Production method for recycled positive electrode active material

Abstract

To provide a production method for a recycled positive electrode active material by which the charge and discharge characteristics of a battery produced using the recycled positive electrode active material can be made further comparable to those of a battery produced using an unused positive electrode active material.SOLUTION: The production method for a recycled positive electrode active material includes the following steps of: (1) 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 so as to obtain a mixture; (2) heating the mixture to a temperature lower than the melting onset temperature of the activation treatment agent so as 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 composite with an activation treatment agent containing an alkali metal compound, heating the mixture to a temperature equal to or higher than the melting point of the activation treatment agent, and removing decomposition products 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] The positive electrode mixture includes the positive electrode mixture in the positive electrode recovered from discarded batteries and the positive electrode mixture in the positive electrode waste generated in the process of manufacturing the positive electrode or the battery. In recent years, not only has recycling of the positive electrode active material from the positive electrode mixture in the positive electrode recovered from discarded batteries been studied, but also recycling of the positive electrode active material from the positive electrode mixture in the positive electrode waste generated in the process of manufacturing the positive electrode or the battery has been studied.

[0006] Therefore, an object of the present invention is to provide a method for producing a recycled positive electrode active material that can 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. [Means for solving the problem]

[0007] The present invention includes, for example, the following [1] to [5]. [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 a temperature lower than the melting point of the activation treatment agent 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 in the step (3), the mixture after heating is heated at a temperature higher than that in the step (2), and the heated positive electrode active material is recovered. [3] The method according to [1] or [2], wherein the positive electrode active material contains a lithium compound. [4] The method according to any one of [1] to [3], 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 [5] The method according to any one of [1] to [4], 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 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. 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 with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture. Step (2): Heating the mixture to a temperature lower than the melting point of the activation treatment agent to obtain a heated mixture. Step (3): A step of recovering the heated positive electrode active material from the heated mixture.

[0011] In one embodiment, a method for producing a recycled cathode active material involves heating a mixture of a cathode composite and an activation agent to a temperature below the melting point of the activation agent, and then recovering the heated cathode active material from the mixture. The inventors have found that it is possible to produce a recycled cathode active material without heating the mixture above the melting point of the activation agent, as in the conventional method. They have also found that the charge-discharge characteristics of a battery produced using the recycled cathode active material can be made more comparable to those of a battery produced using virgin cathode active material. The inventors speculate that the reasons for this are as follows.

[0012] That is, the cathode composites in cathode waste generated during the manufacturing process of cathodes or batteries (e.g., cathode end portions, non-standard cathodes) are hardly degraded. Furthermore, even among cathode composites recovered from discarded batteries, some are relatively degraded. Therefore, when these relatively degraded cathode composites are mixed with an activation treatment agent and the resulting mixture is heated, the cathode active material can be sufficiently activated even at a low heating temperature. Furthermore, the low heating temperature suppresses the elution of metals in the cathode active material into the molten salt reaction field of the activation treatment agent, thereby achieving charge / discharge characteristics comparable to those of batteries manufactured using unused cathode active material. Furthermore, after heating the mixture of the cathode composite and the activation treatment agent, the mixture is heated at a temperature higher than that used in the heating step to sufficiently increase the crystallite size, thereby improving the charge / discharge characteristics. For these reasons, the present invention makes it possible to make the charge-discharge characteristics of a battery manufactured using a recycled cathode active material more comparable to those of a battery manufactured using a virgin cathode active material. However, the mechanism of the present invention is not limited to the above.

[0013] Each step will be described in detail below.

[0014] Pre-process (A): Positive electrode composite preparation process First, a positive electrode mixture containing a positive electrode active material is prepared.

[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 <00,00129>, , ,

[0020] , T , 1 , ,

[0021] , , T , , 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 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 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] [Binder] The positive electrode mixture may contain a binder. When the positive electrode mixture contains a binder, particles of the positive electrode active material may be bound to each other by the binder.

[0031] 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.

