Method for producing recycled positive electrode active material

Abstract

Provided is a method for producing a recycled positive electrode active material that reduces the internal resistance of a battery. A method for producing a recycled positive electrode active material includes: (1) a step in which an activation treatment agent containing one or more alkali metal compounds is mixed with a positive electrode mixture containing a positive electrode active material to obtain a mixture; (2) a step in which the mixture is heated to a temperature equal to or higher than the melting start temperature of the activation treatment agent to obtain a heated mixture; and (3) a step in which a heated positive electrode active material is recovered from the heated mixture. The activation treatment agent further contains one or more alkaline earth metal hydroxides.

Description

Method for manufacturing recycled positive electrode active material

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

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

[0003] For example, Patent Document 1 discloses a method for recovering a positive electrode active material by mixing a positive electrode mixture with an activation treatment agent containing an alkali metal compound, heating the mixture to decompose the binder, and removing the decomposed material and the activation treatment agent with water or the like. This method is cost-effective in that it recovers a positive electrode active material directly from battery waste without using an organic solvent.

[0004] JP 2012-186150 A

[0005] An object of one aspect of the present invention is to provide a method for producing a recycled positive electrode active material that reduces the internal resistance of a battery.

[0006] One aspect of the present invention relates to the following method for producing a recycled positive electrode active material.

[0007] [1] A method for producing a recycled positive electrode active material, comprising the following steps: (1) mixing an activation treatment agent containing one or more alkali metal compounds with a positive electrode composite containing a positive electrode active material to obtain a mixture; (2) heating the mixture to a temperature equal to or higher than the melting start temperature of the activation treatment agent to obtain a heated mixture; and (3) recovering a heated positive electrode active material from the heated mixture, wherein the activation treatment agent further contains one or more alkaline earth metal hydroxides.

[0008] According to one aspect of the present invention, a recycled positive electrode active material that reduces the internal resistance of a battery can be produced.

[0009] A method for producing a recycled positive electrode active material will be described below.

[0010] A method for producing a recycled cathode active material according to an embodiment of the present invention includes the following steps: Step (1): mixing an activation treatment agent containing one or more alkali metal compounds with a cathode composite containing a cathode active material to obtain a mixture; Step (2): heating the mixture to a temperature (e.g., a holding temperature) equal to or higher than the melting start temperature of the activation treatment agent to obtain a heated mixture; and Step (3): recovering a heated cathode active material from the heated mixture. The activation treatment agent further contains one or more alkaline earth metal hydroxides.

[0011] In this specification, the positive electrode active material that has undergone steps (1) to (3) is referred to as a "recycled positive electrode active material." The recycled positive electrode active material that has undergone steps (1) to (3) can be suitably used in the production of positive electrodes and the like. The method for producing a recycled positive electrode active material according to this embodiment may include additional steps before and after steps (1) to (3). In this specification, a positive electrode active material that has undergone steps (1) to (3) and additional steps thereafter is also referred to as a "recycled positive electrode active material." Examples of additional steps other than steps (1) to (3) include a step of preparing a positive electrode composite and a step of washing the positive electrode composite, which are performed before step (1), and steps (4) and (5), which are performed after step (3), which are described below.

[0012] Hereinafter, each step in the method for producing a recycled positive electrode active material according to this embodiment will be described in detail.

[0013] (Positive Electrode Composite Preparation Step) The method for producing a recycled positive electrode active material according to this embodiment may include, prior to step (1), a positive electrode composite preparation step of preparing a positive electrode composite containing a positive electrode active material.

[0014] The positive electrode mixture may contain a binder. In the positive electrode mixture, particles of the positive electrode active material may be bound to each other by a binder. The positive electrode mixture may contain an electrolyte and / or a conductive material in addition to the positive electrode active material and the binder. When the positive electrode mixture contains a conductive agent, the particles of the positive electrode active material and the conductive material may be bound to each other by a binder. The electrolyte is a component derived from the electrolyte solution of the battery and impregnated into the positive electrode mixture. The positive electrode mixture may contain a fluorine compound derived from the binder and / or the electrolyte solution (e.g., the electrolyte in the electrolyte solution).

[0015] <Positive Electrode Active Material> Examples of positive electrode active materials are composite compounds containing 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, or the like as constituent elements.

[0016] The positive electrode active material may be composed of only a single compound, or may be composed of a plurality of compounds.

[0017] An example of a suitable positive electrode active material is a composite oxide containing one or more elements selected from the following element group 1 and one or more elements selected from element group 2: Element group 1: Ni, Co, Mn, Fe, Al, P Element group 2: Li, Na, K, Ca, Sr, Ba, Mg

[0018] Among these, the positive electrode active material is preferably represented by the following chemical formula (Formula A).

[0019] Li １＋ａ M ２ ｂ M １ M Ｔ ｃ O ２＋ｄ X ｅ However, M ２ represents at least one element selected from the group consisting of Na, K, Ca, Sr, Ba, and Mg; １ represents at least one element selected from the group consisting of Ni, Co, Mn, Fe, Al, and P; Ｔrepresents at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metal elements other than O and P, and satisfies the following conditions: -0.4<a<1.5, 0≦b<0.5, 0≦c<0.5, -0.5<d<1.5, 0≦e<0.5.

