Method for producing recycled cathode active material

Abstract

To efficiently remove components other than cathode active materials from a heated mixture.SOLUTION: A method for producing recycled cathode active material powder comprises the following steps: (1) mixing an activation treatment agent with a cathode composite containing cathode active material powder and a carbon-containing material to obtain a mixture; (2) heating the mixture to obtain a post-heating mixture containing post-heating cathode active material powder; and (3) removing components other than the post-heating cathode active material powder from the post-heating mixture. Step (3) comprises the following sub-steps: (A1) contacting the post-heating mixture or a partially removed mixture with a liquid containing water to obtain slurry S1 containing the post-heating cathode active material powder; (A2) wet-classifying the post-heating cathode active material powder in the slurry S1 to obtain slurry S2 containing the post-heating cathode active material powder with a relatively smaller average particle size and slurry S3 containing the post-heating cathode active material powder with a relatively larger average particle size; and (A3) subjecting the slurry S3 to solid-liquid separation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a recycled positive electrode active material. [Background technology]

[0002] The positive electrode active material of a battery contains rare metal components such as cobalt, nickel, manganese, and lithium, and in particular, compounds containing the above rare metal components as main components are used as the positive electrode active material of non-aqueous electrolyte secondary batteries. In order to conserve the resources of rare metal components, a method for reproducing rare metal components from waste battery materials of secondary batteries is desired.

[0003] For example, Patent Document 1 discloses a method for recovering a positive electrode active material by mixing a positive electrode composite with an activation treatment agent containing an alkali metal compound, heating the mixture to decompose the binder to obtain a heated mixture, adding water to the heated mixture to form a slurry, and then performing solid-liquid separation. This method is cost-effective in that it recovers a positive electrode active material directly from battery waste without using an organic solvent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-186150 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 still leaves room for improvement in terms of efficiently removing components other than the positive electrode active material from the mixture after heating.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for producing a recycled positive electrode active material that can efficiently remove components other than the positive electrode active material from a mixture after heating. [Means for solving the problem]

[0007] [1] (1) A step of mixing a positive electrode active material powder and a positive electrode mixture containing a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; (2) heating the mixture to obtain a heated mixture containing a heated positive electrode active material powder; and (3) A method for producing recycled positive electrode active material powder, comprising a step of removing components other than the heated positive electrode active material powder from the heated mixture, Step (3) is (A1) a sub-step of bringing a liquid containing water into contact with the heated mixture or a partially removed mixture obtained by partially removing components other than the heated positive electrode active material powder from the heated mixture, to obtain a slurry S1 containing the heated positive electrode active material powder; (A2) a sub-step of wet-classifying the heated positive electrode active material powder in the slurry S1 to obtain a slurry S2 containing the heated positive electrode active material powder having a relatively small average particle size and a slurry S3 containing the heated positive electrode active material powder having a relatively large average particle size; and (A3) a sub-step of subjecting the slurry S3 to solid-liquid separation.

[0008] [2] The method according to [1], wherein the substep (A1) is a substep of bringing a liquid containing water into contact with the heated mixture to obtain a slurry S1 containing the heated positive electrode active material powder.

[0009] [3] The method according to [1], wherein the substep (A1) is a substep of bringing a liquid containing water into contact with a partially removed mixture obtained by partially removing components other than the heated positive electrode active material powder from the heated mixture, to obtain a slurry S1 containing the heated positive electrode active material powder.

[0010] [4] The method according to [1] or [2], wherein the wet classification in the sub-step (A2) is carried out using a wet sieve or a wet cyclone. [Effects of the Invention]

[0011] According to the present invention, there is provided a method for producing a recycled positive electrode active material, which can efficiently remove components other than the positive electrode active material from a mixture after heating. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flow diagram of step (3) of one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Method of manufacturing recycled positive electrode active material) A method for producing a recycled positive electrode active material will be described below.

[0014] A method for producing a recycled positive electrode active material according to an embodiment of the present invention includes the following steps. Step (1): A step of mixing a positive electrode mixture containing a positive electrode active material powder and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. Step (2): Heating the mixture to obtain a heated mixture containing a heated positive electrode active material powder. Step (3): Removing components other than the heated positive electrode active material powder from the heated mixture. Step (3) is (A1) a sub-step of bringing a liquid containing water into contact with the heated mixture or the heated mixture from which components other than the heated positive electrode active material powder have been partially removed, to obtain a slurry S1 containing the heated positive electrode active material powder; (A2) a sub-step of wet-classifying the heated positive electrode active material powder in the slurry S1 to obtain a slurry S2 containing the heated positive electrode active material powder having a relatively small average particle size and a slurry S3 containing the heated positive electrode active material powder having a relatively large average particle size; and (A3) a sub-step of subjecting the slurry S3 to solid-liquid separation.

[0015] Each step in this embodiment will be described in detail below.

[0016] Pre-process (A): Positive electrode composite preparation process First, a positive electrode mixture containing a positive electrode active material powder and a carbon-containing material is prepared.

[0017] In the positive electrode mixture, the positive electrode active material powders may be bound together by a binder. The positive electrode mixture may contain an electrolyte and / or a conductive material in addition to the positive electrode active material powder and the binder. When the positive electrode mixture contains a conductive material, the positive electrode active material powder and the conductive material may be bound together by a binder. The electrolyte is a component derived from the electrolyte solution of the battery and impregnated into the positive electrode mixture.

[0018] <Cathode active material> Examples of the positive electrode active material are composite compounds containing lithium, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, yttrium, niobium, molybdenum, silver, indium, tungsten, or the like as constituent elements.

[0019] The positive electrode active material may be composed of only a single compound, or may be composed of a plurality of compounds.

[0020] An example of a suitable positive electrode active material is a composite oxide containing one or more elements selected from the following element group 1 and one or more elements selected from element group 2. Element group 1: Ni, Co, Mn, Fe, Al, P Element group 2: Li, Na, K, Ca, Sr, Ba, Mg

[0021] Among these, the positive electrode active material is preferably represented by the following chemical formula (Formula A).

[0022] Li 1+a M 2 b M 1 M T c O 2+d X e However, M2 represents at least one element selected from the group consisting of Na, K, Ca, Sr, Ba, and Mg, M 1 represents at least one element selected from the group consisting of Ni, Co, Mn, Fe, Al, and P, M T represents at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metallic elements excluding O and P, -0.4 < a < 1.5, 0 ≤ b < 0.5, 0 ≤ c < 0.5, -0.5 < d < 1.5, 0 ≤ e < 0.5 are satisfied.

[0023] M T is preferably at least one element selected from the group consisting of Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, Ca, Sr, Ba, Ge, Cr, Sc, Y, La, Ta, Tc, Ru, Rh, Pd, Ag, Cd, and In. Examples of X are F, S, Cl, Br, I, Se, Te, N.

[0024] The positive electrode active material is preferably a composite oxide containing at least Li and Ni.

[0025] Also, in the positive electrode active material, the molar fraction of Ni in M 1 is more preferably 0.3 to 0.95.

