Method for producing recycled positive electrode active material

Abstract

To provide a method for producing a recycled positive electrode active material that can inhibit deterioration of a positive electrode active material due to hot carbon dioxide.SOLUTION: A method for producing a recycled positive electrode active material includes the following steps of: (1) mixing a positive electrode mix containing a positive electrode active material and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; (2) carrying the mixture into a continuous furnace and heating the mixture by supplying air in a direction perpendicular to an advancing direction of the mixture to obtain a heated mixture; and (3) recovering the heated positive electrode active material from the heated mixture.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 the positive electrode active material in a positive electrode mixture, the positive electrode mixture is mixed with an activation treatment agent, and the resulting mixture is then heated. When the mixture is heated, the carbon-containing material in the mixture (e.g., the binder contained in the positive electrode mixture) is burned, generating carbon dioxide. The generated carbon dioxide is then heated to a high temperature in a heating furnace, and it has been found that contact of the high-temperature carbon dioxide with the positive electrode active material in the mixture may cause deterioration of the positive electrode active material.

[0006] Therefore, an object of the present invention is to provide a method for producing a recycled positive electrode active material that can suppress deterioration of the positive electrode active material due to high-temperature carbon dioxide. [Means for solving the problem]

[0007] The present invention includes, for example, the following [1] to [9]. [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 and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) A step of carrying the mixture into a continuous furnace and heating the mixture while blowing air in a direction perpendicular to the direction of travel of the mixture to obtain a heated mixture. (3) recovering the heated positive electrode active material from the heated mixture; [2] The manufacturing method according to [1], wherein the continuous furnace has an air supply port arranged along the bottom surface of the continuous furnace, and the air is supplied through the air supply port. [3] The manufacturing method described in [1], wherein the continuous furnace has an air supply port arranged along the top surface of the continuous furnace, and the air is supplied through the air supply port. [4] The manufacturing method according to any one of [1] to [3], wherein in step (2), when the carbon dioxide concentration in the gas fed into the continuous furnace is compared with the carbon dioxide concentration in the gas exhausted from the continuous furnace, the carbon dioxide concentration in the gas exhausted from the continuous furnace is higher. [5] The method according to any one of [1] to [4], 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. [6] The method according to any one of [1] to [4], wherein in the step (2), the mixture is heated to a temperature below the melting point of the activation treatment agent. [7] The method according to any one of [1] to [6], wherein the positive electrode active material contains a lithium compound. [8] The method according to any one of [1] to [7], wherein the positive electrode active material comprises 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 [9] The method according to any one of [1] to [8], wherein the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds. [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 suppress deterioration of the positive electrode active material due to high-temperature carbon dioxide. 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] A method for producing a recycled positive electrode active material according to one 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 and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. Step (2): The mixture is carried into a continuous furnace, and the mixture is heated while air is blown perpendicular to the direction of the mixture's movement to obtain a heated mixture. Step (3): A step of recovering the heated positive electrode active material from the heated mixture.

[0011] According to one embodiment of the method for producing recycled cathode active material, when a mixture of a cathode composite and an activation treatment agent is heated in a continuous furnace, air is supplied in a direction perpendicular to the direction of travel of the mixture in the continuous furnace. This prevents carbon dioxide from accumulating in the continuous furnace, thereby preventing the carbon dioxide concentration in the continuous furnace from becoming too high. Furthermore, since carbon dioxide is prevented from accumulating in the continuous furnace, it is possible to prevent the carbon dioxide from continuing to heat up in the continuous furnace and becoming too hot. As a result, according to the present invention, it is possible to suppress deterioration of the cathode active material due to high-temperature carbon dioxide. However, the mechanism of the present invention is not limited to the above.

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

[0013] Pre-process (A): Positive electrode composite preparation process First, a positive electrode mixture containing a positive electrode active material and a carbon-containing 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 consist of only a single compound or may be composed of a plurality of 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 2 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 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 Tis 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, and N.

[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 in the above range 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] [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.

[0031] Examples of binders (pre-activation binders) include thermoplastic resins. 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.

[0032] 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.

[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 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).

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

[0036] 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.

[0037] 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.

[0038] 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).

[0039] [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 %.

[0040] The positive electrode mixture may contain a solvent derived from the electrolyte solution, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0041] [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.

[0042] "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.

[0043] 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.

[0044] 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.

[0045] 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 carbon-containing material, etc. 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.