[0020] M Ｔ is preferably at least one element selected from the group consisting of Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, Ca, Sr, Ba, Ge, Cr, Sc, Y, La, Ta, Tc, Ru, Rh, Pd, Ag, Cd, and In. Examples of X are F, S, Cl, Br, I, Se, Te, and N.

[0021] The positive electrode active material is preferably a composite oxide containing at least Li and Ni.

[0022] In addition, in the positive electrode active material, M １ The mole fraction of Ni in the alloy is more preferably 0.3 to 0.95.

[0023] The crystal structure of the composite oxide used as the positive electrode active material is not particularly limited, but a layered structure is preferred, and a hexagonal or monoclinic crystal structure is more preferred.

[0024] The hexagonal crystal structure is P3, 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 ４22, 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.

[0025] The monoclinic crystal structure is P2, P2 １ , C2, Pm, Pc, Cm, Cc, P2 / m, P2 １ / m, C2 / m, P2 / c, P2 １ It belongs to any one space group selected from the group consisting of C1 / c and C2 / c.

[0026] Furthermore, it preferably belongs to the space group R-3m contained in a hexagonal crystal structure or the space group C2 / m contained in a monoclinic crystal structure.

[0027] The crystal structure of the positive electrode active material is identified from a powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα rays as a radiation source.

[0028] The particle size of the positive electrode active material in the positive electrode mixture is not particularly limited, but is typically about 0.001 to 100 μm. The particle size distribution of the positive electrode active material can be measured using a laser diffraction / scattering particle size distribution analyzer (e.g., Malvern Instruments Mastersizer 2000). From the obtained particle size distribution, a volume-based cumulative particle size distribution curve is created, and the particle size (D50) value at 50% accumulation from the fine particle side can be used as the average particle size of the powder.

[0029] <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.

[0030] Specific examples of the carbon-based conductive material include graphite powder, carbon black (for example, acetylene black), and fibrous carbon materials (for example, graphitized carbon fibers, carbon nanotubes).

[0031] The carbonaceous conductive material may be a single carbon material or may be composed of multiple carbon materials.

[0032] The specific surface area of ​​the carbon material used as the carbon-based conductive material is usually 0.1 to 500 m ２ / g.

[0033] In this case, the specific surface area of ​​the conductive material is 30m ２ / g or more, and the specific surface area is 30 m ２ / g or more, and the specific surface area may be 30 m ２ The specific surface area of ​​the carbon-based conductive material may be 30 m / g or more. ２ / g or more 500m ２ / g or less.

[0034] When an activation treatment agent containing an alkali metal compound having oxidizing power, which will be described later, is used, the rate of oxidation treatment of the carbon-based conductive material can be increased, and even carbon materials with a small specific surface area can sometimes be oxidized.

[0035] <Binder> Examples of the binder (pre-activation treatment binder) contained in the positive electrode mixture are thermoplastic resins, and specific examples include fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as 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 (hereinafter sometimes referred to as SBR); and may be a mixture of two or more of these.

[0036] There are no particular limitations on the amounts of the positive electrode active material, conductive material, and binder in the positive electrode mixture. The amount of binder can be 0.5 to 30 parts by weight, or may be 1 to 5 parts by weight, relative to 100 parts by weight of the positive electrode active material. The amount of conductive material can be 0, or may be 0 to 50 parts by weight, or may be 1 to 10 parts by weight, relative to 100 parts by weight of the positive electrode active material.

[0037] <Electrolyte and Solvent> An example of the electrolyte is LiPF ６ , LiBF ４, LiClO ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ F) ２ , LiCF ３ SO ３ The amount of electrolyte contained in the positive electrode mixture is not limited, but can be 0.0005 to 7 mass %.

[0038] The positive electrode mixture may contain a solvent derived from the electrolyte solution, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate.

[0039] <Recovery of Positive Electrode Mixture> Such a positive electrode mix can be obtained by separating and recovering the positive electrode mix from a waste positive electrode having a current collector and a positive electrode mix layer.

[0040] "Waste positive electrodes" can refer to positive electrodes recovered from discarded batteries and waste positive electrodes generated during the manufacturing process of positive electrodes and batteries. Discarded batteries can be used batteries or unused, non-standard batteries. Furthermore, waste positive electrodes can be the ends of positive electrodes generated during the battery manufacturing process and non-standard positive electrodes. Furthermore, waste positive electrode composites that are not attached to current collectors and are generated during the positive electrode composite manufacturing process can also be used as the positive electrode composite.

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

[0042] Methods for separating the positive electrode composite from a waste positive electrode having a positive electrode composite layer and a current collector 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 from the current collector), a method of penetrating a solvent into the interface between the positive electrode composite layer and the current collector to peel the positive electrode composite layer from the current collector, a method of dissolving the current collector using an alkaline or acidic aqueous solution to separate the positive electrode composite layer, etc. The preferred method is the method of mechanically peeling the positive electrode composite layer from the current collector.

[0043] (Positive electrode composite washing step) 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 and the electrolyte is brought into contact with the electrolyte washing solvent to obtain a slurry containing a solid component and a liquid component, and then the slurry is separated into the solid component and the liquid component.

[0044] Solid-liquid separation is a process of separating a slurry into a liquid component and a solid component. The solid-liquid separation method may be a conventionally known method, such as filtration or centrifugation.

[0045] The electrolyte cleaning solvent is not particularly limited, and examples thereof 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.

[0046] The cathode mixture can be brought into contact with the electrolyte cleaning solvent in a known powder-liquid contact device, such as a stirring tank.