[0026] The crystal structure of the composite oxide as the positive electrode active material is not particularly limited, but a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

[0027] The hexagonal crystal structure is P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P 31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63 , P-6, P6 / m, P63 / m, P622, P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm and P63 / mmc.

[0028] The monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c and C2 / c.

[0029] Furthermore, it is preferable that the compound belongs to the space group R-3m contained in a hexagonal crystal structure or the space group C2 / m contained in a monoclinic crystal structure.

[0030] The crystal structure of the positive electrode active material is identified from a powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα radiation as a radiation source.

[0031] The particle size of the positive electrode active material powder in the positive electrode mixture is not particularly limited, but is typically about 0.001 to 100 μm. The particle size distribution of the positive electrode active material powder can be measured using a laser diffraction / scattering particle size distribution analyzer (e.g., Malvern Instruments Mastersizer 2000). From the obtained particle size distribution, a volume-based cumulative particle size distribution curve can be created, and the particle size (D50) value at 50% cumulative accumulation from the fine particle side can be used as the average particle size of the positive electrode active material powder.

[0032] [Carbon-containing materials] Examples of the carbon-containing material contained in the positive electrode mixture include a binder, a conductive material (carbon-based conductive material), and an electrolyte. When the positive electrode mixture contains a binder, particles of the positive electrode active material may be bound to each other by the binder in the positive electrode mixture.

[0033] <Conductive material> Examples of the conductive material include metal-based conductive materials such as metal particles, and carbon-based conductive materials made of carbon materials.

[0034] Specific examples of the carbon-based conductive material include graphite powder, carbon black (eg, acetylene black), and fibrous carbon materials (eg, graphitized carbon fibers, carbon nanotubes).

[0035] The carbonaceous conductive material may be a single carbon material or may be composed of multiple carbon materials.

[0036] The specific surface area of ​​the carbon material used as the carbon-based conductive material is usually 0.1 to 500 m 2 / g.

[0037] In this case, the conductive material is 30m 2 / g or more, and can be made of only carbon-based conductive materials 2 / g or more of carbon black, 2 / g or more of acetylene black may also be used.

[0038] When an activation treatment agent containing an alkali metal compound having oxidizing power, which will be described later, is used, the rate of oxidation treatment of the carbon-based conductive material can be increased, and even carbon materials with a small specific surface area can sometimes be oxidized.

[0039] <Binding material> Examples of the binder (pre-activation binder) contained in the positive electrode mixture are thermoplastic resins, and specific examples include fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene; and styrene-butadiene copolymers (hereinafter sometimes referred to as SBR); and mixtures of two or more of these may also be used.

[0040] There are no particular limitations on the amounts of the positive electrode active material powder, conductive material, and binder in the positive electrode mixture. The amount of binder can be 0.5 to 30 parts by weight, or may be 1 to 5 parts by weight, per 100 parts by weight of the positive electrode active material powder. The amount of conductive material can be 0, or may be 0 to 50 parts by weight, or may be 1 to 10 parts by weight, per 100 parts by weight of the positive electrode active material powder. The content of the binder in the positive electrode mixture may be within the following ranges relative to 100 parts by mass of the positive electrode active material. The content of the binder may be 0.5 parts by mass or more, 1 part by mass or more, or 2 parts by mass or more. The content of the binder may be 30 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less. From these perspectives, the content of the binder may be 0.5 to 30 parts by mass, 1 to 10 parts by mass, 1 to 5 parts by mass, or 2 to 5 parts by mass. The content of the conductive material in the positive electrode mixture is not particularly limited, but may be within the following ranges relative to 100 parts by mass of the positive electrode active material. The content of the conductive material may be 0 parts by mass or more, more than 0 parts by mass, 1 part by mass or more, 3 parts by mass or more, or 5 parts by mass or more. The content of the conductive material may be 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less. From these perspectives, the content of the conductive material may be 0 to 50 parts by mass, more than 0 parts by mass and 40 parts by mass or less, 1 to 30 parts by mass, 1 to 10 parts by mass, 3 to 20 parts by mass, or 5 to 10 parts by mass.

[0041] In addition to the positive electrode active material and the carbon-containing material, the positive electrode mixture may contain a metal-based conductive material such as metal particles and / or an electrolyte. When the positive electrode mixture contains a binder and a conductive material, the particles of the positive electrode active material and the conductive material may be bound to each other by the binder. The electrolyte is a component derived from the battery's electrolyte solution and impregnated into the positive electrode mixture. The positive electrode mixture may contain a fluorine compound derived from the binder and / or the electrolyte solution (e.g., the electrolyte in the electrolyte solution).

[0042] <Electrolytes> Examples of the electrolyte are LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2F)2, and LiCF3SO3. There are no limitations on the amount of electrolyte contained in the positive electrode mixture, but it can be 0.0005 to 7 mass %.

[0043] The positive electrode mixture may contain a solvent derived from the electrolyte solution, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0044] Such a positive electrode mixture can be obtained by separating and recovering the positive electrode mixture from a waste positive electrode having a current collector and a positive electrode mixture layer.

[0045] "Waste positive electrodes" can refer to positive electrodes recovered from discarded batteries and waste positive electrodes generated during the manufacturing process of positive electrodes and batteries. Discarded batteries can be used batteries or unused, non-standard batteries. Furthermore, waste positive electrodes can be the ends of positive electrodes generated during the battery manufacturing process and non-standard positive electrodes. Furthermore, waste positive electrode composites that are not attached to current collectors and are generated during the positive electrode composite manufacturing process can also be used as the positive electrode composite.

[0046] The waste positive electrode has a current collector made of a metal foil such as aluminum foil or copper foil, and a positive electrode composite layer provided on the current collector. The positive electrode composite layer may be provided on one side or both sides of the current collector.

[0047] Methods for separating the positive electrode composite from a waste positive electrode having a positive electrode composite layer and a current collector include a method of mechanically peeling the positive electrode composite layer from the current collector (e.g., a method of scraping the positive electrode composite from the current collector), a method of penetrating a solvent into the interface between the positive electrode composite layer and the current collector to peel the positive electrode composite layer from the current collector, a method of dissolving the current collector using an alkaline or acidic aqueous solution to separate the positive electrode composite layer, etc. The preferred method is the method of mechanically peeling the positive electrode composite layer from the current collector.

[0048] Pre-process (B): Positive electrode mixture cleaning process Next, when the cathode composite contains an electrolyte, it is preferable to bring the prepared cathode composite into contact with an electrolyte washing solvent to remove at least a portion of the electrolyte from the cathode composite. Specifically, the cathode composite containing the cathode active material powder, the binder, and the electrolyte is brought into contact with the electrolyte washing solvent to obtain a slurry containing a solid component and a liquid component, and then the slurry is separated into the solid component and the liquid component.

[0049] Solid-liquid separation is a process of separating a slurry into a liquid component and a solid component. The solid-liquid separation method may be a conventionally known method, such as filtration or centrifugation.

[0050] The electrolyte cleaning solvent is not particularly limited, and examples thereof include carbonate esters such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate; water; ketones such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone; and alcohols such as ethanol, methanol, propanol, and isopropyl alcohol.

