Method for producing recycled cathode active material

Abstract

To provide a method for producing a recycled cathode active material capable of reducing the amount of wastewater generated by washing when performing washing a plurality of times.SOLUTION: There is provided a method for producing a recycled cathode active material, which comprises the following steps: (1) a step of mixing a cathode composite material containing a cathode active material and an activation treatment agent containing one or two or more alkali metal compounds to obtain a mixture, (2) a step of heating the mixture to obtain a mixture after heating, (3) a step of bringing the mixture after heating into contact with a first liquid containing water and an alkali metal compound, followed by obtaining a first solid component and a first liquid component, (4) a step of bringing the first solid component into contact with a second liquid containing water and having a smaller alkali metal compound content than the first liquid, followed by obtaining a second solid component and a second liquid component and (5) a step of recovering a recycled cathode active material from the second solid component.SELECTED DRAWING: None

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 mixture with an activation treatment agent containing an alkali metal compound, heating the mixture to decompose the binder, and removing the decomposed material and the activation treatment agent with water or the like. 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] When recycling a positive electrode active material in a positive electrode mixture, an activation agent containing an alkali metal compound is added to reactivate the positive electrode active material. After the positive electrode active material is reactivated, the mixture containing the positive electrode active material and the activation agent may be washed with water to remove the activation agent. Because it is difficult to remove the activation agent in a single wash, multiple washes may be performed. However, increasing the number of washes increases the amount of wastewater generated, which increases the environmental burden and wastewater treatment costs.

[0006] Therefore, an object of the present invention is to provide a method for producing a recycled positive electrode active material that can reduce the amount of wastewater generated by washing with water when washing with water is performed multiple times. [Means for solving the problem]

[0007] The present invention includes, for example, the following [1] to [8]. [1] A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water and an alkali metal compound, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and having a lower content of alkali metal compounds than the first liquid, and then obtaining a second solid component and a second liquid component; (5) recovering a recycled positive electrode active material from the second solid component [2] The manufacturing method described in [1], wherein the second liquid contains at least a portion of the first liquid component. [3] The manufacturing method according to [1] or [2], wherein the second liquid is in a smaller amount than the first liquid. [4] A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and at least a portion of the first liquid component, and then obtaining a second solid component and a second liquid component; (5) recovering a recycled positive electrode active material from the second solid component [5] The manufacturing method according to [4], wherein the second liquid is in a smaller amount than the first liquid. [6] A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and in an amount smaller than the first liquid, and then obtaining a second solid component and a second liquid component; (5) recovering a recycled positive electrode active material from the second solid component [7] The method according to any one of [1] to [6], wherein in the step (2), the mixture is heated to a temperature equal to or higher than the melting point of the activation treatment agent. [8] The method according to any one of [1] to [6], wherein in the step (2), the mixture is heated to a temperature below the melting point of the activation treatment agent. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a recycled positive electrode active material that can reduce the amount of wastewater generated by washing with water when washing with water is performed multiple times. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Method of manufacturing recycled positive electrode active material) A method for producing a recycled positive electrode active material will be described below.

[0010] [First embodiment] The method for producing a recycled positive electrode active material according to the first 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 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 Step (3): A step of contacting the heated mixture with a first liquid containing water and an alkali metal compound, and then obtaining a first solid component and a first liquid component. Step (4): A step of contacting the first solid component with a second liquid containing water and having a lower content of alkali metal compounds than the first liquid, and then obtaining a second solid component and a second liquid component. Step (5): Recovering the recycled positive electrode active material from the second solid component

[0011] According to the method for producing a recycled cathode active material of the first embodiment, even when water washing is performed multiple times, it is possible to reduce the amount of wastewater generated by water washing. In conventional methods for producing recycled cathode active material, a mixture of a cathode composite and an activation treatment agent is heated, and then the mixture is brought into contact with water to remove alkali metal compounds derived from the activation treatment agent, thereby recovering a recycled cathode active material. However, in some cases, water washing is performed multiple times to remove these components, which may result in the generation of a large amount of wastewater. On the other hand, in the method for producing a recycled cathode active material of the first embodiment, a first liquid containing an alkali metal compound is used as a liquid to contact the mixture after heating the mixture of a cathode composite and an activation treatment agent. The first liquid may be wastewater generated during the production of a recycled cathode active material. Although the wastewater generated during the production of a recycled cathode active material contains alkali metal compounds, the alkali metal compounds in the wastewater have a concentration below saturation. Therefore, when the mixture is washed with wastewater, alkali metal compounds (especially readily soluble alkali metal compounds such as fluorides of sodium, potassium, etc., and carbonates) derived from the activation treatment agent remaining in the mixture can be dissolved, and thus it is possible to remove the alkali metal compounds derived from the activation treatment agent in the same way as with conventional water washing methods using pure water, etc. Therefore, while the mixture is conventionally washed with pure water, etc., it is possible to use wastewater instead of pure water, etc. for water washing, thereby reducing the amount of wastewater generated during the production of recycled positive electrode active material.

[0012] Each step in the first embodiment will be described in detail below.

[0013] Pre-process (A): Positive electrode composite preparation process A positive electrode mixture containing a positive electrode active material is prepared.