[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] The positive electrode mixture may contain a conductive material 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 positive electrode mixture may contain a fluorine compound derived from the binder and / or the electrolytic solution (e.g., the electrolyte in the electrolytic solution).

[0034] Examples of the conductive material include metal-based conductive materials such as metal particles; and carbon-based conductive materials made of carbon materials.

[0035] 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).

[0036] The carbonaceous conductive material may be a single carbon material or may be made up of multiple carbon materials.

[0037] 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.

[0038] 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.

[0039] [Electrolytes and Solvents] The electrolyte is a component derived from the battery's electrolytic solution and impregnated into the positive electrode mixture. Examples of the electrolyte include LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2F)2, and LiCF3SO3. 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 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.

[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; 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 composite.

[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-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.

[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 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.

[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] Process (2): Heating process The heating step is a step of heating the mixture obtained in step (1) (hereinafter sometimes referred to as the "mixture before heating") to a temperature below the melting initiation temperature of the activation treatment agent. The mixture obtained in this heating step is sometimes referred to as the "mixture after heating." In this specification, "heating to a temperature below the melting initiation temperature of the activation treatment agent" means heating while maintaining the temperature below the melting initiation temperature of the activation treatment agent (heating at a temperature maintained below the melting initiation temperature of the activation treatment agent). Furthermore, "heating to a temperature below the melting initiation temperature of the activation treatment agent" means not heating at a temperature equal to or higher than the melting initiation temperature of the activation treatment agent.

[0088] The "melting initiation temperature (Tmp) of the activation treatment agent" means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0089] The melting initiation temperature (Tmp) of the activation treatment agent is a value determined by differential thermal analysis (DTA). That is, 5 mg of the mixture before heating is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10°C / min), and the temperature at which the DTA signal shows an endothermic peak is defined as the melting initiation temperature (Tmp).

[0090] The temperature to which the mixture before heating is heated may be 700°C or lower, 650°C or lower, 600°C or lower, or 550°C or lower, from the viewpoint of suppressing deterioration of the crystalline structure of the positive electrode active material due to contact of hydrogen fluoride, carbon dioxide, and water, which are produced by decomposition of the binder, conductive material, and the like contained in the positive electrode mixture, with the positive electrode active material, and making it easier to achieve charge / discharge characteristics comparable to those of a battery produced using unused positive electrode active material.

[0091] The temperature to which the mixture before heating is heated may be 150°C or higher, 200°C or higher, 250°C or higher, 300°C or higher, 350°C or higher, 400°C or higher, or 450°C or higher, from the viewpoint of promoting decomposition of the binder, conductive material, etc., and making it easier to achieve charge / discharge characteristics comparable to those of a battery produced using an unused positive electrode active material.

[0092] The melting initiation temperature (Tmp) of the activation treatment agent is preferably 900° C. or lower, more preferably 800° C. or lower, even more preferably 700° C. or lower, and particularly preferably 600° C. or lower. There is no lower limit to the melting initiation temperature (Tmp) of the activation treatment agent, but it may be, for example, 150° C.

[0093] The melting point of an 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 (Tmp) of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0094] 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.

[0095] The atmosphere for heating is not particularly limited, and may be an oxygen-containing gas such as air, nitrogen, argon, carbon dioxide, or a mixture of these gases. The pressure of the atmosphere is not particularly limited, and may be atmospheric pressure, a reduced pressure atmosphere, or a pressurized atmosphere.

[0096] In step (2), the mixture before heating is heated to a temperature below the melting initiation temperature (Tmp) of the activation treatment agent as described above, whereby the following effects occur.

[0097] By heating the pre-heating mixture to a temperature below the melting point (Tmp) of the activation treatment agent, hydrogen fluoride and carbon dioxide produced by decomposition of the binder, conductive material, etc. contained in the positive electrode mixture are rapidly generated, and this prevents deterioration of the crystalline structure of the positive electrode active material due to contact of these with the positive electrode active material, making it easier to achieve charge / discharge characteristics comparable to those of a battery manufactured using unused 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.

