Method for producing recycled positive electrode active material

Abstract

To provide a method for producing a recycled positive electrode active material that reduces the internal resistance of a battery.SOLUTION: 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 compounds. The total content of the alkaline earth metal in the activation treatment agent is 0.5 mol% or more.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0006] One aspect of the present invention relates to a method for manufacturing a recycled cathode active material as follows.

[0007] [1] Including the following steps, (1) A step of 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) A step of 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. (3) A step of recovering the heated positive electrode active material from the heated mixture. The activation treatment agent further contains one or more alkaline earth metal compounds. The total content of the alkaline earth metals in the activation treatment agent is 0.5 mol% or more. A method for producing a recycled positive electrode active material.

[0008] [2] The total content of the alkaline earth metals in the activation treatment agent is less than 14.3 mol%. The method for producing a recycled positive electrode active material according to [2]. [Effect of the Invention]

[0009] 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. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, a method for producing a positive electrode active material related to recycling will be described.

[0011] The method for producing a recycled positive electrode active material according to an embodiment of the present invention includes the following steps. Step (1): A step of mixing 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 Step (2): A step of heating the mixture to a temperature (for example, a holding temperature) equal to or higher than the melting start temperature of the activation treatment agent to obtain a heated mixture Step (3): A step of recovering the heated positive electrode active material from the heated mixture The activation treatment agent further contains one or more alkaline earth metal compounds. The total content of alkaline earth metals (Group 2 elements) in the activation treatment agent is 0.5 mol% or more.

[0012] In this specification, the positive electrode active material that has undergone steps (1) to (3) is referred to as the "recycled positive electrode active material". The recycled positive electrode active material that has undergone steps (1) to (3) can be suitably used for manufacturing a positive electrode or the like. The method for manufacturing the recycled positive electrode active material according to this embodiment can include additional steps before and after steps (1) to (3). In this specification, the positive electrode active material that has undergone steps (1) to (3) and subsequent additional steps is also referred to as the "recycled positive electrode active material". Examples of additional steps other than steps (1) to (3) include a preparation step of a positive electrode mixture and a washing step of the positive electrode mixture, which are described below and are carried out before step (1); steps (4) and (5) described below, which are carried out after step (3), and the like.

[0013] Hereinafter, each step in the method for manufacturing the recycled positive electrode active material according to this embodiment will be described in detail.

[0014] (Preparation step of positive electrode mixture) The method for manufacturing the recycled positive electrode active material according to this embodiment may include a preparation step of a positive electrode mixture for preparing a positive electrode mixture containing a positive electrode active material before step (1).

[0015] The positive electrode mixture may include a binder. In the positive electrode mixture, the particles of the positive electrode active material may be bound to each other by the binder. The positive electrode mixture may include an electrolyte and / or a conductive material in addition to the positive electrode active material and the binder. When the positive electrode mixture has 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 impregnated into the positive electrode mixture derived from the electrolyte of the battery. The positive electrode mixture may contain a fluorine compound derived from the binder and / or the electrolyte (for example, the electrolyte in the electrolyte).

[0016] <Positive electrode active material> Examples of the positive electrode active material include composite compounds containing, 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, and the like.

[0017] Note that the positive electrode active material may consist of only a single compound or may be composed of a plurality of compounds.

[0018] Examples of suitable positive electrode active materials are composite oxides containing one or more elements selected from Element Group 1 below 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

[0019] Among them, the positive electrode active material is preferably represented by the following chemical formula (Formula A).

[0020] 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, M 1 represents at least one element selected from the group consisting of Ni, Co, Mn, Fe, Al, and P, M T represents at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, and Fe, X represents at least one element selected from the group consisting of non-metal elements excluding O and P, -0.4 < a < 1.5, 0 ≤ b < 0.5, 0 ≤ c < 0.5, -0.5 < d < 1.5, 0 ≤ e < 0.5 are satisfied.

[0021] 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.

[0022] The positive electrode active material is preferably a composite oxide containing at least Li and Ni.

[0023] Also, in the positive electrode active material, M 1 The molar fraction of Ni is more preferably 0.3 to 0.95.

[0024] The crystal structure of the composite oxide 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.

[0025] The hexagonal crystal structure belongs to any one space group selected from the group consisting of P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63, P-6, P6 / m, P63 / m, P622, P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm, and P63 / mmc.

[0026] The monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c, and C2 / c.

[0027] Furthermore, it is preferably attributed to the space group R-3m included in the hexagonal crystal structure or C2 / m included in the monoclinic crystal structure.

[0028] The crystal structure of the positive electrode active material is identified from the powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement using CuKα ray as the radiation source.

[0029] There is no particular limitation on the particle diameter of the positive electrode active material in the positive electrode composite material, but it is usually about 0.001 to 100 μm. The particle size distribution of the positive electrode active material can be measured using a laser diffraction / scattering particle size distribution measuring device (for example, Mastersizer 2000 manufactured by Malvern). From the obtained particle size distribution, a volume-based cumulative particle size distribution curve can be created, and the value of the particle diameter (D50) at 50% cumulative from the fine particle side can be taken as the average particle diameter of the powder.

[0030] <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.

[0031] Examples of the carbon-based conductive material are specifically graphite powder, carbon black (for example, acetylene black), and fibrous carbon materials (for example, graphitized carbon fiber, carbon nanotube).

[0032] The carbon-based conductive material may be a single carbon material or may be composed of a plurality of carbon materials.

[0033] Also, the specific surface area of the carbon material used as the carbon-based conductive material is usually 0.1 to 500 m 2 / g.