[0051] The cathode mixture can be brought into contact with the electrolyte cleaning solvent in a known powder-liquid contact device, such as a stirring tank.

[0052] In the step of contacting the positive electrode mixture with the electrolyte washing solvent, the positive electrode mixture and the electrolyte washing solvent are preferably stirred to obtain a slurry. The peripheral speed of the tip of the stirring blade can be set to 0.1 to 1.0 m / s.

[0053] In the washing step of the positive electrode composite, after solid-liquid separation, the obtained solid component may be rinsed. Rinsing is an operation in which the obtained solid component is again brought into contact with the electrolyte washing solvent to obtain a slurry, and then the slurry is again separated into a solid component and a liquid component. In washing the positive electrode composite, rinsing may be performed multiple times. The slurry concentration in rinsing can also be the same as above. In rinsing, the slurry can also be stirred as described above.

[0054] The above-mentioned washing process can sufficiently remove the electrolyte from the positive electrode mixture. For example, if the electrolyte remains, the following reaction occurs, causing the structure of the positive electrode active material to change from a layered rock salt structure to a spinel structure. LiPF6+16LiMO2+2O2→6LiF+Li3PO4+8LiM2O4 Furthermore, when lithium carbonate is used as an activator, lithium is consumed by the following reaction: LiPF6+4Li2CO3→6LiF+Li3PO4+4CO2

[0055] The separated solid component can be dried to remove the electrolyte washing solvent by reducing pressure and / or heating, if necessary. The heating temperature can be set to 50 to 200°C.

[0056] Step (1): Activation treatment agent mixing step Next, an activation treatment agent containing one or more alkaline compounds is mixed with the prepared positive electrode mixture to obtain a mixture.

[0057] The method for mixing the positive electrode mixture and the activation treatment agent may be either dry mixing or wet mixing, or a combination of these mixing methods may be used, and the mixing order is not particularly limited.

[0058] During mixing, it is preferable to use a mixer equipped with mixing media such as balls and go through a pulverizing and mixing step, which can improve mixing efficiency.

[0059] Dry mixing is preferred as it allows for simpler mixing. For dry mixing, a V-type mixer, W-type mixer, ribbon mixer, drum mixer, powder mixer equipped with internal stirring blades, ball mill, vibration mill, or a combination of these devices can be used.

[0060] As a mixer used for dry mixing, a powder mixer equipped with an internal stirring blade is preferred, and a specific example is a Loedige Mixer (manufactured by Matsubo Co., Ltd.).

[0061] The activation treatment agent used in this step will be described in detail below.

[0062] <Activation treatment agent> The activation treatment agent contains one or more alkali metal compounds. The activation treatment agent preferably contains at least one compound selected from the group consisting of potassium compounds and sodium compounds. Here, potassium and / or sodium may be referred to as alkali metal element X. In addition to the potassium compound and / or sodium compound, the activation treatment agent may also contain an alkali metal compound containing another alkali metal such as Li.

[0063] When the activation treatment agent comes into contact with the positive electrode active material, the positive electrode active material can be activated. When the alkali metal compound in the activation treatment agent contains a molten portion, the contact between the molten portion and the positive electrode active material is improved, thereby further accelerating the activation of the positive electrode active material.

[0064] Furthermore, the positive electrode mixture may contain a fluorine-containing compound derived from the binder and / or the electrolyte, and by contacting the fluorine-containing compound with the activation treatment agent, the fluorine component is stabilized as an alkali metal fluoride, thereby suppressing the generation of corrosive gases such as hydrogen fluoride. Note that it is desirable to prevent the generation of hydrogen fluoride, as it reduces the activity of the positive electrode active material.

[0065] The proportion of all alkali metal compounds in the activation treatment agent is appropriately set taking into consideration the type of alkali metal compound and the type of target positive electrode active material, but is usually 50% by weight or more, preferably 70% by weight or more (including 100% by weight) of the total weight of the activation treatment agent. The concentration of at least one alkali metal selected from the group consisting of potassium and sodium among the alkali metals contained in the alkali metal compound can be adjusted arbitrarily within the range of 0 to 100 mol %, but is preferably 10 mol % or more, more preferably 20 mol % or more, and is preferably 90 mol % or less, more preferably 80 mol % or less.

[0066] Examples of alkali metal compounds that can be used as components of the activation treatment agent include hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, and tungstates of alkali metals. These can be used alone or in combination as components of the activation treatment agent.

[0067] Specific examples of suitable alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; Borates such as LiBO2, NaBO2, KBO2, RbBO2, and CsBO2; Carbonates such as Li2CO3, Na2CO3, K2CO3, RbCO3, CsCO3; Oxides such as Li2O, Na2O, K2O, Rb2O, and Cs2O; Peroxides such as Li2O2, Na2O2, K2O2, Rb2O2, Cs2O2; Superoxides such as LiO2, NaO2, KO2, RbO2, CsO2, etc.; Nitrates such as LiNO3, NaNO3, KNO3, RbNO3, CsNO3; phosphates such as Li3PO4, Na3PO4, K3PO4, Rb3PO4, Cs3PO4; Sulfates such as Li2SO4, Na2SO4, K2SO4, Rb2SO4, Cs2SO4; chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl; Bromides such as LiBr, NaBr, KBr, RbBr, and CsBr; Vanadates such as LiVO3, NaVO3, KVO3, RbVO3, CsVO3; Molybdates such as Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, CsMoO4; Tungstates such as Li2WO4, Na2WO4, K2WO4, Rb2WO4, and CsWO4.

[0068] Here, in order to further enhance the activation effect of the positive electrode active material, the activation treatment agent may contain, in addition to at least one compound selected from the group consisting of potassium compounds and sodium compounds, the same alkali metal element as the alkali metal element contained in the positive electrode active material in the positive electrode mixture.

[0069] That is, when the positive electrode active material in the positive electrode mixture is a lithium composite oxide, the activation treatment agent preferably contains a lithium compound in addition to at least one compound selected from the group consisting of potassium compounds and sodium compounds. Suitable lithium compounds include LiOH, LiBO2, Li2CO3, Li2O, Li2O2, LiO2, LiNO3, Li3PO4, Li2SO4, LiCl, LiVO3, LiBr, Li2MoO4, and Li2WO4.

[0070] The activation treatment agent may contain a compound other than an alkali metal compound as needed. Examples of compounds other than alkali metal compounds include alkaline earth metal compounds containing alkaline earth metal elements such as magnesium, calcium, and barium. The alkaline earth metal compound is contained in the activation treatment agent together with the alkali metal compound for the purpose of controlling the melting initiation temperature of the activation treatment agent.

[0071] Furthermore, the content of compounds other than the alkali metal compound in the activation treatment agent is selected within a range that does not significantly suppress the effects derived from the above-mentioned molten alkali metal compound, and can be less than 50% by weight of the total weight of the activation treatment agent.

[0072] The amount of activation treatment agent added in the mixture of the positive electrode mixture and the activation treatment agent is preferably 0.001 to 100 times, and more preferably 0.05 to 1 time, the weight of the positive electrode active material contained in the positive electrode mixture.