[0098] The contact of the heated activation treatment agent with the carbon-based conductive material and binder increases the rate of oxidative decomposition of the conductive material and binder. Furthermore, the contact of the heated activation treatment agent with the fluorine compounds derived from the binder, electrolyte, etc. stabilizes the fluorine components as alkali metal fluorides, preventing the generation of hydrogen fluoride, a corrosive gas, and further suppressing deterioration of the crystalline structure of the positive electrode active material.

[0099] 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.

[0100] 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, binder, conductive material, and 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 1000°C, and the holding time is about 10 minutes to 24 hours.

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

[0102] After the heating step, the mixture can be cooled to any temperature (for example, about room temperature) as needed. In this way, a heated mixture containing a heated positive electrode active material is obtained.

[0103] 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 (or the solid component obtained in step (3a), the solid component obtained in step (3b), or the solid component obtained in step (3c)) after the heating step of step (2).

[0104] 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 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 step (3), it is preferable to remove the 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 making it easier to achieve rate characteristics comparable to those of a battery manufactured using unused positive electrode active material.

[0105] 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.

[0106] 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.

[0107] 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), and undecomposed materials of the positive electrode mixture, such as undecomposed conductive material and binder. 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] Process (3b): Drying process Step (3b) is, for example, a step of removing water from the solid component obtained in step (3a) by heating and / or exposing the solid component to a reduced pressure environment.

[0117] 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.

[0118] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 -10 ~1.0×10 3 It can be Pa.

[0119] Process (3c): Annealing process Step (3c) is a step of heating the mixture after heating (or the solid component obtained in step (3a) or the solid component obtained in step (3b)) at a temperature higher than that in step (2).

[0120] The temperature to which the mixture after heating 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 the crystallite size of the positive electrode active material sufficiently large, thereby more easily achieving charge / discharge characteristics comparable to those of a battery produced using unused positive electrode active material.

[0121] The temperature to which the heated mixture is heated may be equal to or higher than the melting temperature of the activation treatment agent, from the viewpoint of making it easier to achieve charge-discharge characteristics comparable to those of a battery manufactured using an unused positive electrode active material by sufficiently increasing the crystallite size of the positive electrode active material. In the annealing step, the heated mixture may be heated at a temperature that is 20°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, 100°C or higher, 150°C or higher, or 200°C or higher than the melting temperature of the activation treatment agent.

[0122] The temperature to which the mixture is heated after heating may be 1500°C or less, 1400°C or less, 1300°C or less, 1200°C or less, 1000°C or less, or 950°C or less, from the viewpoint of suppressing thermal deterioration of the positive electrode active material and making it easier to achieve charge / discharge characteristics comparable to those of a battery produced using an unused positive electrode active material.

[0123] When the heating temperature in step (2) is T1 and the heating temperature in step (3) is T2, T2 / T1 may be 1.4 or more, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, or 2 or more, from the viewpoint of more easily achieving charge / discharge characteristics comparable to those of a battery produced using an unused positive electrode active material, and from the same viewpoint, may be 2.5 or less, 2.4 or less, 2.3 or less, or 2.2 or less.

[0124] When the heating temperature in step (2) is T1 and the heating temperature in step (3) is T2, T2-T1 may be 250°C or higher, 300°C or higher, 350°C or higher, 400°C or higher, 450°C or higher, or 500°C or higher from the viewpoint of more easily achieving charge / discharge characteristics comparable to those of a battery produced using an unused positive electrode active material, and from the same viewpoint, may be 1000°C or lower, 800°C or lower, 700°C or lower, 600°C or lower, or 500°C or lower.

[0125] The atmosphere for the heat treatment is not limited, but an oxygen-containing atmosphere such as air is preferable. The heat treatment holding time can be 1 minute to 24 hours. In particular, it is preferable to heat at a temperature higher than that in step (2) for 0.1 to 5 hours.

