Method for manufacturing recycled positive electrode active material

Abstract

To provide a method for producing a recycled positive electrode active material capable of suppressing deterioration of the positive electrode active material by high-temperature carbon dioxide. 【Solution means】A method for producing a recycled positive electrode active material including the following steps. (1) A step of mixing a positive electrode composite material containing a positive electrode active material and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture (2) A step of introducing the mixture into a heating furnace, heating the mixture, removing carbon dioxide generated by heating the carbon-containing material from the heating furnace, and obtaining a heated mixture (3) A step of recovering the heated positive electrode active material from the heated mixture

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a recycled cathode active material.

Background Art

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

[0003] For example, Patent Document 1 discloses a method in which a cathode composite material and an activating agent containing an alkali metal compound are mixed, the mixture is heated to decompose the binder, and the decomposition product and the activating agent are removed with water or the like to recover the cathode active material. This method is excellent in cost in that the cathode active material is directly recovered from battery waste materials without using an organic solvent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When recycling the cathode active material in the cathode composite material, after mixing the cathode composite material and the activating agent, the resulting mixture is heated. When the mixture is heated, the carbon-containing component in the mixture (for example, the carbon-containing material contained in the cathode composite material) burns and carbon dioxide is generated. Then, although the generated carbon dioxide is also heated in the heating furnace to a high temperature, it has been found that when the high-temperature carbon dioxide comes into contact with the cathode active material in the mixture, it may cause deterioration of the cathode active material.

[0006] Therefore, an object of the present invention is to provide a method for producing a recycled cathode active material that can suppress the deterioration of the cathode active material by high-temperature carbon dioxide.

Means for Solving the Problems

[0007] The present invention includes, for example, the following [1] to [9]. [1] A method for producing a recycled cathode active material including the following steps. (1) A step of mixing a cathode composite material including a cathode active material and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture (2) A step of loading the mixture into a heating furnace, heating the mixture, and removing carbon dioxide generated by heating the carbon-containing material from the heating furnace to obtain a heated mixture (3) A step of recovering the heated cathode active material from the heated mixture [2] The production method according to [1], wherein the carbon dioxide is removed by blowing air. [3] The production method according to [2], wherein when comparing the carbon dioxide concentration in the gas fed into the heating furnace with the carbon dioxide concentration in the gas exhausted from the heating furnace in the step (2), the carbon dioxide concentration of the gas exhausted from the heating furnace is higher. [4] The production method according to any one of [1] to [3], wherein the carbon dioxide is removed by a carbon dioxide adsorbent. [5] The production method according to any one of [1] to [4], wherein in the step (2), the mixture is heated to a temperature equal to or higher than the melting start temperature of the activation treatment agent. [6] The production method according to any one of [1] to [4], wherein in the step (2), the mixture is heated to a temperature lower than the melting start temperature of the activation treatment agent. [7] The production method according to any one of [1] to [6], wherein the cathode active material contains a lithium compound. [8] The production method according to any one of [1] to [7], 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 [9] The production method according to any one of [1] to [8], wherein the activation treatment agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a method for producing a recycled positive electrode active material capable of suppressing the deterioration of the positive electrode active material due to high-temperature carbon dioxide.

Modes for Carrying Out the Invention

[0009] (Method for Producing Recycled Positive Electrode Active Material) Hereinafter, a method for producing a positive electrode active material related to recycling will be described.

[0010] The method for producing a recycled positive electrode active material according to an embodiment of the present invention includes the following steps. Step (1): A step of mixing a positive electrode composite material containing a positive electrode active material and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture Step (2): A step of loading the mixture into a heating furnace, heating the mixture, removing carbon dioxide generated by heating the carbon-containing material from the heating furnace, and obtaining a heated mixture Step (3): A step of recovering the heated positive electrode active material from the heated mixture

[0011] According to the method for producing a recycled cathode active material according to one embodiment, when heating a mixture of a cathode composite material and an activation treatment agent in a heating furnace, while heating the mixture, carbon dioxide generated by heating a carbon-containing material (for example, a binder, a carbon-based conductive material) is removed from the heating furnace. Thereby, since it is possible to prevent carbon dioxide from staying in the heating furnace, it is possible to suppress the concentration of carbon dioxide in the heating furnace from becoming too high. Further, since it is possible to prevent carbon dioxide from staying in the heating furnace, it is possible to suppress carbon dioxide from being continuously heated in the heating furnace and the temperature of carbon dioxide from becoming high. As a result, according to the present invention, it is possible to suppress the deterioration of the cathode active material due to high-temperature carbon dioxide. However, the mechanism of the present invention is not limited to the above.

[0012] Hereinafter, each step will be described in detail.

[0013] Previous step (A): Cathode composite material preparation step First, a cathode composite material containing a cathode active material and a carbon-containing material is prepared.

[0014] [Cathode active material] Examples of the cathode 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, etc. as constituent elements.

[0015] The cathode active material may consist of only a single compound or may be composed of a plurality of compounds.

[0016] The cathode 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

[0017] The positive electrode active material preferably contains a compound represented by the following formula (A).

[0018] Li 1+a M 2 b M 1 M T c O 2+d X e (A) However, M 2 represents at least one element selected from the group consisting of Na, K, Ca, Sr, Ba, and Mg, M 1 represents at least one element selected from the group consisting of Ni, Co, Mn, Fe, Al, and P, M T represents at least one element selected from the group consisting of transition metal elements excluding Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metal elements excluding O and P, -0.4 < a < 1.5, 0 ≤ b < 0.5, 0 ≤ c < 0.5, -0.5 < d < 1.5, and 0 ≤ e < 0.5 are satisfied.

[0019] 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.

[0020] The positive electrode active material preferably contains a composite oxide containing at least Li and Ni.

[0021] In the positive electrode active material, the molar fraction of Ni in M 1 is preferably 0.3 to 0.95.

[0022] The crystal structure of the positive electrode active material (e.g., composite oxide) is not particularly limited, but a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

[0023] 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 belongs to any one space group selected from the group consisting of.

[0024] The monoclinic crystal structure is P2, P2 1 , C2, Pm, Pc, Cm, Cc, P2 / m, P2 1 / m, C2 / m, P2 / c, P2 1 / c, and C2 / c belongs to any one space group selected from the group consisting of.

[0025] The crystal structure of the positive electrode active material preferably belongs to the space group R-3m included in the hexagonal crystal structure or C2 / m included in the monoclinic crystal structure.

[0026] The crystal structure of the positive electrode active material can be identified from the powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα rays as the radiation source.

[0027] The particle size of the positive electrode active material in the positive electrode composite material is not particularly limited, and 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 measuring device (for example, Mastersizer 2000 manufactured by Malvern). From the particle size distribution, a volume-based cumulative particle size distribution curve can be created, and the value of the particle size (D50) at 50% cumulative from the fine particle side can be taken as the average particle size of the positive electrode active material.

[0028] There is no particular limitation on the content of the positive electrode active material in the positive electrode composite material.

[0029] [Carbon-containing material] Examples of the carbon-containing material contained in the positive electrode composite material include a binder, a conductive material (carbon-based conductive material), and an electrolyte. When the positive electrode composite material contains a binder, in the positive electrode composite material, the particles of the positive electrode active material may be bound to each other by the binder.