[0046] 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.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] 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

[0052] Furthermore, when the activation treatment agent contains lithium carbonate, lithium may be consumed by the following reaction. LiPF6+4Li2CO3→ 6LiF+Li3PO4+4CO2

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.).

[0059] The activation treatment agent used in this step will be described in detail below.

[0060] <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.

[0061] 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.

[0062] 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.

[0063] 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).

[0064] 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.

[0065] 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.

[0066] 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, etc.; 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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-containing material (carbon-based conductive material, binder, etc.), 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.

[0078] 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."

[0079] 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 batteries manufactured using the recovered positive electrode active material. The use of an alkaline activation treatment agent can also increase the treatment speed of carbon-containing materials (carbon-based conductive materials, binders, etc.).

[0080] 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.

[0081] 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."

[0082] 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.

[0083] 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.

[0084] 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.

[0085] Details of the oxidizing power of these alkali metal compounds are described in JP 2012-186150 A.

[0086] 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.

[0087] Step (2): Heating and air supply step In step (2) (heating and aeration step), the mixture obtained in step (1) (hereinafter sometimes referred to as the "mixture before heating") is carried into a continuous furnace, and the mixture is heated while aeration is supplied perpendicular to the direction of movement of the mixture before heating in the continuous furnace to obtain a mixture after heating. By supplying aeration perpendicular to the direction of movement of the mixture before heating in the continuous furnace, carbon dioxide can be prevented from stagnating in the continuous furnace, and therefore an increase in the carbon dioxide concentration and temperature in the continuous furnace can be suppressed.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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 of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0092] 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.

[0093] The continuous furnace has at least an inlet for carrying in the mixture before heating and an outlet for carrying out the mixture after heating. The continuous furnace may have an air inlet for feeding air, or an exhaust port for exhausting carbon dioxide and the like. The continuous furnace may have multiple air inlets or multiple exhaust ports.

[0094] When the continuous furnace has an air inlet and / or an exhaust port, the location of the air inlet and / or the exhaust port within the continuous furnace may be determined depending on the structure of the continuous furnace, the amount of the mixture before heating, the components contained in the gas to be supplied, the amount of carbon dioxide generated within the continuous furnace, etc. The continuous furnace may, for example, have an air inlet (or multiple air inlets if there are multiple air inlets) arranged along the bottom surface of the continuous furnace and an exhaust port (or multiple exhaust ports if there are multiple exhaust ports) arranged along the top surface of the continuous furnace, an exhaust port (or multiple exhaust ports if there are multiple exhaust ports) arranged along the bottom surface of the continuous furnace and an air inlet (or multiple air inlets if there are multiple air inlets) arranged along the top surface of the continuous furnace, or an air inlet and an exhaust port (or multiple air inlets and multiple exhaust ports if there are multiple air inlets and multiple exhaust ports) arranged along the side of the continuous furnace. The air inlet may be arranged facing the exhaust port, or may be arranged not facing the exhaust port.

[0095] The air is fed into the continuous furnace in a direction perpendicular to the direction of movement of the mixture in the continuous furnace. Generally, the direction of movement of the mixture is along the bottom, top, or side of the continuous furnace, and therefore the air is fed into the continuous furnace in a direction perpendicular to the bottom, top, or side of the continuous furnace. The air is fed into the continuous furnace, for example, from an air feed port provided on the bottom of the continuous furnace toward an exhaust port provided on the top of the continuous furnace. From the viewpoint of increasing the exhaust efficiency of carbon dioxide and further suppressing deterioration of the positive electrode active material due to high-temperature carbon dioxide, the air may be fed into the continuous furnace not only in a direction perpendicular to the direction of movement of the mixture in the continuous furnace, but also in a direction opposite to the direction of movement of the mixture in the continuous furnace.

[0096] The gas supply into the continuous furnace may be carried out throughout the entire continuous furnace or only in a partial region of the continuous furnace. The gas supply into the continuous furnace may be carried out in a temperature range where the amount of carbon dioxide generated in the continuous furnace is large, from the viewpoint of increasing the carbon dioxide exhaust efficiency and further suppressing deterioration of the positive electrode active material due to high-temperature carbon dioxide. For example, the gas supply may be carried out in a region where the temperature in the continuous furnace is 300 to 900°C, 300 to 700°C, or 300 to 600°C. The gas supply into the continuous furnace is preferably carried out in a region where the temperature is below the melting start temperature of the activation treatment agent.