[0014] In the positive electrode mixture, particles of the positive electrode active material may be bound to one another by a binder. The positive electrode mixture may contain a conductive material and / or an electrolyte in addition to the positive electrode active material and the binder. When the positive electrode mixture contains a conductive material, the particles of the positive electrode active material and the conductive material may be bound to one another by a binder. The electrolyte is a component derived from the electrolyte solution of the battery 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).

[0015] [Cathode active material] Examples of the positive electrode active material include composite compounds containing one or more of the following elements as constituent elements: 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, and tungsten.

[0016] The positive electrode active material may be composed of only a single compound, or may be composed of multiple compounds.

[0017] The positive electrode active material preferably contains a composite oxide containing at least one element selected from the following element group 1 and at least one element selected from the following element group 2. Element group 1: Ni, Co, Mn, Fe, Al, and P Element group 2: Li, Na, K, Ca, Sr, Ba, and Mg

[0018] The positive electrode active material preferably contains a compound represented by the following formula (A).

[0019] Li 1+a M 2 b M 1 M T c O 2+d X e (A) However, M 2represents 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 excluding Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metal elements excluding O and P, -0.4 < a < 1.5, 0 ≤ b < 0.5, 0 ≤ c < 0.5, -0.5 < d < 1.5, and 0 ≤ e < 0.5 are satisfied.

[0020] 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 include F, S, Cl, Br, I, Se, Te, N, etc.

[0021] The positive electrode active material preferably contains a composite oxide containing at least Li and Ni.

[0022] In the positive electrode active material, M 1 The molar fraction of Ni therein is preferably 0.3 to 0.95.

[0023] The crystal structure of the positive electrode active material (for example, composite oxide) is not particularly limited, but a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

[0024] 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.

[0025] 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.

[0026] The crystal structure of the positive electrode active material preferably belongs to the space group R-3m included in the hexagonal crystal structure, or the space group C2 / m included in the monoclinic crystal structure.

[0027] The crystal structure of the positive electrode active material can be identified from a powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα radiation as a radiation source.

[0028] The particle size of the positive electrode active material in the positive electrode mixture is not particularly limited, but may be approximately 0.001 to 100 μm. The particle size distribution of the positive electrode active material can be measured using a laser diffraction / scattering particle size distribution analyzer (e.g., Malvern Instruments' Mastersizer 2000). A volume-based cumulative particle size distribution curve is created from the particle size distribution, and the particle size (D50) value at 50% cumulative from the fine particle side can be used as the average particle size of the positive electrode active material.

[0029] There is no particular limitation on the content of the positive electrode active material in the positive electrode mixture.

[0030] [Binder] Examples of binders (pre-activation binders) contained in the positive electrode mixture include thermoplastic resins, and specific examples include fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as "PVdF"), polytetrafluoroethylene (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 (SBR). The binders may be used alone or in combination of two or more.

[0031] The content of the binder 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 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.

[0032] [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.

[0033] Specific examples of carbon-based conductive materials include graphite powder, carbon black (for example, acetylene black), and fibrous carbon materials (for example, graphitized carbon fibers and carbon nanotubes).

[0034] The carbonaceous conductive material may be a single carbon material or may be made up of multiple carbon materials.

[0035] The specific surface area of ​​the carbon material used as the carbon-based conductive material is 0.1 to 500 m 2 / g. In this case, the conductive material may have a specific surface area of ​​30 m 2 / g or more, and can be made of only carbon-based conductive materials with a specific surface area of ​​30m 2 / g or more of carbon black, and 2 When an activating 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 a carbon material having a small specific surface area can be oxidized in some cases.

[0036] 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.

[0037] [Electrolytes and Solvents] Examples of the electrolyte include LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2F)2, LiCF3SO3, etc. The content of the electrolyte contained in the positive electrode mixture is not particularly limited, but may be 0.0005 to 7 mass %.

[0038] The positive electrode mixture may contain a solvent derived from the electrolyte solution, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0039] [Recovery of cathode mixture] The positive electrode mixture can be obtained by separating and recovering the positive electrode mixture layer from a waste positive electrode having a current collector and a positive electrode mixture layer.

[0040] "Waste positive electrodes" may refer to positive electrodes recovered from discarded batteries, or to waste positive electrodes generated during the manufacturing process of positive electrodes or batteries. Discarded batteries may be used batteries, or unused but non-standard batteries. The waste positive electrodes may be the ends of positive electrodes generated during the battery manufacturing process, or non-standard positive electrodes. As the positive electrode composite, waste positive electrode composite not attached to a current collector (waste generated during the positive electrode composite manufacturing process) may also be used.

[0041] 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.

[0042] Examples of methods for separating the positive electrode composite layer from a waste positive electrode having a current collector and a positive electrode composite layer 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 layer from the current collector), a method of penetrating a solvent into the interface between the current collector and the positive electrode composite layer 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. Preferably, the method is one in which the positive electrode composite layer is mechanically peeled from the current collector.

[0043] 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, 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.

[0044] Solid-liquid separation is an operation for separating a slurry into a solid component and a liquid component. Examples of the solid-liquid separation method may be conventionally known methods, such as filtration and centrifugation.

[0045] The electrolyte cleaning solvent is not particularly limited, and examples of the electrolyte cleaning solvent include carbonates 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.

[0046] The positive electrode mixture can be brought into contact with the electrolyte washing solvent using a known powder-liquid contact device (for example, a stirring tank).