[0030] Examples of the binder (binder before activation treatment) include thermoplastic resins and the like. Specifically, fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as "PVdF"), polytetrafluoroethylene (PTFE), ethylene tetrafluoride - hexafluoropropylene - vinylidene fluoride copolymer, hexafluoropropylene - vinylidene fluoride copolymer, ethylene tetrafluoride - perfluorovinyl ether copolymer; polyolefin resins such as polyethylene and polypropylene; styrene-butadiene copolymer (SBR), etc. The binder may be used alone or in combination of two or more.

[0031] The content of the binder in the positive electrode composite material is not particularly limited, but may be in the following range with respect 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 viewpoints, the content of the binder may be 0.5 to 30 parts by mass, 1 to 10 parts by mass, 1 to 5 parts by mass, or 2 to 5 parts by mass.

[0032] Specific examples of the carbon-based conductive material include graphite powder (graphite), carbon black (e.g., acetylene black), fibrous carbon materials (e.g., graphitized carbon fibers and carbon nanotubes), and the like.

[0033] The carbon-based conductive material may be a single carbon material or may be composed of a plurality of carbon materials.

[0034] The specific surface area of the carbon material used as the carbon-based conductive material may be 0.1 to 500 m 2 / g. In that case, the carbon-based conductive material can be composed only of a carbon-based conductive material having a specific surface area of 30 m 2 / g or more, and may be carbon black having a specific surface area of 30 m 2 / g or more, or may be acetylene black having a specific surface area of 30 m 2 / g or more. When using the activation treatment agent described later containing an alkali metal compound having oxidizing power, the oxidation treatment rate of the carbon-based conductive material can be increased, and even a carbon-based conductive material having a small specific surface area may be able to be oxidized.

[0035] The content of the carbon-based conductive material in the positive electrode composite material is not particularly limited, but may be within the following range with respect to 100 parts by mass of the positive electrode active material. The content of the carbon-based 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 viewpoints, the content of the carbon-based 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.

[0036] In addition to the positive electrode active material and the carbon-containing material, the positive electrode composite material may contain a metal-based conductive material such as metal particles and / or an electrolyte. When the positive electrode composite material contains a binder and a conductive material, the particles of the positive electrode active material and the conductive material may be bound to each other by the binder. The electrolyte is a component derived from the electrolyte solution of the battery and impregnated in the positive electrode composite material. The positive electrode composite material may contain a fluorine compound derived from the binder and / or the electrolyte solution (for example, the electrolyte in the electrolyte solution).

[0037] 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 and the like. The content of the electrolyte contained in the positive electrode composite material is not particularly limited, but may be 0.0005 to 7% by mass.

[0038] The positive electrode composite material may contain a solvent derived from the electrolyte solution. Examples of the solvent include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like.

[0039] [Recovery of Positive Electrode Composite Material] The positive electrode composite material can be obtained by separating and recovering the positive electrode composite material layer from a waste positive electrode having a current collector and a positive electrode composite material layer.

[0040] The "waste positive electrode" may be a positive electrode recovered from a discarded battery and a waste product of the positive electrode generated during the manufacturing process of the positive electrode or the battery. The discarded battery may be a used battery or a battery that is unused but out of specification. The waste product of the positive electrode may be the end portion of the positive electrode generated in the battery manufacturing process or an out-of-specification positive electrode. It is also possible to use a waste product of the positive electrode composite material that is not attached to the current collector (a waste product generated in the positive electrode composite material manufacturing process) as the positive electrode composite material.

[0041] The waste positive electrode has a current collector that is a metal foil such as an aluminum foil or a copper foil, and a positive electrode composite material layer provided on the current collector. The positive electrode composite material layer may be provided on one side of the current collector or on both sides.

[0042] Examples of methods for separating the positive electrode composite material layer from the waste positive electrode having a current collector and a positive electrode composite material layer include a method of mechanically peeling the positive electrode composite material layer from the current collector (for example, a method of scraping off the positive electrode composite material layer from the current collector), a method of permeating a solvent into the interface between the current collector and the positive electrode composite material layer to peel the positive electrode composite material layer from the current collector, and a method of dissolving the current collector using an alkaline or acidic aqueous solution to separate the positive electrode composite material layer. Preferably, it is a method of mechanically peeling the positive electrode composite material layer from the current collector.

[0043] Previous step (B): Cleaning step of the positive electrode composite material Subsequently, when the positive electrode composite material contains an electrolyte, it is preferable to bring the prepared positive electrode composite material into contact with an electrolyte cleaning solvent to remove at least a part of the electrolyte from the positive electrode composite material. Specifically, a positive electrode composite material containing a positive electrode active material, a carbon-containing material, etc. is brought into contact with an electrolyte cleaning solvent to obtain a slurry containing a solid component and a liquid component, and then the slurry is separated into a solid component and a liquid component.

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

[0045] There is no particular limitation on the electrolyte cleaning solvent. Examples of the electrolyte cleaning solvent include carbonates such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate; water; ketones such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone; and alcohols such as ethanol, methanol, propanol, and isopropyl alcohol.

[0046] Contacting the positive electrode composite material with the electrolyte cleaning solvent can be carried out using a known contact device for powder and liquid (e.g., a stirring tank).

[0047] In the step of contacting the positive electrode composite material with the electrolyte cleaning solvent, it is preferable to stir the positive electrode composite material and the electrolyte cleaning solvent to obtain a slurry. The peripheral speed of the tip of the stirring blade may be 0.1 to 1.0 m / s.

[0048] In the cleaning step of the positive electrode composite material, after solid-liquid separation, rinsing of the solid component may be carried out. Rinsing is an operation of contacting the solid component with the electrolyte cleaning solvent again to obtain a slurry and then separating the slurry into the solid component and the liquid component again. In the cleaning step of the positive electrode composite material, rinsing may be carried out multiple times. The slurry concentration in rinsing can be arbitrarily adjusted. In rinsing as well, the slurry can be stirred as described above.

[0049] The above cleaning can sufficiently remove the electrolyte from the positive electrode composite material. For example, if the electrolyte remains, the following reaction may occur, and the structure of the positive electrode active material may change from a layered rock salt structure to a spinel structure. LiPF 6 +16LiMO 2 +2O 2 → 6LiF+Li 3 PO 4 +8LiM 2 O 4

[0050] When the activating agent contains lithium carbonate, lithium consumption may occur due to the following reaction. LiPF6 +4Li 2 CO 3 → 6LiF+Li 3 PO 4 +4CO 2

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

[0052] Step (1): Activating agent mixing step Next, the prepared positive electrode composite material is mixed with an activating agent containing one or more alkali compounds to obtain a mixture.

[0053] When the positive electrode composite material contains a binder, the particles of the positive electrode active material may be bound to each other by the binder. The positive electrode composite material may contain an electrolyte and / or a conductive material in addition to the positive electrode active material and the binder. When the positive electrode composite material has a conductive material, the particles of the positive electrode active material and the conductive material may be bound to each other by the binder. The electrolyte is a component derived from the electrolyte solution of the battery and impregnated into the positive electrode composite material.

[0054] The mixing method of the positive electrode composite material and the activating agent may be either dry mixing or wet mixing, or a combination of these mixing methods. The mixing order of the positive electrode composite material and the activating agent is not particularly limited.

[0055] When mixing, it is preferable to go through a step of pulverizing and mixing using a mixing device equipped with a mixing medium such as balls, thereby improving the mixing efficiency.

