other than lithium that constitute the Ni-containing lithium transition metal oxides, or a Ni composite oxide obtained by further heat-treating the Ni composite hydroxide, with a lithium compound, the resulting lithium mixture is fired. Examples of the lithium compound include lithium carbonate, lithium hydroxide, etc.

[0019] The Ni-containing lithium transition metal oxides can contain elements other than 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, W, etc. Examples of the Ni-containing lithium transition metal oxides include the general formula: Li b Ni 1-x M x O 2＋β (where 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, W) of the oxide.

[0020] The water washing can be a well-known method. For example, a lithium transition metal oxide containing Ni and water or an aqueous solution are put into a reaction tank with a stirring device, and they are stirred. As the water washing process proceeds, the molar ratio of Li / Ni on the particle surface of the lithium transition metal oxide containing Ni decreases. It is preferred to carry out the water washing process until the molar ratio of Li / Ni becomes 1.5 or less. Thereby, in the subsequent addition step of adding a solution containing a sulfonic acid compound, the attachment of the sulfonic acid compound to the particle surface of the lithium transition metal oxide containing Ni can be promoted. In the present embodiment, for example, the slurry during water washing can be periodically sampled, and the molar ratio of Li / Ni on the particle surface of the lithium transition metal oxide containing Ni can be measured. Additionally, alternatively, the elapsed time of the water washing process and the molar ratio of Li / Ni on the particle surface of the lithium transition metal oxide containing Ni can be measured through preliminary experiments, and the time when the molar ratio of Li / Ni becomes 1.5 or less can be obtained in advance. The molar ratio of Li / Ni on the surface of the lithium transition metal oxide containing Ni can be measured by X-ray photoelectron spectroscopy (XPS).

[0021] 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 lithium transition metal oxide containing Ni mixed with 1 L of water or an aqueous solution. When the slurry concentration is less than 500 g / L, there is a risk that lithium is washed away excessively from the lithium transition metal oxide containing Ni, which may sometimes affect the battery characteristics.

[0022] The water washing temperature is, for example, 10°C or more and 40°C or less. Additionally, 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 lithium transition metal oxide containing Ni, 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. Additionally, 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.

[0023] (Solid-liquid separation process)

[0024] The solid-liquid separation step is a step of subjecting the slurry to solid-liquid separation to obtain a filter cake containing 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 3.0% by mass or more. When the water content of the filter cake is 3.0% by mass or more, in the subsequent addition step of adding a solution containing a sulfonic acid compound, the solution containing the sulfonic acid compound penetrates into the water in the filter cake and diffuses throughout the filter cake. That is, the case where the sulfonic acid compound is concentrated in a part of the lithium transition metal oxide is suppressed, and it is dispersed throughout the lithium transition metal oxide and adheres to the surface of its particles.

[0025] In addition, the water content of the filter cake obtained by solid-liquid separation is preferably 3% by mass or more and 10% by mass or less. The filter cake is usually transported to the next step by a belt conveyor, but if the water content of the filter cake exceeds 10% by mass, the filter cake may adhere to the belt conveyor, resulting in a reduction in the transportability of the belt conveyor.

[0026] (Addition step)

[0027] The addition step is a step of adding a solution containing a sulfonic acid compound to the filter cake after solid-liquid separation. Thereby, the sulfonic acid compound can be made to adhere to the surface of the particles of the lithium transition metal oxide. The method of adding the solution containing the sulfonic acid compound to the filter cake can be any method. For example, in the case of transporting the filter cake, commonly used transport devices such as a belt conveyor, a ladder conveyor, a screw conveyor, etc. can be used, and a solution containing a sulfonic acid compound can also be added to the filter cake being transported using the transport device. In addition, a solution containing a sulfonic acid compound can also be added while charging the filter cake into a mixer, etc. It should be noted that the mixer is used in the subsequent mixing step.

[0028] The sulfonic acid compound in the solution containing the sulfonic acid compound is represented by the following general formula (I).

[0029] [Chemical formula 2]

[0030]

[0031] In the general formula (I), A is H, Li or Na. R is H or a hydrocarbon group. The hydrocarbon group is preferably, for example, a hydrocarbon having 1 to 24 carbon atoms. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, an aryl group, etc. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group (including a n-propyl group and an isopropyl group), a butyl group (including a n-butyl group, a tert-butyl group, an isobutyl group and a sec-butyl group), and a hexyl group (including their branched and linear isomers). Examples of the alkenyl group include a vinyl group, an allyl group, a hexenyl group (including their branched and linear isomers). Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, etc.

