Method for producing recycled positive electrode active material

Abstract

Provided is a method for producing a recycled positive electrode active material including the following steps.　Step (1): a step for obtaining a mixture by mixing a positive electrode mixture containing a positive electrode active material and an activation treatment agent containing one or more alkali metal compounds; step (2): a step for heating the mixture to a temperature equal to or higher than the melting start temperature of the activation treatment agent in the presence of nitrogen having a flow rate equal to or higher than 0.070 L / min per 1 L heating space to obtain a heated mixture; and step (3): a step for recovering the heated positive electrode active material from the heated mixture.

Description

Method for manufacturing recycled positive electrode active material

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

[0002] Positive electrode active materials for batteries contain 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 positive electrode active materials for non-aqueous electrolyte secondary batteries. In order to conserve resources for rare metal components, a method for recycling (reproducing) the rare metal components from waste battery materials of secondary batteries is desired (see, for example, Patent Document 1 below).

[0003] JP 2010-34021 A

[0004] From the viewpoint of recycling rare metal components in a positive electrode active material, it is conceivable to obtain a recycled positive electrode active material by subjecting a positive electrode active material obtained from a waste positive electrode to various treatments. In this case, from the viewpoint of obtaining excellent battery characteristics using the recycled positive electrode active material, it is required to obtain a recycled positive electrode active material with a large crystallite size.

[0005] An object of one aspect of the present invention is to provide a method for producing a recycled positive electrode active material that can produce a recycled positive electrode active material with a large crystallite size.

[0006] In some aspects, the present invention relates to the following [1] to [8]. [1] A method for producing a recycled cathode active material, comprising the following steps: Step (1): mixing a cathode composite containing a cathode 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 equal to or higher than the melting initiation temperature of the activation treatment agent in the presence of nitrogen at a flow rate of 0.070 L / min or more per liter of heating space to obtain a heated mixture; and Step (3): recovering a heated cathode active material from the heated mixture. [2] The method according to [1], wherein the flow rate of the nitrogen in step (2) is 0.070 to 0.600 L / min. [3] The method according to [1] or [2], wherein the proportion of the nitrogen in the atmospheric gas in step (2) is more than 70 vol% and not more than 80 vol%. [4] The method according to any one of [1] to [3], wherein the mixture in step (2) is heated to 600 to 1000°C. [5] The manufacturing 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. [6] The manufacturing method according to any one of [1] to [4], wherein the positive electrode active material contains a lithium compound, and the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds, and a lithium compound. [7] The manufacturing method according to any one of [1] to [6], wherein the positive electrode active material 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 [8] The manufacturing method according to any one of [1] to [7], wherein the positive electrode active material contains a compound represented by the following formula (A): Li １＋ａ M ２ ｂ M １ M Ｔ ｃ O ２＋ｄ X ｅ (A) However, M ２represents at least one element selected from the group consisting of Na, K, Ca, Sr, Ba, and Mg; M １ represents at least one element selected from the group consisting of Ni, Co, Mn, Fe, Al, and P; M Ｔ represents at least one element selected from the group consisting of transition metal elements excluding Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metal elements excluding O and P, and the following conditions are satisfied: -0.4<a<1.5, 0≦b<0.5, 0≦c<0.5, -0.5<d<1.5, and 0≦e<0.5.

[0007] According to one aspect of the present invention, it is possible to provide a method for producing a recycled positive electrode active material that is capable of obtaining a recycled positive electrode active material with a large crystallite size.

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0009] The method for producing recycled cathode active material according to this embodiment includes the following steps: Step (1): Mixing a cathode composite containing a cathode 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 equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent in the presence of nitrogen at a flow rate of 0.070 L / min or more per L of heating space to obtain a heated mixture; and Step (3): Recovering the heated cathode active material from the heated mixture.

[0010] According to the method for producing a recycled cathode active material of this embodiment, a recycled cathode active material with a large crystallite size can be obtained. According to the method for producing a recycled cathode active material of this embodiment, a crystallite size of, for example, 60 nm or more (preferably, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more) can be obtained in the evaluation method described in the Examples below.

[0011] When the activation treatment agent comes into contact with the positive electrode active material, it can activate the positive electrode active material and suppress deterioration of the crystalline structure of the positive electrode active material (and in some cases, even achieve a crystalline structure repair effect). In particular, in step (2), the pre-heating mixture is heated to a temperature equal to or higher than the melting initiation temperature of the activation treatment agent, causing the activation treatment agent to melt (melt). This improves contact between the activation treatment agent (molten activation treatment agent) and the positive electrode active material, thereby promoting activation of the positive electrode active material. Furthermore, if the pre-heating mixture contains a fluorine compound (a compound containing fluorine) derived from the binder and / or the electrolyte (e.g., the electrolyte in the electrolyte), contact of the molten activation treatment agent with the fluorine compound stabilizes the fluorine component as an alkali metal fluoride. This prevents the generation of corrosive hydrogen fluoride, which can reduce the activity of the positive electrode active material. Because it is necessary to thoroughly remove components other than the positive electrode active material when obtaining recycled positive electrode active material, in step (2), components other than the positive electrode active material may oxidize and decompose, generating acidic gases such as carbon dioxide. Furthermore, although an activation treatment agent is used in step (2), hydrogen fluoride may be generated as an acidic gas. The presence of these acidic gases may deteriorate the crystalline structure of the positive electrode active material. On the other hand, according to the method for producing a recycled positive electrode active material according to this embodiment, by heating a mixture containing an activation treatment agent in the presence of nitrogen at the specific flow rate, the acidic gas is easily discharged outside the system and is easily inactivated by dilution with inert nitrogen. This effectively suppresses the deterioration of the crystalline structure of the positive electrode active material, thereby allowing a recycled positive electrode active material with a large crystallite size to be obtained. However, the factors that result in a recycled positive electrode active material with a large crystallite size are not limited to the above factors.

[0012] According to one aspect of the method for producing a recycled cathode active material of this embodiment, excellent battery characteristics can be obtained. For example, although the crystallite size of the cathode active material may become finer due to deterioration of the cathode active material during battery use, according to one aspect of the method for producing a recycled cathode active material of this embodiment, the crystallite size can be restored, thereby restoring the battery characteristics. According to one aspect of the method for producing a recycled cathode active material of this embodiment, excellent discharge rate characteristics (e.g., discharge rate characteristics of a lithium ion battery) can be obtained, and in the evaluation method described in the Examples below (discharge rate test: 5C), a discharge capacity of, for example, 130 mAh / g or more (preferably, 135 mAh / g or more, 138 mAh / g or more) can be obtained. According to one aspect of the method for producing a recycled cathode active material of this embodiment, excellent discharge capacity retention (e.g., discharge capacity retention of a lithium ion battery) can be obtained, and in the evaluation method described in the Examples below, a discharge capacity retention of, for example, 70% or more (preferably, 80% or more, 85% or more) can be obtained. According to one aspect of the method for producing a recycled positive electrode active material according to the present embodiment, it is possible to obtain an excellent initial charge-discharge efficiency (for example, the initial charge-discharge efficiency of a lithium ion battery), and in the evaluation method described in the examples below, it is possible to obtain an initial charge-discharge efficiency of, for example, 90% or more (preferably, 91% or more, 92% or more, etc.).