[0056] As a mixing method, dry mixing is preferable in terms of easier mixing. In dry mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a powder mixer equipped with stirring blades inside, a ball mill, a vibration mill, or a combination of these devices can be used.

[0057] As a mixing device for dry mixing, a powder mixer equipped with stirring blades inside is preferable, and specifically, a Lodige mixer (manufactured by Matsubo Co., Ltd.) can be mentioned.

[0058] Hereinafter, the activating agent used in this step will be described in detail.

[0059] <Activating agent> The activating agent contains one or more alkali metal compounds. It is preferable that the activating agent 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 an alkali metal element X. The activating agent may contain an alkali metal compound containing other alkali metals such as Li in addition to potassium compounds and / or sodium compounds.

[0060] When the activating 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 activating agent particularly contains a molten part, the contact property between the molten part and the positive electrode active material is improved, so that the activation of the positive electrode active material is further promoted.

[0061] When the positive electrode composite material contains a binder and / or an electrolyte, the positive electrode composite material may contain a fluorine-containing compound derived from the binder and / or the electrolyte. However, by bringing the fluorine-containing compound into contact with the activating agent, the fluorine component is stabilized as an alkali metal fluoride, so that the generation of corrosive gases such as hydrogen fluoride can be suppressed. Since hydrogen fluoride reduces the activity of the positive electrode active material, it is desirable to prevent its generation.

[0062] The ratio of the total alkali metal compounds in the activating agent is appropriately set in consideration of the type of the alkali metal compound, the type of the target positive electrode active material, etc. Usually, it is 50% by mass or more, preferably 70% by mass or more, based on the total mass of the activating agent, and may be 100% by mass (in the case where the activating agent consists of an alkali metal compound in a practical sense).

[0063] The concentration of at least one alkali metal selected from the group consisting of potassium and sodium in the alkali metal contained in the alkali metal compound can be arbitrarily adjusted within the range of 0 to 100 mol%, preferably 10 mol% or more, more preferably 20 mol% or more, preferably 90 mol% or less, and more preferably 80 mol% or less.

[0064] Examples of the alkali metal compound that becomes a component 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 alone or in combination as components of the activation treatment agent.

[0065] 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 and other borates; Li 2 CO 3 、Na 2 CO 3 、K 2 CO 3 、RbCO 3 、CsCO 3 and other carbonates; Li 2 O、Na 2 O、K 2 O、Rb 2 O、Cs 2 O and other oxides; Li 2 O 2 、Na 2 O 2 、K 2 O 2 、Rb 2 O 2 、Cs 2 O 2 and other peroxides; LiO2 、 NaO 2 、 KO 2 、 RbO 2 、 CsO 2 and other superoxides; LiNO 3 、 NaNO 3 、 KNO 3 、 RbNO 3 、 CsNO 3 and other nitrates; Li 3 PO 4 、 Na 3 PO 4 、 K 3 PO 4 、 Rb 3 PO 4 、 Cs 3 PO 4 and other phosphates; Li 2 SO 4 、 Na 2 SO 4 、 K 2 SO 4 、 Rb 2 SO 4 、 Cs 2 SO 4 and other sulfates; Chlorides such as LiCl, NaCl, KCl, RbCl, CsCl; Bromides such as LiBr, NaBr, KBr, RbBr, CsBr; LiVO 3 、 NaVO 3 、 KVO 3 、 RbVO 3 、 CsVO 3 and other vanadates; Li 2 MoO 4 、 Na 2 MoO 4 、 K 2 MoO 4 、 Rb 2 MoO 4 、 CsMoO 4 and other molybdates; and Li 2 WO 4 、 Na 2 WO 4 、 K 2 WO4 , Rb 2 WO 4 , CsWO 4 and tungstates such as these; may be mentioned.

[0066] Here, in order to enhance the activation effect of the positive electrode active material, in addition to at least one compound selected from the group consisting of potassium compounds and sodium compounds, the activation treatment agent may contain the same alkali metal element as the alkali metal element contained in the positive electrode active material in the positive electrode composite material.

[0067] That is, when the positive electrode active material in the positive electrode composite material is a lithium composite oxide, it is preferable that the activation treatment agent 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, LiBO 2 , Li 2 CO 3 , Li 2 O, Li 2 O 2 , LiO 2 , LiNO 3 , Li 3 PO 4 , Li 2 SO 4 , LiCl, LiVO 3 , LiBr, Li 2 MoO 4 , and Li 2 WO 4 may be mentioned.

[0068] The activation treatment agent may contain a compound other than an alkali metal compound as necessary. Examples of the compound other than an alkali metal compound 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 start temperature of the activation treatment agent.

[0069] In addition, the content of the compound other than the alkali metal compound in the activation treatment agent is selected within a range that does not significantly suppress the effect derived from the above-mentioned molten alkali metal compound, and can be less than 50% by mass based on the total mass of the activation treatment agent.

[0070] The addition amount of the activation treatment agent in the mixture of the positive electrode composite material and the activation treatment agent is preferably 0.001 to 100 times, and more preferably 0.05 to 1 times, based on the mass of the positive electrode active material contained in the positive electrode composite material.

[0071] When the activation treatment agent contains a potassium compound and a lithium compound, the ratio of the content of lithium (in terms of mol) to the content of potassium (in terms of mol) (content of lithium / content of potassium) is 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 the battery manufactured using the recycled positive electrode active material comparable to those of the battery manufactured using the unused positive electrode active material.

[0072] When the activation treatment agent contains a sodium compound and a lithium compound, the ratio of the content of lithium (in terms of mol) to the content of sodium (in terms of mol) (content of lithium / content of sodium) is 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 the battery manufactured using the recycled positive electrode active material comparable to those of the battery manufactured using the unused positive electrode active material.

[0073] When the activation treatment agent contains a potassium compound, the content of potassium (in terms of mol) contained in the activation treatment agent is 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% based on the content of fluorine (in terms of mol) contained in the positive electrode composite material, from the viewpoint of making it easier to make the charge-discharge characteristics of the battery manufactured using the recycled positive electrode active material comparable to those of the battery manufactured using the unused positive electrode active material.

[0074] When the activating agent contains a sodium compound, the content of sodium contained in the activating agent (in terms of moles) is 1 to 200%, 10 to 200%, 50 to 200%, or 100 to 200%, 1% or more and less than 150%, 10% or more and less than 150%, 50% or more and less than 150%, or 100% or more and less than 150% with respect to the content of fluorine contained in the positive electrode composite material (in terms of moles), from the viewpoint of making it easier to make the charge and discharge characteristics of the battery manufactured using the recycled positive electrode active material more comparable to the charge and discharge characteristics of the battery manufactured using the unused positive electrode active material.

[0075] The number of moles of the alkali metal compound in the activating agent in the mixture of the positive electrode composite material and the activating agent can be added so that the number of moles of the alkali metal element is 0.001 to 200 times when the number of moles of the positive electrode active material (for example, formula A) contained in the positive electrode composite material is 1.

[0076] By appropriately controlling the ratio of the activating agent in the mixture, the cost of recovering the positive electrode active material from the positive electrode composite material can be reduced, the oxidation decomposition rate of the carbon-containing material (carbon-based conductive material, binder, etc.) can be increased, the effect of preventing the generation of corrosive gas in the heating process can be improved, and furthermore, the discharge capacity of the battery manufactured using the obtained positive electrode active material can be increased more.