[0047] In the step of contacting the positive electrode mixture with the electrolyte washing solvent, the positive electrode mixture and the electrolyte washing solvent are preferably stirred to obtain a slurry. The peripheral speed of the tip of the stirring blade can be set to 0.1 to 1.0 m / s.

[0048] In the washing step of the positive electrode composite, after solid-liquid separation, the obtained solid component may be rinsed. Rinsing is an operation in which the obtained solid component is again brought into contact with the electrolyte washing solvent to obtain a slurry, and then the slurry is again separated into a solid component and a liquid component. In washing the positive electrode composite, rinsing may be performed multiple times. The slurry concentration in rinsing may also be the same as above. In rinsing, the slurry may also be stirred as described above.

[0049] The above-described cleaning process can sufficiently remove the electrolyte from the positive electrode mixture. For example, if the electrolyte remains, the following reaction occurs, causing the structure of the positive electrode active material to change from a layered rock salt structure to a spinel structure: LiPF ６ +16LiMO ２ +20 ２ → 6LiF + Li ３ P.O. ４ +8LiM ２ O ４ Furthermore, when lithium carbonate is included as an activator, lithium is consumed by the following reaction: LiPF ６ +4Li ２ CO ３ → 6LiF + Li ３ P.O. ４ +4CO ２

[0050] The separated solid component can be dried to remove the electrolyte washing solvent by reducing pressure and / or heating, if necessary. The heating temperature can be 50 to 200°C.

[0051] (Step (1): Activation Treatment Agent Mixing Step) In step (1), an activation treatment agent is mixed with a positive electrode mixture containing a positive electrode active material to obtain a mixture. The activation treatment agent contains one or more alkali compounds and one or more alkaline earth metal hydroxides.

[0052] The method for mixing the positive electrode mixture and the activation treatment agent may be either dry mixing or wet mixing, or a combination of these mixing methods may be used, and the mixing order is not particularly limited.

[0053] When mixing, it is preferable to use a mixer equipped with mixing media such as balls and go through a pulverizing and mixing step, which can improve mixing efficiency.

[0054] Dry mixing is preferred as a mixing method because it allows for simpler mixing. For dry mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a powder mixer equipped with internal stirring blades, a ball mill, a vibration mill, or a combination of these devices can be used.

[0055] The mixing device used for dry mixing is preferably a powder mixer equipped with an internal stirring blade, and specifically, a Loedige Mixer (manufactured by Matsubo Co., Ltd.) can be mentioned.

[0056] The activation treatment agent used in this step will be described in detail below.

[0057] <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.

[0058] When the activation treatment agent comes into contact with the positive electrode active material, the positive electrode active material can be activated. When the alkali metal compound in the activation treatment agent contains a molten portion, the contact between the molten portion and the positive electrode active material is improved, thereby further accelerating the activation of the positive electrode active material.

[0059] Furthermore, the positive electrode mixture may contain a fluorine-containing compound derived from the binder and / or the electrolyte, and by contacting the fluorine-containing compound with the activation treatment agent, the fluorine component is stabilized as an alkali metal fluoride, thereby suppressing the generation of corrosive gases such as hydrogen fluoride. Note that it is desirable to prevent the generation of hydrogen fluoride, as it reduces the activity of the positive electrode active material.

[0060] The proportion of all alkali metal compounds in the activation treatment agent is appropriately set taking into consideration the type of alkali metal compound, the type of target positive electrode active material, etc., but is typically 50 wt % or more, preferably 70 wt % or more (including 100 wt %) of the total weight of the activation treatment agent. The concentration of at least one alkali metal selected from the group consisting of potassium and sodium among the alkali metals contained in the alkali metal compound can be adjusted arbitrarily from 0 to 100 mol %, but is preferably 10 mol % or more, more preferably 20 mol % or more, and preferably 90 mol % or less, more preferably 80 mol % or less.

[0061] Examples of alkali metal compounds that can be used as components of the activation treatment agent include hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, and tungstates of alkali metals. These can be used alone or in combination as components of the activation treatment agent.

[0062] Specific examples of suitable alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; LiBO ２ , NaBO ２ , KBO ２ , RbBO ２ , CsBO ２ Boric acid compounds such as Li ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , RbCO ３ , CsCO ３ Carbonates such as Li ２ O, Na ２ O.K. ２ O, Rb ２ O, Cs ２ Oxides such as Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb ２ O ２ , Cs ２ O２ peroxides such as LiO ２ , NaO ２ , K.O. ２ , RbO ２ , CsO ２ superoxides such as LiNO ３ , NaNO ３ , KNO ３ , RbNO ３ , CsNO ３ Nitrates such as Li ３ P.O. ４ , Na ３ P.O. ４ , K. ３ P.O. ４ , Rb ３ P.O. ４ , Cs ３ P.O. ４ phosphates such as Li ２ SO ４ , Na ２ SO ４ , K. ２ SO ４ , Rb ２ SO ４ , Cs ２ SO ４ chlorides such as LiCl, NaCl, KCl, RbCl, and CsCl; bromides such as LiBr, NaBr, KBr, RbBr, and CsBr; LiVO ３ , NaVO ３ , K.V.O. ３ , RbVO ３ , CsVO ３ vanadates such as Li ２ MoO ４ , Na ２ MoO ４ , K. ２ MoO ４ , Rb ２ MoO ４ , CsMoO ４ Molybdates such as Li ２ WO ４ , Na ２ WO ４ , K. ２ WO ４ , Rb ２ WO ４ , CsWO ４ tungstates such as:

[0063] Here, in order to further enhance the activation effect of the positive electrode active material, the activation treatment agent may contain, in addition to at least one compound selected from the group consisting of potassium compounds and sodium compounds, the same alkali metal element as the alkali metal element contained in the positive electrode active material in the positive electrode mixture.