[0073] When the activation treatment agent contains a potassium compound and a lithium compound, the ratio of the lithium content (molar basis) to the potassium content (molar basis) (lithium content / potassium content) may be 0.01 to 100, 0.1 to 10, or 0.2 to 4, from the viewpoint of making it easier to make the charge / discharge characteristics of a battery produced using a recycled positive electrode active material more comparable to the charge / discharge characteristics of a battery produced using an unused positive electrode active material.

[0074] When the activation treatment agent contains a sodium compound and a lithium compound, the ratio of the lithium content (molar basis) to the sodium content (molar basis) (lithium content / sodium content) may be 0.01 to 100, 0.1 to 10, or 0.2 to 4, from the viewpoint of making it easier to make the charge / discharge characteristics of a battery produced using a recycled positive electrode active material more comparable to the charge / discharge characteristics of a battery produced using an unused positive electrode active material.

[0075] When the activation treatment agent contains a potassium compound, the potassium content (molar basis) contained in the activation treatment agent may be 1% or more and less than 500%, 10% or more and less than 400%, 50% or more and less than 300%, 100% or more and less than 250%, or 150% or more and less than 250% of the fluorine content (molar basis) contained in the positive electrode composite, from the viewpoint of making it easier to make the charge / discharge characteristics of a battery produced using a recycled positive electrode active material more comparable to the charge / discharge characteristics of a battery produced using an unused positive electrode active material.

[0076] When the activation treatment agent contains a sodium compound, the content of sodium (by mole) contained in the activation treatment agent may be 1% or more and less than 500%, 10% or more and less than 400%, 50% or more and less than 300%, 100% or more and less than 250%, or 150% or more and less than 250% of the content of fluorine (by mole) contained in the positive electrode composite, from the viewpoint of making it easier to make the charge / discharge characteristics of a battery produced using a recycled positive electrode active material more comparable to the charge / discharge characteristics of a battery produced using an unused positive electrode active material.

[0077] The number of moles of the alkali metal compound in the activation treatment agent in the mixture of the positive electrode composite and the activation treatment agent can be added so that the number of moles of the alkali metal element is 0.001 to 200 times the number of moles of the positive electrode active material (for example, Formula A) contained in the positive electrode composite, which is taken as 1.

[0078] By appropriately controlling the ratio of the activation treatment agent in the mixture, it is possible to reduce the cost of recovering the positive electrode active material powder from the positive electrode mixture, increase the oxidative decomposition rate of the carbon-based conductive material and binder, improve the effect of preventing the generation of corrosive gases during the heating process, and further increase the discharge capacity of the battery manufactured using the resulting positive electrode active material.

[0079] It is also preferred that at least one of the alkali metal compounds contained in the activation treatment agent is an alkali metal compound that exhibits alkalinity when dissolved in water. When an activation treatment agent containing such an alkali metal compound is dissolved in pure water, the pH of the solution becomes greater than 7. Hereinafter, such an activation treatment agent may be referred to as an "alkaline activation treatment agent."

[0080] The use of an alkaline activation treatment agent can further suppress the generation of corrosive gases during the heating process, thereby increasing the discharge capacity of a battery manufactured using the recovered positive electrode active material. In addition, the use of an alkaline activation treatment agent can also increase the treatment speed of the carbon-based conductive material and binder.

[0081] Examples of alkali metal compounds that exhibit alkalinity when dissolved in water and are contained in the alkaline activation treatment agent include hydroxides, carbonates, bicarbonates, oxides, peroxides, and superoxides of alkali metals. Specific examples include LiOH, NaOH, KOH, RbOH, and CsOH; Li2CO3, Na2CO3, K2CO3, RbCO3, and CsCO3; LiHCO3, NaHCO3, KHCO3, RbHCO3, and CsHCO3; Li2O, Na2O, K2O, Rb2O, and Cs2O; Li2O2, Na2O2, K2O2, Rb2O2, and Cs2O2; and LiO2, NaO2, K2O2, RbO2, and CsO2. These compounds may be contained alone or in combination in the activation treatment agent.

[0082] Furthermore, when the conductive material contained in the positive electrode composite is a carbon-based conductive material, at least one of the alkali metal compounds contained in the activation treatment agent may be an alkali metal compound having an oxidizing power that oxidizes and decomposes the carbon-based conductive material at the temperature of the heating step. Note that, hereinafter, an activation treatment agent containing such an alkali metal compound may be referred to as an "activation treatment agent having an oxidizing power."

[0083] Use of an activation treatment agent having such oxidizing power is particularly effective in promoting the oxidation of the conductive material, which is a carbon material, to carbon dioxide, and promoting the oxidation of the binder, which is a hydrocarbon material, to carbon dioxide and water vapor, and can further increase the discharge capacity of a battery manufactured using the obtained positive electrode active material, and can also sometimes improve the effect of preventing the generation of corrosive gases during the heating process.

[0084] Examples of alkali metal compounds having the oxidizing power necessary to oxidize carbonaceous conductive materials and hydrocarbons into carbon dioxide and water vapor include alkali metal peroxides, superoxides, nitrates, sulfates, vanadates, and molybdates, which may be used alone or in combination of two or more.

[0085] Specific examples include Li2O2, Na2O2, K2O2, Rb2O2, Cs2O2; LiO2, NaO2, KO2, RbO2, CsO2; LiNO3, NaNO3, KNO3, RbNO3, CsNO3; Li2SO4, Na2SO4, K2SO4, Rb2SO4, Cs2SO4; LiVO3, NaVO3, KVO3, RbVO3, CsVO3; Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, CsMoO4.

[0086] Details of the oxidizing power of these alkali metal compounds are described in JP 2012-186150 A.

[0087] The alkali metal compound may be a carbonate or a sulfate, or may be at least one selected from the group consisting of Li2CO3, Na2SO4, Na2CO3, and K2CO3, from the viewpoint of making it easier to make the charge / discharge characteristics of a battery produced using a recycled positive electrode active material more comparable to those of a battery produced using an unused positive electrode active material.

[0088] Process (2): Heating process The heating step is a step of heating the mixture obtained in step (1) (hereinafter, sometimes referred to as the "mixture before heating"). The mixture obtained in this heating step is sometimes referred to as the "mixture after heating."

[0089] The mixture before heating may be heated to a temperature equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent, or may be heated to a temperature lower than the melting initiation temperature (Tmp) of the activation treatment agent.

[0090] In this specification, "the temperature in the heating step is lower than the melting initiation temperature of the activation treatment agent" means that the temperature in the heating step is maintained at a temperature lower than the melting initiation temperature of the activation treatment agent (heating is performed at a temperature maintained below the melting initiation temperature of the activation treatment agent). Also, "the temperature in the heating step is lower than the melting initiation temperature of the activation treatment agent" means that the temperature in the heating step is not set to a temperature equal to or higher than the melting initiation temperature of the activation treatment agent. The temperature in the heating step (maximum temperature in the heating space) may be, for example, 300 to 600°C, 350 to 575°C, or 400 to 550°C.