[0077] In addition, at least one of the alkali metal compounds contained in the activating agent is preferably an alkali metal compound that exhibits alkalinity when dissolved in water. When an activating agent containing such an alkali metal compound is dissolved in pure water, the pH of the solution becomes greater than 7. Hereinafter, such an activating agent may sometimes be referred to as an "alkaline activating agent".

[0078] By using an alkaline activating agent, the generation of corrosive gas in the heating process can be further suppressed, so that the discharge capacity of a battery manufactured using the recovered cathode active material can be further increased. Further, by using an alkaline activating agent, the treatment rate of a carbon-containing material (carbon-based conductive material, binder, etc.) can also be increased.

[0079] Examples of the alkali metal compound that exhibits alkalinity when dissolved in water contained in the alkaline activating agent include hydroxides, carbonates, bicarbonates, oxides, peroxides, and superoxides of alkali metals. Specifically, hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; Li 2 CO 3 , Na 2 CO 3 , K 2 CO 3 , RbCO 3 , CsCO 3 , etc.; carbonates such as LiHCO 3 , NaHCO 3 , KHCO 3 , RbHCO 3 , CsHCO 3 , etc.; bicarbonates such as Li 2 O, Na 2 O, K 2 O, Rb 2 O, Cs 2 O, etc.; oxides such as Li 2 O 2 , Na 2 O 2 , K 2 O 2 , Rb 2 O 2 , Cs 2 O 2 , etc.; peroxides such as LiO 2 , NaO 2 , KO 2 , RbO 2 , CsO 2 , etc.; superoxides. These may be included in the activating agent alone or in combination of two or more.

[0080] Also, when the conductive material contained in the positive electrode composite material 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 to oxidatively decompose 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 oxidizing power".

[0081] When using such an activation treatment agent having oxidizing power, it is particularly effective in promoting the oxidation of the carbon-based conductive material, which is a carbon material, to carbon dioxide, and promoting the oxidation of the binder, which is a hydrocarbon material, to carbon dioxide and water vapor, and can further increase the discharge capacity of a battery manufactured using the obtained positive electrode active material, and may further improve the effect of preventing the generation of corrosive gases in the heating step.

[0082] Examples of the alkali metal compound having an oxidizing power necessary for oxidizing the carbon-based conductive material and hydrocarbon to carbon dioxide and water vapor include alkali metal peroxides, superoxides, nitrates, sulfates, vanadates, and molybdates. These may be used alone or in combination of two or more.

[0083] Specifically, superoxides such as Li 2 O 2 , Na 2 O 2 , K 2 O 2 , Rb 2 O 2 , Cs 2 O 2 ; LiO 2 , NaO 2 , KO 2 , RbO 2 , CsO 2 ; LiNO 3 , NaNO 3 , KNO 3 , RbNO 3 , CsNO 3 ; nitrates such as Li 2 SO 4 , Na 2 SO 4 , K 2 SO4 , Rb 2 SO 4 , Cs 2 SO 4 and other sulfates; LiVO 3 , NaVO 3 , KVO 3 , RbVO 3 , CsVO 3 and other vanadates; Li 2 MoO 4 , Na 2 MoO 4 , K 2 MoO 4 , Rb 2 MoO 4 , CsMoO 4 and other molybdates; may be mentioned.

[0084] Details of the oxidizing power of these alkali metal compounds are described in Japanese Patent Application Laid-Open No. 2012-186150.

[0085] From the viewpoint that the alkali metal compound can more easily make the charge and discharge characteristics of the battery manufactured using the recycled positive electrode active material comparable to those of the battery manufactured using the unused positive electrode active material, it may be a carbonate or a sulfate, and may be at least one selected from the group consisting of Li 2 CO 3 , Na 2 SO 4 , Na 2 CO 3 , and K 2 CO 3 selected from the group consisting of.

[0086] Step (2): Heating step Step (2) (heating step) is a step of loading the mixture obtained in step (1) (hereinafter sometimes referred to as "the mixture before heating") into a heating furnace, heating the mixture before heating, and removing carbon dioxide generated by heating a carbon-containing material (carbon-based conductive material, binder, etc.) from the heating furnace to obtain a mixture after heating. By removing carbon dioxide from the heating furnace, it is possible to prevent carbon dioxide from staying in the heating furnace, so that the concentration and temperature rise of carbon dioxide in the heating furnace can be suppressed.

[0087] Examples of the heating furnace include gas furnaces, electric furnaces, infrared heating furnaces, plasma heat treatment furnaces, heavy oil furnaces, light oil furnaces, hydrogen heat treatment furnaces, induction heating furnaces, vacuum furnaces, salt bath furnaces, tunnel furnaces, roller hearth kilns, rotary furnaces, walking beam furnaces, carbon furnaces, mesh belt furnaces, rotary kilns, shuttle kilns, fluidized bed firing furnaces, and other heating furnaces. The heating furnace is a space where the mixture to be heated is accommodated, which may be a closed space or an open space having an opening for carrying the mixture in or out. The heating furnace may be a batch furnace, a continuous furnace, or a fluidized furnace. For example, the rotary kiln may be a batch-type rotary kiln or a continuous-type rotary kiln. When the heating furnace is a continuous furnace, the heating space may be a gas furnace, an electric furnace, an infrared heating furnace, a plasma heat treatment furnace, a heavy oil furnace, a light oil furnace, a hydrogen heat treatment furnace, an induction heating furnace, a walking beam furnace, a mesh belt furnace, a continuous rotary kiln, or a continuous shuttle kiln. The fluidized bed firing furnace may have multiple stages, and the temperature may be changed at each stage.

[0088] The carbon dioxide in the heating furnace may be removed by blowing air. By blowing air in the heating furnace, carbon dioxide can be discharged from the heating furnace, and the retention of carbon dioxide in the heating furnace can be prevented. Therefore, the increase in the concentration and temperature of carbon dioxide in the heating furnace can be suppressed.

[0089] The direction of blowing air in the heating furnace may be determined according to the structure of the heating furnace, the amount of the mixture before heating, the contained components of the blown gas, etc. For example, the air may be blown from the top surface, side surface, or bottom surface of the heating furnace toward the opposite surface. Also, for example, when the heating furnace is a continuous furnace, the air may be blown in a direction opposite to the advancing direction of the mixture, or in a direction perpendicular to the advancing direction of the mixture.

[0090] The continuous furnace has at least a carry-in port for carrying in the mixture before heating and a carry-out port for carrying out the mixture after heating. The continuous furnace may have an air supply port for supplying air, and may also have an exhaust port for exhausting carbon dioxide or the like. The continuous furnace may have a plurality of air supply ports and may also have a plurality of exhaust ports.

[0091] By supplying air in the direction opposite to the advancing direction of the mixture, the carbon dioxide generated by heating is transferred to the carry-in port side of the continuous furnace. Since the temperature in the continuous furnace generally increases from the carry-in port toward the carry-out port, the carry-in port side of the continuous furnace is a region with a relatively low temperature in the continuous furnace. Therefore, by transferring the carbon dioxide generated by heating to the carry-in port side, which is relatively low temperature in the continuous furnace, it is possible to prevent the carbon dioxide from becoming high temperature, and thereby further suppress the contact between the high-temperature carbon dioxide and the positive electrode active material.

[0092] In the continuous furnace, the temperature may change along the advancing direction of the mixture. For example, the continuous furnace may have a region where the temperature gradually increases along the advancing direction of the mixture. The temperature in the continuous furnace (the temperature at any position in the continuous furnace) may be, for example, in the range of room temperature to 2000 °C.