[0032] The solution containing a sulfonic acid compound is not particularly limited as long as it contains a sulfonic acid compound, and a solution in which a sulfonic acid compound is dissolved in an aqueous alkali solution such as lithium hydroxide or sodium hydroxide is preferred. 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.

[0033] Preferably, the addition amount of the solution containing the sulfonic acid compound is adjusted so that, for example, the ratio of the mass of the sulfonic acid compound in the solution to the mass of the Ni-containing lithium transition metal oxide is 0.05% by mass or more. If the addition amount of the solution containing the sulfonic acid compound is too small, the coverage rate of the sulfonic acid compound on the particle surface of the Ni-containing lithium transition metal oxide is low, and the effect of improving battery characteristics may sometimes be small.

[0034] (Mixing step)

[0035] The mixing step is a step of mixing the filter cake with the solution containing the sulfonic acid compound. Here, the mixing method is not particularly limited. For example, the filter cake and the solution containing the sulfonic acid compound are mixed by stirring, vibrating, or shaking them. When mixing the filter cake with the solution containing the sulfonic acid compound, a usual mixer can be used. For example, a shaking mixer, a Loedige mixer, a Julia mixer, a V-type mixer, a drum mixer, a container blender, a Nauta mixer, etc. can be cited.

[0036] The mixing step can be carried out in the above addition step or after the addition step. For example, the solution containing the sulfonic acid compound can be added to the filter cake put into the mixer (i.e., in the addition step), and they can be mixed with the mixer at the same time. In addition, for example, after adding the solution containing the sulfonic acid compound to the filter cake being conveyed by a conveying device such as a belt conveyor or a screw conveyor (i.e., after the addition step), the filter cake and the solution containing the sulfonic acid compound can be mixed by a mixer.

[0037] By combining the addition of the solution containing the sulfonic acid compound to the filter cake having a water content of 3.0% by mass or more and the mixing step, the uneven presence of the sulfonic acid compound in a part of the Ni-containing lithium transition metal oxide is further suppressed. That is, the sulfonic acid compound can be dispersed throughout the lithium transition metal oxide and adhere to its surface. Therefore, according to the manufacturing method of the present embodiment, a positive electrode active material in which the uneven presence of the sulfonic acid compound is suppressed can be obtained. And it is considered that by using this positive electrode active material to fabricate a positive electrode, the low resistance of the positive electrode can be achieved, which is related to suppressing the decrease in discharge capacity and charge-discharge efficiency.

[0038] The mixing step is preferably performed for 5 minutes or longer. By performing the mixing step for 5 minutes or longer, for example, the dispersibility of the sulfonic acid compound can be further improved.

[0039] (Drying process)

[0040] The drying step is a step of drying the mixture comprising the filter cake and the solution containing the sulfonic acid compound (i.e., the mixture of the Ni-containing lithium transition metal oxide and the solution containing the sulfonic acid compound). In the drying step, for example, to suppress degradation of battery characteristics when used as a positive electrode active material for a secondary battery, the mixture is preferably dried until the moisture content is 1.0% by mass or less. Drying conditions are preferably, for example, drying at a temperature of 100°C to 250°C in an oxygen atmosphere or a vacuum atmosphere. The drying time is preferably set to, for example, 0.5 hours or longer.

[0041] The positive electrode active material obtained by such a manufacturing method is preferably subjected to a screening treatment to remove coarse particles as needed. This allows the positive electrode active material to be adjusted to a predetermined particle size. Examples of devices used in the screening treatment include a vibrating screen and a centrifugal classifier. Furthermore, the positive electrode active material before screening can be crushed using a jet mill, a roller mill, a mass colloider, or the like as needed. Crushing refers to the dispersion or loosening of agglomerated particles (Japanese: 解きほぐす).

[0042] 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.

[0043] The electrolyte has, for example, ion conductivity (eg, lithium ion conductivity) and may be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0044] 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.