[0013] The recycled positive electrode active material according to this embodiment is a recycled positive electrode active material obtained by the method for producing a recycled positive electrode active material according to this embodiment (a recycled positive electrode active material finally obtained by the method for producing a recycled positive electrode active material according to this embodiment). The recycled positive electrode active material obtained from a battery mixture or the like by using the method for producing a recycled positive electrode active material according to this embodiment can be reused in the same way as unused active material. Well-known methods can be used to produce a positive electrode or a battery using the recycled positive electrode active material. The recycled positive electrode active material according to this embodiment and its method for producing the same may be used in various batteries, such as nonaqueous electrolyte batteries (e.g., nonaqueous electrolyte secondary batteries), and lithium ion batteries (e.g., lithium ion secondary batteries). The recycled positive electrode active material according to this embodiment may be a positive electrode active material for a lithium battery. The discharge capacity of the recycled positive electrode active material according to this embodiment may be, for example, 150 mAh / g or more.

[0014] The crystallite size of the recycled positive electrode active material according to this embodiment may be in the following ranges. The crystallite size may be 60 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, or 105 nm or more. The crystallite size may be 120 nm or less, 110 nm or less, 100 nm or less, or 95 nm or less. From these viewpoints, the crystallite size may be 60 to 120 nm, 60 to 110 nm, 60 to 100 nm, 80 to 120 nm, 80 to 110 nm, 80 to 100 nm, 100 to 120 nm, or 100 to 110 nm. The crystallite size can be measured by the method described in the examples, and can be calculated by the Scherrer equation using diffraction peaks in an X-ray diffraction spectrum using CuKα radiation as a radiation source. For measuring the crystallite size, for example, "X-ray structural analysis - determining the atomic arrangement -" (3rd edition published on April 30, 2002, written by Waseda Yoshio and Matsubara Eiichiro) can be referred to.

[0015] In this specification, the 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 positive electrodes and the like. The method for producing a recycled positive electrode active material according to this embodiment may include additional steps before and after steps (1) to (3). In this specification, a positive electrode active material that has undergone steps (1) to (3) and additional steps thereafter is also referred to as a "recycled positive electrode active material." Examples of additional steps other than steps (1) to (3) include a step of preparing a positive electrode composite and a step of washing the positive electrode composite, which are performed before step (1), and steps (4) and (5), which are performed after step (3), which are described below.

[0016] Hereinafter, each step in the method for producing a recycled positive electrode active material according to this embodiment will be described in detail.

[0017] (Positive Electrode Composite Preparation Step) The method for producing a recycled positive electrode active material according to this embodiment may include, prior to step (1), a positive electrode composite preparation step of preparing a positive electrode composite containing a positive electrode active material.

[0018] The positive electrode mixture may contain, in addition to the positive electrode active material, a carbon-containing material and at least one selected from the group consisting of a binder, a 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. When the positive electrode mixture contains a binder and a conductive agent, 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).

[0019] [Positive Electrode Active Material] Examples of the positive electrode active material include composite compounds containing one or more of lithium, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, yttrium, niobium, molybdenum, silver, indium, tungsten, and the like as constituent elements.

[0020] The positive electrode active material may be composed of only a single compound, or may be composed of multiple compounds.

[0021] From the viewpoint of facilitating the production of a recycled positive electrode active material with a large crystallite size, 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

[0022] The positive electrode active material preferably contains a compound represented by the following formula (A), from the viewpoint of facilitating the production of a recycled positive electrode active material with a large crystallite size.

[0023] 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, and the following conditions are satisfied: -0.4<a<1.5, 0≦b<0.5, 0≦c<0.5, -0.5<d<1.5, and 0≦e<0.5.

[0024] M Ｔ From the viewpoint of facilitating the production of a recycled positive electrode active material with a large crystallite size, it is preferable that X is 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.

[0025] The positive electrode active material preferably contains a composite oxide containing at least Li and Ni, from the viewpoint of facilitating the production of a recycled positive electrode active material with a large crystallite size.

[0026] In the positive electrode active material, M １ The molar fraction of Ni in the above range is preferably 0.3 to 0.95, from the viewpoint of facilitating the production of a recycled positive electrode active material with a large crystallite size.

[0027] The crystal structure of the positive electrode active material (e.g., composite oxide) is not particularly limited, but from the viewpoint of facilitating the production of recycled positive electrode active materials with large crystallite sizes, a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

[0028] The hexagonal crystal structure is P3, P3 １ , P3 ２ , R3, P-3, R-3, P312, P321, P3 １ 12. P3 １ 21, P3 ２ 12. P3 ２ 21, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P6 １ , P6 ５ , P6 ２ , P6 ４ , P6 ３ , P-6, P6 / m, P6 ３ / m, P622, P6 １ 22, P6 ５ 22, P6 ２ 22, P6 ４ 22, P6 ３ 22, P6mm, P6cc, P6 ３ cm, P6 ３ mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P6 ３ / mcm, and P6 ３ / mmc.

[0029] The monoclinic crystal structure is P2, P2 １ , C2, Pm, Pc, Cm, Cc, P2 / m, P2 １ / m, C2 / m, P2 / c, P2 １ It belongs to any one space group selected from the group consisting of C1 / c, C2 / c, and C3 / c.

[0030] From the viewpoint of facilitating the production of recycled positive electrode active materials with large crystallite sizes, the crystal structure of the positive electrode active material preferably belongs to the R-3m space group contained in a hexagonal crystal structure or the C2 / m space group contained in a monoclinic crystal structure.

[0031] 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.

[0032] The particle size of the positive electrode active material in the positive electrode mixture is not particularly limited, but may be about 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% accumulation from the fine particle side can be used as the average particle size of the positive electrode active material.

[0033] There is no particular limitation on the content of the positive electrode active material in the positive electrode mixture.

[0034] [Binder] Examples of binders 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; styrene-butadiene copolymers (SBR); etc. One type of binder may be used alone, or two or more types may be used in combination.

[0035] 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.

[0036] [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.

[0037] 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).

[0038] The carbonaceous conductive material may be a single carbon material or may be made up of multiple carbon materials.

[0039] The specific surface area of ​​the carbon material used as the carbon-based conductive material is 0.1 to 500 m ２ The carbon-based conductive material may have a specific surface area of ​​30 m ２ / g or more of a carbon material, and ２ / g or more, and ２ / g or more of carbon black, and ２ / g or more, and ２ / g or more, and the specific surface area is 30 m ２ When an activation treatment agent containing an alkali metal compound having oxidizing power, which will be described later, is used, the rate of oxidation treatment of the carbon-based conductive material can be increased, and even a carbon material having a small specific surface area can be oxidized in some cases.

[0040] The content of the conductive material in the positive electrode mixture is not particularly limited, but may be within the following ranges relative to 100 parts by mass of the positive electrode active material. The content of the conductive material may be 0 parts by mass or more, more than 0 parts by mass, 1 part by mass or more, 3 parts by mass or more, or 5 parts by mass or more. The content of the conductive material may be 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less. From these perspectives, the content of the conductive material may be 0 to 50 parts by mass, more than 0 parts by mass and 40 parts by mass or less, 1 to 30 parts by mass, 1 to 10 parts by mass, 3 to 20 parts by mass, or 5 to 10 parts by mass.

[0041] [Electrolyte and Solvent] Examples of the electrolyte include LiPF ６ , LiBF ４ , LiClO ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ F) ２ , LiCF ３ SO ３ The content of the electrolyte contained in the positive electrode mixture is not particularly limited, but may be 0.0005 to 7 mass %.

[0042] The positive electrode mixture may contain a solvent derived from the electrolyte solution, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0043] [Recovery of Positive Electrode Mixture] The positive electrode mix can be obtained by separating and recovering the positive electrode mix layer from a waste positive electrode having a current collector and a positive electrode mix layer.