[0126] 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 used in the same way as a virgin cathode active material. The method for producing a cathode and a battery using the recycled cathode active material is the same as the method for producing a cathode and a battery using a virgin cathode active material and is well known.

[0127] The charge / discharge characteristics of a battery manufactured using a cathode active material obtained by the method for producing a recycled cathode active material according to one embodiment of the present invention are comparable to those of a battery manufactured using a virgin cathode active material. Specifically, for example, when a battery manufactured using a cathode active material obtained by the method for producing a recycled cathode active material according to one embodiment is subjected to constant-current charging at a current value of 0.2 C up to a maximum charging voltage of 4.3 V in an environment of 25° C., the recyclability of the initial charge capacity (initial charge capacity of a battery manufactured using a recycled cathode active material / initial charge capacity of a battery manufactured using a virgin cathode active material) is 0.98 to 1.02, which is comparable to the initial charge capacity of a battery manufactured using a virgin cathode active material. Furthermore, when a battery manufactured using a positive electrode active material obtained by a method for manufacturing a recycled positive electrode active material according to one embodiment is subjected to constant-current discharge at a current value of 0.2 C to a minimum discharge voltage of 2.5 V in an environment of 25°C, the recycle degree of the initial discharge capacity (initial discharge capacity of a battery manufactured using a recycled positive electrode active material / initial discharge capacity of a battery manufactured using an unused positive electrode active material) is 0.9 to 1.1, which is equivalent to the initial charge capacity of a battery manufactured using an unused positive electrode active material.

[0128] 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). [Example]

[0129] 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.

[0130] <Production of positive electrodes> The positive electrode described below was fabricated according to the following procedure. A mixture was obtained by mixing 90 parts by mass of a positive electrode active material (unused positive electrode active material or recycled positive electrode active material), 3 parts by mass of a binder (manufactured by Kureha Corporation, product number: PVdF#1100), and 7 parts by mass of carbon black (conductive material, manufactured by Denka Company, product number: HS100). A binder solution prepared by dissolving PVdF in NMP in advance was used as the binder PVdF. The mixture was kneaded in an agate mortar 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 52% by mass.

[0131] A 20 μm thick aluminum foil 1085 (manufactured by Nippon Foil Co., Ltd.) for lithium ion secondary battery positive electrode current collector was attached to one side of the foil in an amount of 10.0 ± 0.2 mg / cm of positive electrode active material. 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.

[0132] <Battery manufacturing> The coin-type battery described below was fabricated by the following procedure. A coin-type battery (non-aqueous electrolyte secondary 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 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. The separator used was a laminated film separator in which a heat-resistant porous layer was laminated on a porous film (made of polyethylene). Metallic lithium was used as the negative electrode.

[0133] <Production of positive electrodes before recycling> The positive electrode active material is composed of Li 1.05 Ni 0.34 Co 0.33 Mn 0.33 A positive electrode active material NCM111 was prepared, which had a crystal structure of R-3m and a rated capacity of 160 mAh / g. The rated capacity of this positive electrode active material was 160 mAh / g, and the 1C current was 160 mA / g. The coin-type battery described above was fabricated using this positive electrode active material (unused positive electrode active material), and the initial charge / discharge was performed under the following conditions while maintaining the temperature at 25°C. The initial charge capacity was 178.1 mAh / g, and the initial discharge capacity was 163.1 mAh / g. (conditions) Maximum charging voltage: 4.3V, charging current: 0.2C, constant current / constant voltage charging Minimum discharge voltage: 2.5V, discharge current: 0.2C, constant current discharge

[0134] Example 1 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. 30 g of the electrode composite removed from the cathode was mixed with activation agents (10 mol of Li2CO3 per 100 mol of cathode active material and 10 mol of Na2SO4 per 100 mol of cathode active material) to obtain a mixture (pre-heating mixture). The activation agent had a melting point of 510°C.

[0135] 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.