[0093] The continuous furnace may have, for example, a low-temperature region that is relatively low temperature in the continuous furnace and exists near the carry-in port, a temperature-rising region where the temperature gradually increases from the low-temperature region toward the carry-out port side, a constant-temperature region where the temperature is substantially constant, and a temperature-falling region where the temperature gradually decreases from the constant-temperature region toward the vicinity of the carry-out port. The temperature of each region and the volume of the space occupied by each region in the continuous furnace can be appropriately determined according to the structure of the continuous furnace, the amount of the mixture before heating, the contained components of the supplied gas, the amount of carbon dioxide generated in the continuous furnace, and the like. The air supply in the continuous furnace may be performed in at least one region selected from the group consisting of the low-temperature region, the temperature-rising region, the constant-temperature region, and the temperature-falling region.

[0094] When the continuous furnace has air inlets and / or exhaust outlets, the locations for installing the air inlets and / or exhaust outlets inside the continuous furnace may be determined according to the structure of the continuous furnace, the amount of the mixture before heating, the components contained in the gas to be supplied, the amount of carbon dioxide generated inside the continuous furnace, etc. For example, the continuous furnace may have air inlets (if there are multiple air inlets, multiple air inlets) arranged along the bottom surface of the continuous furnace, and exhaust outlets (if there are multiple exhaust outlets, multiple exhaust outlets) arranged along the top surface of the continuous furnace. Or, exhaust outlets (if there are multiple exhaust outlets, multiple exhaust outlets) may be arranged along the bottom surface of the continuous furnace, and air inlets (if there are multiple air inlets, multiple air inlets) may be arranged along the top surface of the continuous furnace. Also, air inlets and exhaust outlets (if there are multiple air inlets and multiple exhaust outlets respectively, multiple air inlets and multiple exhaust outlets) may be arranged along the side surface of the continuous furnace respectively. The air inlets may be arranged facing the exhaust outlets, or may not be arranged facing the exhaust outlets.

[0095] The air supply inside the continuous furnace may be performed in a direction perpendicular to the advancing direction of the mixture inside the continuous furnace. Generally, since the advancing direction of the mixture is a direction along the bottom surface, top surface, or side surface of the continuous furnace, performing air supply in a direction perpendicular to the advancing direction of the mixture inside the continuous furnace means performing air supply in a direction perpendicular to the bottom surface, top surface, or side surface of the continuous furnace. When performing in a direction perpendicular to the advancing direction of the mixture inside the continuous furnace, the air supply is, for example, performed from the air inlet provided on the bottom surface of the continuous furnace towards the exhaust outlet provided on the top surface of the continuous furnace.

[0096] The gas supplied into the heating furnace is not particularly limited, and may be, for example, an oxygen-containing gas such as air, or an inert gas such as nitrogen or argon. Since the gas supplied into the heating furnace is exhausted together with the carbon dioxide generated inside the heating furnace, the carbon dioxide concentration in the gas exhausted from the heating furnace may be higher than the carbon dioxide concentration in the gas supplied into the heating furnace. The gas exhausted from the heating furnace may be sent back into the heating furnace again after removing carbon dioxide.

[0097] The air supply in the heating furnace may be performed throughout the entire heating furnace or only in a partial area of the heating furnace. The air supply in the heating furnace may be performed in a temperature range where the amount of carbon dioxide generated in the heating furnace increases, from the viewpoint of enhancing the exhaust efficiency of carbon dioxide and further suppressing the degradation of the positive electrode active material by high-temperature carbon dioxide. For example, the air supply may be performed in a region where the temperature in the heating furnace is 300 to 900 °C, 300 to 700 °C, or 300 to 600 °C. The air supply in the heating furnace is preferably performed in a region where the temperature is lower than the melting start temperature of the activation treatment agent.

[0098] The flow rate per liter of the heating space 1L of the gas supplied into the heating furnace may be, for example, 0.001 to 1.0 L / min or 0.01 to 0.6 L / min. The flow rate per liter of the heating space of the gas can be appropriately adjusted according to the structure of the heating furnace, the amount of the mixture before heating, the contained components of the gas to be supplied, the amount of carbon dioxide generated in the heating furnace, etc. For example, from the viewpoint of further suppressing the degradation of the positive electrode active material, in order to make the concentration of carbon dioxide in the heating furnace lower, the flow rate per liter of the heating space of the gas may be adjusted to increase. From the viewpoint of enhancing the energy efficiency, in order to reduce the pressure loss, the flow rate per liter of the heating space of the gas may be adjusted to decrease. Also, the flow rate per liter of the heating space of the gas may be adjusted to an amount such that the carbon dioxide concentration per liter of the heating space becomes a specific value or less (for example, 10% by volume or less). The flow rate per liter of the heating space of the gas supplied into the heating furnace may be substantially the same throughout the entire heating furnace or may be different at various locations in the heating furnace.

[0099] The carbon dioxide in the heating furnace may be removed by a carbon dioxide adsorbent (for example, zeolite 13X). Also, the carbon dioxide in the heating furnace may be removed by a carbon dioxide absorbent. Also, the carbon dioxide in the heating furnace may be removed by a carbon dioxide separation membrane.

[0100] The heating of the mixture may be performed by heating the mixture to a temperature equal to or higher than the melting start temperature of the activation treatment agent. The "melting start temperature (Tmp) of the activation treatment agent" means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0101] The melting start temperature (Tmp) of the activation treatment agent is a value determined by differential thermal measurement (DTA). That is, for 5 mg of the mixture before heating, the temperature at which the DTA signal shows an endothermic peak in differential thermal measurement (DTA, measurement conditions: heating rate: 10 °C / min) is defined as the melting start temperature (Tmp).

[0102] The melting start temperature (Tmp) of the activation treatment agent is preferably 700 °C or lower, and more preferably 600 °C or lower. There is no lower limit for the melting start temperature (Tmp) of the activation treatment agent, but for example, it may be 150 °C or higher.

[0103] In step (2), by heating the mixture before heating to a temperature equal to or higher than the melting start temperature (Tmp) of the activation treatment agent, the following effects occur. That is, when the activation treatment agent in a molten state comes into contact with the positive electrode active material, deterioration of the crystal structure of the positive electrode active material can be suppressed. Also, a crystal structure repair effect can be obtained.

[0104] When the activation treatment agent in a molten state comes into contact with a carbon-containing material (carbon-based conductive material, binder, etc.), the rate of oxidative decomposition of the conductive material and the binder is improved. Further, when the activation treatment agent in a molten state comes into contact with a fluorine compound derived from the binder and the electrolytic solution, the fluorine component is stabilized as an alkali metal fluoride, preventing the generation of hydrogen fluoride, which is a corrosive gas, and suppressing deterioration of the crystal structure of the positive electrode active material.

[0105] Furthermore, when the activation treatment agent contains the same alkali metal as the positive electrode active material, it is also possible to supply the alkali metal that is deficient in the positive electrode active material.

[0106] The maximum temperature in the heating furnace (the highest temperature among the temperatures at any position in the heating furnace) may be, for example, equal to or higher than the melting start temperature of the activation treatment agent. The maximum temperature in the heating furnace (the highest temperature at any position in the heating furnace) may be, for example, 300 - 900 °C, 300 - 700 °C, or 300 - 600 °C.