[0097] The gas sent into the continuous furnace is not particularly limited, and may be, for example, an oxygen-containing gas such as air, or an inert gas such as nitrogen or argon. Since the gas sent into the continuous furnace is exhausted together with the carbon dioxide generated in the continuous furnace, the carbon dioxide concentration in the gas exhausted from the continuous furnace will be higher than the carbon dioxide concentration in the gas sent into the continuous furnace. The gas exhausted from the continuous furnace may be sent into the continuous furnace again after carbon dioxide has been removed.

[0098] The flow rate of the gas fed into the continuous furnace per 1 L of heating space may be, for example, 0.001 to 1.0 L / min or 0.01 to 0.6 L / min. The flow rate of the gas fed into the continuous furnace per 1 L of heating space can be adjusted appropriately depending on the structure of the continuous furnace, the amount of the mixture before heating, the components contained in the fed gas, the amount of carbon dioxide generated in the continuous furnace, and the like. For example, the flow rate of the gas fed into the continuous furnace per 1 L of heating space may be increased to further reduce the carbon dioxide concentration in the continuous furnace in order to further suppress deterioration of the positive electrode active material. Alternatively, the flow rate of the gas fed into the continuous furnace per 1 L of heating space may be decreased to reduce pressure loss in order to improve energy efficiency. The flow rate of the gas fed into the continuous furnace per 1 L of heating space may be adjusted so that the carbon dioxide concentration in the continuous furnace is equal to or less than a specific value (e.g., 10% by volume or less). The flow rate of the gas fed into the continuous furnace per 1 L of heating space may be substantially the same throughout the continuous furnace, or may vary from one location to another.

[0099] The continuous furnace may be equipped with a means for separating or removing carbon dioxide (for example, a carbon dioxide separating or removing device) from the viewpoint of reducing the carbon dioxide concentration in the continuous furnace. Examples of the means for separating or removing carbon dioxide include a carbon dioxide adsorbent, a carbon dioxide absorbent, and a carbon dioxide separation membrane.

[0100] The residence time of the mixture in the continuous furnace (the time from passing through the inlet to adding the outlet) can be adjusted by adjusting the moving speed of the mixture. The residence time of the mixture in the continuous furnace may be determined depending on the temperature inside the continuous furnace, the amount of the mixture before heating, etc. The residence time of the mixture in the continuous furnace may be, for example, 10 minutes to 24 hours.

[0101] In the continuous furnace, the temperature may change along the direction of movement of the mixture. For example, the continuous furnace may have a region where the temperature gradually increases along the direction of movement of the mixture. The temperature in the continuous furnace (the temperature at any position in the continuous furnace) may be, for example, within a range from room temperature to 2000°C.

[0102] The continuous furnace may have, for example, a low-temperature region located near the inlet, which is a relatively low temperature within the furnace; a temperature-rising region where the temperature gradually increases from the low-temperature region toward the outlet; a constant-temperature region where the temperature is approximately constant; and a temperature-reducing region where the temperature gradually decreases from the constant-temperature region toward the outlet. The temperature of each region and the volume of the space occupied by each region within the continuous furnace can be determined appropriately depending on the structure of the continuous furnace, the amount of the mixture before heating, the components contained in the gas to be fed, the amount of carbon dioxide generated within the continuous furnace, etc. The gas feeding within the continuous furnace may be performed in at least one region selected from the group consisting of the low-temperature region, the temperature-rising region, the constant-temperature region, and the temperature-reducing region.

[0103] The maximum temperature in the continuous furnace (the maximum temperature at any position in the continuous furnace) may be, for example, equal to or higher than the melting point of the activation treatment agent, and may be, for example, 300 to 900°C, 300 to 700°C, or 300 to 600°C.

[0104] In step (2), the pre-heating mixture is heated to a temperature equal to or higher than the melting initiation temperature (Tmp) 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.

[0105] 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.

[0106] 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.

[0107] The maximum temperature in the continuous furnace (the maximum temperature at any position in the continuous furnace) is preferably higher than the melting point of the alkali metal compound contained in the activation treatment agent. When two or more alkali metal compounds are mixed, the melting point of the alkali metal compound may be lower than the melting point of each alkali metal compound alone. When the activation treatment agent contains two or more alkali metal compounds, the eutectic point is taken as the melting point of the alkali metal compound.

[0108] The time for which the mixture is heated at or above the melting 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 or above the melting temperature of the activation treatment agent may be, for example, 1 minute to 24 hours.