[0091] The "melting initiation temperature (Tmp) of the activation treatment agent" means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0092] The melting initiation temperature (Tmp) of the activation treatment agent is a value determined by differential thermal analysis (DTA). That is, 5 mg of the mixture before heating is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10°C / min), and the temperature at which the DTA signal shows an endothermic peak is defined as the melting initiation temperature (Tmp).

[0093] The melting start temperature (Tmp) of the activation treatment agent is preferably 700° C. or lower, and more preferably 600° C. or lower. There is no lower limit to the melting start temperature (Tmp) of the activation treatment agent, but it may be, for example, 150° C.

[0094] The melting point of the activation treatment agent refers to the lowest temperature at which a part of the activation treatment agent becomes liquid when heated alone. By mixing the positive electrode composite and the activation treatment agent, the melting initiation temperature (Tmp) of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0095] The melting point of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, 5 mg of the activation treatment agent is subjected to differential thermal analysis (DTA, measurement conditions: temperature rise rate: 10°C / min), and the melting point of the activation treatment agent is determined as the temperature at which the DTA signal shows an endothermic peak.

[0096] The atmosphere for heating is not particularly limited, and may be an oxygen-containing gas such as air, nitrogen, argon, or carbon dioxide. The pressure of the atmosphere is not particularly limited, and may be atmospheric pressure, a reduced pressure atmosphere, or a pressurized atmosphere.

[0097] (Heating above the melting point (Tmp) of the activation treatment agent) In step (2), the mixture before heating is heated to a temperature equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent as described above, whereby the following effects occur.

[0098] The contact of the molten activation treatment agent with the positive electrode active material can suppress deterioration of the crystal structure of the positive electrode active material, and in some cases can even restore the crystal structure.

[0099] When the molten activation treatment agent comes into contact with the carbon-containing material (carbon-based conductive material and binder), the rate of oxidative decomposition of the conductive material and binder is increased. Furthermore, when the molten activation treatment agent comes into contact with the binder and fluorine compounds derived from the electrolyte, the fluorine components are stabilized as alkali metal fluorides, preventing the generation of hydrogen fluoride, a corrosive gas, and suppressing deterioration of the crystalline structure of the positive electrode active material.

[0100] Furthermore, when the activation treatment agent contains the same alkali metal as the positive electrode active material, it is possible to supply the alkali metal that is insufficient for the positive electrode active material.

[0101] The temperature of the heating step is preferably higher than the melting point of the alkali metal compound contained in the activation treatment agent. Note that the melting point of the alkali metal compound may be lower than the melting point of each compound alone when multiple types of compounds are mixed. When the activation treatment agent contains two or more types of alkali metal compounds, the eutectic point is the melting point of the alkali metal compound.

[0102] (Heating below the melting point (Tmp) of the activation treatment agent) In step (2), the pre-heating mixture is heated to a temperature below the melting point of the activation treatment agent, thereby suppressing deterioration of the crystalline structure of the positive electrode active material due to high-temperature heating, and making it easier to achieve charge / discharge characteristics comparable to those of a battery manufactured using a virgin positive electrode active material. In addition, heating the pre-heating mixture together with the activation treatment agent can also provide a crystalline structure repair effect.

[0103] When the heated activation treatment agent comes into contact with a carbon-containing material (such as a carbon-based conductive material or binder), the rate of oxidative decomposition of the conductive material and binder is increased. Furthermore, when the heated activation treatment agent comes into contact with a fluorine compound derived from the binder and the electrolyte, the fluorine component is stabilized as an alkali metal fluoride, preventing the generation of hydrogen fluoride, a corrosive gas, and suppressing deterioration of the crystalline structure of the positive electrode active material.

[0104] The time for which the mixture is heated at a temperature below the melting initiation temperature of the activation treatment agent may be determined depending on the amount of the mixture before heating, etc. The time for which the mixture is heated at a temperature below the melting initiation temperature of the activation treatment agent may be, for example, 1 minute to 24 hours.

[0105] The temperature of the heating step and the holding time at that temperature can be appropriately adjusted depending on the types and combinations of the positive electrode active material, conductive material, binder, alkali metal compound and other compounds contained in the activation treatment agent that constitute the positive electrode mixture. Typically, the temperature is in the range of 100 to 1500°C, and the holding time is about 10 minutes to 24 hours.

[0106] After the heating step, the mixture can be cooled to any temperature, such as about room temperature, if desired. In this way, a heated mixture containing the heated positive electrode active material powder is obtained.

[0107] Step (3): Removing components other than the positive electrode active material powder from the heated mixture Step (3) is a step of removing components other than the post-heating positive electrode active material powder from the post-heating mixture obtained in the heating step (2).

[0108] The heated mixture contains not only the heated positive electrode active material powder, but also components derived from the activation treatment agent (such as alkali metal compounds), undecomposed carbon-containing materials (such as conductive materials and binders), and other undecomposed substances of the positive electrode mixture. Furthermore, if the positive electrode mixture contains an electrolyte solution containing a fluorine component, the mixture may also contain a fluorine component derived from the electrolyte.

[0109] Removing components other than the positive electrode active material powder from the heated mixture involves multiple removal steps, and therefore "removing components other than the positive electrode active material powder from the heated mixture" also includes an operation of further removing components other than the positive electrode active material powder from the mixture from which components other than the positive electrode active material powder have been partially removed (sometimes referred to as a partially removed mixture).

[0110] One example of a method for removing components other than the positive electrode active material powder from the heated mixture or the partially removed mixture is a slurrying and solid-liquid separation method in which a liquid containing water is added to the heated mixture or the partially removed mixture to form a slurry, and then the slurry is subjected to solid-liquid separation. Another example of the above method is a vaporization separation method in which the heated mixture or the partially removed mixture is heated to vaporize and separate the components other than the heated positive electrode active material powder.

[0111] In this embodiment, step (3) comprises performing at least one slurrying and solid-liquid separation process, and in at least one of the slurrying and solid-liquid separation processes, wet classification is performed in the slurry after slurrying and before solid-liquid separation.

[0112] That is, in step (3), as shown in FIG. (A1) a sub-step of bringing a liquid containing water into contact with the heated mixture or the partially removed mixture to obtain a slurry S1 containing a heated positive electrode active material powder; (A2) a sub-step of wet-classifying the heated positive electrode active material powder in the slurry S1 to obtain a slurry S2 containing the heated positive electrode active material powder having a relatively small average particle size and a slurry S3 containing the heated positive electrode active material powder having a relatively large average particle size; and (A3) a sub-step of subjecting the slurry S3 to solid-liquid separation.

[0113] In the step (A1), a liquid containing water is brought into contact with the heated mixture or the partially removed mixture to obtain a slurry S1 containing the heated positive electrode active material powder.

[0114] As described above, the heated mixture contains not only the heated positive electrode active material powder, but also components derived from the activation treatment agent (such as alkali metal compounds), undecomposed conductive materials and binders, and other undecomposed materials of the positive electrode composite. Furthermore, if the positive electrode composite contains an electrolyte solution containing a fluorine component, the mixture may also contain a fluorine component derived from the electrolyte. By adding a liquid containing water to the mixture to form a slurry, components other than the heated positive electrode active material powder are dissolved in the liquid.