[0064] 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, LiBO, ２ , Li ２ CO ３ , Li ２ O, Li ２ O ２ , LiO ２ , LiNO ３ , Li ３ P.O. ４ , Li ２ SO ４ , LiCl, LiVO ３ , LiBr, Li ２ MoO ４ , Li ２ WO ４ Examples include:

[0065] The activation treatment agent contains one or more alkaline earth metal hydroxides. The alkaline earth metal hydroxides are contained in the activation treatment agent together with an alkali metal compound for the purpose of controlling the melting onset temperature of the activation treatment agent. Furthermore, the alkaline earth metal hydroxides can reduce the internal resistance (impedance or DC resistance) of a battery using a recycled positive electrode active material in the positive electrode. In other words, the internal resistance of a battery using a recycled positive electrode active material manufactured using both an alkali metal compound and an alkaline earth metal hydroxide as an activation treatment agent is lower than the internal resistance of a battery using a recycled positive electrode active material manufactured using only an alkali metal compound as an activation treatment agent. The inventors speculate that the formation of a high-temperature reaction field containing not only an alkali metal compound but also an alkaline earth metal hydroxide promotes the regeneration of the crystalline structure on the surface of the positive electrode active material, thereby reducing (restoring) the battery's reaction resistance (resistance component due to the rate limit of the chemical reaction).

[0066] The total alkaline earth metal content in the activation treatment agent may be 0.5 mol% or more. Having a total alkaline earth metal content in the activation treatment agent of 0.5 mol% or more facilitates reducing the internal resistance of a battery using a recycled positive electrode active material in a positive electrode. When the amount of alkaline earth metal (Group 2 element) in the activation treatment agent (unit: mole) is represented by m and the total amount of alkali metal compound (molecule) and alkaline earth compound (molecule) in the activation treatment agent is represented by M, the total alkaline earth metal content in the activation treatment agent may be expressed as {100 × (m / M)} mol%. The upper limit of the total alkaline earth metal content in the activation treatment agent is not limited. For example, the total alkaline earth metal content in the activation treatment agent may be 0.5 mol% or more and 50 mol% or less. The total content of alkaline earth metals in the activation treatment agent may preferably be 0.5 mol% or more and less than 14.3 mol%, or 0.5 mol% or more and 9.1 mol% or less. When the total content of alkaline earth metals in the activation treatment agent is less than 14.3 mol% or 9.1 mol% or less, the rate characteristics (discharge capacity at each C rate) of a battery using a recycled positive electrode active material as a positive electrode tend to be improved. The total content of alkaline earth metals in the activation treatment agent may more preferably be 0.5 mol% or more and less than 9.1 mol%, or 0.5 mol% or more and 3.2 mol% or less. When the total content of alkaline earth metals in the activation treatment agent is less than 9.1 mol% or 3.2 mol% or less, the initial charge capacity, initial discharge capacity, initial charge / discharge efficiency, and initial discharge capacity recovery rate tend to be improved. The total content of alkaline earth metals in the activation treatment agent may be 0.5 mol% or more and 14.3 mol mol% or less, 0.5 mol% or more and 11.7 mol% or less, 0.5 mol% or more and 9.1 mol% or less, 0.5 mol% or more and 6.2 mol% or less, 0.5 mol% or more and 3.2 mol% or less, 0.5 mol% or more and 2.4 mol% or less, 0.5 mol% or more and 1.6 mol% or less, 1.6 mol% or more and 14.3 mol% or less, 1.6 mol% or more and 11.7 mol% or less, 1.6 mol% or more and 9.1 mol% or less, 1.6 mol% or more and 6.2 mol% or less, 1.6 mol% or more and 3.2 mol% or less, or 1.6 mol% or more and 2.4 mol% or less.

[0067] The alkaline earth metal contained in the alkaline earth metal hydroxide may be one or more elements selected from the group consisting of beryllium, magnesium, calcium, strontium, and barium. The alkaline earth metal contained in the alkaline earth metal hydroxide is preferably one or both of magnesium and calcium. The alkaline earth metal hydroxide is preferably Be(OH) ２ , Mg(OH) ２ , Ca(OH) ２ , Sr(OH) ２ , and Ba(OH) ２ The hydroxide may be one or more hydroxides selected from the group consisting of:

[0068] The activation treatment agent may contain compounds other than alkali metal compounds and alkaline earth metal hydroxides as needed. The content of the 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, and can be less than 50 wt % of the total weight of the activation treatment agent.

[0069] The amount of activation treatment agent added in the mixture of the positive electrode mixture and the activation treatment agent is preferably 0.001 to 100 times, and more preferably 0.05 to 1 time, the weight of the positive electrode active material contained in the positive electrode mixture.

[0070] The number of moles of the alkali metal compound in the activation treatment agent in the mixture of the positive electrode composite and the activation treatment agent can be added so that the number of moles of the alkali metal element is 0.001 to 200 times the number of moles of the positive electrode active material (e.g., Formula A) contained in the positive electrode composite, which is taken as 1.