[0045] In addition, as the solid electrolyte, for example, a solid or gel polymer electrolyte, an inorganic solid electrolyte, etc. can be used. The polymer electrolyte contains, for example, 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 and gels is used. As the polymer material, for example, fluororesin, acrylic resin, polyether resin, etc. can be cited. As the inorganic solid electrolyte, for example, materials well-known 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 can also be an aqueous electrolyte.

[0046] The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The positive electrode mixture layer is preferably formed on both sides of the positive electrode current collector. As the positive electrode current collector, a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, a film having the metal disposed on the surface layer, etc. can be used. The positive electrode mixture layer contains the positive electrode active material produced by the above manufacturing method. In addition, the positive electrode mixture layer can contain a binder, a conductive agent, etc. The positive electrode can be produced, for example, by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. on the positive electrode current collector, drying the coating film, and then performing rolling to form a positive electrode mixture layer on the positive electrode current collector.

[0047] As the conductive agent, carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite, etc. can be exemplified. They can be used alone or in combination of two or more.

[0048] As the binder, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, carboxymethyl cellulose (CMC) or its salts, poly(ethylene oxide) (PEO), etc. can be used in combination. They can be used alone or in combination of two or more.

[0049] 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. As the negative electrode current collector, a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode, a film having the metal disposed on the surface layer, etc. can be used. 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 coating a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on the negative electrode current collector, drying the coating film, and then performing rolling to form a negative electrode mixture layer on the negative electrode current collector.

[0050] As the negative electrode active material contained in the negative electrode mixture layer, there is no particular limitation as long as it can reversibly absorb and release lithium ions, and carbon-based active materials such as graphite are usually used. The graphite can be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, massive artificial graphite, graphitized mesophase carbon microspheres, and other artificial graphites. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium titanium composite oxides can also be used. As the negative electrode active material other than the carbon-based active material, a silicon-based active material is preferred. As the silicon-based active material, for example, a Si-containing compound represented by SiO x (0.5 ≤ x ≤ 1.6), or Li 2y SiO （2＋y） (0 < y < 2), a Si-containing compound in which fine particles of Si 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, more preferably 5% by mass to 10% by mass, based on the total mass of the negative electrode active material.

[0051] Examples of the binder contained in the negative electrode mixture layer are the same as those of the positive electrode. In addition, the negative electrode mixture layer may contain a conductive agent. Examples of the conductive agent are the same as those of the positive electrode.

[0052] The separator is, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous membranes, woven fabrics, non-woven fabrics, etc. As the material of the separator, olefin-based resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. In addition, it may be a multi-layer separator including a polyethylene layer and a polypropylene layer, or a separator in which a material such as an aromatic polyamide-based resin or ceramic is coated on the surface of the separator.

[0053] Examples

[0054] Hereinafter, the present invention will be further described by way of examples, but the present invention is not limited to these examples.

[0055] <Example 1>

[0056] A slurry obtained by mixing 1000 kg of a Ni-containing lithium transition metal oxide (LiNi 0.9 Co 0.05 Al 0.05 O2) and 1000 L of pure water was stirred, and a water washing step of 30 minutes was carried out. The Ni-containing lithium transition metal oxide (LiNi 0.9 Co 0.05 Al 0.05 O2) was obtained by mixing an oxide mainly composed of Ni with lithium hydroxide and then firing.

[0057] The slurry after water washing was subjected to solid-liquid separation using a filter press to obtain a filter cake containing Ni-containing lithium transition metal oxide (solid-liquid separation step). The water content of the obtained filter cake was 4.5% by mass. Then, when the filter cake was transported to the mixer in the next step using a belt conveyor, a solution containing a sulfonic acid compound was added to the filter cake (addition step). The solution containing the sulfonic acid compound used a 33% by mass lithium methanesulfonate aqueous solution prepared by adding 500 g of methanesulfonic acid with a concentration of 98% and dissolving 220 g of lithium hydroxide monohydrate in 1.00 kg of pure water. In addition, the solution containing the sulfonic acid compound was sprayed onto the filter cake so that the ratio of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide became 1.71% by mass.

[0058] Next, the filter cake sprayed with the solution containing the sulfonic acid compound was heated to 200 °C using a vacuum dryer and dried for 5 hours (drying step). The dried powder was sieved through a sieve with a mesh size of 100 μm to remove coarse particles. Thus, a positive electrode active material was obtained.