[0044] "Waste positive electrodes" may refer to positive electrodes recovered from discarded batteries and waste positive electrodes generated during the manufacturing process of positive electrodes or batteries. Discarded batteries may be used batteries or unused, non-standard batteries. 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.

[0045] 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.

[0046] 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.

[0047] (Positive Electrode Composite Washing Step) When the positive electrode composite contains an electrolyte, the method for producing a recycled positive electrode active material according to this embodiment may include a washing step (positive electrode composite washing step) for removing at least a portion (partial or all) of the electrolyte from the positive electrode composite after the positive electrode composite preparation step. In the positive electrode composite washing step, it is preferable to bring the positive electrode composite into contact with an electrolyte washing solvent to remove at least a portion of the electrolyte from the positive electrode composite. Specifically, a positive electrode composite containing a positive electrode active material and an electrolyte is brought into contact with an 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.

[0048] 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.

[0049] 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.

[0050] The cathode mixture can be brought into contact with the electrolyte cleaning solvent in a known powder-liquid contact device (for example, a stirring tank).

[0051] 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.

[0052] 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.

[0053] The above-described washing process can sufficiently remove the electrolyte from the positive electrode mixture. For example, if the electrolyte remains, the following reaction occurs, which may change the structure of the positive electrode active material from a layered rock salt structure to a spinel structure: LiPF ６ +16LiMO ２ +20 ２ → 6 LiF + Li ３ P.O. ４ +8LiM ２ O ４

[0054] Furthermore, when the activation treatment agent contains lithium carbonate, lithium may be consumed by the following reaction: LiPF ６ +4Li ２ CO ３ → 6 LiF + Li ３ P.O. ４ +4CO ２

[0055] The separated solid component may 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.

[0056] (Step (1): Activation Treatment Agent Mixing Step) Step (1) (activation treatment agent mixing step) is a step of mixing a cathode composite containing a cathode active material (for example, a cathode composite obtained in a cathode composite washing step) with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture.

[0057] 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 mixing methods. The order in which the positive electrode mixture and the activation treatment agent are mixed is not particularly limited.

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

[0059] As a mixing method, dry mixing is preferred from the viewpoint of easy mixing. For dry mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a powder mixer equipped with an internal stirring blade, a ball mill, a vibration mill, or a combination of these devices can be used.

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

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

[0062] [Activation Treatment Agent] The activation treatment agent contains one or more alkali metal compounds. From the viewpoint of further enhancing the activation effect of the positive electrode active material, the activation treatment agent preferably contains at least one compound selected from the group consisting of potassium compounds and sodium compounds. In addition to the potassium compound and / or the sodium compound, the activation treatment agent may also contain an alkali metal compound containing another alkali metal such as Li.

[0063] The proportion of all alkali metal compounds in the activation treatment agent is appropriately set in consideration of the type of alkali metal compound, the type of target positive electrode active material, etc., and is preferably 50 mass % or more, more preferably 70 mass % or more, and may be 100 mass % relative to the total mass of the activation treatment agent.

[0064] Of the alkali metals contained in the alkali metal compound, the concentration of at least one alkali metal selected from the group consisting of potassium and sodium 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 are components of the activation treatment agent include alkali metal hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, tungstates, etc. These can be used as components of the activation treatment agent either individually or in combination.

[0066] Specific examples of suitable alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; LiBO ２ , NaBO ２ , KBO ２ , RbBO ２ , CsBO ２ Boric acid compounds such as Li ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , RbCO ３ , CsCO ３ Carbonates such as Li ２ O, Na ２ O.K. ２ O, Rb ２ O, Cs ２ Oxides such as Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb２ O ２ , Cs ２ O ２ Peroxides such as LiO ２ , NaO ２ , K.O. ２ , RbO ２ , CsO ２ superoxides such as LiNO ３ , NaNO ３ , KNO ３ , RbNO ３ , CsNO ３ Nitrates such as Li ３ P.O. ４ , Na ３ P.O. ４ , K. ３ P.O. ４ , Rb ３ P.O. ４ , Cs ３ P.O. ４ phosphates such as Li ２ SO ４ , Na ２ SO ４ , K. ２ SO ４ , Rb ２ SO ４ , Cs ２ SO ４ chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl; bromides such as LiBr, NaBr, KBr, RbBr, and CsBr; LiVO ３ , NaVO ３ , K.V.O. ３ , RbVO ３ , CsVO ３ vanadates such as Li ２ MoO ４ , Na ２ MoO ４ , K. ２ MoO ４ , Rb ２ MoO ４ , CsMoO ４ Molybdates such as Li ２ WO ４ , Na ２ WO ４ , K. ２ WO ４ , Rb ２WO ４ , CsWO ４ and the like tungstates.

[0067] From the viewpoint of further enhancing the activation effect of the positive electrode active material, the activation treatment agent can contain at least one compound selected from the group consisting of potassium compounds and sodium compounds, and a compound (excluding potassium compounds and sodium compounds) containing the same alkali metal element as the alkali metal element contained in the positive electrode active material in the positive electrode composite.

[0068] For example, when the positive electrode active material in the positive electrode mixture contains a lithium compound (a compound containing lithium, such as a lithium composite oxide), the activation treatment agent preferably contains at least one compound selected from the group consisting of potassium compounds and sodium compounds, and a lithium compound. Examples of suitable lithium compounds include LiOH, LiBO, ２ , Li ２ CO ３ , Li ２ O, Li ２ O ２ , LiO ２ , LiNO ３ , Li ３ P.O. ４ , Li ２ SO ４ , LiCl, LiVO ３ , LiBr, Li ２ MoO ４ , Li ２ WO ４ etc.

[0069] The activation treatment agent may contain a compound other than an alkali metal compound, if necessary. 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 may be 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] The content of compounds other than alkali metal compounds in the activation treatment agent may be less than 50% by mass of the total mass of the activation treatment agent.

[0071] The content of the activation treatment agent 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] In the activation treatment agent in the mixture of the positive electrode composite and the activation treatment agent, when the number of moles of the positive electrode active material (for example, the compound represented by the above formula (A)) contained in the positive electrode composite is taken as 1, the number of moles of the alkali metal element in the alkali metal compound in the activation treatment agent may be 0.001 to 200 times.

[0073] By appropriately controlling the ratio of the activation treatment agent in the mixture, the cost of recovering the positive electrode active material from the positive electrode mixture can be reduced, and the treatment speed (oxidative decomposition treatment speed) of the carbon-based conductive material, binder, etc. can be increased. Furthermore, the effect of preventing the generation of corrosive gas in step (2) can be improved. Furthermore, the discharge capacity of a battery manufactured using the recycled positive electrode active material obtained by the method for manufacturing a recycled positive electrode active material according to this embodiment can be further increased.

[0074] 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. The pH of a solution obtained by dissolving an activation treatment agent containing such an alkali metal compound in pure water is greater than 7. Hereinafter, such an activation treatment agent may be referred to as an "alkaline activation treatment agent."

[0075] The use of an alkaline activation treatment agent can further suppress the generation of corrosive gases in step (2), thereby further increasing the discharge capacity of a battery manufactured using the recycled cathode active material obtained by the method for manufacturing a recycled cathode active material according to this embodiment. In addition, the use of an alkaline activation treatment agent can also increase the treatment speed of the carbon-based conductive material, binder, etc.