[0071] By appropriately controlling the ratio of the activation treatment agent in the mixture, it is possible to reduce the cost of recovering the positive electrode active material from the positive electrode mixture, increase the oxidative decomposition rate of the carbon-based conductive material and binder, improve the effect of preventing the generation of corrosive gases during the heating process, and further increase the discharge capacity of a battery manufactured using the resulting positive electrode active material.

[0072] Preferably, at least one of the alkali metal compounds contained in the activation treatment agent is an alkali metal compound that exhibits alkalinity when dissolved in water. When an activation treatment agent containing such an alkali metal compound is dissolved in pure water, the pH of the solution becomes greater than 7. Hereinafter, such an activation treatment agent may be referred to as an "alkaline activation treatment agent."

[0073] The use of an alkaline activation treatment agent can further suppress the generation of corrosive gases during the heating process, thereby increasing the discharge capacity of a battery manufactured using the recovered positive electrode active material. In addition, the use of an alkaline activation treatment agent can also increase the treatment speed of the carbon-based conductive material and binder.

[0074] Examples of alkali metal compounds that exhibit alkalinity when dissolved in water and are contained in an alkaline activation treatment agent include hydroxides, carbonates, hydrogen carbonates, oxides, peroxides, and superoxides of alkali metals. Specific examples include LiOH, NaOH, KOH, RbOH, and CsOH; Li ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , RbCO ３ , CsCO ３ ; LiHCO ３ , NaHCO ３ , KHCO ３ , RbHCO ３ , CsHCO ３ ; Li ２ O, Na ２ O.K. ２ O, Rb ２ O, Cs ２ O; Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb ２ O ２ , Cs ２ O ２ LiO ２ , NaO ２ , K.O. ２ , RbO２ , CsO ２ One or more of these may be contained in the activation treatment agent.

[0075] Furthermore, when the conductive material contained in the positive electrode composite is a carbon-based conductive material, at least one of the alkali metal compounds contained in the activation treatment agent may be an alkali metal compound having an oxidizing power that oxidizes and decomposes the carbon-based conductive material at the temperature of the heating step. Note that, hereinafter, an activation treatment agent containing such an alkali metal compound may be referred to as an "activation treatment agent having an oxidizing power."

[0076] Use of an activation treatment agent having such oxidizing power is particularly effective in promoting the oxidation of the conductive material, which is a carbon material, to carbon dioxide, and promoting the oxidation of the binder, which is a hydrocarbon material, to carbon dioxide and water vapor, and can further increase the discharge capacity of a battery manufactured using the obtained positive electrode active material, and can also sometimes improve the effect of preventing the generation of corrosive gases during the heating process.

[0077] Examples of alkali metal compounds having the oxidizing power necessary to oxidize carbonaceous conductive materials and hydrocarbons into carbon dioxide and water vapor include alkali metal peroxides, superoxides, nitrates, sulfates, vanadates, and molybdates, which may be used alone or in combination of two or more.

[0078] Specifically, Li ２ O ２ , Na ２ O ２ , K. ２ O ２ , Rb ２ O ２ , Cs ２ O ２ LiO ２ , NaO ２ , K.O. ２ , RbO ２ , CsO ２ ; LiNO ３ , NaNO ３ , KNO ３ , RbNO ３ , CsNO ３ ; Li ２ SO４ , Na ２ SO ４ , K. ２ SO ４ , Rb ２ SO ４ , Cs ２ SO ４ ; LiVO ３ , NaVO ３ , K.V.O. ３ , RbVO ３ , CsVO ３ ; Li ２ MoO ４ , Na ２ MoO ４ , K. ２ MoO ４ , Rb ２ MoO ４ , CsMoO ４ ; are examples.

[0079] Details of the oxidizing power of these alkali metal compounds are described in JP 2012-186150 A.

[0080] (Step (2): Heating Step) The heating step is a step in which the mixture obtained in step (1) (hereinafter sometimes referred to as the "mixture before heating") is heated to a temperature equal to or higher than the melting initiation temperature of the activation treatment agent. For example, the temperature of the mixture in the heating step may be maintained at a temperature equal to or higher than the melting initiation temperature of the activation treatment agent. However, the temperature of the mixture in the heating step does not always need to be equal to or higher than the melting initiation temperature of the activation treatment agent. The mixture obtained in this heating step may be referred to as the "mixture after heating."

[0081] The "melting initiation temperature (Tmp) of the activation treatment agent" means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0082] The melting initiation temperature (Tmp) of the activation treatment agent is a value determined by differential thermal analysis (DTA). That is, 5 mg of the mixture before heating is subjected to differential thermal analysis (DTA, measurement conditions: temperature rise rate: 10°C / min), and the temperature at which the DTA signal shows an endothermic peak is defined as the melting initiation temperature (Tmp).

[0083] 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 to the melting start temperature (Tmp) of the activation treatment agent, but it may be, for example, 150° C.

[0084] The melting point of the activation treatment agent refers to the lowest temperature at which a part of the activation treatment agent becomes liquid when heated alone. By mixing the positive electrode composite and the activation treatment agent, the melting initiation temperature (Tmp) of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0085] The melting point of the activation treatment agent is a value determined by differential thermal analysis (DTA). Specifically, 5 mg of the activation treatment agent is subjected to differential thermal analysis (DTA, measurement conditions: temperature rise rate: 10°C / min), and the melting point of the activation treatment agent is determined as the temperature at which the DTA signal shows an endothermic peak.