[0107] The melting point of the activation treatment agent means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase when only the activation treatment agent is heated. By mixing the positive electrode composite material and the activation treatment agent, the melting start temperature (Tmp) of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0108] The melting point of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, for 5 mg of the activation treatment agent, the temperature at which the DTA signal shows an endothermic peak under differential thermal analysis (DTA, measurement conditions: heating rate: 10 °C / min) is defined as the melting point of the activation treatment agent.

[0109] The maximum temperature in the heating furnace (the maximum temperature at any position in the heating furnace) is preferably higher than the melting point of the alkali metal compound contained in the activation treatment agent. The melting point of the alkali metal compound may be lower than the melting point of each single alkali metal compound by mixing two or more kinds of alkali metal compounds. When the activation treatment agent contains two or more kinds of alkali metal compounds, the eutectic point is defined as the melting point of the alkali metal compound.

[0110] The residence time of the mixture in the heating furnace (the time from when the mixture is introduced into the heating furnace until it is discharged) may be determined according to the temperature in the heating furnace, the amount of the mixture before heating, etc. The residence time of the mixture in the heating furnace may be, for example, 10 minutes to 24 hours.

[0111] The heating time of the mixture at a temperature equal to or higher than the melting start temperature of the activation treatment agent may be determined according to the amount of the mixture before heating, etc. The heating time of the mixture at a temperature equal to or higher than the melting start temperature of the activation treatment agent may be, for example, 1 minute to 24 hours.

[0112] The heating of the mixture may heat the mixture to a temperature below the melting start temperature of the activating treatment agent. By heating the mixture before heating to a temperature below the melting start temperature (Tmp) of the activating treatment agent, deterioration of the crystal structure of the positive electrode active material due to heating at a high temperature is suppressed, and it becomes easier to achieve charge and discharge characteristics comparable to those of a battery manufactured using an unused positive electrode active material. Further, by heating the mixture before heating together with the activating treatment agent, a crystal structure repairing action can also be obtained. In this specification, "heating to a temperature below the melting start temperature of the activating treatment agent" means heating while maintaining the temperature below the melting start temperature of the activating treatment agent (heating at a holding temperature below the melting start temperature of the activating treatment agent). Further, "heating to a temperature below the melting start temperature of the activating treatment agent" means not heating at a temperature equal to or higher than the melting start temperature of the activating treatment agent.

[0113] When the heated activating treatment agent comes into contact with a carbon-containing material (carbon-based conductive material, binder, etc.), the rate of oxidative decomposition of the conductive material and the binder is improved. Further, when the heated activating treatment agent comes into contact with a fluorine compound derived from the binder and the electrolytic solution, the fluorine component is stabilized as an alkali metal fluoride, generation of hydrogen fluoride, which is a corrosive gas, is prevented, and deterioration of the crystal structure of the positive electrode active material is suppressed.

[0114] The maximum temperature in the heating furnace (the highest temperature among the temperatures at any position in the heating furnace) may be, for example, below the melting start temperature of the activating treatment agent. The maximum temperature in the heating furnace (the highest temperature at any position in the heating furnace) may be, for example, 300 to 600 °C, 350 to 575 °C, or 400 to 550 °C.

[0115] The time for heating the mixture below the melting start temperature of the activating treatment agent may be determined according to the amount of the mixture before heating and the like. The time for heating the mixture below the melting start temperature of the activating treatment agent may be, for example, 1 minute to 24 hours.

[0116] After the heating step, if necessary, the mixture can be cooled to any temperature, for example, about room temperature. In this way, a heated mixture containing the heated positive electrode active material is obtained.

[0117] Step (3): Positive electrode active material recovery step The positive electrode active material recovery step is a step of recovering the heated positive electrode active material from the heated mixture after the heating step in step (2).

[0118] In the heated mixture, in addition to the heated positive electrode active material, components derived from the activation treatment agent (such as alkali metal compounds), undecomposed carbon-containing materials (carbon-based conductive materials, binders, etc.), and undecomposed materials of other positive electrode composite materials are included. Further, when the positive electrode composite agent contains an electrolyte containing a fluorine component, it may also contain a fluorine component derived from the electrolyte.

[0119] As a method for separating and recovering the heated positive electrode active material from the heated mixture, a solid-liquid separation method in which a solvent such as water is added to the mixture to form a slurry and then solid-liquid separation is performed, a vaporization separation method in which the mixture is heated to vaporize and separate components other than the heated positive electrode active material, and the like can be mentioned. Hereinafter, the solid-liquid separation method will be described.

[0120] Step (3a): Solid-liquid separation step Step (3a) is a step of bringing the heated mixture into contact 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.

[0121] In order to separate and recover the heated positive electrode active material from the heated mixture, a liquid (liquid) containing water is added to the mixture to form a slurry, and then solid-liquid separation is performed to separate it into a solid component and a liquid component.

[0122] 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. Components other than water may be added to the liquid to adjust the pH in order to increase the solubility of the water-soluble components or increase the treatment rate. Preferable examples of the liquid containing water include pure water and alkaline cleaning liquids. Examples of the alkaline cleaning liquid include aqueous solutions of one or more anhydrides selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate, and their hydrates. Further, ammonia can also be used as the alkali.

[0123] The resulting slurry contains a solid component mainly composed of 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 contains an alkali metal component derived from the activation treatment agent and / or a fluorine component derived from the binder and the electrolytic solution.

[0124] The amount of the liquid added to the mixture is appropriately determined in consideration of the amounts of the positive electrode active material after heating and the water-soluble components other than the positive electrode active material contained in the mixture.

[0125] In step (3a), it is preferable to stir the mixture after heating and the liquid containing water to obtain a slurry. Thereby, the dissolution of the water-soluble components is promoted. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m / s.

[0126] 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. As the method of solid-liquid separation, a conventionally known method may be used, for example, filtration or centrifugation.

[0127] In step (3a), after solid-liquid separation, rinsing of the obtained solid component may be performed. Rinsing is an operation of contacting the obtained solid component with a liquid containing water again to obtain a slurry, and then separating the slurry into a solid component and a liquid component again. In step (3a), rinsing may be performed multiple times. The slurry concentration in rinsing can also be the same as above.

[0128] 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 for manufacturing a positive electrode or the like. The manufacturing method of the recycled positive electrode active material can include additional steps before and after steps (1) to (3). In this specification, the 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 the additional steps other than steps (1) to (3) are pre-steps (A) and (B) performed before step (1), and the following steps (4) and (5) performed after step (3), for example, after step (3a).

[0129] Step (4): Drying step Step (4) is, for example, a step of removing water from the solid component by exposing the solid component obtained in step (3a) to a heating and / or reduced-pressure environment.

[0130] The heating temperature is preferably 100°C or higher to remove water. To more sufficiently remove water, it is preferably 150°C or higher. Particularly, at a temperature of 250°C or higher, it is preferable because the discharge capacity of the battery manufactured using the obtained positive electrode active material further increases. 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 less than 900°C.

[0131] The reduced-pressure range reached can be, for example, 1.0×10 -10 ~1.0×10 3 Pa.

[0132] Step (5): Annealing (re-firing) step When the activating agent is heated at a temperature equal to or higher than the melting start temperature in step (5), step (5) may be a step of heat-treating the solid component after step (4) at a temperature lower than 900°C.