[0076] Examples of alkali metal compounds that exhibit alkalinity when dissolved in water include hydroxides, carbonates, bicarbonates, oxides, peroxides, superoxides, etc. of alkali metals. Specific examples of such alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , RbCO ３ , CsCO ３ Carbonates such as LiHCO ３ , NaHCO ３ , KHCO ３ , RbHCO ３ , CsHCO ３ hydrogen carbonates such as Li ２ O, Na ２ O.K. ２ O, Rb ２ O, Cs ２ Oxides such as Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb ２ O ２ , Cs ２ O ２ peroxides such as LiO ２ , NaO ２ , K.O. ２ , RbO ２ , CsO ２ The activation treatment agent may contain one or more alkali metal compounds that exhibit alkaline properties when dissolved in water.

[0077] When the conductive material contained in the positive electrode mixture includes 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 step (2). Hereinafter, an activation treatment agent containing such an alkali metal compound may be referred to as an "activation treatment agent having an oxidizing power."

[0078] The use of an activation treatment agent having such oxidizing power is particularly effective in promoting the oxidation of conductive materials such as carbon-based conductive materials to carbon dioxide and in promoting the oxidation of binders such as hydrocarbon materials to carbon dioxide and water vapor, thereby further increasing the discharge capacity of batteries manufactured using the recycled cathode active material obtained by the method for manufacturing a recycled cathode active material according to this embodiment. Furthermore, the effect of preventing the generation of corrosive gases in step (2) may also be improved.

[0079] Examples of alkali metal compounds having the oxidizing power necessary to oxidize a carbonaceous conductive material or a hydrocarbon material into carbon dioxide and water vapor include alkali metal peroxides, superoxides, nitrates, sulfates, vanadates, molybdates, etc. Such alkali metal compounds may be used alone or in combination of two or more.

[0080] Specific examples of alkali metal compounds include Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb ２ O ２ , Cs ２ O ２ peroxides such as LiO ２ , NaO ２ , K.O. ２ , RbO ２ , CsO ２ superoxides such as LiNO ３ , NaNO ３ , KNO ３ , RbNO ３ , CsNO ３ Nitrates such as Li ２ SO ４ , Na ２ SO ４ , K. ２ SO ４ , Rb ２ SO ４ , Cs ２ SO ４ Sulfates such as LiVO ３ , NaVO ３ , K.V.O. ３ , RbVO３ , CsVO ３ vanadates such as Li ２ MoO ４ , Na ２ MoO ４ , K. ２ MoO ４ , Rb ２ MoO ４ , CsMoO ４ and the like molybdates.

[0081] (Step (2): Heating Step) Step (2) (heating step) is a step in which the mixture obtained in step (1) (hereinafter sometimes referred to as the "mixture before heating") is heated to a temperature (e.g., a holding temperature) equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent to obtain a mixture (hereinafter sometimes referred to as the "mixture after heating"). In step (2), if the mixture before heating contains a binder, the molten activation treatment agent can contact the binder to increase the rate of oxidative decomposition of the binder. In step (2), if the mixture before heating contains a carbon-based conductive material, the molten activation treatment agent can contact the carbon-based conductive material to increase the rate of oxidative decomposition of the carbon-based conductive material. In step (2), if the activation treatment agent contains the same alkali metal as the positive electrode active material, the deficient alkali metal can be supplied to the positive electrode active material.

[0082] In step (2), the mixture before heating is heated in the presence of nitrogen at a flow rate of 0.070 L / min or more per 1 L of heating space (in an atmosphere containing nitrogen at that flow rate). By setting the nitrogen flow rate to 0.070 L / min or more, a recycled positive electrode active material with large crystallite size can be obtained, and excellent discharge rate characteristics, discharge capacity retention rate, and initial charge / discharge efficiency can be obtained.

[0083] The flow rate of nitrogen per 1 L of heating space (unit: L / min; hereinafter, the units of various flow rates will be omitted in some cases) is 0.070 or more as described above, and may be in the following ranges from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining excellent initial charge / discharge efficiency. The flow rate of nitrogen may be 0.080 or more, 0.090 or more, 0.100 or more, 0.150 or more, 0.200 or more, 0.250 or more, 0.300 or more, 0.350 or more, 0.400 or more, 0.450 or more, or 0.500 or more. The nitrogen flow rate may be 3.000 or less, 2.500 or less, 2.000 or less, 1.500 or less, 1.000 or less, 0.900 or less, 0.800 or less, 0.700 or less, 0.600 or less, 0.550 or less, 0.500 or less, 0.450 or less, 0.400 or less, 0.350 or less, 0.300 or less, 0.250 or less, 0.200 or less, 0.150 or less, or 0.100 or less. From these viewpoints, the flow rate of nitrogen is set to 0.070 to 3.000, 0.070 to 0.600, 0.070 to 0.400, 0.070 to 0.300, 0.070 to 0.200, 0.070 to 0.100, 0.100 to 3.000, 0.100 to 0.600, 0.100 to 0.400, 0.100 to 0. 0.300, 0.100 to 0.200, 0.200 to 3.000, 0.200 to 0.600, 0.200 to 0.400, 0.200 to 0.300, 0.300 to 3.000, 0.300 to 0.600, 0.300 to 0.400, 0.400 to 3.000, or 0.400 to 0.600.

[0084] In step (2), from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining excellent initial charge-discharge efficiency, the mixture before heating may be heated in the presence of nitrogen at the following flow rate (unit: L / min) per 1 L of heating space and per 1 g of the mixture before heating (in an atmosphere containing nitrogen at the flow rate): －３ That's it, 2.5 x 10 －３ That's it, 3.0 x 10 －３ That's it, 4.0 x 10 －３That's it, 5.0 x 10 －３ That's it, 6.0 x 10 －３ That's it, 7.0 x 10 －３ That's it, 8.0 x 10 －３ That's it, 9.0 x 10 －３ That's it, 1.0 x 10 －２ or more, or 1.2 x 10 －２ The flow rate of nitrogen may be 1.0×10 －１ Below, 5.0 x 10 －２ Below, 3.0 x 10 －２ Below, 2.0 x 10 －２ Below, 1.8 x 10 －２ Below, 1.5 x 10 －２ Below, 1.2 x 10 －２ Below, 1.0 x 10 －２ Below, 9.0 x 10 －３ Below, 8.0 x 10 －３ Below, 7.0 x 10 －３ Below, 6.0 x 10 －３ Below, 5.0 x 10 －３ Below, 4.0 x 10 －３ Below, 3.0 x 10 －３ or less, or 2.5 x 10 －３ From these viewpoints, the flow rate of nitrogen may be 2.0×10 －３ ~1.0 x 10 －１ , 2.0 × 10 －３ ~2.0 x 10 －２ , 2.0 × 10 －３ ~1.0 x 10 －２ , 2.0 × 10 －３ ~8.0 x 10 －３ , 2.0 × 10 －３ ~5.0 x 10 －３ , 2.0 × 10 －３ ~3.0 x 10 －３ , 3.0 × 10 －３ ~1.0 x 10 －１ , 3.0 × 10 －３ ~2.0 x 10 －２ , 3.0 × 10 －３ ~1.0 x 10 －２ , 3.0 × 10 －３ ~8.0 x 10 －３ , 3.0 × 10 －３ ~5.0 x 10 －３ , 5.0 × 10－３ ~1.0 x 10 －１ , 5.0 × 10 －３ ~2.0 x 10 －２ , 5.0 × 10 －３ ~1.0 x 10 －２ , 5.0 × 10 －３ ~8.0 x 10 －３ , 8.0 × 10 －３ ~1.0 x 10 －１ , 8.0 × 10 －３ ~2.0 x 10 －２ , 8.0 × 10 －３ ~1.0 x 10 －２ , 1.0×10 －２ ~1.0 x 10 －１ , or 1.0 × 10 －２ ~2.0 x 10 －２ It may be.