[0086] The atmosphere for heating is not particularly limited, and may be 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.

[0087] In step (2), the mixture before heating is heated to a temperature equal to or higher than the melting initiation temperature (Tmp) of the activation treatment agent as described above, whereby the following effects occur.

[0088] The contact of the molten activation treatment agent with the positive electrode active material can suppress deterioration of the crystalline structure of the positive electrode active material, and in some cases can even restore the crystalline structure.

[0089] When the molten activation treatment agent comes into contact with the carbon-based conductive material and binder, the rate of oxidative decomposition of the conductive material and binder is increased. Furthermore, when the molten activation treatment agent comes into contact with the binder and a fluorine compound derived from the electrolyte, the fluorine component is stabilized as an alkali metal fluoride, preventing the generation of hydrogen fluoride, a corrosive gas, and suppressing deterioration of the crystalline structure of the positive electrode active material.

[0090] Furthermore, when the activation treatment agent contains the same alkali metal as the positive electrode active material, it is possible to supply the alkali metal that is insufficient for the positive electrode active material.

[0091] The temperature of the heating step and the holding time at that temperature can be appropriately adjusted depending on the types and combinations of the positive electrode active material, conductive material, binder, alkali metal compound and other compounds contained in the activation treatment agent that constitute the positive electrode mixture. Typically, the temperature is in the range of 100 to 1500°C, and the holding time is about 10 minutes to 24 hours.

[0092] 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 compound.

[0093] After the heating step, the mixture can be cooled to any temperature, such as about room temperature, as needed. In this way, a heated mixture containing a heated positive electrode active material is obtained.

[0094] (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 of step (2).

[0095] The mixture after heating contains not only the heated positive electrode active material, but also components derived from the activation treatment agent (such as alkali metal compounds), undecomposed conductive material and binder, and other undecomposed substances of the positive electrode mixture. Furthermore, if the positive electrode mixture contains an electrolyte solution containing a fluorine component, the mixture may also contain a fluorine component derived from the electrolyte.

[0096] Examples of methods for separating and recovering the heated positive electrode active material from the heated mixture include a solid-liquid separation method in which a solvent such as water is added to the mixture to form a slurry, followed by solid-liquid separation, and a vaporization separation method in which the mixture is heated to vaporize and separate components other than the heated positive electrode active material. The solid-liquid separation step in which the solid-liquid separation method is performed will be described below.

[0097] Step (3a): Solid-Liquid Separation Step Step (3a) is a step of contacting the heated mixture with a liquid containing water to obtain a slurry containing a solid component and a liquid component, and then separating the slurry into the solid component and the liquid component.

[0098] The heated mixture contains not only the heated positive electrode active material, but also components derived from the activation treatment agent (such as alkali metal compounds and alkaline earth metal hydroxides), undecomposed conductive material and binder, and other undecomposed substances of the positive electrode composite. Furthermore, if the positive electrode composite contains an electrolyte solution containing a fluorine component, the heated mixture may also contain a fluorine component derived from the electrolyte.

[0099] In order to separate and recover the heated positive electrode active material from the heated mixture, a liquid containing water (liquid) is added to the mixture to form a slurry, and then the mixture is subjected to solid-liquid separation to separate the solid component and the liquid component.

[0100] 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 water-soluble components or to increase the processing speed. Suitable examples of liquids containing water include pure water and alkaline cleaning solutions. Examples of alkaline cleaning solutions include aqueous solutions of one or more anhydrides and hydrates thereof selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate. Ammonia can also be used as the alkali.

[0101] The resulting slurry contains a solid component mainly containing the positive electrode active material after heating and a liquid component containing water-soluble components other than the positive electrode active material, including alkali metal components, alkaline earth metal components derived from the activation treatment agent, and / or fluorine components derived from the binder and the electrolyte.

[0102] The amount of liquid to be added to the mixture is appropriately determined taking into consideration the amounts of the post-heating positive electrode active material and the water-soluble components other than the positive electrode active material contained in the mixture.

[0103] In step (3a), it is preferable to obtain a slurry by stirring the heated mixture with a liquid containing water. This promotes dissolution of the water-soluble components. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m / s.

[0104] The slurry formed in the slurrying step is then subjected to solid-liquid separation. Solid-liquid separation is a step of separating the slurry into a liquid component and a solid component. The solid-liquid separation method may be a conventionally known method, such as filtration or centrifugation.

[0105] In step (3a), after solid-liquid separation, the obtained solid component may be rinsed. Rinsing is an operation in which the obtained solid component is again brought into contact with a liquid containing water to obtain a slurry, and then the slurry is again separated into a solid component and a liquid component. In step (3a), rinsing may be performed multiple times. The slurry concentration in the rinse can also be the same as above.

[0106] (Step (4): Drying Step) Step (4) is a step of removing water from the solid component obtained in step (3a) by heating and / or exposing it to a reduced pressure environment.

[0107] 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. A temperature of 250°C or higher is particularly preferable because it further increases the discharge capacity of a battery manufactured using the resulting positive electrode active material. The temperature in the drying step may be constant or may be changed stepwise or continuously. The temperature range reached by heating can be, for example, 10°C or higher and lower than 900°C.

[0108] The ultimate pressure range of the reduced pressure is, for example, 1.0 x 10 －１０ ~1.0 x 10 ３ Pa.