[0059] [Fabrication of positive electrode]

[0060] The positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride as a binder material were mixed at a mass ratio of 98:1:1 to prepare a positive electrode mixture paste with a solid content of 70%. The paste was coated on both sides of an aluminum foil with a thickness of 15 μm. After drying the coating film, the coating film was calendered using a calender roll, thereby fabricating a positive electrode having a positive electrode active material layer formed on both sides of the positive electrode current collector.

[0061] [Fabrication of negative electrode]

[0062] Graphite powder as a negative electrode active material, carboxymethyl cellulose (CMC) as a binder material, and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 98:1:1. An appropriate amount of water was added to the mixture to prepare a negative electrode mixture paste. The paste was coated on both sides of a copper foil with a thickness of 8 μm. After drying the coating film, the coating film was calendered using a calender roll, thereby fabricating a negative electrode having a negative electrode active material layer formed on both sides of the negative electrode current collector.

[0063] [Preparation of non-aqueous electrolyte]

[0064] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 1:3 in volume ratio), and LiPF6 was dissolved at a concentration of 1 mol / L to prepare a non-aqueous electrolyte.

[0065] [Fabrication of non-aqueous electrolyte secondary battery]

[0066] 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.

[0067] <Example 2>

[0068] A filter cake having a water content of 3.6% by mass was obtained through the solid-liquid separation step. The concentration of lithium methanesulfonate in the solution containing the sulfonic acid compound used in the addition step was set to 90% by mass. The solution containing the sulfonic acid compound was added (sprayed) to the filter cake so that the mass ratio of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 0.70% by mass. The mixing time in the mixing step was set to 300 minutes. A positive electrode active material was then produced in the same manner as in Example 1. A non-aqueous electrolyte secondary battery was then produced using this positive electrode active material in the same manner as in Example 1.

[0069] <Example 3>

[0070] A filter cake having a water content of 9.1% by mass was obtained through the solid-liquid separation step. The concentration of lithium methanesulfonate in the solution containing the sulfonic acid compound used in the addition step was set to 5% by mass. The solution containing the sulfonic acid compound was added (sprayed) to the filter cake so that the mass ratio of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 0.90% by mass. The mixing time in the mixing step was set to 20 minutes. A positive electrode active material was then produced in the same manner as in Example 1. A non-aqueous electrolyte secondary battery was then produced using this positive electrode active material in the same manner as in Example 1.

[0071] <Example 4>

[0072] A filter cake having a water content of 5.8% by mass was obtained through the solid-liquid separation step. The concentration of lithium methanesulfonate in the solution containing the sulfonic acid compound used in the addition step was set to 90% by mass. The solution containing the sulfonic acid compound was added (sprayed) to the filter cake so that the mass ratio of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 0.30% by mass. The mixing time in the mixing step was set to 20 minutes. A positive electrode active material was then produced in the same manner as in Example 1. A non-aqueous electrolyte secondary battery was then produced using this positive electrode active material in the same manner as in Example 1.

[0073] <Example 5>

[0074] As a Ni-containing lithium transition metal oxide obtained by firing a mixture of an oxide mainly composed of Ni and lithium hydroxide, LiNi 0.9 Co 0.05 Mn 0.05 O2 was used. A filter cake with a water content of 5.2% by mass was obtained through a solid-liquid separation process. In the addition process, a solution containing a sulfonic acid compound was added (sprayed) to the filter cake so that the ratio of the mass of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 3.41% by mass. Except for this, a positive electrode active material was produced in the same manner as in Example 1. Then, 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 1>

[0076] A filter cake with a water content of 2.9% by mass was obtained through a solid-liquid separation process. In the solution containing a sulfonic acid compound used in the addition process, the concentration of lithium methanesulfonate was set to 90% by mass. The solution containing the sulfonic acid compound was added (sprayed) to the filter cake so that the ratio of the mass of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 0.30% by mass. The mixing time in the mixing process was set to 20 minutes. Except for this, a positive electrode active material was produced in the same manner as in Example 1. Then, using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0077] <Comparative Example 2>