[0085] The flow rate of nitrogen may be adjusted by supplying only nitrogen (e.g., nitrogen gas) or by supplying a mixture containing nitrogen and other components (e.g., air containing oxygen and nitrogen). The flow rate of nitrogen may be the amount of nitrogen supplied to the heating space.

[0086] The proportion of nitrogen (unit: vol%) in the atmospheric gas in step (2) may be in the following ranges based on the total volume of the atmospheric gas, from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge / discharge efficiency. The proportion of nitrogen may be more than 0%, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, more than 50%, 60% or more, 70% or more, more than 70%, 75% or more, or 80% or more. The proportion of nitrogen may be 80% or less, 75% or less, 70% or less, 60% or less, 50% or less, less than 50%, or 40% or less. From these viewpoints, the proportion of nitrogen may be more than 0% and not more than 80%, 20 to 80%, 50 to 80%, 70 to 80%, more than 70% and not more than 80%, 75 to 80%, more than 0% and not more than 50%, or 20 to 50%.

[0087] In step (2), the mixture before heating may be heated in the presence of oxygen and nitrogen (in an atmosphere containing oxygen and nitrogen). This makes it easy to increase the crystallite size of the recycled positive electrode active material and to obtain excellent discharge rate characteristics, discharge capacity retention rate, and initial charge / discharge efficiency. In step (2), the mixture before heating may be heated in an atmosphere free of oxygen.

[0088] In step (2), from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge-discharge efficiency, the mixture before heating may be heated in the presence of oxygen at the following flow rate per liter of heating space (unit: L / min) (in an atmosphere containing oxygen at this flow rate): The flow rate of oxygen may be greater than 0, 0.010 or more, 0.020 or more, 0.030 or more, 0.040 or more, 0.050 or more, 0.060 or more, 0.070 or more, 0.080 or more, 0.090 or more, 0.100 or more, 0.110 or more, or 0.120 or more. The flow rate of oxygen may be 0.300 or less, 0.250 or less, 0.200 or less, 0.150 or less, 0.130 or less, 0.120 or less, 0.110 or less, 0.100 or less, 0.090 or less, 0.080 or less, 0.070 or less, 0.060 or less, or 0.050 or less. From these viewpoints, the flow rate of oxygen may be more than 0 and 0.300 or less, more than 0 and 0.200 or less, more than 0 and 0.150 or less, more than 0 and 0.120 or less, more than 0 and 0.100 or less, more than 0 and 0.080 or less, more than 0 and 0.050 or less, 0.010 to 0.300, 0.010 to 0.200, 0.010 to 0.150, 0.010 to 0.120, 0.010 to 0.100, 0.0 10 to 0.080, 0.010 to 0.050, 0.020 to 0.300, 0.020 to 0.200, 0.020 to 0.150, 0.020 to 0.120, 0.020 to 0.100, 0.020 to 0.080, 0.020 to 0.050, 0.030 to 0.300, 0.030 to 0.200, 0.030 to 0.150, 0.030 to 0.1 20, 0.030-0.100, 0.030-0.080, 0.030-0.050, 0.040-0.300, 0.040-0.200, 0.040-0.150, 0.040-0.120, 0.040-0.100, 0.040-0.080, 0.040-0.050, 0.050-0.300, 0.050-0.200, 0.0 0.50 to 0.150, 0.050 to 0.120, 0.050 to 0.100, 0.050 to 0.080, 0.080 to 0.300, 0.080 to 0.200, 0.080 to 0.150, 0.080 to 0.120, 0.080 to 0.100, 0.100 to 0.300, 0.100 to 0.200, or 0.100 to 0.150.

[0089] In step (2), from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining excellent initial charge-discharge efficiency, the mixture before heating may be heated in the presence of oxygen at the following flow rate (unit: L / min) per 1 L of heating space and per 1 g of the mixture before heating (in an atmosphere containing oxygen at this flow rate). －４ That's it, 3.0 x 10 －４ That's it, 5.0 x 10 －４ That's it, 6.0 x 10 －４ That's it, 7.0 x 10 －４ That's it, 8.0 x 10 －４ That's it, 1.0 x 10 －３ That's it, 1.2 x 10 －３ That's it, 1.5 x 10 －３ That's it, 1.8 x 10 －３ That's it, 2.0 x 10 －３ That's it, 2.5 x 10 －３ or more, or 3.0 x 10 －３ The flow rate of oxygen may be 1.0×10 －２ Below, 9.0 x 10 －３ Below, 8.0 x 10 －３ Below, 7.0 x 10 －３ Below, 6.0 x 10 －３ Below, 5.0 x 10 －３ Below, 4.0 x 10 －３ Below, 3.5 x 10 －３ Below, 3.0 x 10 －３ Below, 2.5 x 10 －３ Below, 2.0 x 10 －３ Below, 1.8 x 10 －３ Below, 1.5 x 10 －３ Below, 1.2 x 10 －３ or less, or 1.0 x 10 －３ From these viewpoints, the flow rate of oxygen may be greater than 0 and less than 1.0 × 10 －２ Below, over 0 4.0 x 10 －３ Below, over 0 3.0 x 10 －３ Below, over 0 2.0 x 10 －３ Below, over 0, 1.5 x 10 －３ Below, 5.0 x 10 －４~1.0 x 10 －２ , 5.0 × 10 －４ ~4.0 x 10 －３ , 5.0 × 10 －４ ~3.0 x 10 －３ , 5.0 × 10 －４ ~2.0 x 10 －３ , 5.0 × 10 －４ ~1.5 x 10 －３ , 1.5 × 10 －３ ~1.0 x 10 －２ , 1.5 × 10 －３ ~4.0 x 10 －３ , 1.5 × 10 －３ ~3.0 x 10 －３ , 1.5 × 10 －３ ~2.0 x 10 －３ , 2.0 × 10 －３ ~1.0 x 10 －２ , 2.0 × 10 －３ ~4.0 x 10 －３ , 2.0 × 10 －３ ~3.0 x 10 －３ , 3.0 × 10 －３ ~1.0 x 10 －２ , or 3.0 × 10 －３ ~4.0 x 10 －３ It may be.

[0090] The flow rate of oxygen may be adjusted by supplying only oxygen (e.g., oxygen gas) or by supplying a mixture containing oxygen and other components (e.g., air containing oxygen and nitrogen). The flow rate of oxygen may be the amount of oxygen supplied to the heating space.

[0091] The oxygen ratio (unit: vol%) in the atmospheric gas in step (2) may be within the following ranges based on the total volume of the atmospheric gas, from the viewpoint of easily obtaining a recycled cathode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge / discharge efficiency. The oxygen ratio may be 20% or more, 25% or more, 30% or more, 40% or more, 50% or more, more than 50%, or 60% or more. The oxygen ratio may be less than 100%, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, less than 50%, 40% or less, 30% or less, less than 30%, 25% or less, or 20% or less. From these viewpoints, the proportion of oxygen may be 20% or more and less than 100%, 20 to 80%, 20 to 50%, 20 to 30%, 20% or more and less than 30%, 20 to 25%, 50% or more and less than 100%, or 50 to 80%.