[0109] (Step (5): Annealing (Re-firing) Step) Step (5) is preferably a step of heat treating the solid component after step (4) at a temperature of less than 900°C.

[0110] The atmosphere for the heat treatment is not limited, but an oxygen-containing atmosphere such as air is preferable. The heat treatment temperature can be 100°C or higher. The heat treatment temperature may be 100°C or higher and lower than 900°C, or may be 350°C or higher and lower than 900°C. The holding time for the heat treatment can be 1 minute to 24 hours. In particular, it is preferable to heat at a holding temperature of 350°C or higher for 0.1 hours to 5 hours.

[0111] The recycled cathode active material obtained from the battery mixture by using the method for producing the recycled cathode active material of the present invention can be reused in the same way as unused active material. Methods for producing cathodes and batteries using recycled cathode active materials are well known.

[0112] The final discharge capacity of the recycled positive electrode active material according to the embodiment of the present invention may be 150 mAh / g or more.

[0113] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not changed.

[0114] (Example 1) 100 parts by mass of LiNi ０．６ Co ０．２ Mn ０．２ O ２ (positive electrode active material), 5 parts by mass of carbon black (conductive material), and 3 parts by mass of PVdF (binder) were mixed together to prepare a simulated composite (positive electrode composite).

[0115] In step (1), an activation treatment agent was mixed with the simulated composite to obtain a mixture. The activation treatment agent consisted of a Li supplement, activator 1, and activator 2. The Li supplement was Li ２ CO ３ and activator 1 is K ２ SO ４ and activator 2 is Mg(OH) ２The amounts of the Li supplement, activator 1, and activator 2 in the activation treatment agent were adjusted to the values ​​shown in Table 1 below. The total content of alkaline earth metals in the activation treatment agent was adjusted to the value shown in Table 1 below. "Substance amount of positive electrode active material" in Table 1 below means the substance amount of the positive electrode active material in the simulated composite. "Proportion of Li supplement" in Table 1 below means the proportion of the Li supplement relative to 100 mol% of the positive electrode active material (positive electrode active material in the simulated composite). "Proportion of activator 1" in Table 1 below means the proportion of activator 1 relative to 100 mol% of the positive electrode active material (positive electrode active material in the simulated composite). "Proportion of activator 2" in Table 1 below means the proportion of activator 2 relative to 100 mol% of the positive electrode active material (positive electrode active material in the simulated composite).

[0116] In step (2) following step (1), 5 g of the mixture was placed in an alumina boat-shaped container and placed in a gas furnace. The atmosphere in the gas furnace was air. The mixture in the gas furnace was heated at 700°C for 3 hours. 700°C was a temperature equal to or higher than the melting point of the activation treatment agent. The heated mixture was allowed to cool to room temperature by natural cooling, and then removed from the gas furnace.

[0117] In step (3) following step (2), the heated mixture was pulverized. Distilled water was added to the pulverized mixture to prepare a slurry. The content of the mixture in the slurry was adjusted to 2 mass%. After stirring the slurry, the slurry was decanted. After decantation, the slurry was filtered to separate and recover the solid phase from the slurry. The recovered solid phase was rinsed with water.

[0118] In step (4) following step (3), the solid phase was vacuum dried at 100°C.

[0119] In step (5) following step (4), the solid phase was heated in air at 700° C. for 1 hour.

[0120] By the above-described manufacturing method, the recycled positive electrode active material of Example 1 was obtained.

[0121] <Production of Positive Electrode> The recycled positive electrode active material of Example 1, a binder solution, and a conductive material were kneaded in a rotation / revolution mixer (ARE-310, manufactured by Thinky Corporation) to produce a positive electrode composite paste. The weight ratio of recycled positive electrode active material: binder: conductive material was adjusted to 92:3:5. The binder solution used was NMP (N-methyl-2-pyrrolidone) in which the binder PVdF (#1100, manufactured by Kureha Corporation) was dissolved. The composition of the binder solution was adjusted by adding NMP so that the total weight of the positive electrode active material, conductive material, and binder in the positive electrode composite paste was 50 wt %. Acetylene black (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, product number: Denka Black HS100) was used as the conductive material.

[0122] The positive electrode mixture paste was applied to the surface of the current collector. The mass of the positive electrode active material on the surface of the current collector was 3.0±0.1 mg / cm. ２ The current collector coated with the positive electrode composite paste was vacuum dried at 150°C for 8 hours to obtain a positive electrode. The electrode area of ​​the positive electrode was 1.65 cm ２ The current collector used was an aluminum foil (1085 manufactured by Nippon Foil Co., Ltd.) and had a thickness of 20 μm.

[0123] <Manufacture of Battery> The above-described positive electrode, electrolyte, separator, and negative electrode were combined to manufacture a nonaqueous electrolyte lithium ion secondary battery (coin-type battery) of Example 1. The battery was assembled in a glove box under an argon atmosphere.

[0124] The electrolyte in the electrolytic solution is LiPF ６ The electrolyte solution was LiPF ６ The concentration of was adjusted to 1.0 mol / L. A mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used as a solvent for the electrolyte. The volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was adjusted to 30:35:35.

[0125] The separator used was a laminated film separator in which a heat-resistant porous layer was laminated on a polyethylene porous film, and metallic lithium was used as the negative electrode.