[0115] The liquid used for slurrying is not particularly limited as long as it contains water. The amount of water in the liquid may be 50% by mass or more. In order to increase the solubility of water-soluble components or to increase the processing speed, components other than water may be added to the liquid to adjust the pH.

[0116] Suitable examples of the water-containing liquid include pure water and alkaline cleaning solutions. Examples of alkaline cleaning solutions include aqueous solutions of one or more anhydrides and hydrates selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate. Ammonia can also be used as the alkali.

[0117] The resulting slurry contains a solid phase mainly containing the heated positive electrode active material powder and a liquid phase containing water-soluble components other than the heated positive electrode active material powder, including alkali metal components derived from the activation treatment agent and / or fluorine components derived from the binder and the electrolyte.

[0118] The amount of liquid to be added to the heated mixture or the partially removed mixture is determined appropriately taking into consideration the amounts of the heated positive electrode active material powder and the water-soluble components other than the positive electrode active material powder contained in each mixture.

[0119] In the sub-step (A1), the mixture after heating or the partially removed mixture is preferably stirred with a liquid containing water to obtain a slurry S1. This promotes dissolution of the water-soluble components. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m / s.

[0120] In sub-step (A2), the heated positive electrode active material powder in the slurry S1 is wet classified to obtain a slurry S2 containing a heated positive electrode active material powder having a relatively small average particle size, and a slurry S3 containing a heated positive electrode active material powder having a relatively large average particle size.

[0121] The specific means for wet classification is not particularly limited, and may be a wet cyclone or a wet sieve. An example of a wet sieve is a so-called slurry screener, which uses centrifugal force generated by the rotation of a screw disposed inside a mesh screen cylinder to discharge fine powder from the screen.

[0122] The average particle size may be D50 in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer. The average particle size in slurry S3 may be 10 to 20 μm. The difference between the average particle size of slurry S3 and the average particle size of slurry S2 may be 1 to 10 μm.

[0123] In step (A3), the slurry S3 is subjected to solid-liquid separation. Solid-liquid separation is a step of separating the slurry into a liquid phase and a solid phase. The solid-liquid separation method may be a conventionally known method, such as filtration or centrifugation.

[0124] In this embodiment, the step (3) has the sub-steps (A1) to (A3), which provides the following effects. First, by going through step (A1), water-soluble components other than the post-heating positive electrode active material powder are removed from the solid phase in the slurry and transferred to the liquid phase, and then by going through step (A3), the resulting solid phase is one from which components other than the post-heating positive electrode active material have been removed.

[0125] Furthermore, the positive electrode active material powder in the positive electrode composite obtained from the waste positive electrodes tends to have a broader particle size distribution or a smaller average particle size (e.g., D50) due to cracking caused by expansion and contraction during charging and discharging. According to this embodiment, the positive electrode active material powder after heating in the slurry S1 is subjected to substep (A2), i.e., wet classification to obtain a slurry S2 containing the positive electrode active material powder after heating with a relatively small average particle size and a slurry S3 containing the positive electrode active material powder after heating with a relatively large average particle size. The slurry S3 is then subjected to solid-liquid separation in the subsequent substep (A3). Therefore, the amount of fine powder in the positive electrode active material powder after heating in the slurry S3 is reduced, which makes it easier to ensure a flow path for the liquid to drain within the solid-phase cake during solid-liquid separation in the slurry S3. This improves the drainage of the liquid from the solid-phase cake, resulting in effects such as a reduction in the time required for solid-liquid separation and / or a reduction in the moisture content of the resulting solid-phase cake.

[0126] Furthermore, when the solid cake is subsequently dried as required, a flow path for water vapor to escape from within the solid cake is easily ensured, so that the amount of energy and time required for drying can be reduced.

[0127] The above sub-steps (A1) to (A3) may be carried out at least once in the step (3) of removing components other than the heated positive electrode active material powder from the heated mixture or the partially removed mixture.

[0128] For example, the sub-step (A1) may be a step of bringing a liquid containing water into contact with the "heated mixture" to obtain a slurry S1 containing the heated positive electrode active material powder.

[0129] Even if the substeps (A1) to (A3) are performed once, the solid phase obtained by solid-liquid separation of the slurry S3 in the substep (A3) often contains trace amounts of components other than the positive electrode active material powder after heating, and corresponds to the above-mentioned "partially removed mixture." Therefore, the solid phase obtained in the substep (A3) may be directly subjected to the drying step described below, or a substep of removing remaining components other than the positive electrode active material powder from the "partially removed mixture" may be further performed.

[0130] The step of further removing components other than the remaining positive electrode active material powder from the "partially removed mixture" may be carried out by the vaporization separation method described above, but is preferably carried out by the slurrying and solid-liquid separation method (also called rinsing in this case).

[0131] For example, step (3) may include, after sub-step (A3), (B1) a sub-step of bringing a liquid containing water into contact with the “partially removed mixture” to obtain a slurry Q1 containing a heated positive electrode active material powder; and (B3) A sub-step of solid-liquid separation of the slurry Q1 may be included, which will result in a higher purity solid phase.

[0132] The combination of the sub-steps (B1) and (B3) performed after the sub-step (A3) may be repeated multiple times.

[0133] Between the substeps (B1) and (B3), a substep (B2) may be included in which the heated positive electrode active material powder in the slurry Q1 is wet-classified to obtain a slurry Q2 containing the heated positive electrode active material powder having a relatively small average particle size, and a slurry Q3 containing the heated positive electrode active material powder having a relatively large average particle size. In this case, the slurry Q3 may be subjected to solid-liquid separation in the substep (B3).

[0134] The solid phase obtained in the sub-step (B3) can be subjected to the drying step described below.

[0135] Furthermore, the above sub-steps (A1) to (A3) may be performed in a step of removing components other than the heated positive electrode active material powder from the "partially removed mixture" rather than in a step of removing components other than the heated positive electrode active material powder from the "heated mixture." In this case, the step of removing components other than the heated positive electrode active material powder from the "heated mixture" may be the vaporization separation method described above, but is preferably the slurrying and solid-liquid separation method described above.

[0136] In this specification, the positive electrode active material powder that has undergone steps (1) to (3) is referred to as recycled positive electrode active material powder. The recycled positive electrode active material powder that has undergone steps (1) to (3) can be suitably used for manufacturing positive electrodes, etc. The manufacturing method for recycled positive electrode active material powder may include additional steps before and after steps (1) to (3). In this specification, positive electrode active material powder that has undergone additional steps other than steps (1) to (3) is also referred to as recycled positive electrode active material powder. Examples of additional steps other than steps (1) to (3) are pre-steps (A) and (B) performed before step (1), and the following steps (4) and (5) performed after step (3), for example, after step (3a).

[0137] Process (4): Drying process Step (4) is a step of removing water from the solid component by exposing the solid phase obtained in step (3) to a heated and / or reduced pressure environment.