[0092] In step (2), from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge-discharge efficiency, the mixture before heating may be heated in the presence of oxygen and nitrogen at the following total flow rate (unit: L / min) per liter of heating space (in an atmosphere containing oxygen and nitrogen at this total flow rate): The total flow rate of oxygen and nitrogen may be greater than 0.070, 0.100 or more, 0.150 or more, 0.200 or more, 0.250 or more, 0.300 or more, 0.350 or more, 0.400 or more, 0.450 or more, 0.500 or more, 0.550 or more, or 0.600 or more. The combined oxygen and nitrogen flow rate may be 3.000 or less, 2.500 or less, 2.000 or less, 1.500 or less, 1.000 or less, 0.900 or less, 0.800 or less, 0.750 or less, 0.700 or less, 0.650 or less, 0.600 or less, 0.550 or less, 0.500 or less, 0.450 or less, 0.400 or less, 0.350 or less, 0.300 or less, or 0.250 or less. From these viewpoints, the total flow rate of oxygen and nitrogen is greater than 0.070 and not greater than 3.000, greater than 0.070 and not greater than 0.800, greater than 0.070 and not greater than 0.600, greater than 0.070 and not greater than 0.500, greater than 0.070 and not greater than 0.400, greater than 0.070 and not greater than 0.300, 0.100 to 3.000, 0.100 to 0.800, 0.100 to 0.600, 0.100 to 0.500, 0.100 to 0.400, 0.100 to 0.300, 0.200 to 3.000, 0.200 It may be up to 0.800, 0.200 to 0.600, 0.200 to 0.500, 0.200 to 0.400, 0.200 to 0.300, 0.300 to 3.000, 0.300 to 0.800, 0.300 to 0.600, 0.300 to 0.500, 0.300 to 0.400, 0.400 to 3.000, 0.400 to 0.800, 0.400 to 0.600, 0.400 to 0.500, 0.500 to 3.000, or 0.500 to 0.800.

[0093] In step (2), from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge-discharge efficiency, the mixture before heating may be heated in the presence of oxygen and nitrogen at the following total flow rate (unit: L / min) per 1 L of heating space and per 1 g of the mixture before heating (in an atmosphere containing oxygen and nitrogen at the total flow rate): －３ That's it, 2.0 x 10 －３ That's it, 2.5 x 10 －３ That's it, 3.0 x 10 －３ That's it, 4.0 x 10 －３ That's it, 5.0 x 10 －３ That's it, 6.0 x 10 －３ That's it, 7.0 x 10 －３ That's it, 8.0 x 10 －３ That's it, 9.0 x 10 －３ That's it, 1.0 x 10 －２ That's it, 1.2 x 10 －２ or more, or 1.5 x 10 －２ The total flow rate of oxygen and nitrogen may be 1.0×10 －１ Below, 5.0 x 10 －２ Below, 3.0 x 10 －２ Below, 2.0 x 10 －２ Below, 1.8 x 10 －２ Below, 1.5 x 10 －２ Below, 1.2 x 10 －２ Below, 1.0 x 10 －２ Below, 9.0 x 10 －３ Below, 8.0 x 10 －３ Below, 7.0 x 10 －３ or less, or 6.0 x 10 －３ From these viewpoints, the total flow rate of oxygen and nitrogen may be greater than 0 and 1.0 × 10 －１ Below, over 0 2.0 x 10 －２ Below, over 0, 1.5 x 10 －２ Below, over 0 1.0×10 －２ Below, over 0 8.0 x 10 －３ Below, 2.5 x 10 －３ ~1.0 x 10 －１ , 2.5 × 10 －３ ~2.0 x 10 －２, 2.5 × 10 －３ ~1.5 x 10 －２ , 2.5 × 10 －３ ~1.0 x 10 －２ , 2.5 × 10 －３ ~8.0 x 10 －３ , 5.0 × 10 －３ ~1.0 x 10 －１ , 5.0 × 10 －３ ~2.0 x 10 －２ , 5.0 × 10 －３ ~1.5 x 10 －２ , 5.0 × 10 －３ ~1.0 x 10 －２ , 5.0 × 10 －３ ~8.0 x 10 －３ , 8.0 × 10 －３ ~1.0 x 10 －１ , 8.0 × 10 －３ ~2.0 x 10 －２ , 8.0 × 10 －３ ~1.5 x 10 －２ , 8.0 × 10 －３ ~1.0 x 10 －２ , 1.0×10 －２ ~1.0 x 10 －１ , 1.0×10 －２ ~2.0 x 10 －２ , 1.0×10 －２ ~1.5 x 10 －２ , 1.5 × 10 －２ ~1.0 x 10 －１ , or 1.5 × 10 －２ ~2.0 x 10 －２ It may be.

[0094] The total flow rate of oxygen and nitrogen may be adjusted by supplying only oxygen (e.g., oxygen gas), by supplying only nitrogen (e.g., nitrogen gas), by supplying a mixture containing oxygen and other components (e.g., air containing oxygen and nitrogen), or by supplying a mixture containing nitrogen and other components (e.g., air containing oxygen and nitrogen). The total flow rate of oxygen and nitrogen may be the total supply amount of oxygen and nitrogen supplied to the heating space.

[0095] The ratio of oxygen to nitrogen in the atmospheric gas in step (2) (oxygen / nitrogen: volume basis) may be within the following ranges from the viewpoint of easily obtaining a recycled positive electrode active material with a large crystallite size, easily obtaining excellent discharge rate characteristics, easily obtaining an excellent discharge capacity retention rate, or easily obtaining an excellent initial charge / discharge efficiency. The ratio of oxygen to nitrogen may be 0.25 or more, 0.30 or more, 0.50 or more, 0.80 or more, 1.00 or more, more than 1.00, 1.20 or more, or 1.50 or more. The ratio of oxygen to nitrogen may be 3.00 or less, 2.50 or less, 2.00 or less, 1.50 or less, 1.20 or less, 1.00 or less, less than 1.00, 0.80 or less, 0.50 or less, 0.30 or less, or 0.25 or less. In view of these, the ratio of oxygen to nitrogen may be 0.25 to 3.00, 0.25 to 2.00, 0.25 to 0.50, 0.25 to 0.30, 0.50 to 3.00, or 0.50 to 2.00.

[0096] Components other than oxygen and nitrogen may be present in the heating space, examples of which include argon, carbon dioxide, etc.

[0097] In step (2), the mixture before heating can be heated in the heating space of the heating means. Examples of the heating means include, but are not limited to, heating furnaces such as gas furnaces, electric furnaces, infrared heating furnaces, plasma heat treatment furnaces, heavy oil furnaces, intermediate furnaces, hydrogen heat treatment furnaces, and induction heating furnaces. The heating furnace may be a batch furnace or a continuous furnace. The "heating space" is a space in which the mixture to be heated is accommodated, and may be a closed space or an open space with an opening for carrying the mixture in or out. In the heating space, an atmospheric gas may be supplied while being discharged, and the volume of the heating space may be the volume from the supply part of the atmospheric gas to the discharge part of the atmospheric gas in the heating space, as the volume of the space in which the atmospheric gas can be present.

[0098] The "melting initiation temperature (Tmp) of the activation treatment agent" refers to the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0099] The melting initiation temperature of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, in differential thermal analysis (heating rate 10°C / min) using 5 mg of the activation treatment agent, the temperature at which the DTA signal shows an endothermic peak is taken as the melting initiation temperature of the activation treatment agent. When the activation treatment agent contains two or more compounds, the lowest temperature at which the DTA signal shows an endothermic peak is taken as the melting initiation temperature of the activation treatment agent. The melting initiation temperature of the activation treatment agent may be the melting initiation temperature of the alkali metal compound.