[0126] <Charge / Discharge Test> The initial charge capacity and initial discharge capacity of the battery of Example 1 were measured. The temperature of the battery during the measurement was maintained at 25°C. The initial charge / discharge efficiency was calculated by dividing the initial discharge capacity by the initial charge capacity. The initial charge / discharge was carried out under the following conditions: Maximum charge voltage: 4.3 V, charge rate: 0.2 C, constant current / constant voltage charge Minimum discharge voltage: 2.5 V, discharge rate: 0.2 C, constant current discharge

[0127] The initial discharge capacity recovery rate was calculated from the initial discharge capacity of the battery of Example 1 (battery using recycled positive electrode active material). When the initial discharge capacity of the battery using recycled positive electrode active material is X mAh / g and the discharge capacity (standard value) in the initial charge / discharge at 0.2 C of the battery (Reference Example 1) using an unused simulated composite as the positive electrode material is Y mAh / g (= 179 mAh / g), the initial discharge capacity recovery rate was calculated using the following formula (a): Initial discharge capacity recovery rate (%) = X / Y × 100 (a)

[0128] Following the initial charge / discharge, the discharge capacity was measured in each of the following charge / discharge cycles. The battery temperature during the measurements was maintained at 25°C. The minimum discharge voltage in each charge / discharge cycle was 2.5V. 2nd cycle (charge rate: 0.2C, discharge rate: 0.2C) 3rd cycle (charge rate: 0.2C, discharge rate: 0.5C) 4th cycle (charge rate: 0.2C, discharge rate: 1C) 5th cycle (charge rate: 0.2C, discharge rate: 2C) 6th cycle (charge rate: 0.2C, discharge rate: 5C) The rate retention was calculated by dividing the discharge capacity in the 5th cycle (2C) by the discharge capacity in the 2nd cycle (0.2C).

[0129] <Internal Resistance Measurement> The internal resistance (charge transfer resistance) of the battery of Example 1 at 100% SOC (State of Charge) was measured using the following AC impedance method. The battery was subjected to constant-current / constant-voltage charging at a maximum charging voltage of 4.3 V and a charging current of 0.2 C, and a Cole-Cole plot was created by sweeping the frequency in the range of 1 MHz to 0.1 Hz using an AC impedance measurement device. The vertical axis of the Cole-Cole plot represents the imaginary part of the complex impedance, and the horizontal axis represents the real part of the complex impedance. Next, the arc portion of the Cole-Cole plot between 100 Hz and 1 Hz was fitted with a circle to determine the diameter of the circle, i.e., the charge transfer resistance. A frequency response analyzer Solartron 1260 and a potentio / galvanostat Solartron 1287 were used as AC impedance measurement devices.

[0130] The results of the above measurements are shown in Table 2 below.

[0131] (Examples 2 to 4) The blending amounts of the Li supplement, activator 1, and activator 2 in the activation treatment agents of Examples 2 to 4 were adjusted to the values ​​shown in Table 1 below. The total content of alkaline earth metals in the activation treatment agents of Examples 2 to 4 was adjusted to the values ​​shown in Table 1 below. Except for the above-mentioned details, recycled positive electrode active materials and batteries of Examples 2 to 4 were produced in the same manner as Example 1. Measurements were carried out using the batteries of Examples 2 to 4 in the same manner as Example 1. The measurement results of Examples 2 to 4 are shown in Table 2 below.

[0132] (Examples 5 to 8) The activator 2 contained in each of the activation treatment agents of Examples 5 to 8 was Mg(OH). ２ Instead of Ca(OH) ２The amounts of the Li supplement, activator 1, and activator 2 in the activation treatment agents of Examples 5 to 8 were adjusted to the values ​​shown in Table 1 below. The total content of alkaline earth metals in the activation treatment agents of Examples 5 to 8 was adjusted to the values ​​shown in Table 1 below. Except for the above-mentioned details, recycled positive electrode active materials and batteries of Examples 5 to 8 were produced in the same manner as in Example 1. Measurements were carried out using the batteries of Examples 5 to 8 in the same manner as in Example 1. The measurement results of Examples 5 to 8 are shown in Table 2 below.

[0133] (Comparative Example 1) In the production of the recycled positive electrode active material of Comparative Example 1, activator 2 was not used. The recycled positive electrode active material and battery of Comparative Example 1 were produced in the same manner as in Example 1, except for the above-mentioned points. Measurements were carried out using the battery of Comparative Example 1 in the same manner as in Example 1. The measurement results of Comparative Example 1 are shown in Table 2 below.

[0134] (Reference Example 1) In the production of the battery of Reference Example 1, a simulated composite was used instead of the cathode material containing the recycled cathode active material. The battery of Reference Example 1 was produced in the same manner as in Example 1, except for the above-mentioned points. Measurements were carried out using the battery of Reference Example 1 in the same manner as in Example 1. The measurement results of Reference Example 1 are shown in Table 2 below.

[0135]

[0136]

Claims

1. A method for producing a recycled positive electrode active material, comprising the steps of: (1) mixing an activation treatment agent containing one or more alkali metal compounds with a positive electrode composite material containing a positive electrode active material to obtain a mixture; (2) heating the mixture to a temperature equal to or higher than the melting start temperature of the activation treatment agent to obtain a heated mixture; and (3) recovering a heated positive electrode active material from the heated mixture, wherein the activation treatment agent further contains one or more alkaline earth metal hydroxides.

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