[0109] The maximum temperature in the continuous furnace (the maximum temperature at any position in the continuous furnace) may be, for example, not more than the melting temperature of the activation treatment agent, and may be, for example, 300 to 600°C, 350 to 575°C, or 400 to 550°C.

[0110] In step (2), the pre-heating mixture is heated to a temperature below the melting point of the activation 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 unused positive electrode active material. Furthermore, heating the pre-heating mixture together with the activation agent can also restore the crystalline structure. In this specification, "heating to a temperature below the melting point of the activation agent" means heating while maintaining the temperature below the melting point of the activation agent (heating at a temperature maintained below the melting point of the activation agent). Furthermore, "heating to a temperature below the melting point of the activation agent" means not heating at a temperature equal to or higher than the melting point of the activation agent.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Step (3): Positive electrode active material recovery step The positive electrode active material recovery step is a step of recovering the heated positive electrode active material from the heated mixture after the heating step (2).

[0115] The mixture after heating contains not only the heated positive electrode active material, but also components derived from the activation treatment agent (such as alkali metal compounds), undecomposed carbon-containing materials (such as carbon-based 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.

[0116] Examples of methods for separating and recovering the heated positive electrode active material from the heated mixture include a solid-liquid separation method in which a solvent such as water is added to the mixture to form a slurry, followed by solid-liquid separation, and a vaporization separation method in which the mixture is heated to vaporize and separate components other than the heated positive electrode active material. The solid-liquid separation method will be described below.

[0117] Step (3a): Solid-liquid separation step Step (3a) is a step of contacting the heated mixture with a liquid containing water to obtain a slurry containing a solid component and a liquid component, and then separating the slurry into the solid component and the liquid component.

[0118] The heated mixture contains not only the heated positive electrode active material, but also components derived from the activation treatment agent (such as alkali metal compounds), undecomposed carbon-containing materials (such as carbon-based conductive materials and binders), and other undecomposed substances 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.

[0119] In order to separate and recover the heated positive electrode active material from the heated mixture, a liquid containing water (liquid) is added to the mixture to form a slurry, which is then subjected to solid-liquid separation to separate the solid component and the liquid component.

[0120] The liquid used in the slurrying step 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. 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.

[0121] The resulting slurry contains a solid component mainly containing the positive electrode active material after heating and a liquid component containing water-soluble components other than the positive electrode active material, including an alkali metal component derived from the activation treatment agent and / or a fluorine component derived from the binder and the electrolyte.

[0122] The amount of liquid to be added to the mixture is appropriately determined taking into consideration the amounts of the post-heating positive electrode active material and the water-soluble components other than the positive electrode active material contained in the mixture.

[0123] In step (3a), it is preferable to obtain a slurry by stirring the heated mixture with a liquid containing water. 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.

[0124] The slurry formed in the slurrying step is then subjected to solid-liquid separation. Solid-liquid separation is a step of separating the 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.

[0125] In step (3a), 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 a liquid containing water to obtain a slurry, and then the slurry is again separated into a solid component and a liquid component. In step (3a), rinsing may be performed multiple times. The slurry concentration in the rinse can also be the same as above.

[0126] In this specification, a positive electrode active material that has undergone steps (1) to (3) is referred to as a recycled positive electrode active material. The recycled positive electrode active material that has undergone steps (1) to (3) can be suitably used in the production of a positive electrode, etc. The method for producing a recycled positive electrode active material may include additional steps before and after steps (1) to (3). In this specification, a positive electrode active material that has undergone additional steps other than steps (1) to (3) is also referred to as a recycled positive electrode active material. Examples of additional steps other than steps (1) to (3) are pre-steps (A) and (B) that are performed before step (1), and the following steps (4) and (5) that are performed after step (3), for example, step (3a).

[0127] Process (4): Drying process Step (4) is a step of removing water from the solid component obtained in step (3a), for example, by heating and / or exposing the solid component to a reduced pressure environment.

[0128] 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.

[0129] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 -10 ~1.0×10 3 It can be Pa.

[0130] Step (5): Annealing (re-firing) step Step (5) may be a step of heat treating the solid component after step (4) at a temperature lower than 900°C when the activation treatment agent is heated to a temperature equal to or higher than the melting initiation temperature.

[0131] When the activation treatment agent is heated at a temperature lower than the melting initiation temperature, step (5) may be a step of heating the solid component obtained after step (4) at a temperature higher than that of step (2). In this case, the temperature to which the mixture is heated after heating 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.

[0132] The heat treatment atmosphere 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 holding temperature of 350°C or higher for 0.1 to 5 hours is preferable.