[0138] The heating temperature is preferably 100°C or higher to remove water. Furthermore, a temperature of 150°C or higher is preferable to thoroughly remove water. Temperatures of 250°C or higher are particularly preferable because they further increase the discharge capacity of a battery manufactured using the resulting positive electrode active material. The temperature in the drying step may be constant or may be changed stepwise or continuously. The temperature range reached by heating can be, for example, 10°C or higher and lower than 900°C.

[0139] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 -10 ~1.0×10 3 It can be Pa.

[0140] Step (5): Annealing (re-firing) step Step (5) is preferably a step of heat-treating the solid component (sometimes referred to as the dried solid component) obtained after step (4). When the pre-heating mixture is heated to a temperature equal to or higher than the melting initiation temperature in step (2), the annealing step may be, for example, a step of heat-treating the dried solid component at a temperature lower than 900°C.

[0141] When the mixture before heating in step (2) is heated at a temperature lower than the melting initiation temperature, the annealing step may be, for example, a step of heating the dried solid component at a temperature higher than that in step (2). In this case, the temperature at which the dried solid component is heated may be greater than 700°C, 750°C or higher, 800°C or higher, 850°C or higher, or 900°C or higher, from the viewpoint of vaporizing components other than the positive electrode active material and removing impurities, and from the viewpoint of sufficiently increasing the crystallite size of the positive electrode active material, thereby more easily achieving charge / discharge characteristics comparable to those of a battery produced using unused positive electrode active material.

[0142] The atmosphere for the heat treatment is not limited, but an oxygen-containing atmosphere such as air is preferable. The heat treatment temperature can be 100°C or higher. The heat treatment holding time can be 1 minute to 24 hours. In particular, heating at a temperature of 350°C or higher for 0.1 to 5 hours is preferable.

[0143] By using the method for producing recycled positive electrode active material powder of the present invention, the recycled positive electrode active material powder obtained from a battery mix can be reused in the same way as unused active material. Methods for producing positive electrodes and batteries using recycled positive electrode active material powder are well known.

[0144] The final discharge capacity of the recycled positive electrode active material according to the embodiment of the present invention can be 150 mAh / g or more. [Example]

[0145] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not changed.

[0146] Example 1 A. Manufacturing of cathode A The positive electrode active material is composed of Li 1.04 Ni 0.60 Co 0.20 Mn 0.20 The positive electrode active material is O2 and has a crystal structure of R-3m. Acetylene Black HS100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) is used as the conductive material. As for the binder and solvent, NMP solvent was further added to an NMP solution (manufactured by Kureha Corporation) containing 12 wt % of PVdF#1100 as the binder to achieve a predetermined ratio.

[0147] The mass ratio of the positive electrode active material, binder, and conductive material in the positive electrode mixture is 92:3:5. The blending amount of the solvent is 50 mass % with respect to the entire positive electrode mixture paste.

[0148] The positive electrode composite paste was applied to a 20 μm thick aluminum foil 1085 (manufactured by Nippon Foil Co., Ltd.) for lithium ion secondary battery positive electrode current collector using a doctor blade coater, and then dried to obtain a positive electrode A. The amount of positive electrode active material on the aluminum foil was 20 mg / cm. 2 Let's say.

[0149] B. Recovery of electrode mixture from positive electrode A From the positive electrode A, the electrode mixture is mechanically peeled off from the current collector.

[0150] C. Electrolyte immersion process The exfoliated electrode mixture is pulverized into powder. An electrolyte solution is added to the electrode mixture powder to a slurry concentration of 1500 g / L. The electrolyte solution used here is a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with LiPF6 dissolved as the electrolyte at a ratio of 1.0 mol / L. The electrode mixture slurry is stirred for 1 minute at a maximum flow rate of 0.550 m / sec. The slurry is then filtered to separate the solid phase, which is then dried under reduced pressure for 24 hours to obtain an electrolyte-containing electrode mixture. The electrolyte immersion process is performed in a glove box under an argon atmosphere.

[0151] D. Cleaning process of electrolyte-containing electrode mixture The resulting electrolyte-containing electrode mixture was slurried with water as an electrolyte washing solvent to a slurry concentration of 5 g / L, stirred for 1,437 minutes at a peripheral speed of 0.942 m / s, and then filtered for 3 minutes to separate the solid and liquid components. The resulting solid component was dried under reduced pressure at 100°C for 1 hour, and the washed electrode mixture was recovered.

[0152] E. Activation treatment agent mixing process (corresponding to process (1)) After cleaning, the electrode mixture was mixed with 0.15 mol of Li2CO3 and 0.15 mol of K2SO4 as activation agents for each mol of the positive electrode active material in the electrode mixture to obtain a mixture (mixture before heating). The melting point of the activation agent was 550°C.

[0153] F. Heating process (corresponding to process (2)) The resulting unheated mixture is placed in an alumina firing container and placed in an electric furnace. The mixture is activated at atmospheric pressure at 700°C for 3 hours. The heating rate is 300°C / hour, and the mixture is cooled naturally to room temperature. After cooling to room temperature, the heated mixture is recovered.

[0154] G. Step of removing components other than the heated positive electrode active material powder from the heated mixture (corresponding to step (3)) The heated mixture was pulverized, water was added, and the mixture was stirred for 1 minute to form a slurry with a concentration of 20 g / L, yielding slurry S1. The heated positive electrode active material powder in slurry S1 was then wet-classified using a slurry screener manufactured by Accor Japan Co., Ltd., yielding slurry S2 containing a heated positive electrode active material powder with a relatively small average particle size, and slurry S3 containing a heated positive electrode active material powder with a relatively large average particle size. The screen had an opening of 13 μm. The slurry was then filtered to separate it into a solid phase and a liquid phase.

[0155] H. Drying process of the positive electrode active material (corresponding to process (4)) The resulting solid phase is dried under reduced pressure at 100°C for 1 hour.

[0156] H. Re-baking process of the positive electrode active material (corresponding to process (6)) The recovered, washed cathode active material is placed in an alumina firing container and placed in an electric furnace. The mixture is heated at 700°C under atmospheric pressure for 1 hour. The heating rate is 300°C / hour, and the mixture is cooled to room temperature by natural cooling. After cooling to room temperature, the reactivated cathode active material is recovered.

[0157] A coin-type battery is manufactured using the recovered reactivated positive electrode active material, and a charge-discharge test is performed. The discharge capacity and internal resistance are measured in the charge-discharge test, and the initial discharge capacity recovery rate and internal resistance recovery rate are calculated.

[0158] (Reference example 1) <Production of positive electrodes> The positive electrode described below was fabricated according to the following procedure. A mixture was obtained by mixing 92 parts by mass of positive electrode active material (unused positive electrode active material or recycled positive electrode active material), 3 parts by mass of PVdF (binder, manufactured by Kureha Corporation, product number: #1100), and 5 parts by mass of acetylene black (conductive material, manufactured by Denka Company, product number: HS100). A binder solution prepared by dissolving PVdF in NMP was used as the binder. The mixture was kneaded in a rotation-revolution mixer (ARE-310 manufactured by Thinky Corporation) to prepare a positive electrode composite paste. NMP was added so that the total mass of the positive electrode active material, binder, and conductive material in the positive electrode composite paste was 50% by mass.