[0100] The melting start temperature of the activation treatment agent may be 700°C or less, 650°C or less, 600°C or less, or 550°C or less. The melting start temperature of the activation treatment agent may be 150°C or more, 200°C or more, 250°C or more, 300°C or more, 350°C or more, 400°C or more, 450°C or more, 500°C or more, or 550°C or more. From these viewpoints, the melting start temperature of the activation treatment agent may be 150 to 700°C, 150 to 650°C, 150 to 600°C, 300 to 700°C, 300 to 650°C, 300 to 600°C, 500 to 700°C, 500 to 650°C, or 500 to 600°C.

[0101] By mixing the positive electrode composite with the activation treatment agent, the melting initiation temperature of the activation treatment agent becomes lower than the melting point of the activation treatment agent, which means the lowest temperature at which a part of the activation treatment agent becomes liquid when heated alone.

[0102] The melting point of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, the melting point of the activation treatment agent is determined as the temperature at which the DTA signal shows an endothermic peak in differential thermal analysis (heating rate 10°C / min) using 5 mg of the activation treatment agent.

[0103] The heating temperature (temperature of the heating step) may be 100°C or higher, 200°C or higher, 300°C or higher, 400°C or higher, 500°C or higher, 550°C or higher, 600°C or higher, 650°C or higher, or 700°C or higher. The heating temperature may be 1500°C or lower, 1200°C or lower, 1000°C or lower, 900°C or lower, 850°C or lower, 800°C or lower, 750°C or lower, or 700°C or lower. From these viewpoints, the heating temperature may be 100 to 1500°C, 100 to 1000°C, 100 to 800°C, 400 to 1500°C, 400 to 1000°C, 400 to 800°C, 600 to 1500°C, 600 to 1000°C, or 600 to 800°C.

[0104] The holding time at the heating temperature may be 10 minutes to 24 hours. The heating temperature and holding time can be appropriately adjusted depending on the types and combinations of the components constituting the positive electrode mixture (positive electrode active material; alkali metal compound and other compounds contained in the activation treatment agent; conductive material; binder, etc.). The rate of temperature increase up to the heating temperature is not particularly limited.

[0105] The heating temperature is preferably higher than the melting point of the alkali metal compound contained in the activation treatment agent. When multiple types of compounds are mixed, the melting point of the alkali metal compound may be lower than the melting point of each compound alone. 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.

[0106] The pressure of the atmosphere in step (2) is not particularly limited, and may be atmospheric pressure, a reduced pressure atmosphere, or a pressurized atmosphere.

[0107] The amount of the mixture before heating, the container that contains the mixture before heating, the layer thickness of the mixture before heating in the container, the method and position for supplying the atmospheric gas, and the like are not particularly limited.

[0108] After the heating in step (2), the heated mixture can be cooled to any temperature (for example, about room temperature (25° C.; the same applies hereinafter)) if necessary.

[0109] (Step (3): Positive Electrode Active Material Recovery Step) Step (3) (positive electrode active material recovery step) is a step of recovering the heated positive electrode active material from the heated mixture after step (2). In step (3), at least a portion (partial or all) of the alkali metal compound may be removed from the heated mixture to recover the heated positive electrode active material.

[0110] The mixture after heating may contain, in addition to the heated positive electrode active material, components derived from the activation treatment agent (such as alkali metal compounds), undecomposed conductive material and binder, other undecomposed substances of the positive electrode mixture, etc. When the positive electrode mixture contains an electrolyte containing a fluorine component, the mixture after heating may contain a fluorine component derived from the electrolyte.

[0111] 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 the heated mixture is mixed with a solvent such as water to form a slurry and then solid-liquid separation is performed; and a vaporization separation method in which the heated mixture is heated to vaporize and separate components other than the heated positive electrode active material. Below, the solid-liquid separation step in which the solid-liquid separation method is performed will be described.

[0112] [Step (3a): Solid-Liquid Separation Step] Step (3a) is a step of mixing (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 a solid component and a liquid component. In order to separate and recover the heated positive electrode active material from the heated mixture, the heated mixture is mixed with a liquid containing water to form a slurry, and then the slurry is separated into a solid component and a liquid component by solid-liquid separation.

[0113] The liquid used for slurrying is not particularly limited as long as it contains water. The amount of water in the liquid may be 50% by mass or more. In order to increase the solubility of water-soluble components or to increase the processing speed, components other than water may be added to the liquid to adjust the pH.

[0114] Suitable examples of the water-containing liquid include pure water and alkaline cleaning solutions. Examples of alkaline cleaning solutions include an aqueous solution of at least one anhydride or hydrate thereof 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.

[0115] The slurry may contain 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. The liquid component may contain an alkali metal component derived from the activation treatment agent, a fluorine component derived from the binder and / or the electrolytic solution (e.g., the electrolyte in the electrolytic solution), etc.

[0116] The amount of liquid to be mixed with the heated mixture can be determined appropriately taking into consideration the amounts of each of the components contained in the heated mixture (the heated positive electrode active material, water-soluble components other than the positive electrode active material, etc.).

[0117] In step (3a), the heated mixture is preferably stirred with a liquid containing water to obtain a slurry, which promotes dissolution of the water-soluble components.

[0118] The slurry is subjected to solid-liquid separation. Solid-liquid separation is an operation for separating the 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.

[0119] In step (3a), 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 a liquid containing water to obtain a slurry, and the slurry is then separated again into a solid component and a liquid component. In step (3a), rinsing may be performed multiple times. The slurry concentration in rinsing can be adjusted as desired.

[0120] (Step (4): Drying Step) The method for producing a recycled positive electrode active material according to this embodiment may include, after step (3), step (4) (drying step) of drying the undried material containing the solid component obtained in step (3a). Step (4) is a step of exposing the undried material containing the solid component obtained in step (3a) to a heated and / or reduced pressure environment to remove water from the undried material. If the undried material does not contain water, the method for producing a recycled positive electrode active material according to this embodiment may not include step (4).

[0121] The heating temperature in step (4) may be 80° C. or higher, 90° C. or higher, or 100° C. or higher from the viewpoint of facilitating water removal. The heating temperature may be 900° C. or lower, less than 900° C., 700° C. or lower, 500° C. or lower, 300° C. or lower, 200° C. or lower, or 100° C. or lower. From these viewpoints, the heating temperature may be 100 to 900° C.

[0122] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 －１０ ~1.0 x 10 ３ It may be Pa.

[0123] (Step (5): Annealing (Re-baking) Step) The method for producing a recycled positive electrode active material according to this embodiment may include step (5) (annealing step) of heat-treating the solid component (e.g., the solid component obtained in step (4)). Step (5) is preferably a step of heat-treating the solid component at a temperature of less than 900°C. The method for producing a recycled positive electrode active material according to this embodiment does not necessarily include step (5).

[0124] The atmosphere for the heat treatment in step (5) is not particularly limited, but is preferably an oxygen-containing atmosphere such as air. The heat treatment temperature (e.g., holding temperature) may be, for example, 100°C or higher. The holding time for the heat treatment may be, for example, 1 minute to 24 hours. In particular, in step (5), heating at a temperature (e.g., holding temperature) of 350°C or higher for 0.1 to 5 hours is preferred.

[0125] 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.

[0126] <Activation treatment agent mixing step> 90 parts by mass of LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ A positive electrode composite (simulated composite) was prepared by mixing 100 parts by mass of the positive electrode composite (positive electrode active material), 3 parts by mass of PVdF (binder), 4 parts by mass of graphite (conductive material), and 3 parts by mass of carbon black (conductive material). ２ CO ３ 10.3 parts by mass and K ２ CO ３ 19.3 parts by mass of the activation treatment agent were mixed to obtain a mixture A (mixture before heating). The melting initiation temperature of the activation treatment agent was 550°C.

[0127] <Heating Step> 40 g of mixture A was placed in an alumina container (rectangular sagger, dimensions: 90 mm × 90 mm × 25 mm), and the container was placed in an electric furnace (heating space volume: 2.4 L). The layer thickness of mixture A in the container was 5 mm. Under atmospheric pressure, the temperature was increased from room temperature to 700°C at a rate of 300°C / hour, and mixture A was subjected to a heat treatment (activation treatment) at a holding temperature of 700°C for 6 hours (excluding the temperature increase time). After natural cooling to room temperature, the heated mixture was recovered. During the heat treatment, while exhausting the atmospheric gas, air was supplied to the heating space at the following flow rates in Comparative Example 1 and Examples 1 to 4, and air and oxygen gas were supplied to the heating space at the following flow rates in Example 5. The oxygen flow rate, nitrogen flow rate, and their total flow rate per 1 L of heating space, as well as the proportions of oxygen and nitrogen in the atmospheric gas, are shown in Table 1. The oxygen flow rate and nitrogen flow rate were calculated assuming that the air was a mixture consisting of 20% by volume of oxygen and 80% by volume of nitrogen.

[0128] Comparative Example 1: Air 0.2 L / min Example 1: Air 0.5 L / min Example 2: Air 0.8 L / min Example 3: Air 1.1 L / min Example 4: Air 1.5 L / min Example 5: Air 0.25 L / min and oxygen gas 0.25 L / min

[0129] <Solid-liquid separation step> The heated mixture was pulverized and then mixed with water (5°C) to obtain a slurry with a concentration of 2% by mass. The slurry was stirred for 5 minutes at a stirrer rotation speed of 500 rpm, and then filtered for 5 minutes to separate the slurry into a solid component and a liquid component.

[0130] <Drying Step> The solid component was dried under reduced pressure at 100°C for 1 hour.

[0131] <Annealing step> The dried solid component was placed in an alumina container and placed in an electric furnace. Under atmospheric pressure, the ambient gas was exhausted and air was supplied, while the temperature was increased from room temperature to 700°C at a rate of 300°C / hour. The solid component was then heat-treated at a holding temperature of 700°C for 1 hour (excluding the heating time). After natural cooling to room temperature, the recycled positive electrode active material was collected.

[0132] <Measurement of Crystallite Size> First, an X-ray diffraction spectrum (diffraction pattern) was obtained by powder X-ray diffraction measurement (ray source: CuKα, measurement range of diffraction angle 2θ: 10 to 90°, sampling width: 0.02, scan speed: 4° / min). From this X-ray diffraction spectrum, the maximum diffraction peak within the range of 2θ = 18.5 ± 1° was determined. A Bruker D8 Advance X-ray diffractometer was used in the powder X-ray diffraction measurement. The half-width of the maximum diffraction peak was calculated, and the crystallite size was calculated using the Scherrer formula "L = Kλ / B cos θ" (L: crystallite size, K: Scherrer constant, B: half-width of the diffraction peak). The results are shown in Table 1.

[0133] <Production of Positive Electrode> A mixture was obtained by mixing 92 parts by mass of the recycled positive electrode active material, 3 parts by mass of a binder (manufactured by Kureha Corporation, product number: PVdF #1100), and 5 parts by mass of carbon black (conductive material, manufactured by Denka Co., Ltd., product number: HS100). A binder solution prepared by dissolving PVdF in NMP was used as the binder. NMP was added to adjust the total mass of the positive electrode active material, binder, and conductive material in the positive electrode mixture paste to 52% by mass. The mixture was kneaded in an agate mortar to prepare a positive electrode mixture paste.

[0134] A 20 μm thick aluminum foil 1085 (manufactured by Nippon Foil Co., Ltd.) for a lithium ion secondary battery positive electrode current collector was applied on one side thereof with a positive electrode active material amount of 10.0±0.2 mg / cm ２ The positive electrode composite paste was applied so that the positive electrode composite paste was formed as follows: the positive electrode composite paste was then dried with hot air at 60°C for 1 hour, pressed at 0.5 MPa, and then vacuum dried at 150°C for 8 hours to obtain a positive electrode. The electrode area of ​​this positive electrode was 1.65 cm ２ It was.

[0135] <Battery Production> A coin-type battery (non-aqueous electrolyte secondary battery) was produced 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 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, with LiPF ６ A solution of 1.0 mol / L of the above was used. A laminated film separator was used as the 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.

[0136] <Battery Characteristics> The coin-type battery was subjected to the following charge-discharge test (25° C.). The results are shown in Table 1.

[0137] (Discharge rate characteristics) While the discharge current was changed in sequence for each cycle, charging and discharging were repeated, in which constant current charging was performed at a current of 1 C up to 4.3 V and then constant current discharging was performed down to 2.5 V. The discharge current was changed in the sequence of 0.2 C, 0.5 C, 1 C, 2 C, 3 C, and 5 C. The discharge capacity (unit: mAh / g) after discharging at 5 C was measured.

[0138] (Discharge Capacity Retention Rate) 50 cycles of charge and discharge were performed, in which constant-current charging at a current of 1 C was performed up to a voltage of 4.3 V, followed by constant-current discharging at a current of 2 C down to a voltage of 2.5 V, and the discharge capacities at the 1st cycle and the 50th cycle were measured. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle ([50 cycles / 1 cycle] × 100%) was calculated as the discharge capacity retention rate.

[0139] (Initial charge-discharge efficiency) A constant current charge of 0.2 C was performed up to 4.3 V, and then a constant current discharge of 0.2 C was performed up to 2.5 V. The charge capacity and discharge capacity were measured, and the ratio of the discharge capacity to the charge capacity ([discharge capacity / charge capacity]×100%) was calculated as the initial charge-discharge efficiency.

[0140]

Claims

1. A method for producing a recycled positive electrode active material, comprising the following steps: Step (1): A step of mixing a cathode composite containing a cathode active material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; Step (2): A step of heating the mixture to a temperature equal to or higher than the melting initiation temperature of the activation treatment agent in the presence of nitrogen at a flow rate of 0.070 L / min or more per liter of a heating space to obtain a heated mixture; and Step (3): A step of recovering the heated cathode active material from the heated mixture.

2. The manufacturing method according to claim 1, wherein the flow rate of the nitrogen in step (2) is 0.070 to 0.600 L / min.

3. The manufacturing method according to claim 1, wherein the proportion of the nitrogen in the atmospheric gas in step (2) is more than 70% by volume and not more than 80% by volume.

4. The method according to claim 1, wherein the mixture is heated to 600 to 1000°C in step (2).

5. The manufacturing method according to any one of claims 1 to 4, wherein the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds.

6. The manufacturing method according to any one of claims 1 to 4, wherein the positive electrode active material contains a lithium compound, and the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds, and a lithium compound.

7. The manufacturing method according to any one of claims 1 to 4, 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 8. The method according to any one of claims 1 to 4, wherein the positive electrode active material contains a compound represented by the following formula (A): 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, and the following conditions are satisfied: -0.4<a<1.5, 0≦b<0.5, 0≦c<0.5, -0.5<d<1.5, and 0≦e<0.5.

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