[0136] The heated mixture was pulverized, and distilled water was added and stirred to obtain a slurry. The obtained slurry was filtered to separate the solid and liquid components. The solid component was then collected and dried under reduced pressure at 100°C for 1 hour.

[0137] The dried solid component was placed in an electric furnace and heated in an air atmosphere at 700°C for 60 minutes to obtain a recycled cathode active material. The 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. A coin-type battery was fabricated using the recycled cathode active material and subjected to initial charge / discharge tests at 25°C under the above conditions. The initial charge capacity was 178.5 mAh / g and the initial discharge capacity was 160.0 mAh / g.

[0138] Example 2 A recycled positive electrode active material was obtained in the same manner as in Example 1, except that the temperature at which the dried solid component was heated was changed to 900°C. The composition, crystal structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 180.5 mAh / g, and the initial discharge capacity was 161.1 mAh / g.

[0139] Example 3 A recycled positive electrode active material was obtained in the same manner as in Example 1, except that the temperature at which the dried solid component was heated was changed to 950°C. The composition, crystal structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 180.4 mAh / g, and the initial discharge capacity was 160.8 mAh / g.

[0140] Example 4 A recycled positive electrode active material was obtained in the same manner as in Example 2, except that 10 mol of Na2CO3 (melting onset temperature: 851°C) was used as an activation treatment agent per 100 mol of positive electrode active material, and 10 g of electrode composite removed from the positive electrode was mixed with the activation treatment agent to obtain a pre-heated mixture. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material were comparable to those of unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 180.4 mAh / g, and the initial discharge capacity was 159.7 mAh / g.

[0141] Example 5 A recycled positive electrode active material was obtained in the same manner as in Example 4, except that the temperature at which the dried solid component was heated was changed to 950°C. The composition, crystal structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 180.7 mAh / g, and the initial discharge capacity was 159.5 mAh / g.

[0142] Example 6 A recycled positive electrode active material was obtained in the same manner as in Example 2, except that 10 mol of K2CO3 (melting onset temperature: 891°C) was used as an activation treatment agent for 100 mol of positive electrode active material, and 10 g of electrode composite removed from the positive electrode was mixed with the activation treatment agent to obtain a pre-heated mixture. The composition, crystal structure, average particle size, and specific surface area of ​​the resulting recycled positive electrode active material were comparable to those of unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 174.0 mAh / g, and the initial discharge capacity was 157.1 mAh / g.

[0143] Example 7 A recycled positive electrode active material was obtained in the same manner as in Example 6, except that the temperature at which the dried solid component was heated was changed to 950°C. The composition, crystal structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 174.4 mAh / g, and the initial discharge capacity was 157.0 mAh / g.

[0144] (Comparative Example 1) A recycled positive electrode active material was obtained in the same manner as in Example 1, except that the temperature at which the mixture was heated before heating was changed to 700°C (above the melting initiation temperature). The composition, crystalline structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions while maintained at 25°C. The initial charge capacity was 172.2 mAh / g, and the initial discharge capacity was 155.9 mAh / g.

[0145] (Comparative Example 2) A recycled positive electrode active material was obtained in the same manner as in Example 2, except that the temperature at which the mixture was heated before heating was changed to 700°C (above the melting initiation temperature). The composition, crystalline structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 172.8 mAh / g, and the initial discharge capacity was 155.9 mAh / g.

[0146] <Production of positive electrodes before recycling> The positive electrode active material is composed of Li 1.18 Ni 0.34 Co 0.33 Mn 0.33 A positive electrode active material NCM111 was prepared, which had a crystal structure of R-3m and a rated capacity of 160 mAh / g. The rated capacity of this positive electrode active material was 160 mAh / g, and the 1C current was 160 mA / g. The coin-type battery described above was fabricated using this positive electrode active material (unused positive electrode active material), and the initial charge / discharge was performed under the following conditions while maintaining the temperature at 25°C. The initial charge capacity was 168.9 mAh / g, and the initial discharge capacity was 156.0 mAh / g. (conditions) Maximum charging voltage: 4.3V, charging current: 0.2C, constant current / constant voltage charging Minimum discharge voltage: 2.5V, discharge current: 0.2C, constant current discharge

[0147] Example 8 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 agents (10 mol of Li2CO3 per 100 mol of cathode active material and 10 mol of Na2SO4 per 100 mol of cathode active material) to obtain a mixture (pre-heating mixture). The activation agent had a melting point of 510°C.