[0078] A filter cake with a water content of 4.9% by mass was obtained through a solid-liquid separation process. In the addition process, the solution containing the sulfonic acid compound was added (sprayed) to the filter cake so that the ratio of the mass of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide was 1.80% by mass. The mixing process was not carried out. Except for this, a positive electrode active material was produced in the same manner as in Example 1. Then, using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0079] <Comparative Example 3>

[0080] As a Ni-containing lithium transition metal oxide obtained by firing a mixture of an oxide mainly composed of Ni and lithium hydroxide, LiNi 0.9 Co 0.05 Mn 0.05O2, a filter cake with a water content of 6.0 mass% was obtained through a solid-liquid separation process. In the addition process, a solution containing a sulfonic acid compound was added (sprayed) to the filter cake so that the ratio of the mass of the solution containing the sulfonic acid compound to the mass of the Ni-containing lithium transition metal oxide became 1.88 mass%. No mixing process was carried out, and except for this, a positive electrode active material was produced in the same manner as in Example 1. Then, using this positive electrode active material, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0081] <Reference Example>

[0082] The water washing process and the solid-liquid separation process were carried out in the same manner as in Example 1, and a filter cake with a water content of 10.7 mass% was obtained. However, since the filter cake with a water content of 10.7 mass% could not be transported by a belt conveyor, the subsequent processes were aborted. When using a filter cake with a water content exceeding 10 mass%, it is preferable to adopt a transportation method other than a belt conveyor, such as putting it into a container for transportation.

[0083] [Charge and Discharge Test]

[0084] The non-aqueous electrolyte secondary batteries of each Example and each Comparative Example were charged at a constant current of 0.1C until the battery voltage reached 4.2V in a temperature environment of 25°C, and then discharged at a constant current of 0.1C until the battery voltage reached 2.5V. This charge and discharge cycle was carried out 100 times, and the charge capacity and discharge capacity of the 100th cycle were obtained. In addition, the charge and discharge efficiency was calculated by the following formula.

[0085] Charge and discharge efficiency = (Discharge capacity of the 100th cycle / Charge capacity of the 100th cycle) × 100

[0086] The results of the discharge capacity and charge and discharge efficiency of the 100th cycle of Examples 1 to 4 and Comparative Examples 1 to 2 are summarized in Table 1. Among them, regarding the discharge capacity and charge and discharge efficiency in Table 1, based on the value of Comparative Example 1 (100.0), Examples 1 to 4 and Comparative Examples 1 to 2 are recorded in relative values. In addition, the results of the charge and discharge capacity and charge and discharge efficiency of the 100th cycle of Example 5 and Comparative Example 3 are summarized in Table 2. Among them, regarding the discharge capacity and charge and discharge efficiency in Table 2, based on the value of Comparative Example 3 (100.0), Example 5 is recorded in relative values.

[0087] [Table 1]

[0088]

[0089] [Table 2]

[0090]

[0091] Compared with Comparative Examples 1 and 2, Examples 1 to 4 have high discharge capacities and charge-discharge efficiencies in the 100th cycle. In addition, compared with Comparative Example 3, Example 5 has high discharge capacity and charge-discharge efficiency in the 100th cycle. Thus, it can be said that by adding and mixing a solution containing a sulfonic acid compound to a filter cake having a water content of 3% by mass or more obtained by washing with water and solid-liquid separation, a positive electrode active material capable of suppressing a decrease in discharge capacity and charge-discharge efficiency can be obtained.

Claims

1. A method for manufacturing a positive electrode active material for a secondary battery, 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 to wash the Ni-containing lithium transition metal oxide; 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; an addition step of adding a solution containing a sulfonic acid compound to the filter cake; a mixing step of mixing the filter cake with the solution containing the sulfonic acid compound; and a drying step of drying a mixture containing the filter cake and the solution containing the sulfonic acid compound, wherein the water content of the filter cake obtained by the solid-liquid separation step is 3% by mass or more, the sulfonic acid compound is represented by the following general formula (I), in the general formula (I), A is H, Li or Na, and R is H or a hydrocarbon group.

2. The manufacturing method of the positive electrode active material for a secondary battery according to claim 1, wherein, The water content of the filter cake obtained by the solid-liquid separation step is 3% by mass or more and 10% by mass or less.

3. The method for manufacturing a positive electrode active material for a secondary battery according to claim 1 or 2, wherein, The mixing step is carried out for 5 minutes or more.

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