[0133] Step (5) may be a step of heating the solid component after step (4) at a temperature higher than that in step (2) when the activating agent is heated below the melting start temperature. In this case, the temperature for heating the mixture after heating may be higher than 700 °C, 750 °C or higher, 800 °C or higher, 850 °C or higher, or 900 °C or higher from the viewpoints of vaporizing components other than the positive electrode active material to remove impurities and making it easier to achieve charge and 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.

[0134] Although there is no limitation on the atmosphere for the heat treatment, an oxygen-containing atmosphere such as air is preferably used. Further, the heat treatment temperature can be 100 °C or higher. Further, the holding time for the heat treatment can be from 1 minute to 24 hours. In particular, it is preferable to heat at a holding temperature of 350 °C or higher for 0.1 hour or more and 5 hours or less.

[0135] By using the method for producing a recycled positive electrode active material of the present invention, the recycled positive electrode active material obtained from the battery composite material can be reused in the same manner as an unused active material. Methods for manufacturing a positive electrode and a battery using the recycled positive electrode active material are well known.

[0136] Finally, the discharge capacity of the recycled positive electrode active material according to the embodiment of the present invention can be 150 mAh / g or more.

Examples

[0137] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless the gist thereof is changed.

[0138] Measurements of the physical properties of the positive electrode active material and the recycled positive electrode active material and charge and discharge tests using the battery using the positive electrode active material were performed as follows.

[0139] [Element content] For the solution and the acid solution in which the powder was dissolved, the content of alkali metal elements contained in the solution and the powder was analyzed using an ICP emission spectrometer (for example, SPS3000 manufactured by SII NanoTechnology Inc.).

[0140] (Reference Example 1) (Reference Example 1) (Manufacture of the positive electrode) The positive electrode described below was prepared by the following procedure. 92 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 PVdF (binder, manufactured by Kureha Corporation, product number: #1100), and 5 parts by mass of acetylene black (conductive material, manufactured by Denka Co., Ltd., product number: HS100) were mixed to obtain a mixture. As the PVdF as the binder, a binder solution in which PVdF was previously dissolved in NMP was used. The mixture was kneaded with a rotation / revolution mixer (ARE-310 manufactured by Shin Kee Co., Ltd.) to prepare a positive electrode mixture paste. NMP was added and adjusted so that the total mass of the positive electrode active material, binder, and conductive material in the positive electrode mixture paste was 50% by mass.

[0141] On one side of an aluminum foil 1085 (manufactured by Nippon Foil Mfg. Co., Ltd.) for a positive electrode current collector of a lithium-ion secondary battery with a thickness of 20 μm, the positive electrode mixture paste was applied so that the amount of the positive electrode active material was 3.0 ± 0.1 mg / cm 2 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 was used.

[0142] (Manufacture of the battery) The coin-type battery described below was prepared by the following procedure. The above positive electrode, electrolyte, separator, and negative electrode were combined to manufacture a non-aqueous electrolyte secondary battery (coin-type battery). The battery was assembled inside a glove box under an argon atmosphere. As the electrolyte, LiPF was added to a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. 6A solution dissolved at a ratio of 1.0 mol / L was used. As the separator, a laminated film separator in which a heat-resistant porous layer was laminated on a porous film (made of polyethylene) was used. As the negative electrode, metallic lithium was used.

[0143] <Manufacture of the positive electrode before recycling> As the positive electrode active material, the composition is Li 1.07 Ni 0.47 Mn 0.48 Fe 0.05 O 2 and a positive electrode active material having a crystal structure of R-3m was prepared. Using this positive electrode active material (unused positive electrode active material), the above coin-type battery was fabricated, and the following charge-discharge test (rate test) was conducted while maintaining at 25 °C. The 0.2C discharge capacity was 138 mAh / g, and the 5C discharge capacity was 106 mAh / g. A larger 0.2C discharge capacity means that a higher rated capacity can be obtained, and a larger 5C discharge capacity means that higher output characteristics can be obtained. (Conditions) Maximum charge voltage: 4.3 V Charge current: 0.2 mA / cm 2 Charge time: 8 hours Minimum discharge voltage: 2.5 V 0.2C discharge current: 0.2 mA / cm 2 5C discharge current: 5.0 mA / cm 2

[0144] From the positive electrode used in the above battery, the electrode mixture was mechanically shaved off to peel the electrode mixture from the current collector. To 5 g of the electrode mixture taken out from the positive electrode, 0.1 mol of K 2 CO 3 per 1 mol of the positive electrode active material and 0.1 mol of Na 2 CO 3 per 1 mol of the positive electrode active material were mixed to obtain a mixture (mixture before heating). The melting start temperature of the activation treatment agent was 700 °C.

[0145] The mixture before heating was placed in an electric furnace and heated under an air atmosphere at a heating temperature of 700 °C (above the melting start temperature of the activation treatment agent) for a heating time of 240 minutes.

[0146] The mixture after heating was pulverized, distilled water was added and stirred to obtain a slurry. The obtained slurry was filtered and separated into a solid component and a liquid component. Subsequently, the solid component was recovered and dried to obtain a recycled cathode active material. The composition, crystal structure, average particle size, and specific surface area of the obtained recycled cathode active material were comparable to those of the unused cathode active material. When the above coin-type battery was fabricated using the recycled cathode active material and a charge-discharge test was conducted under the above conditions while maintaining at 25 °C, the 0.2C discharge capacity was 135 mAh / g, the 5C discharge capacity was 94 mAh / g, which was comparable to the discharge capacity of the coin-type battery fabricated using the unused cathode active material.

[0147] (Reference Example 2) (Manufacture of the cathode before recycling) As the cathode active material, a cathode active material NCM111 with a composition of LiNi 0.33 Co 0.33 Mn 0.33 O 2 and a crystal structure of R-3m was prepared. When the above coin-type battery was fabricated using this cathode active material (unused cathode active material), the initial charge capacity was 178.3 mAh / g, and the initial discharge capacity (0.2C) was 163.4 mAh / g. Also, when the following charge-discharge test (rate test) was conducted while maintaining at 25 °C, the 0.2C discharge capacity was 163.1 mAh / g, and the 5C discharge capacity was 141.3 mAh / g.

[0148] From the cathode of the process end material generated when fabricating the above cathode, the electrode mixture was mechanically shaved off to peel the electrode mixture from the current collector. To 5 g of the electrode mixture taken out from the cathode, 0.1 mol of Li 2 CO 3 per 1 mol of the cathode active material and 0.1 mol of Na 2 SO 4They were mixed to obtain a mixture (the mixture before heating). The melting start temperature of the activating agent was 510°C.

[0149] 30 g of the mixture before heating was placed in an electric furnace and heated under an air atmosphere at a heating rate of 300°C / h, a heating temperature of 450°C (below the melting start temperature of the activating agent), and a heating time of 360 minutes.

[0150] The mixture after heating was pulverized, distilled water was added and stirred to obtain a slurry. The obtained slurry was filtered to separate it into a solid component and a liquid component. Then, the solid component was recovered and suction-dried at 100°C for 1 hour.

[0151] The solid component after drying was placed in an electric furnace and heated under an air atmosphere at a heating temperature of 900°C and a heating time of 60 minutes to obtain a recycled positive electrode active material after heating. Then, the recycled positive electrode active material after heating was naturally cooled to room temperature, and it was confirmed that the composition, crystal structure, average particle diameter, and specific surface area of the obtained recycled positive electrode active material were comparable to those of the unused positive electrode active material. When the coin-type battery was fabricated using the recycled positive electrode active material, the initial charge capacity was 180.5 mAh / g, and the initial discharge capacity was 161.1 mAh / g. Also, when the first charge-discharge (rate test) was performed under the above conditions while maintaining at 25°C, the 0.2C discharge capacity was 160.2 mAh / g, and the 5C discharge capacity was 133.9 mAh / g.

[0152] (Example 1) A mixture before heating is obtained in the same manner as in Reference Example 1. The obtained mixture before heating is put into a continuous furnace, and in the continuous furnace, heating is performed while blowing air in the direction opposite to the advancing direction of the mixture before heating. The maximum temperature in the continuous furnace is 700 °C (equal to or higher than the melting start temperature of the activating agent), and the mixture before heating is heated under the condition of a residence time of 240 minutes in the continuous furnace. At this time, the carbon-containing materials (PVdF, acetylene black) contained in the mixture before heating generate carbon dioxide by heating, but are removed from the heating furnace (continuous furnace) by blowing air. Therefore, when comparing the carbon dioxide concentration in the gas blown into the heating furnace with the carbon dioxide concentration in the gas exhausted from the heating furnace, the carbon dioxide concentration in the gas exhausted from the heating furnace is higher. By blowing air in the heating furnace, the contact between the high-temperature carbon dioxide and the positive electrode active material is suppressed, so that the deterioration of the positive electrode active material due to the high-temperature carbon dioxide can be suppressed.

[0153] A recycled positive electrode active material is obtained from the mixture after heating in the same manner as in Reference Example 1. The composition, crystal structure, average particle diameter, and specific surface area of the obtained recycled positive electrode active material are comparable to those of the unused positive electrode active material. When the above coin-type battery is fabricated using the recycled positive electrode active material and a charge-discharge test is performed under the above conditions while maintaining at 25 °C, the discharge capacity is comparable to that of the coin-type battery fabricated using the unused positive electrode active material.

[0154] (Example 2) A mixture before heating is obtained in the same manner as in Reference Example 1. The obtained mixture before heating and a carbon dioxide adsorbent are put into an electric furnace, and the mixture before heating is put into the electric furnace and heated under the conditions of a heating temperature of 700 °C (equal to or higher than the melting start temperature of the activating agent) and a heating time of 240 minutes in an air atmosphere. At this time, the carbon-containing materials (PVdF, acetylene black) contained in the mixture before heating generate carbon dioxide by heating, but are removed from the heating furnace (electric furnace) by the carbon dioxide adsorbent. By the carbon dioxide adsorbent, the contact between the high-temperature carbon dioxide and the positive electrode active material is suppressed, so that the deterioration of the positive electrode active material due to the high-temperature carbon dioxide can be suppressed.

[0155] In the same manner as in Reference Example 1, a recycled positive electrode active material is obtained from the mixture after heating. The composition, crystal structure, average particle diameter, and specific surface area of the obtained recycled positive electrode active material are comparable to those of the unused positive electrode active material. When a coin-type battery is fabricated using the recycled positive electrode active material and a charge-discharge test is conducted under the above conditions while maintaining the temperature at 25°C, the discharge capacity is comparable to that of the coin-type battery fabricated using the unused positive electrode active material.

[0156] (Example 3) A mixture before heating is obtained in the same manner as in Reference Example 2. The obtained mixture before heating is placed in a continuous furnace, and heating is performed while blowing air in a direction opposite to the advancing direction of the mixture before heating in the continuous furnace. The maximum temperature in the continuous furnace is 450°C (below the melting start temperature of the activation treatment agent), and the mixture before heating is heated under the condition of a residence time of 360 minutes in the continuous furnace. At this time, the carbon-containing materials (PVdF, acetylene black) contained in the mixture before heating generate carbon dioxide by heating, but are removed from the heating furnace (continuous furnace) by blowing air. Therefore, when comparing the carbon dioxide concentration in the gas blown into the heating furnace with the carbon dioxide concentration in the gas exhausted from the heating furnace, the carbon dioxide concentration in the gas exhausted from the heating furnace is higher. By blowing air in the heating furnace, the contact between high-temperature carbon dioxide and the positive electrode active material is suppressed, so that the deterioration of the positive electrode active material due to high-temperature carbon dioxide can be suppressed.

[0157] In the same manner as in Reference Example 2, a recycled positive electrode active material is obtained from the mixture after heating. The composition, crystal structure, average particle diameter, and specific surface area of the obtained recycled positive electrode active material are comparable to those of the unused positive electrode active material. When a coin-type battery is fabricated using the recycled positive electrode active material and a charge-discharge test is conducted under the above conditions while maintaining the temperature at 25°C, the discharge capacity is comparable to that of the coin-type battery fabricated using the unused positive electrode active material.

[0158] (Example 4) A mixture before heating is obtained in the same manner as in Reference Example 2. The obtained mixture before heating and the carbon dioxide adsorbent are placed in an electric furnace. The mixture before heating is placed in the electric furnace and heated under the conditions of a heating temperature of 450 °C (equal to or higher than the melting start temperature of the activation treatment agent) and a heating time of 360 minutes in an air atmosphere. At this time, the carbon-containing materials (PVdF, acetylene black) contained in the mixture before heating generate carbon dioxide by heating, but are removed from the heating furnace (electric furnace) by the carbon dioxide adsorbent. Since the contact between the high-temperature carbon dioxide and the positive electrode active material is suppressed by the carbon dioxide adsorbent, deterioration of the positive electrode active material due to the high-temperature carbon dioxide can be suppressed.

[0159] A recycled positive electrode active material is obtained from the mixture after heating in the same manner as in Reference Example 2. The composition, crystal structure, average particle diameter, and specific surface area of the obtained recycled positive electrode active material are comparable to those of the unused positive electrode active material. When the above coin-type battery is fabricated using the recycled positive electrode active material and a charge-discharge test is conducted under the above conditions while maintaining at 25 °C, the discharge capacity is comparable to that of the coin-type battery fabricated using the unused positive electrode active material.

Claims

1. A method for producing a recycled positive electrode active material, comprising: (1) A step of mixing a positive electrode mixture containing a positive electrode active material and a carbon-containing material with an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; (2) carrying the mixture into a heating furnace, and removing carbon dioxide generated by heating the carbon-containing material from the heating furnace while heating the mixture to obtain a heated mixture; and (3) recovering the heated positive electrode active material from the heated mixture; Including, The method of manufacturing the cathode active material,

2. The method of claim 1 , wherein the carbon dioxide is removed by blowing air.

3. 3. The manufacturing method according to claim 2, wherein in the step (2), when a carbon dioxide concentration in the gas fed into the heating furnace is compared with a carbon dioxide concentration in the gas exhausted from the heating furnace, the gas exhausted from the heating furnace has a higher carbon dioxide concentration.

4. The method according to any one of claims 1 to 3, wherein the carbon dioxide is removed by a carbon dioxide adsorbent.

5. The method according to any one of claims 1 to 3, wherein in the step (2), the mixture is heated to a temperature equal to or higher than a melting start temperature of the activation treatment agent.

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

7. The positive electrode active material comprises a composite oxide containing at least one element selected from the following element group 1 and at least one element selected from the following element group 2. The manufacturing method according to any one of claims 1 to 3. Element group 1: Ni, Co, Mn, Fe, Al, and P Element group 2: Li, Na, K, Ca, Sr, Ba, and Mg

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