[0148] 40 g of the mixture before heating was placed in an electric furnace and heated in an air atmosphere at a heating rate of 300°C / h, a heating temperature of 500°C (below the melting point of the activation treatment agent), and a heating time of 60 minutes. The air flow rate was 0.5 L / min, and the gas-powder ratio was 5.8 m 3 / kg.

[0149] The heated mixture was pulverized, and distilled water was added and stirred to obtain a slurry. The obtained slurry was filtered to separate the solid and liquid components. The solid component was then collected and dried under reduced pressure at 100°C for 1 hour.

[0150] The dried solid component was placed in an electric furnace and heated in an air atmosphere at 900°C for 360 minutes to obtain a recycled cathode active material. The 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. A coin-type battery was fabricated using the recycled cathode active material and subjected to initial charge / discharge tests at 25°C under the above conditions. The initial charge capacity was 171.9 mAh / g and the initial discharge capacity was 153.0 mAh / g.

[0151] Example 9 The air flow rate when heating the mixture before heating was 1 L / min, and the gas-powder ratio was 11.5 m 3 A recycled positive electrode active material was obtained in the same manner as in Example 8, except that the concentration was changed to 1 / kg. The composition, crystalline structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of the unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 170.2 mAh / g, and the initial discharge capacity was 151.2 mAh / g.

[0152] (Comparative Example 3) The amount of the mixture before heating was 20 g, the temperature at which the mixture before heating was heated was 700°C, the heating time was 360 minutes, the air flow rate was 0.85 L / min, and the gas-powder ratio was 28.7 m3 A recycled positive electrode active material was obtained in the same manner as in Example 8, except that the concentration was changed to 1 / kg. The composition, crystalline structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of the unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 167.6 mAh / g, and the initial discharge capacity was 138.9 mAh / g.

[0153] Comparative Example 4 A recycled positive electrode active material was obtained in the same manner as in Example 8, except that the temperature at which the dried solid component was heated was changed to 950°C. The composition, crystal structure, average particle size, and specific surface area of ​​the obtained recycled positive electrode active material were comparable to those of an unused positive electrode active material. A coin-type battery was fabricated using the recycled positive electrode active material and initially charged and discharged under the above conditions at 25°C. The initial charge capacity was 170.1 mAh / g, and the initial discharge capacity was 135.7 mAh / g.

[0154] Tables 1 and 2 show the heating temperature of the mixture before heating (T1), the heating temperature of the solid component after drying (T2), the ratio of the heating temperature of the mixture before heating to the heating temperature of the solid component after drying (T2 / T1), the difference between the heating temperature of the mixture before heating and the heating temperature of the solid component after drying (T2-T1), the measured initial charge capacity and recycling degree, and the measured initial discharge capacity and recycling degree for each example and comparative example, respectively.

[0155] [Table 1]

[0156] [Table 2]

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 a temperature lower than the melting point of the activation treatment agent to obtain a heated mixture. (3) A step of recovering the heated positive electrode active material from the heated mixture.

2. The method according to claim 1 , wherein in the step (3), the heated mixture is heated at a temperature higher than that in the step (2), and the heated positive electrode active material is recovered.

3. The method of claim 1 , wherein the positive electrode active material comprises a lithium compound.

4. The manufacturing method according to claim 1 , 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

5. The method according to claim 1 , wherein the activation treatment agent comprises at least one compound selected from the group consisting of potassium compounds and sodium compounds.

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