[0133] The recycled cathode active material obtained from the battery mixture by using the method for producing the recycled cathode active material 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.

[0134] 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]

[0135] 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.

[0136] 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.

[0137] [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.).

[0138] (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.

[0139] 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.

[0140] <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.

[0141] <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

[0142] 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.

[0143] 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.

[0144] 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.

[0145] (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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] Example 1 The electrode mixture is mechanically scraped off from the positive electrode prepared above, and the electrode mixture is peeled off from the current collector. 5 g of the electrode mixture removed from the positive electrode is mixed with 0.1 mol of K2CO3 and 0.1 mol of Li2CO3 as activation treatment agents per 1 mol of the positive electrode active material in the electrode mixture to obtain a mixture (mixture before heating).

[0151] The pre-heated mixture is loaded into a continuous furnace. The furnace has an air inlet at the bottom, which feeds air perpendicular to the direction of the mixture's movement, and an exhaust port at the top. The mixture is heated while air is fed perpendicular to the direction of the mixture's movement through the furnace from the air inlet to the exhaust port. The air is fed in a continuous furnace at temperatures between 350 and 500°C. The mixture is then heated in the same furnace at temperatures above the activation treatment agent's melting point (700°C). The heating in the series of continuous furnaces is controlled so that the temperature gradually increases from the inlet to the outlet. The maximum temperature of the continuous furnace is 750°C, the residence time is 24 hours, and the heating time above the activation treatment agent's melting point (700°C) is 5 hours. Comparing the carbon dioxide concentration in the gas fed to the continuous furnace with that in the gas exhausted from the continuous furnace, the carbon dioxide concentration in the gas exhausted from the continuous furnace is higher than the carbon dioxide concentration in the gas fed to the continuous furnace. Next, the mixture discharged from the continuous furnace is naturally cooled to room temperature, and the heated mixture is recovered.

[0152] The heated mixture is pulverized, distilled water is added, and the mixture is stirred to obtain a slurry. The resulting slurry is filtered to separate the solid and liquid components. The solid component is then collected and dried at 300°C for 6 hours. The dried solid component is placed in an alumina container, which is then placed in an electric furnace. Under atmospheric pressure, the ambient gas is evacuated and air is supplied. The temperature is increased from room temperature to 700°C at a rate of 300°C / hour, and the solid component is then heat-treated at 700°C for 1 hour (excluding the heating time). After natural cooling to room temperature, the recycled positive electrode active material is obtained. 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 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).

[0153] In Example 1, by supplying air in a direction perpendicular to the direction of travel of the mixture in the continuous furnace, it is possible to exhaust part of the carbon dioxide generated by heating in the continuous furnace and prevent carbon dioxide from accumulating in the continuous furnace. This makes it possible to prevent the carbon dioxide generated in the continuous furnace from becoming highly concentrated and heated, and therefore makes it possible to produce a recycled cathode active material while suppressing deterioration of the cathode active material due to high-temperature carbon dioxide.

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 and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. (2) A step of carrying the mixture into a continuous furnace and heating the mixture while blowing air in a direction perpendicular to the direction of travel of the mixture to obtain a heated mixture. (3) A step of recovering the heated positive electrode active material from the heated mixture.

2. The manufacturing method according to claim 1 , wherein the continuous furnace has an air supply port disposed along a bottom surface of the continuous furnace, and the air is supplied through the air supply port.

3. The manufacturing method according to claim 1 , wherein the continuous furnace has an air supply port arranged along a top surface of the continuous furnace, and the air is supplied through the air supply port.

4. The manufacturing method according to any one of claims 1 to 3, wherein in the step (2), when the carbon dioxide concentration in the gas fed into the continuous furnace is compared with the carbon dioxide concentration in the gas exhausted from the continuous furnace, the carbon dioxide concentration in the gas exhausted from the continuous furnace is higher.

5. The method according to any one of claims 1 to 3, 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.

6. The method according to any one of claims 1 to 3, wherein in the step (2), the mixture is heated to a temperature below the melting point of the activation treatment agent.

7. The method according to any one of claims 1 to 3, wherein the positive electrode active material contains a lithium compound.

8. The positive electrode active material comprises 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. The manufacturing method according to any one of claims 1 to 3. Element group 1: Ni, Co, Mn, Fe, Al, and P Element group 2: Li, Na, K, Ca, Sr, Ba, and Mg

9. The method according to any one of claims 1 to 3, wherein the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds.