WO2025204689A1 - Method for producing recycled positive electrode active material - Google Patents

Abstract

This method for producing a recycled positive electrode active material involves the following steps: (1) a step for mixing a positive electrode mixture containing a positive electrode active material and an activation treatment agent containing one or more alkali metal compounds to obtain a mixture; (2) a step for heating the mixture to obtain a heated mixture; (3) a step for bringing the heated mixture into contact with a first liquid containing water and an alkali metal compound to obtain a first solid component and a first liquid component; (4) a step for bringing the first solid component into contact with a second liquid containing water and containing an alkali metal compound at an amount smaller than that in the first liquid to obtain a second solid component and a second liquid component; and (5) a step for recovering a recycled positive electrode active material from the second solid component.

Description

Method for manufacturing recycled positive electrode active material

This disclosure relates to a method for producing recycled positive electrode active materials.

Battery positive electrode active materials contain rare metal components such as cobalt, nickel, manganese, and lithium, and compounds primarily composed of these rare metal components are used as the positive electrode active material for non-aqueous electrolyte secondary batteries in particular. In order to conserve rare metal component resources, there is a need for a method to regenerate rare metal components from waste secondary battery materials.

For example, Patent Document 1 discloses a method of recovering positive electrode active material by mixing a positive electrode mixture with an activation treatment agent containing an alkali metal compound, heating the mixture to decompose the binder, and then removing the decomposed material and activation treatment agent with water or the like. This method is cost-effective in that it recovers positive electrode active material directly from battery waste without using organic solvents.

JP 2012-186150 A

When recycling the positive electrode active material in a positive electrode mixture, an activating agent containing an alkali metal compound is added to reactivate the positive electrode active material. After the positive electrode active material has been reactivated, the mixture containing the positive electrode active material and activating agent may be washed with water to remove the activating agent. Because it is difficult to remove the activating agent in a single wash, multiple washes may be performed. However, increasing the number of washes increases the amount of wastewater generated, placing a greater burden on the environment and increasing wastewater treatment costs.

The present disclosure therefore aims to provide a method for producing recycled positive electrode active material that can reduce the amount of wastewater generated by water washing when washing with water multiple times.

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

This disclosure provides a method for producing recycled positive electrode active material that can reduce the amount of wastewater generated by water washing when washing with water multiple times.

(Method for producing recycled positive electrode active material)
A method for producing a recycled positive electrode active material will be described below.

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

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

The following describes each step in the first embodiment in detail.

Pre-process (A): Positive Electrode Composite Preparation Process A positive electrode composite containing a positive electrode active material is prepared.

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

[Cathode active material]
Examples of the positive electrode active material include composite compounds containing one or more of the following elements as constituent elements: lithium, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, yttrium, niobium, molybdenum, silver, indium, tungsten, etc. The positive electrode active material may contain a lithium compound.

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

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

The positive electrode active material preferably 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)
Here, ^M2 represents at least one element selected from the group consisting of Na, K, Ca, Sr, Ba, and Mg;
^M1 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-metallic elements excluding O and P;
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.

Preferably, M ^T 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.

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

In the positive electrode active material, the molar fraction of Ni in ^M1 is preferably 0.3 to 0.95.

There are no particular restrictions on the crystal structure of the positive electrode active material (e.g., composite oxide), but a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

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 It belongs to any one space group selected from the group consisting of P6/mmm, P6 _/ cc, P6 _/ cm, P6/mc, _P6 /mcm, and _P6 /mmc.

The monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, P2 ₁ , C2, Pm, Pc, Cm, Cc, P2/m, P2 ₁ /m, C2/m, _P2 /c, P2 1 /c, and C2/c.

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

The crystalline 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 radiation as the radiation source.

The particle size of the positive electrode active material in the positive electrode mixture is not particularly limited, but may be between 0.001 and 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 can be created from the particle size distribution, and the particle size (D50) at 50% cumulative from the fine particle side can be used as the average particle size of the positive electrode active material.

There are no particular restrictions on the amount of positive electrode active material contained in the positive electrode mixture.

[Binder]
Examples of the binder (pre-activation binder) contained in the positive electrode mixture include thermoplastic resins, and specific examples include fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as "PVdF"), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene; and styrene-butadiene copolymers (SBR). One type of binder may be used alone, or two or more types may be used in combination.

The binder content in the positive electrode mixture is not particularly limited, but may be within the following ranges per 100 parts by mass of the positive electrode active material. The binder content may be 0.5 parts by mass or more, 1 part by mass or more, or 2 parts by mass or more. The binder content 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 binder content 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.

[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.

Specific examples of carbon-based conductive materials include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon materials (e.g., graphitized carbon fiber and carbon nanotubes).

The carbon-based conductive material may be a single carbon material or may be composed of multiple carbon materials.

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 this case, the conductive material may consist solely of a carbon-based conductive material with a specific surface area of 30 ^{m 2} /g or more, or may be carbon black with a specific surface area of 30 m 2 /g or more, or acetylene black with a specific surface area of 30 m ² /g or more. When an activating treatment agent containing an alkali metal compound having oxidizing power, which will be described later, is used, the rate of oxidation treatment of the carbon-based conductive material can be increased, and even carbon materials with a small specific surface area may be able to be oxidized.

The content of the conductive material in the positive electrode mixture is not particularly limited, but may be within the following ranges per 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.

[Electrolytes and Solvents]
Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ F) ₂ , and 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 %.

The positive electrode mixture may contain a solvent derived from the electrolyte. Examples of solvents include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

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

"Waste positive electrodes" may refer to positive electrodes recovered from discarded batteries, or to waste positive electrodes generated during the manufacturing process of positive electrodes or batteries. Discarded batteries may be used batteries, or unused, non-standard batteries. Waste positive electrodes may be the ends of positive electrodes generated during the battery manufacturing process, or non-standard positive electrodes. Discarded positive electrode composites that are not attached to current collectors (waste generated during the positive electrode composite manufacturing process) may also be used as the positive electrode composite.

Waste positive electrodes have a current collector made of 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.

Examples of methods for separating a positive electrode composite layer from a used 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, and a method of dissolving the current collector using an alkaline or acidic aqueous solution to separate the positive electrode composite layer. The method of separating a positive electrode composite layer from a used positive electrode having a current collector and a positive electrode composite layer is preferably a method of mechanically peeling the positive electrode composite layer from the current collector.

Pre-process (B): Positive Electrode Composite Washing Process Next, when the positive electrode composite contains an electrolyte, it is preferable to bring the prepared 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, the positive electrode composite containing the positive electrode active material, the binder, and the electrolyte is brought into contact with the electrolyte washing solvent to obtain a slurry containing a solid component and a liquid component, and then the slurry is subjected to solid-liquid separation into the solid component and the liquid component.

Solid-liquid separation is the process of separating a slurry into solid and liquid components. Examples of solid-liquid separation methods include conventionally known methods such as filtration and centrifugation.

There are no particular restrictions on the electrolyte cleaning solvent. Examples of electrolyte cleaning solvents include carbonate esters 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.

The electrolyte cleaning solvent can be brought into contact with the positive electrode mixture using a known powder-liquid contact device (e.g., a stirring tank).

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

In the positive electrode composite washing process, 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 solid and liquid components. In the positive electrode composite washing process, rinsing may be performed multiple times. The slurry concentration in rinsing can be adjusted as desired. The slurry can also be stirred during rinsing, as described above.

The above-described washing can sufficiently remove the electrolyte from the positive electrode mixture. For example, if the electrolyte remains, the following reaction occurs, which may cause the structure of the positive electrode active material to change from a layered rock salt structure to a spinel structure. However, by removing the electrolyte from the positive electrode mixture, the following reaction can be suppressed.
LiPF ₆ +16LiMO ₂ +2O ₂ → 6LiF+Li ₃ PO ₄ +8LiM ₂ O ₄

Furthermore, when the activation treatment agent contains lithium carbonate, lithium may be consumed by the following reaction, but the following reaction can be suppressed by removing the electrolyte from the positive electrode mixture.
LiPF ₆ +4Li ₂ CO ₃ → 6LiF + Li ₃ PO ₄ +4CO ₂

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

Step (1): Activation Treatment Agent Mixing Step Next, the prepared positive electrode mixture and an activation treatment agent containing one or more alkaline compounds are mixed to obtain a mixture.

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. There are also no particular restrictions on the order in which the positive electrode mixture and the activation treatment agent are mixed.

When mixing, it is preferable to use a mixer equipped with mixing media such as balls and go through a grinding and mixing process, which can improve mixing efficiency.

As a mixing method, dry mixing is preferred because it allows for easier mixing. For dry mixing, a V-type mixer, W-type mixer, ribbon mixer, drum mixer, powder mixer equipped with internal stirring blades, ball mill, vibration mill, or a combination of these devices can be used.

The mixing device used for dry mixing is preferably a powder mixer equipped with internal stirring blades, and a specific example is the Lödige Mixer (manufactured by Matsubo Co., Ltd.).

The activation treatment agent used in this process is described in detail below.

<Activation treatment agent>
The activation treatment agent contains one or more alkali metal compounds. The activation treatment agent preferably contains at least one compound selected from the group consisting of potassium compounds and sodium compounds. Here, potassium and/or sodium may be referred to as alkali metal element X. In addition to the potassium compound and/or sodium compound, the activation treatment agent may also contain an alkali metal compound containing another alkali metal such as Li.

When the activation treatment agent comes into contact with the positive electrode active material, it can activate the positive electrode active material. When the alkali metal compound in the activation treatment agent contains a molten portion, the contact between the molten portion and the positive electrode active material is improved, further promoting activation of the positive electrode active material.

In addition, the positive electrode mixture may contain fluorine-containing compounds derived from the binder and/or electrolyte. By bringing the fluorine-containing compounds into contact with the activation treatment agent, the fluorine components are stabilized as alkali metal fluorides, thereby preventing the generation of corrosive gases such as hydrogen fluoride. It is desirable to prevent the generation of hydrogen fluoride, as it reduces the activity of the positive electrode active material.

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

The concentration of at least one alkali metal selected from the group consisting of potassium and sodium in the alkali metals contained in the alkali metal compound can be adjusted arbitrarily between 0 and 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.

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, and tungstates. These can be used alone or in combination as components of the activation treatment agent.

Specific examples of suitable alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH;
Borates such as _LiBO2 , _NaBO2 , _KBO2 , _RbBO2 , and _CsBO2 ;
Carbonates such _{as Li2CO3} , _Na2CO3 , _{K2CO3 , RbCO3} , _{CsCO3 ;}
oxides such as Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O;
_{peroxides such as Li2O2} , _Na2O2 , _{K2O2 , Rb2O2} , _{Cs2O2 ;}
superoxides such as _LiO2 , _NaO2 , _KO2 , _RbO2 , _CsO2 ;
nitrates such as _LiNO3 , _NaNO3 , _KNO3 , _RbNO3 , _CsNO3 ;
_phosphates such _{as Li3PO4} , _Na3PO4 , _{K3PO4 , Rb3PO4 , Cs3PO4 ;}
sulfates such _{as Li2SO4 , Na2SO4 , K2SO4} , _{Rb2SO4 , Cs2SO4 ;}
Chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl;
Bromides such as LiBr, NaBr, KBr, RbBr, and CsBr;
vanadates such as _LiVO3 , _NaVO3 , _KVO3 , _RbVO3 , _CsVO3 ;
_{Examples include} molybdates such as _Li2MoO4 , _Na2MoO4 , _K2MoO4 , _{Rb2MoO4 ,} and _{CsMoO4 ;} and tungstates such _{as Li2WO4} , _{Na2WO4 , K2WO4 , Rb2WO4} , _{and CsWO4} .

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

That is, when the positive electrode active material in the positive electrode mixture is a lithium composite oxide, the activation treatment agent preferably contains a lithium compound in addition to at least one compound selected from the group consisting of potassium compounds and sodium compounds. _Suitable lithium compounds include LiOH, _LiBO2 , _Li2CO3 , _Li2O , _Li2O2 , _LiO2 , _LiNO3 , _Li3PO4 , _Li2SO4 , _LiCl , _LiVO3 , _{LiBr , Li2MoO4} , _{and Li2WO4 .}

The activation treatment agent may contain compounds other than alkali metal compounds as needed. Examples of compounds other than alkali metal compounds include alkaline earth metal compounds containing alkaline earth metal elements such as magnesium, calcium, and barium. The alkaline earth metal compounds are contained in the activation treatment agent together with the alkali metal compounds for the purpose of controlling the melting onset temperature of the activation treatment agent.

Furthermore, the content of compounds other than alkali metal compounds in the activation treatment agent is selected within a range that does not significantly suppress the effects derived from the molten alkali metal compound described above, and can be less than 50 mass% of the total mass of the activation treatment agent.

The amount of activation treatment agent added in the mixture of the positive electrode composite and 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 composite.

When the activation treatment agent contains a potassium compound and a lithium compound, the ratio of the lithium content (by mole) to the potassium content (by mole) (lithium content/potassium content) may be 0.01 to 100, 0.1 to 10, or 0.2 to 4, from the viewpoint of making the charge/discharge characteristics of a battery manufactured using recycled positive electrode active material more comparable to those of a battery manufactured using unused positive electrode active material.

When the activation treatment agent contains a sodium compound and a lithium compound, the ratio of the lithium content (by mole) to the sodium content (by mole) (lithium content/sodium content) may be 0.01 to 100, 0.1 to 10, or 0.2 to 4, from the viewpoint of making the charge/discharge characteristics of a battery manufactured using recycled positive electrode active material more comparable to those of a battery manufactured using unused positive electrode active material.

When the activation treatment agent contains a potassium compound, the potassium content (by mole) contained in the activation treatment agent may be 1% or more but less than 500%, 10% or more but less than 400%, 50% or more but less than 300%, 100% or more but less than 250%, or 150% or more but less than 250% of the fluorine content (by mole) contained in the positive electrode composite, from the viewpoint of making it easier to make the charge/discharge characteristics of a battery manufactured using recycled positive electrode active material more comparable to the charge/discharge characteristics of a battery manufactured using unused positive electrode active material.

If the activation treatment agent contains a sodium compound, the sodium content (by mole) contained in the activation treatment agent may be 1 to 200%, 10 to 200%, 50 to 200%, 100 to 200%, 1% to less than 150%, 10% to less than 150%, 50% to less than 150%, or 100% to less than 150% of the fluorine content (by mole) contained in the positive electrode composite, from the viewpoint of making it easier to make the charge/discharge characteristics of a battery manufactured using recycled positive electrode active material more comparable to the charge/discharge characteristics of a battery manufactured using unused positive electrode active material.

In a mixture of a positive electrode composite and an activation treatment agent, the number of moles of alkali metal compound in the activation treatment agent can be added so that the number of moles of alkali metal element is 0.001 to 200 times the number of moles of the positive electrode active material (e.g., Formula A) contained in the positive electrode composite, taken as 1.

By appropriately controlling the proportion of the activation treatment agent in the mixture, it is possible to reduce the cost of recovering the positive electrode active material from the positive electrode mixture and increase the oxidative decomposition rate of the carbon-based conductive material and binder. It also improves the effectiveness of preventing the generation of corrosive gases during the heating process, and further increases the discharge capacity of batteries manufactured using the resulting positive electrode active material.

Furthermore, it is preferable that at least one of the alkali metal compounds contained in the activation treatment agent is an alkali metal compound that exhibits alkaline properties when dissolved in water. When an activation treatment agent containing such an alkali metal compound is dissolved in pure water, the pH of the solution becomes greater than 7. Hereinafter, such an activation treatment agent may be referred to as an "alkaline activation treatment agent."

By using an alkaline activation treatment agent, the generation of corrosive gases during the heating process can be further suppressed, thereby increasing the discharge capacity of batteries manufactured using the recovered positive electrode active material. Furthermore, by using an alkaline activation treatment agent, the processing speed of carbon-based conductive materials and binders can also be increased.

Examples of alkali metal compounds that exhibit alkalinity when dissolved in water and are contained in alkaline activation treatment agents include hydroxides, carbonates, hydrogen carbonates, oxides, peroxides, and superoxides of alkali metals. Specific examples of alkaline alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, _RbOH , and CsOH; carbonates such as _Li2CO3 , _Na2CO3 , _K2CO3 , _RbCO3 , and CsCO3; hydrogen carbonates such as _LiHCO3 , _NaHCO3 , _{KHCO3 , RbHCO3} , and _CsHCO3 ; oxides such as _Li2O , _Na2O , _K2O , _Rb2O , and _Cs2O ; peroxides such _{as Li2O2 , Na2O2} , _{K2O2 , Rb2O2 , and Cs2O2} ; _and superoxides such as _LiO2 , _NaO2 , _KO2 , _RbO2 , _{and CsO2 .} One or more of these may be contained in the activation treatment agent.

Furthermore, when the conductive material contained in the positive electrode mixture 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 that has the oxidizing power to oxidize and 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."

The use of an activating treatment agent with such oxidizing power is particularly effective in promoting the oxidation of the conductive carbon material to carbon dioxide, and the oxidation of the binder hydrocarbon material to carbon dioxide and water vapor, thereby increasing the discharge capacity of batteries manufactured using the resulting positive electrode active material and may also improve the effectiveness of preventing the generation of corrosive gases during the heating process.

Alkali metal compounds with the oxidizing power necessary to oxidize carbon-based conductive materials and hydrocarbons into 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.

Specific examples of alkali metal compounds having oxidizing power include superoxides such as _Li2O2 , _Na2O2 , _K2O2 , _Rb2O2 , _{and Cs2O2 ;} nitrates such _{as LiNO3, NaNO3 , KNO3 , RbNO3 , and CsNO3} ; sulfates such as _Li2SO4 , _Na2SO4 , _K2SO4 , _Rb2SO4 , and _{Cs2SO4 ; vanadates such as LiVO3 , NaVO3 , KVO3 , RbVO3} , and _{CsVO3 ; and} vanadates _{such as Li2MoO4 , Na2MoO4} , _K molybdates such as _{Rb 2} MoO ₄ , Rb ₂ MoO ₄ , and CsMoO ₄ ;

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

The alkali metal compound may be a carbonate or a sulfate, or 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 , from the viewpoint of making it easier to make the charge/discharge characteristics of a battery produced using a recycled positive _electrode active material more comparable to those of a _battery produced using an unused positive electrode active material.

Step (2): Heating Step The heating step is a step of heating the mixture obtained in step (1) (hereinafter, sometimes referred to as the "mixture before heating") to obtain a heated mixture.

The mixture before heating may be heated to a temperature equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent, or may be heated to a temperature lower than the melting initiation temperature (Tmp) of the activation treatment agent.

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

The melting initiation 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 to the melting initiation temperature of the activation treatment agent, but it may be, for example, 150°C or higher, 250°C or higher, 350°C or higher, 450°C or higher, or 500°C or higher.

Furthermore, the melting point of an activating treatment agent refers to the lowest temperature at which a portion of the activating treatment agent becomes liquid when heated alone. By mixing the positive electrode composite and activating treatment agent, the melting initiation temperature (Tmp) of the activating treatment agent becomes lower than the melting point of the activating treatment agent.

The melting point of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, when 5 mg of the activation treatment agent is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10°C/min), the melting point of the activation treatment agent is determined to be the temperature at which the DTA signal shows an endothermic peak.

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

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

The temperature of the heating process may be, for example, equal to or higher than the melting point of the activation treatment agent. The temperature of the heating process (maximum temperature within the heating space) may be, for example, 300 to 900°C, 300 to 700°C, or 300 to 600°C.

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

When the molten activation treatment agent comes into contact with the positive electrode active material, it can suppress deterioration of the positive electrode active material's crystalline structure. In some cases, it can also have the effect of repairing the crystalline structure.

When the molten activation treatment agent comes into contact with the carbon-based conductive material and binder, the rate of oxidative decomposition of the conductive material and binder increases. Furthermore, when the molten activation treatment agent comes into contact with the binder and fluorine compounds derived from the electrolyte, the fluorine components are stabilized as alkali metal fluorides, preventing the generation of hydrogen fluoride, a corrosive gas, and suppressing deterioration of the crystalline structure of the positive electrode active material.

Furthermore, if the activation treatment agent contains the same alkali metal as the positive electrode active material, it is possible to supply any alkali metal that is lacking in the positive electrode active material.

The temperature of the heating process and the holding time at that temperature can be adjusted as appropriate depending on the type and combination of the positive electrode active material, conductive material, binder, and alkali metal compound and other compounds contained in the activation treatment agent that make up the positive electrode mixture. Typically, the temperature is in the range of 100 to 1500°C, and the holding time is approximately 10 minutes to 24 hours.

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

The temperature of the heating step may be, for example, below the melting start temperature of the activation treatment agent. In this specification, "the temperature of the heating step is below the melting start temperature of the activation treatment agent" means that the temperature of the heating step is maintained at a temperature below the melting start temperature of the activation treatment agent (heating is performed at a temperature maintained below the melting start temperature of the activation treatment agent). Also, "the temperature of the heating step is below the melting start temperature of the activation treatment agent" means that the temperature of the heating step is not set to a temperature equal to or higher than the melting start temperature of the activation treatment agent. The temperature of the heating step (maximum temperature within the heating space) may be, for example, 300 to 600°C, 350 to 575°C, or 400 to 550°C.

In step (2), by heating the pre-heating mixture to a temperature below the melting point of the activating agent, deterioration of the crystalline structure of the positive electrode active material due to high-temperature heating is suppressed, making it easier to achieve charge/discharge characteristics comparable to those of a battery manufactured using unused positive electrode active material. Furthermore, heating the pre-heating mixture together with the activating agent can also restore the crystalline structure.

When the heated activation treatment agent comes into contact with the carbon-based conductive material and binder, the rate of oxidative decomposition of the conductive material and binder increases. Furthermore, when the heated activation treatment agent comes into contact with the binder and fluorine compounds derived from the electrolyte, the fluorine components are stabilized as alkali metal fluorides, preventing the generation of hydrogen fluoride, a corrosive gas, and suppressing deterioration of the crystalline structure of the positive electrode active material.

After the heating step, the mixture can be cooled to any desired temperature (e.g., room temperature (20°C)) as needed. In this way, a heated mixture containing a heated positive electrode active material is obtained.

Step (3): First Water-Washing Step The first water-washing step is a step of, after the heating step of step (2), bringing the heated mixture into contact with a first liquid containing water and an alkali metal compound, and then obtaining a first solid component (the heated mixture or the solid component containing the heated positive electrode active material) and a first liquid component.

In addition to the heated positive electrode active material, the heated mixture contains components derived from the activation treatment agent (such as alkali metal compounds), undecomposed conductive materials and binders, and other undecomposed materials of the positive electrode mixture. Furthermore, if the positive electrode mixture contains an electrolyte containing a fluorine component, the mixture may also contain fluorine components derived from the electrolyte. In the first water washing step, it is preferable to remove components derived from the activation treatment agent (such as alkali metal compounds), unreacted activation treatment agent, undecomposed conductive materials and binders, and other undecomposed materials of the positive electrode mixture, from the perspective of increasing the purity of the positive electrode active material and making it easier to achieve rate characteristics comparable to those of a battery manufactured using unused positive electrode active material.

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

Specific examples of the alkali metal compound contained in the first liquid include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH;
Borates such as _LiBO2 , _NaBO2 , _KBO2 , _RbBO2 , and _CsBO2 ;
Carbonates such _{as Li2CO3} , _Na2CO3 , _{K2CO3 , RbCO3} , _{CsCO3 ;}
oxides such as Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O;
_{peroxides such as Li2O2} , _Na2O2 , _{K2O2 , Rb2O2} , _{Cs2O2 ;}
superoxides such as _LiO2 , _NaO2 , _KO2 , _RbO2 , _CsO2 ;
nitrates such as _LiNO3 , _NaNO3 , _KNO3 , _RbNO3 , _CsNO3 ;
_phosphates such _{as Li3PO4} , _Na3PO4 , _{K3PO4 , Rb3PO4 , Cs3PO4 ;}
sulfates such _{as Li2SO4 , Na2SO4 , K2SO4} , _{Rb2SO4 , Cs2SO4 ;}
Chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl;
Bromides such as LiBr, NaBr, KBr, RbBr, and CsBr;
vanadates such as _LiVO3 , _NaVO3 , _KVO3 , _RbVO3 , _CsVO3 ;
_{Examples include} molybdates such as _Li2MoO4 , _Na2MoO4 , _K2MoO4 , _{Rb2MoO4 ,} and _{CsMoO4 ;} and tungstates such _{as Li2WO4} , _{Na2WO4 , K2WO4 , Rb2WO4} , _{and CsWO4} .

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

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

The first water washing step may involve, for example, contacting the heated mixture with a first liquid to obtain a first slurry, and then subjecting the first slurry to solid-liquid separation to obtain a first solid component and a first liquid component.

In the first water washing step, the heated mixture may be mixed with a first liquid and then stirred to obtain a first slurry. This promotes dissolution of the water-soluble components. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m/s.

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

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

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

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

In addition to the positive electrode active material, the first solid component may contain components (such as alkali metal compounds) derived from the activation treatment agent that were not completely removed in the first water washing step, as well as fluorine components derived from the electrolyte. The second water washing step further removes any undecomposed conductive material and binder remaining in the first solid component, as well as other undecomposed materials of the positive electrode mixture, and fluorine components derived from the electrolyte.

The second liquid contains at least water. The second liquid also contains a smaller amount of alkali metal compounds than the first liquid. The second liquid may contain 0% by mass of alkali metal compounds (an embodiment in which the second liquid contains substantially no alkali metal compounds).

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

Specific examples of the alkali metal compound contained in the second liquid include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH;
Borates such as _LiBO2 , _NaBO2 , _KBO2 , _RbBO2 , and _CsBO2 ;
Carbonates such _{as Li2CO3} , _Na2CO3 , _{K2CO3 , RbCO3} , _{CsCO3 ;}
oxides such as Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O;
_{peroxides such as Li2O2} , _Na2O2 , _{K2O2 , Rb2O2} , _{Cs2O2 ;}
superoxides such as _LiO2 , _NaO2 , _KO2 , _RbO2 , _CsO2 ;
nitrates such as _LiNO3 , _NaNO3 , _KNO3 , _RbNO3 , _CsNO3 ;
_phosphates such _{as Li3PO4} , _Na3PO4 , _{K3PO4 , Rb3PO4 , Cs3PO4 ;}
sulfates such _{as Li2SO4 , Na2SO4 , K2SO4} , _{Rb2SO4 , Cs2SO4 ;}
Chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl;
Bromides such as LiBr, NaBr, KBr, RbBr, and CsBr;
vanadates such as _LiVO3 , _NaVO3 , _KVO3 , _RbVO3 , _CsVO3 ;
_{Examples include} molybdates such as _Li2MoO4 , _Na2MoO4 , _K2MoO4 , _{Rb2MoO4 ,} and _{CsMoO4 ;} and tungstates such _{as Li2WO4} , _{Na2WO4 , K2WO4 , Rb2WO4} , _{and CsWO4} .

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

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

The second liquid may be in a smaller amount than the first liquid. For example, the amount of the second liquid may be 90% or less, 80% or less, 70% or less, or 60% or less of the first liquid. The smaller the amount of the second liquid, the greater the amount of wastewater that can be reduced.

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

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

When a second slurry is obtained in the second water washing step, the second slurry is subjected to solid-liquid separation to separate the second slurry into a second liquid component and a second solid component. The method for solid-liquid separation of the second slurry may be a conventionally known method, such as filtration or centrifugation.

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

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

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

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

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

In the drying process, the heating temperature is preferably 100°C or higher to remove water. Furthermore, a temperature of 150°C or higher is preferable to thoroughly remove water. Temperatures of 250°C or higher are particularly preferable, as they further increase the discharge capacity of batteries manufactured using the resulting positive electrode active material. The temperature in the drying process may be constant, or may be changed stepwise or continuously. The temperature range reached by heating can be, for example, from 10°C to less than 900°C.

The ultimate pressure range of the reduced pressure can be, for example, 1.0×10 ⁻¹⁰ to 1.0×10 ³ Pa.

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

When the activation treatment agent is heated below the melting initiation temperature and the positive electrode active material recovery step includes a drying step, the annealing step may be, for example, a step of heating the dried solid component at a temperature higher than that of step (2). In this case, the temperature to which the dried solid component is heated may be greater than 700°C, 750°C or higher, 800°C or higher, 850°C or higher, or 900°C or higher, from the perspective of vaporizing components other than the positive electrode active material and removing impurities, and from the perspective of making it easier to achieve charge/discharge characteristics comparable to those of a battery manufactured using unused positive electrode active material by sufficiently increasing the crystallite size of the positive electrode active material.

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

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

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

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

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

By using the manufacturing method for recycled positive electrode active material according to each embodiment of the present disclosure, recycled positive electrode active material obtained from a battery mixture can be reused in the same way as unused active material. Methods for manufacturing positive electrodes and batteries using recycled positive electrode active material are well known.

The final discharge capacity of the recycled positive electrode active material according to each embodiment of the present disclosure can be 150 mAh/g or more.

The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to the following examples as long as they do not alter the gist of the disclosure.

Measurements of the physical properties of the positive electrode active material and recycled positive electrode active material, and charge/discharge tests using batteries using the positive electrode active material were carried out as follows.

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

(Reference example 1)
<Production of positive electrode>
The positive electrode described below was prepared by the following procedure. 92 parts by mass of positive electrode active material (unused positive electrode active material or recycled positive electrode active material), 3 parts by mass of PVdF (binder, manufactured by Kureha Corporation, product number: #1100), and 5 parts by mass of acetylene black (conductive material, manufactured by Denka Co., Ltd., product number: HS100) were mixed to obtain a mixture. As the binder, PVdF was used as a binder solution in which PVdF was previously dissolved in NMP (N-methyl-2-pyrrolidone). The mixture was kneaded with a rotation/revolution mixer (ARE-310 manufactured by Thinky Corporation) to prepare a positive electrode composite paste. NMP was added to adjust the total mass of the positive electrode active material, binder, and conductive material in the positive electrode composite paste to 50% by mass.

The positive electrode composite paste was applied to one side of a 20 μm thick aluminum foil 1085 (manufactured by Nippon Foil Co., Ltd.) for use as a positive electrode current collector for lithium ion secondary batteries so that the amount of positive electrode active material ^was 3.0±0.1 mg/cm², 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 ^cm² .

<Battery manufacturing>
The coin-type battery described below was fabricated according to the following procedure. A nonaqueous electrolyte secondary battery (coin-type battery) was manufactured by combining the above-mentioned positive electrode, electrolyte, separator, and negative electrode. The battery was assembled in a glove box under an argon atmosphere. The electrolyte solution used was a solution prepared by dissolving _LiPF6 at a ratio of 1.0 mol/L in a 30:35:35 (volume ratio) mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. A laminated film separator consisting of a heat-resistant porous layer laminated on a porous film (made of polyethylene) was used as the separator, and metallic lithium was used as the negative electrode.

<Production of positive electrodes before recycling>
A positive electrode active material having a composition _{of Li1.07Ni0.47Mn0.48Fe0.05O2 and} a crystal structure of R-3m was prepared as _{the positive electrode active} material. The coin-type battery described above was fabricated using this positive electrode active material (unused positive electrode active material), and the following charge-discharge test (rate test) was performed while maintaining the battery at 25°C. The 0.2C discharge capacity was 138 mAh/g, and the 5C discharge capacity was 106 mAh/g. A higher 0.2C discharge capacity means a higher rated capacity can be obtained, and a higher 5C discharge capacity means that higher output characteristics can be obtained.
(conditions)
Maximum charging voltage: 4.3V
Charging current: 0.2mA/ ^cm2
Charging time: 8 hours Minimum discharge voltage: 2.5V
0.2C discharge current: 0.2mA/ ^cm2
5C discharge current: 5.0mA/ ^cm2

The electrode mixture was mechanically scraped off from the positive electrode used in the above battery, and the electrode mixture was peeled off from the current collector. 5 g of the electrode mixture removed from the positive electrode was mixed with 0.1 mol of K ₂ CO ₃ per mol of positive electrode active material and 0.1 mol of Na ₂ CO ₃ per mol of positive electrode active material as an activation treatment agent to obtain a mixture (mixture before heating). The melting start temperature of the activation treatment agent was 700 ° C.

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

The heated mixture was pulverized, and distilled water was added and stirred to obtain a slurry. The resulting slurry was filtered to separate it into a solid component and a liquid component. The solid component was then collected and dried to obtain a recycled positive electrode active material. The composition, crystal structure, average particle size, and specific surface area of the resulting recycled positive electrode active material were comparable to those of unused positive electrode active material. The above coin-type battery was fabricated using the recycled positive electrode active material, and a charge-discharge test was performed under the above conditions while maintaining the temperature at 25°C. The 0.2C discharge capacity was 135 mAh/g, and the 5C discharge capacity was 94 mAh/g, which were comparable to the discharge capacities of coin-type batteries fabricated using unused positive electrode active material.

(Reference example 2)
<Production of positive electrodes before recycling>
As the positive electrode active material, a positive _electrode active material NCM111 having a composition _{of LiNi0.33Co0.33Mn0.33O2 and} a crystal structure of R-3m was prepared. When the above coin-type battery was produced using this positive electrode active material (unused positive electrode active material), the initial charge capacity was 178.3 mAh/g and the initial discharge capacity (0.2C) was 163.4 mAh/g. In addition, when the following charge/discharge test (rate test) was performed while maintaining the temperature at 25°C, the 0.2C discharge capacity was 163.1 mAh/g and the 5C discharge capacity was 141.3 mAh/g.

The electrode composite was mechanically scraped off from the cathode of the process waste material generated during the preparation of the above cathode, and the electrode composite was peeled off from the current collector. 5 g of the electrode composite removed from the cathode was mixed with 0.1 mol of Li ₂ CO ₃ per mol of cathode active material and 0.1 mol of Na ₂ SO ₄ per mol of cathode active material as an activation treatment agent to obtain a mixture (mixture before heating). The melting start temperature of the activation treatment agent was 510 °C.

30 g of the unheated mixture was placed in an electric furnace and heated in an air atmosphere at a heating rate of 300°C/h, a heating temperature of 450°C (below the melting point of the activation treatment agent), and a heating time of 360 minutes.

After heating, the mixture was pulverized, distilled water was added, and the mixture was stirred to obtain a slurry. The resulting slurry was filtered to separate the solid and liquid components. The solid component was then recovered and suction dried at 100°C for 1 hour.

The dried solid component was placed in an electric furnace and heated in an air atmosphere at 900°C for 60 minutes, yielding a heated recycled positive electrode active material. The heated recycled positive electrode active material was then allowed to cool naturally to room temperature (20°C), and it was confirmed that the composition, crystal structure, average particle size, and specific surface area of the resulting recycled positive electrode active material were comparable to those of unused positive electrode active material. When a 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. Furthermore, when an initial charge/discharge (rate test) was performed under the above conditions while maintaining the temperature at 25°C, the 0.2C discharge capacity was 160.2 mAh/g and the 5C discharge capacity was 133.9 mAh/g.

(Comparative Example 1)
A pre-heated mixture is obtained in the same manner as in Reference Example 1. The mixture is placed in an alumina firing container and placed in an electric furnace, where it is heated at a temperature increase rate of 200°C/hour to a heating temperature of 700°C (above the melting point of the activation treatment agent) for 240 minutes. The heated mixture is allowed to cool naturally to room temperature (20°C), and then the heated mixture is recovered.

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

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

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

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

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

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

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

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

(Comparative Example 2)
A pre-heated mixture is obtained in the same manner as in Reference Example 2. The mixture is placed in an alumina firing container and placed in an electric furnace, where it is heated at a heating rate of 300°C/hour, at a heating temperature of 450°C (below the melting start temperature of the activation treatment agent), and for 360 minutes. The heated mixture is allowed to cool naturally to room temperature (20°C), and then the heated mixture is recovered.

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

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

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

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

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

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

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

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

In Example 1, the wastewater from Comparative Example 1 is reused to wash the mixture after heating, and in Example 4, the wastewater from Comparative Example 2 is reused to wash the mixture after heating. This makes it possible to reduce the amount of wastewater in the process for producing recycled positive electrode active material compared to using distilled water for washing.

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

In Examples 3 and 6, the amount of distilled water D2 and H2 used during the second water wash was reduced compared to the amount of distilled water D1 and H1 used during the first water wash, thereby reducing the amount of wastewater generated during the production of recycled positive electrode active material.

Claims (8)

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