[0047] 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 may be 0.1 to 1.0 m / s.

[0048] In the washing step of the positive electrode composite, after solid-liquid separation, the solid component may be rinsed. Rinsing is an operation in which the solid component is again brought into contact with the electrolyte washing solvent to obtain a slurry, and the slurry is then separated again into a solid component and a liquid component. In the washing step of the positive electrode composite, rinsing may be performed multiple times. The slurry concentration in rinsing can be adjusted as desired. During rinsing, the slurry can also be stirred as described above.

[0049] The above-described washing can sufficiently remove the electrolyte from the positive electrode mixture. For example, if the electrolyte remains, the following reaction may occur, which may change the structure of the positive electrode active material from a layered rock salt structure to a spinel structure. LiPF6+16LiMO2+2O2→ 6LiF+Li3PO4+8LiM2O4

[0050] Furthermore, when the activation treatment agent contains lithium carbonate, lithium may be consumed by the following reaction. LiPF6+4Li2CO3→ 6LiF+Li3PO4+4CO2

[0051] The separated solid component can be dried to remove the electrolyte washing solvent by reducing pressure and / or heating, if necessary. The heating temperature may be 50 to 200°C.

[0052] Step (1): Activation treatment agent mixing step Next, the prepared positive electrode mixture is mixed with an activation treatment agent containing one or more alkaline compounds to obtain a mixture.

[0053] The positive electrode mixture and the activation treatment agent may be mixed by either dry mixing or wet mixing, or by a combination of these methods. The order in which the positive electrode mixture and the activation treatment agent are mixed is not particularly limited.

[0054] 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.

[0055] Dry mixing is preferred as a mixing method because it allows for easier 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.

[0056] 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.).

[0057] The activation treatment agent used in this step will be described in detail below.

[0058] <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.

[0059] 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.

[0060] Furthermore, the positive electrode mixture may contain a fluorine-containing compound derived from the binder and / or the electrolyte, but 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.

[0061] The proportion of all alkali metal compounds in the activation treatment agent is appropriately set taking into consideration the type of alkali metal compound, the type of target positive electrode active material, etc., but is usually 50 mass% or more, preferably 70 mass% or more, relative to the total mass of the activation treatment agent, and may be 100 mass% (an embodiment in which the activation treatment agent is essentially composed of alkali metal compounds).

[0062] The concentration of at least one alkali metal selected from the group consisting of potassium and sodium in 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.

[0063] Examples of alkali metal compounds that can be used as components of the activation treatment agent include alkali metal hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, and tungstates. These can be used as components of the activation treatment agent either alone or in combination.

[0064] 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; and Tungstates such as Li2WO4, Na2WO4, K2WO4, Rb2WO4, and CsWO4.

[0065] 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 composite.

[0066] 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.

[0067] 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.

[0068] 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 mass% relative to the total mass of the activation treatment agent.

[0069] 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 mass of the positive electrode active material contained in the positive electrode mixture.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] When the activation treatment agent contains a sodium compound, the content of sodium (by mole) contained in the activation treatment agent may be 1 to 200%, 10 to 200%, 50 to 200%, 100 to 200%, 1% or more but less than 150%, 10% or more but less than 150%, 50% or more but less than 150%, or 100% or more but less than 150% 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 the recycled positive electrode active material more comparable to the charge / discharge characteristics of a battery produced using an unused positive electrode active material.

[0074] 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.

[0075] 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 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 a battery manufactured using the resulting positive electrode active material.

[0076] Furthermore, at least one of the alkali metal compounds contained in the activation treatment agent is preferably 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."

[0077] 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.

[0078] Examples of alkali metal compounds that exhibit alkalinity when dissolved in water and are included in the alkaline activation treatment agent include hydroxides, carbonates, bicarbonates, oxides, peroxides, and superoxides of alkali metals. Specific examples include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; carbonates such as LiCO3, NaCO3, KCO3, RbCO3, and CsCO3; bicarbonates such as LiHCO3, NaHCO3, KHCO3, RbHCO3, and CsHCO3; oxides such as LiO, NaO, KO, RbO, and CsO; peroxides such as LiO2, NaO2, K2O2, RbO2, and CsO2; and superoxides such as LiO2, NaO2, K02, RbO2, and CsO2. The activation treatment agent may contain one or more of these compounds.

[0079] 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. Hereinafter, an activation treatment agent containing such an alkali metal compound may be referred to as an "activation treatment agent having an oxidizing power."

[0080] 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, thereby making it possible to further increase the discharge capacity of a battery manufactured using the obtained positive electrode active material, and furthermore, in some cases to improve the effect of preventing the generation of corrosive gases during the heating process.

[0081] 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.

[0082] Specific examples include superoxides such as Li2O2, Na2O2, K2O2, Rb2O2, and Cs2O2; LiO2, NaO2, KO2, RbO2, and CsO2; nitrates such as LiNO3, NaNO3, KNO3, RbNO3, and CsNO3; sulfates such as Li2SO4, Na2SO4, K2SO4, Rb2SO4, and Cs2SO4; vanadates such as LiVO3, NaVO3, KVO3, RbVO3, and CsVO3; and molybdates such as Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, and CsMoO4.

[0083] Details of the oxidizing power of these alkali metal compounds are described in JP 2012-186150 A.

[0084] 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.

[0085] Process (2): Heating process The heating step is a step in which the mixture obtained in step (1) (hereinafter, sometimes referred to as "mixture before heating") is heated to obtain a heated mixture.

[0086] 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.

[0087] The "melting initiation temperature (Tmp) of the activation treatment agent" refers to the lowest temperature at which a portion of the activation treatment agent exhibits a liquid phase. The melting initiation temperature of the activation treatment agent is a value determined by differential thermal analysis (DTA). That is, when 5 mg of the mixture before heating is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10°C / min), the melting initiation temperature is determined as the temperature at which the DTA signal shows an endothermic peak.

[0088] The melting start temperature 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 of the activation treatment agent, but it may be, for example, 150° C. or higher.

[0089] The melting point of the activation treatment agent refers to the lowest temperature at which a portion 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 of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0090] 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.

[0091] The atmosphere for heating is not particularly limited and may be, for example, 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.

[0092] Examples of heating spaces include gas furnaces, electric furnaces, infrared heating furnaces, plasma heat treatment furnaces, heavy oil furnaces, light oil furnaces, hydrogen heat treatment furnaces, induction heating furnaces, vacuum furnaces, salt bath furnaces, tunnel furnaces, roller hearth kilns, rotary kilns, walking beam furnaces, carbot furnaces, mesh belt furnaces, rotary kilns, shuttle kilns, and fluidized bed furnaces. The heating space is a space in which the mixture to be heated is accommodated, and may be a closed space or an open space with an opening for loading or unloading the mixture. The heating space may be a batch furnace, a continuous furnace, or a fluidized bed furnace. For example, a rotary kiln may be a batch-type rotary kiln or a continuous rotary kiln. When the heating space is a continuous furnace, the heating space may be a gas furnace, electric furnace, infrared heating furnace, plasma heat treatment furnace, heavy oil furnace, light oil furnace, hydrogen heat treatment furnace, induction heating furnace, walking beam furnace, mesh belt furnace, continuous rotary kiln, or continuous shuttle kiln. The fluidized bed calciner may have multiple stages, and the temperature may be changed in each stage.

[0093] The temperature in the heating step may be, for example, the melting start temperature of the activation treatment agent or higher. The temperature in the heating step (maximum temperature in the heating space) may be, for example, 300 to 900°C, 300 to 700°C, or 300 to 600°C.

[0094] In step (2), the pre-heating mixture is heated to a temperature equal to or higher than the melting temperature of the activation treatment agent, which produces the following effects: The contact of the molten activation treatment agent with the positive electrode active material can suppress deterioration of the crystalline structure of the positive electrode active material. It can also restore the crystalline structure.

[0095] The contact of the molten activation treatment agent with the positive electrode active material can suppress deterioration of the crystalline structure of the positive electrode active material, and in some cases can even restore the crystalline structure.

[0096] When the molten activation treatment agent comes into contact with the 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 a fluorine compound derived from 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The temperature in the heating step may be, for example, lower than the melting initiation temperature of the activation treatment agent. 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 lower than the melting initiation temperature of the activation treatment agent). Furthermore, "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.

[0101] 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.

[0102] The heated activation treatment agent comes into contact with the carbon-based conductive material and binder, thereby increasing the rate of oxidative decomposition of the conductive material and binder. Furthermore, the heated activation treatment agent comes into contact with the binder and a fluorine compound derived from the electrolyte, thereby stabilizing the fluorine component 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.

[0103] After the heating step, the mixture can be cooled to any temperature, such as about room temperature, as needed. In this way, a heated mixture containing a heated positive electrode active material is obtained.

[0104] Step (3): First washing step The first water-washing step is a step in which, after the heating step of step (2), the heated mixture is brought into contact with a first liquid containing water and an alkali metal compound, and then a first solid component and a first liquid component are obtained.

[0105] The heated mixture contains, in addition to the heated positive electrode active material, components derived from the activation treatment agent (such as alkali metal compounds), undecomposed conductive material and binder, and other undecomposed materials 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. In the first water-washing step, it is preferable to remove components derived from the activation treatment agent (such as alkali metal compounds), unreacted activation treatment agent, undecomposed conductive material and binder, and other undecomposed materials of the positive electrode mixture, from the viewpoint of increasing the purity of the positive electrode active material and thereby more easily achieving rate characteristics comparable to those of a battery manufactured using unused positive electrode active material.

[0106] Examples of alkali metal compounds contained in the first liquid include hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, and tungstates of alkali metals. The first liquid may contain one or more alkali metal compounds.

[0107] Specific examples of the alkali metal compound contained in the first liquid 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; and Tungstates such as Li2WO4, Na2WO4, K2WO4, Rb2WO4, and CsWO4.

[0108] The alkali metal compound contained in the first liquid may be derived from an activation treatment agent. For example, the first liquid may contain at least a portion of the waste liquid generated after washing the heated mixture with water. That is, the first liquid may be a recycled waste liquid generated after washing the heated mixture with water. For example, at least a portion of the second liquid component generated in the second water-washing step described below may be recycled and used as the first liquid. By using the waste liquid generated after washing the heated mixture with water, it is possible to reduce the amount of waste water generated by water washing when water washing is performed multiple times.

[0109] The amount of water in the first liquid may be 50% by mass or more. The pH of the first liquid may be adjusted by adding components other than water and alkali metal compounds to the first liquid in order to increase the solubility of water-soluble components or to increase the processing speed. For example, the first liquid may contain ammonia as an alkali.

[0110] In the first water-washing step, for example, the heated mixture may be brought into contact with a first liquid to obtain a first slurry, and then the first slurry may be subjected to solid-liquid separation to obtain a first solid component and a first liquid component.

[0111] In the first water-washing step, the heated mixture may be mixed with a first liquid and then stirred to obtain a first slurry. 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.

[0112] The first slurry is separated into a first liquid component and a first solid component by solid-liquid separation. The method for solid-liquid separation of the first slurry may be a conventionally known method, such as filtration or centrifugation.

[0113] The first solid component mainly contains a positive electrode active material. The first liquid component contains water-soluble components other than the positive electrode active material. The first liquid component contains an alkali metal compound, a binder, a fluorine component derived from the electrolyte, and the like.

[0114] The amount of the first liquid to be brought into contact with the heated mixture is appropriately determined taking into consideration the amounts of the positive electrode active material and the water-soluble components other than the positive electrode active material contained in the heated mixture.

[0115] Step (4): Second washing step The second water-washing step is a step of contacting the first solid component with a second liquid that contains water and has a lower content of alkali metal compounds than the first liquid, and then obtaining a second solid component and a second liquid component.

[0116] In addition to the positive electrode active material, the first solid component may contain components (such as alkali metal compounds) derived from the activation treatment agent that were not completely removed in the first water-washing step, and fluorine components derived from the electrolyte. In the second water-washing step, undecomposed conductive material and binder remaining in the first solid component, other undecomposed substances of the positive electrode composite, and fluorine components derived from the electrolyte are further removed.

[0117] The second liquid contains at least water. The second liquid has a lower alkali metal compound content than the first liquid. The second liquid may have an alkali metal compound content of 0% by mass (an embodiment in which the second liquid is substantially free of alkali metal compounds).

[0118] When the second liquid contains an alkali metal compound, examples of the alkali metal compound contained in the second liquid include alkali metal hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, tungstates, etc. The second liquid may contain one or more alkali metal compounds.

[0119] Specific examples of the alkali metal compound contained in the second liquid 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; and Tungstates such as Li2WO4, Na2WO4, K2WO4, Rb2WO4, and CsWO4.

[0120] The alkali metal compound contained in the second liquid may be derived from the activation treatment agent. For example, the second liquid may contain at least a portion of the waste liquid generated after washing the heated mixture with water. In other words, the second liquid may be a recycled waste liquid generated after washing the heated mixture with water. For example, the second liquid may contain at least a portion of the components of the first liquid. This makes it possible to reduce the amount of waste water generated by washing with water when washing with water is performed multiple times.

[0121] The amount of water in the second liquid may be 50% by mass or more. The pH of the second liquid may be adjusted by adding components other than water and alkali metal compounds to the second liquid in order to increase the solubility of the water-soluble components or to increase the processing speed. For example, the second liquid may contain ammonia as an alkali.

[0122] The second liquid may be in a smaller amount than the first liquid. For example, the amount of the second liquid may be 90% or less, 80% or less, 70% or less, or 60% or less of the amount of the first liquid. The smaller the amount of the second liquid, the greater the reduction in the amount of wastewater.

[0123] The second water-washing step may involve, for example, contacting the first solid component with a second liquid to obtain a second slurry, and then subjecting the second slurry to solid-liquid separation to obtain the second solid component and the second liquid component. Alternatively, if the first solid component and the first liquid component are obtained by filtering the first slurry in the first water-washing step, the second water-washing step may involve contacting the filtered first solid component (the first solid component present as a cake on the filter paper) with the second liquid to wash the first solid component with water without forming a slurry, thereby obtaining the second solid component and the second liquid component.

[0124] In the second water-washing step, when a second slurry is obtained, the first solid component and the second liquid may be mixed and then stirred to obtain the second slurry. This promotes dissolution of the water-soluble component. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m / s.

[0125] In the second water washing step, when a second slurry is obtained, the second slurry is subjected to solid-liquid separation to separate the second slurry into a second liquid component and a second solid component. The method for solid-liquid separation of the second slurry may be a conventionally known method, for example, filtration or centrifugation.

[0126] The second solid component mainly contains a positive electrode active material. The second liquid component contains a water-soluble component other than the positive electrode active material. The second liquid component contains an alkali metal compound, a binder, a fluorine component derived from the electrolyte, and the like. The content of the alkali metal compound in the second liquid component may be smaller than the content of the alkali metal compound in the first liquid component.

[0127] The amount of the second liquid to be brought into contact with the first solid component is determined appropriately taking into consideration the amounts of the positive electrode active material and the water-soluble component other than the positive electrode active material contained in the second solid component.

[0128] Step (5): Positive electrode active material recovery step The positive electrode active material recovery step is a step of recovering a recycled positive electrode active material from the second solid component after the second water washing step of step (4).

[0129] After the second water-washing step, further water washing may be performed to further remove components derived from the activation treatment agent, fluorine components derived from the electrolyte, etc. In other words, the positive electrode active material recovery step may include a third, fourth, fifth, ..., nth water-washing step (n is an integer of 3 or more).

[0130] The positive electrode active material recovery step may include, for example, a step of exposing the second solid component to a heated and / or reduced pressure environment to remove water from the second solid component (drying step). When further water washing is performed after the second water washing step, the drying step is a step of exposing the solid component obtained after the final water washing step to a heated and / or reduced pressure environment to remove water from the solid component.

[0131] In the drying step, 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 heating temperature range can be, for example, 10°C or higher and lower than 900°C.

[0132] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 -10 ~1.0×10 3 It can be Pa.

[0133] The positive electrode active material recovery step may include, for example, a step of heat-treating the second solid component (annealing step). When the activation treatment agent is heated to a temperature equal to or higher than the melting initiation temperature and the positive electrode active material recovery step includes a drying step, the annealing step may be, for example, a step of heat-treating the dried solid component at a temperature lower than 900°C.

[0134] When the activation treatment agent is heated at a temperature below the melting initiation temperature and the positive electrode active material recovery step includes a drying step, the annealing step may be, for example, a step of heating the dried solid component at a temperature higher than that of 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 making it easier to achieve charge-discharge characteristics comparable to those of a battery produced using unused positive electrode active material by sufficiently increasing the crystallite size of the positive electrode active material.

[0135] In the annealing step, the atmosphere for the heat treatment is not particularly limited, but it is preferably an oxygen-containing atmosphere such as air. The heat treatment temperature can be 100°C or higher. The heat treatment holding time can be 1 minute to 24 hours. In particular, it is preferable to heat at a temperature of 350°C or higher for 0.1 to 5 hours.

[0136] [Second embodiment] The method for producing a recycled positive electrode active material according to the second embodiment of the present invention includes the following steps: Note that, to the extent technically possible, the description of the first embodiment can be applied to the second embodiment as appropriate. Step (1): A step of mixing a positive electrode mixture containing a positive electrode active 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 Step (3): A step of contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component. Step (4): A step of contacting the first solid component with a second liquid containing water and at least a portion of the first liquid component, and then obtaining a second solid component and a second liquid component. Step (5): Recovering the recycled positive electrode active material from the second solid component

[0137] The method for producing a recycled cathode active material according to the second embodiment also makes it possible to reduce the amount of wastewater generated by water washing, even when multiple water washings are performed. In the method for producing a recycled cathode active material according to the second embodiment, a liquid containing at least a portion of the first liquid component generated in the first water washing is used as the liquid for the second water washing. The waste liquid (first liquid component) generated in the first water washing contains alkali metal compounds derived from the activation treatment agent, but the alkali metal compounds in the first liquid are present at a concentration below saturation. Therefore, even when the first liquid component is used as the liquid for the second water washing, the liquid for the second water washing can dissolve alkali metal compounds derived from the activation treatment agent (especially readily soluble alkali metal compounds such as fluorides of sodium and potassium, carbonates, etc.). Therefore, alkali metal compounds derived from the activation treatment agent can be removed in the same manner as in conventional water washing methods using pure water, etc. Therefore, by reusing the first liquid component as the second liquid, it is possible to reduce the amount of wastewater while removing alkali metal compounds derived from the activation treatment agent in the same manner as in conventional methods.

[0138] [Third embodiment] A method for producing a recycled positive electrode active material according to a third embodiment of the present invention includes the following steps: Note that, to the extent technically possible, the description of the first embodiment can be applied appropriately to the third embodiment. Step (1): A step of mixing a positive electrode mixture containing a positive electrode active 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 Step (3): A step of contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component. Step (4): A step of contacting the first solid component with a second liquid containing water and in an amount smaller than the first liquid, and then obtaining a second solid component and a second liquid component. Step (5): Recovering the recycled positive electrode active material from the second solid component

[0139] The method for producing a recycled cathode active material according to the third embodiment also makes it possible to reduce the amount of wastewater generated by water washing when washing with water multiple times. In the method for producing a recycled cathode active material according to the third embodiment, the liquid (second liquid) used in the second water wash is smaller than the liquid (first liquid) used in the first water wash. The inventors' research has revealed that even if the second liquid is smaller than the first liquid, the first water wash can remove most of the components derived from the activation treatment agent and the fluorine components derived from the electrolyte. Therefore, even if the second liquid is used in a small amount, it is possible to sufficiently remove the remaining components derived from the activation treatment agent and the fluorine components derived from the electrolyte. Therefore, when producing a recycled cathode active material, by using a second liquid in a smaller amount than the first liquid, it is possible to reduce the amount of wastewater while removing undecomposed conductive material, fluorine components derived from the electrolyte, and the like, as in conventional methods.

[0140] The recycled cathode active material obtained from the battery mixture by using the method for producing the recycled cathode active material according to each embodiment of the present invention can be reused in the same way as unused active material. Methods for producing cathodes and batteries using recycled cathode active materials are well known.

[0141] The discharge capacity of the finally obtained recycled positive electrode active material according to each embodiment of the present invention can be 150 mAh / g or more. [Example]

[0142] 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.

[0143] Measurement of the physical properties of the positive electrode active material and the recycled positive electrode active material, and charge / discharge tests using a battery using the positive electrode active material were carried out as follows.

[0144] [Element content] The content of alkali metal elements in the solution and the acid solution in which the powder was dissolved was analyzed using an ICP optical emission spectrometer (for example, SPS3000 manufactured by SII NanoTechnology Inc.).

[0145] (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.

[0146] 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.