[0159] A 20 μm thick aluminum foil 1085 (manufactured by Nippon Foil Co., Ltd.) for lithium ion secondary battery positive electrode current collector was applied on one side with a positive electrode active material amount of 3.0 ± 0.1 mg / cm 2 The positive electrode composite paste was applied so that the surface area was 1.65 cm2, and then vacuum dried at 150°C for 8 hours to obtain a positive electrode. 2 It was decided.

[0160] <Battery manufacturing> The coin-type battery described below was fabricated by the following procedure. A nonaqueous electrolyte secondary battery (coin-type battery) was manufactured by combining the above-mentioned positive electrode, electrolyte, separator, and negative electrode. The battery was assembled in a glove box under an argon atmosphere. The electrolyte used was a solution prepared by dissolving LiPF6 at a ratio of 1.0 mol / L in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. A laminated film separator, in which a heat-resistant porous layer was laminated on a porous film (made of polyethylene), was used as the separator, and metallic lithium was used as the negative electrode.

[0161] <Production of positive electrodes before recycling> The positive electrode active material is composed of Li 1.07 Ni 0.47 Mn 0.48 Fe 0.05A positive electrode active material having a crystal structure of R-3m was prepared. The coin-type battery described above was fabricated using this positive electrode active material (unused positive electrode active material), and the following charge-discharge test (rate test) was performed at 25°C. The 0.2C discharge capacity was 138 mAh / g, and the 5C discharge capacity was 106 mAh / g. A higher 0.2C discharge capacity indicates a higher rated capacity, and a higher 5C discharge capacity indicates a higher output characteristic. (conditions) Maximum charging voltage: 4.3V Charging current: 0.2mA / cm 2 Charging time: 8 hours Minimum discharge voltage: 2.5V 0.2C discharge current: 0.2mA / cm 2 5C discharge current: 5.0mA / cm 2

[0162] The electrode composite was mechanically scraped off from the positive electrode used in the above battery, and the electrode composite was peeled off from the current collector. 5 g of the electrode composite removed from the positive electrode was mixed with an activation treatment agent: 0.1 mol of K2CO3 per mol of positive electrode active material, and 0.1 mol of Na2CO3 per mol of positive electrode active material, to obtain a mixture (mixture before heating). The melting point of the activation treatment agent was 700°C.

[0163] The mixture before heating was placed in an electric furnace and heated in an air atmosphere at a heating temperature of 700°C (above the melting point of the activation treatment agent) for 240 minutes.

[0164] The heated mixture was pulverized, and distilled water was added and stirred to obtain a slurry. The resulting slurry was filtered to separate the solid and liquid components. The solid component was then collected and dried to obtain a recycled cathode active material. The composition, crystalline structure, average particle size, and specific surface area of ​​the resulting recycled cathode active material were comparable to those of unused cathode active material. A coin-type battery was fabricated using the recycled cathode active material and subjected to a charge-discharge test under the above conditions at 25°C. The 0.2C discharge capacity was 135 mAh / g, and the 5C discharge capacity was 94 mAh / g, both of which were comparable to the discharge capacities of coin-type batteries fabricated using unused cathode active material.

[0165] (Reference example 2) <Production of positive electrodes before recycling> The positive electrode active material is LiNi 0.33 Co 0.33 Mn 0.33 A positive electrode active material NCM111 having a crystal structure of R-3m was prepared. When the above coin-type battery was fabricated using this positive electrode active material (unused positive electrode active material), the initial charge capacity was 178.3 mAh / g and the initial discharge capacity (0.2 C) was 163.4 mAh / g. Furthermore, when the following charge / discharge test (rate test) was performed at 25°C, the 0.2 C discharge capacity was 163.1 mAh / g and the 5 C discharge capacity was 141.3 mAh / g.

[0166] The electrode composite was mechanically scraped off from the cathode waste material generated during the fabrication of the above cathode, and the electrode composite was peeled off from the current collector. 5 g of the electrode composite removed from the cathode was mixed with activation treatment agents: 0.1 mol of Li2CO3 per mol of cathode active material, and 0.1 mol of Na2SO4 per mol of cathode active material, to obtain a mixture (pre-heating mixture). The activation treatment agent had a melting point of 510°C.

[0167] 30 g of the mixture before heating was placed in an electric furnace and heated in an air atmosphere at a temperature increase rate of 300°C / h, a heating temperature of 450°C (below the melting start temperature of the activation treatment agent), and a heating time of 360 minutes.

[0168] The heated mixture was pulverized, and distilled water was added and stirred to obtain a slurry. The obtained slurry was filtered to separate a solid component and a liquid component. The solid component was then collected and dried under suction at 100°C for 1 hour.

[0169] The dried solid component was placed in an electric furnace and heated in an air atmosphere at 900°C for 60 minutes to obtain a recycled cathode active material. The heated recycled cathode active material was then allowed to cool to room temperature. The composition, crystalline structure, average particle size, and specific surface area of ​​the resulting recycled cathode active material were confirmed to be comparable to those of virgin cathode active material. When a coin-type battery was fabricated using the recycled cathode active material, the initial charge capacity was 180.5 mAh / g and the initial discharge capacity was 161.1 mAh / g. Furthermore, when the initial charge / discharge (rate test) was performed under the above conditions at 25°C, the 0.2C discharge capacity was 160.2 mAh / g and the 5C discharge capacity was 133.9 mAh / g.

Claims

1. (1) A step of mixing a positive electrode mixture containing a positive electrode active material powder and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; (2) heating the mixture to obtain a heated mixture containing a heated positive electrode active material powder; and (3) A method for producing recycled positive electrode active material powder, comprising: removing components other than the heated positive electrode active material powder from the heated mixture, Step (3) is (A1) a sub-step of bringing a liquid containing water into contact with the heated mixture or a partially removed mixture obtained by partially removing components other than the heated cathode active material powder from the heated mixture, to obtain a slurry S1 containing the heated cathode active material powder; (A2) a sub-step of wet-classifying the heated positive electrode active material powder in the slurry S1 to obtain a slurry S2 containing the heated positive electrode active material powder having a relatively small average particle size and a slurry S3 containing the heated positive electrode active material powder having a relatively large average particle size; and (A3) A method comprising a sub-step of solid-liquid separating the slurry S3.

2. The method according to claim 1 , wherein the substep (A1) is a substep of bringing a liquid containing water into contact with the heated mixture to obtain a slurry S1 containing the heated positive electrode active material powder.

3. 2. The method according to claim 1, wherein the substep (A1) is a substep of bringing a liquid containing water into contact with a partially removed mixture obtained by partially removing components other than the heated positive electrode active material powder from the heated mixture, to obtain a slurry S1 containing the heated positive electrode active material powder.

4. The method according to claim 1 or 2, wherein the wet classification in the sub-step (A2) is carried out using a wet sieve or a hydrocyclone.

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