[0147] <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.

[0148] <Production of positive electrodes before recycling> The positive electrode active material is composed of Li 1.07 Ni 0.47 Mn 0.48 Fe 0.05 A 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

[0149] 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.

[0150] 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.

[0151] 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.

[0152] (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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] (Comparative Example 1) A pre-heated mixture is obtained in the same manner as in Reference Example 1. The mixture is placed in an alumina firing container and placed in an electric furnace, where it is heated at a rate of 200°C / hour, to a heating temperature of 700°C (above the melting point of the activation treatment agent), and for 240 minutes. The heated mixture is allowed to cool naturally to room temperature, and then the heated mixture is recovered.

[0158] The heated mixture is pulverized, and distilled water A1 is added and stirred to obtain slurry A. The obtained slurry A is subjected to suction filtration to separate into a cake on the filter paper (solid component A1) and a filtrate (liquid component A1). Distilled water A2 in an amount equal to the amount of distilled water A1 is added to the cake on the filter paper (solid component A1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component A2) and a filtrate (liquid component A2). Both liquid components A1 and A2 contain K2CO3 and Na2CO3.

[0159] The cake on the filter paper (solid component A2) is collected and dried at 300°C for 6 hours to obtain recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are comparable to those of the positive electrode active material before recycling (unused active material). In charge-discharge tests using coin-type batteries fabricated using the recycled positive electrode active material, the 0.2C and 5C discharge capacities measured are comparable to those of the positive electrode active material before recycling (unused active material).

[0160] Example 1 The heated mixture is pulverized in the same manner as in Comparative Example 1. The pulverized heated mixture is mixed with the same amount of liquid component A2 as distilled water A1 in Comparative Example 1 to obtain slurry B. The obtained slurry B is subjected to suction filtration to separate into a cake on the filter paper (solid component B1) and a filtrate (liquid component B1). Distilled water B2 in an amount equal to the liquid component A2 is added to the cake on the filter paper (solid component B1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component B2) and a filtrate (liquid component B2).

[0161] The cake on the filter paper (solid component B2) is collected and dried at 300°C for 6 hours to obtain recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are similar to those of the positive electrode active material before recycling (unused active material). The discharge capacity measured in a charge / discharge test using a coin-type battery made using the recycled positive electrode active material is similar to that of the positive electrode active material before recycling (unused active material).

[0162] Example 2 The heated mixture is pulverized in the same manner as in Comparative Example 1. The pulverized heated mixture is mixed with distilled water C1 in an amount equal to the distilled water A1 in Comparative Example 1 to obtain slurry C. The obtained slurry C is subjected to suction filtration to separate into a cake on the filter paper (solid component C1) and a filtrate (liquid component C1). A mixture of distilled water and liquid component C1 (distilled water:liquid component = 1:1 (volume ratio)) is added to the cake on the filter paper (solid component C1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component C2) and a filtrate (liquid component C2).

[0163] The cake on the filter paper (solid component C2) is collected and dried at 300°C for 6 hours to obtain recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are similar to those of the positive electrode active material before recycling (unused active material). The discharge capacity measured in a charge / discharge test using a coin-type battery made using the recycled positive electrode active material is similar to that of the positive electrode active material before recycling (unused active material).

[0164] Example 3 The heated mixture is pulverized in the same manner as in Comparative Example 1. The pulverized heated mixture is mixed with distilled water D1 in an amount equal to the distilled water A1 in Comparative Example 1 to obtain slurry D. The obtained slurry D is subjected to suction filtration to separate it into a cake on the filter paper (solid component D1) and a filtrate (liquid component D1). Distilled water D2 is added to the cake on the filter paper (solid component D1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component D2) and a filtrate (liquid component D2). The amount of distilled water D2 is made less than the amount of distilled water D1.

[0165] The cake on the filter paper (solid component D2) is collected and dried at 300°C for 6 hours to obtain recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are similar to those of the positive electrode active material before recycling (unused active material). The discharge capacity measured in a charge / discharge test using a coin-type battery made using the recycled positive electrode active material is similar to that of the positive electrode active material before recycling (unused active material).

[0166] (Comparative Example 2) A pre-heated mixture is obtained in the same manner as in Reference Example 2. The mixture is placed in an alumina firing container and placed in an electric furnace, where it is heated at a temperature increase rate of 300°C / hour, at a heating temperature of 450°C (below the melting point of the activation treatment agent), and for 360 minutes. The heated mixture is allowed to cool naturally to room temperature, and then the heated mixture is recovered.

[0167] The heated mixture is pulverized, and distilled water E1 is added and stirred to obtain slurry E. The obtained slurry E is subjected to suction filtration to separate into a cake on the filter paper (solid component E1) and a filtrate (liquid component E1). Distilled water E2 in an amount equal to the distilled water E1 is added to the cake on the filter paper (solid component E1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component E2) and a filtrate (liquid component E2). Both liquid components E1 and E2 contain Li2CO3 and Na2SO4.

[0168] The cake on the filter paper (solid component E2) is collected and dried at 300°C for 6 hours. The solid component E2 is then heated in an air atmosphere at 900°C for 60 minutes to obtain a recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are comparable to those of the unrecycled positive electrode active material (unused active material). Furthermore, the 0.2C and 5C discharge capacities measured in charge-discharge tests using coin-type batteries made using the recycled positive electrode active material are comparable to those of the unrecycled positive electrode active material (unused active material).

[0169] Example 4 The heated mixture is pulverized in the same manner as in Comparative Example 2. The pulverized heated mixture is mixed with a liquid component E2 in an amount equal to the distilled water E1 in Comparative Example 2 to obtain a slurry F. The obtained slurry F is subjected to suction filtration to separate it into a cake on the filter paper (solid component F1) and a filtrate (liquid component F1). Distilled water F2 in an amount equal to the liquid component E2 is added to the cake on the filter paper (solid component F1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component F2) and a filtrate (liquid component F2).

[0170] The cake on the filter paper (solid component F2) is collected and dried at 300°C for 6 hours. The solid component F2 is then heated in an air atmosphere at 900°C for 60 minutes to obtain a recycled cathode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled cathode active material are comparable to those of the unrecycled cathode active material (unused active material). The discharge capacity measured in a charge-discharge test using a coin-type battery fabricated using the recycled cathode active material is comparable to that of the unrecycled cathode active material (unused active material).

[0171] Example 5 The heated mixture is pulverized in the same manner as in Comparative Example 2. The pulverized heated mixture is mixed with distilled water G1 in an amount equal to the distilled water E1 in Comparative Example 2 to obtain slurry G. The obtained slurry G is subjected to suction filtration to separate into a cake on the filter paper (solid component G1) and a filtrate (liquid component G1). A mixture of distilled water and liquid component G1 (distilled water:liquid component = 1:1 (volume ratio)) is added to the cake on the filter paper (solid component G1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component G2) and a filtrate (liquid component G2).

[0172] The cake on the filter paper (solid component G2) is collected and dried at 300°C for 6 hours. The solid component G2 is then heated in an air atmosphere at 900°C for 60 minutes to obtain a recycled cathode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled cathode active material are comparable to those of the unrecycled cathode active material (unused active material). The discharge capacity measured in a charge-discharge test using a coin-type battery fabricated using the recycled cathode active material is comparable to that of the unrecycled cathode active material (unused active material).

[0173] Example 6 The heated mixture is pulverized in the same manner as in Comparative Example 2. The pulverized heated mixture is mixed with distilled water H1 in an amount equal to the distilled water E1 in Comparative Example 1 to obtain slurry H. The obtained slurry H is subjected to suction filtration to separate it into a cake on the filter paper (solid component H1) and a filtrate (liquid component H1). Distilled water H2 is poured into the cake on the filter paper (solid component H1), and then suction filtration is performed again to obtain a cake on the filter paper (solid component H2) and a filtrate (liquid component H2). The amount of distilled water H2 is made less than the amount of distilled water H1.

[0174] The cake on the filter paper (solid component H2) is collected and dried at 300°C for 6 hours. The solid component H2 is then heated in an air atmosphere at 900°C for 60 minutes to obtain recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material are comparable to those of the unrecycled positive electrode active material (unused active material). The discharge capacity measured in a charge-discharge test using a coin-type battery fabricated using the recycled positive electrode active material is comparable to that of the unrecycled positive electrode active material (unused active material).

[0175] In Example 1, the wastewater from Comparative Example 1 is reused to wash the mixture after heating, and in Example 4, the wastewater from Comparative Example 2 is reused to wash the mixture after heating, thereby making it possible to reduce the amount of wastewater in the process for producing a recycled positive electrode active material compared to the case where distilled water is used for washing.

[0176] In Examples 2 and 5, the amount of wastewater generated during the production of recycled positive electrode active materials can be reduced by reusing the wastewater (filtrate) generated when the mixture after heating is washed with water.

[0177] In Examples 3 and 6, the amount of distilled water D2 and H2 used in the second water wash was made smaller than the amount of distilled water D1 and H1 used in the first water wash, thereby reducing the amount of wastewater generated during the production of recycled positive electrode active material.

Claims

1. A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water and an alkali metal compound, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and having a lower content of alkali metal compounds than the first liquid, and then obtaining a second solid component and a second liquid component; (5) A step of recovering a recycled positive electrode active material from the second solid component.

2. The method of claim 1 , wherein the second liquid comprises at least a portion of the first liquid component.

3. The method of claim 1 , wherein the second liquid is present in a smaller amount than the first liquid.

4. A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and at least a portion of the first liquid component, and then obtaining a second solid component and a second liquid component; (5) A step of recovering a recycled positive electrode active material from the second solid component.

5. The method of claim 4 , wherein the second liquid is present in a smaller amount than the first liquid.

6. A method for producing a recycled positive electrode active material, comprising the following steps: (1) A step of mixing a positive electrode mixture containing a positive electrode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) a step of heating the mixture to obtain a heated mixture; (3) contacting the heated mixture with a first liquid containing water, and then obtaining a first solid component and a first liquid component; (4) contacting the first solid component with a second liquid containing water and in an amount smaller than the first liquid, and then obtaining a second solid component and a second liquid component; (5) A step of recovering a recycled positive electrode active material from the second solid component.

7. The method according to any one of claims 1 to 6, wherein in the step (2), the mixture is heated to a temperature equal to or higher than the melting point of the activation treatment agent.

8. The method according to any one of claims 1 to 6, wherein in the step (2), the mixture is heated to a temperature below the melting point of the activation treatment agent.