[0034] In that case, the conductive material can be composed only of a carbon-based conductive material of 30 m 2 / g or more, and may be carbon black of 30 m 2 / g or more, or may be acetylene black of 30 m 2 / g or more.

[0035] In addition, when using an activating agent containing an alkali metal compound with oxidizing power described later, the rate of the oxidation treatment of the carbon-based conductive material can be increased, and even a carbon material with a small specific surface area may be able to be subjected to the oxidation treatment.

[0036] <Binder> Examples of the binder (pre-activation treatment binder) contained in the positive electrode composite material are thermoplastic resins, specifically, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene·hexafluoropropylene·vinylidene fluoride copolymer, hexafluoropropylene·vinylidene fluoride copolymer, and tetrafluoroethylene·perfluorovinyl ether copolymer and other fluororesins; polyolefin resins such as polyethylene and polypropylene; styrene-butadiene copolymer (hereinafter sometimes referred to as SBR); and mixtures of two or more of these may be used.

[0037] There is no particular limitation on the blending amounts of the positive electrode active material, conductive material, and binder in the positive electrode composite material. The blending amount of the binder can be 0.5 to 30 parts by weight, and may be 1 to 5 parts by weight with respect to 100 parts by weight of the positive electrode active material. The blending amount of the conductive material may be 0, but can be 0 to 50 parts by weight, and may be 1 to 10 parts by weight with respect to 100 parts by weight of the positive electrode active material.

[0038] <Electrolyte and Solvent> Examples of the electrolyte are LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2F)2, LiCF3SO3. There is no limitation on the amount of the electrolyte contained in the positive electrode composite material, but it can be 0.0005 to 7% by mass.

[0039] The positive electrode composite material may contain a solvent derived from the electrolytic solution. Examples of the solvent are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0040] <Recovery of Positive Electrode Composite Material> Such a positive electrode composite material can be obtained by separating and recovering the positive electrode composite material from a waste positive electrode having a current collector and a positive electrode composite material layer.

[0041] The "waste positive electrode" can be a positive electrode recovered from a discarded battery and waste of the positive electrode generated during the manufacturing process of the positive electrode and the battery. The discarded battery may be a used battery or an off-specification battery that is unused. Also, the waste of the positive electrode can be the end portion of the positive electrode generated in the battery manufacturing process and an off-specification positive electrode. Further, as the positive electrode composite material, waste products of the positive electrode composite material that are not attached to the current collector and are generated in the positive electrode composite material manufacturing process can also be used.

[0042] The waste positive electrode has a current collector that is a metal foil such as an aluminum foil and a copper foil, and a positive electrode composite material layer provided on the current collector. The positive electrode composite material layer may be provided on one side of the current collector or on both sides.

[0043] As a method for separating the positive electrode composite material from the waste positive electrode having the positive electrode composite material layer and the current collector, there are a method of mechanically peeling the positive electrode composite material layer from the current collector (for example, a method of scraping off the positive electrode composite material from the current collector), a method of infiltrating a solvent into the interface between the positive electrode composite material layer and the current collector to peel the positive electrode composite material layer from the current collector, and a method of dissolving the current collector using an alkaline or acidic aqueous solution to separate the positive electrode composite material layer. Preferably, it is a method of mechanically peeling the positive electrode composite material layer from the current collector.

[0044] (Washing step of the positive electrode composite material) Subsequently, when the positive electrode composite material contains an electrolyte, it is preferable to bring the prepared positive electrode composite material into contact with an electrolyte washing solvent to remove at least a part of the electrolyte from the positive electrode composite material. Specifically, a positive electrode composite material containing a positive electrode active material and an electrolyte is brought into contact with an electrolyte washing solvent to obtain a slurry containing a solid component and a liquid component, and then the slurry is separated into a solid component and a liquid component.

[0045] Solid-liquid separation is a process of separating a slurry into a liquid component and a solid component. As a method of solid-liquid separation, a conventionally known method may be used, for example, filtration or centrifugation.

[0046] The electrolyte washing solvent is not particularly limited. For example, 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 can be mentioned.

[0047] Contacting the positive electrode composite material with the electrolyte washing solvent can be performed using a known contact device for powder and liquid, such as a stirring tank.

[0048] In the step of contacting the positive electrode composite material with the electrolyte washing solvent, it is preferable to stir the positive electrode composite material and the electrolyte washing solvent to obtain a slurry. The peripheral speed of the tip of the stirring blade can be 0.1 to 1.0 m / s.

[0049] In the washing step of the positive electrode composite material, after solid-liquid separation, rinsing of the obtained solid component may be performed. Rinsing is an operation in which the obtained solid component is again contacted with the electrolyte washing solvent to obtain a slurry, and then the slurry is separated again into a solid component and a liquid component. In the washing of the positive electrode composite material, rinsing may be performed a plurality of times. The slurry concentration in rinsing can also be the same as above. Also in rinsing, the slurry can be stirred as described above.

[0050] The above washing can sufficiently remove the electrolyte from the positive electrode composite material. For example, if the electrolyte remains, the following reaction occurs, and the structure of the positive electrode active material changes from a layered rock salt structure to a spinel structure. LiPF6 + 16LiMO2 + 2O2 → 6LiF + Li3PO4 + 8LiM2O4 Also, when lithium carbonate is included as an activator, consumption of lithium due to the following reaction also occurs. LiPF6 + 4Li2CO3 → 6LiF + Li3PO4 + 4CO2

[0051] The separated solid component can be dried with an electrolyte washing solvent by decompression and / or heating as necessary. The heating temperature can be 50 to 200°C.

[0052] (Step (1): Activating agent mixing step) In step (1), an activating agent is mixed with a positive electrode composite material containing a positive electrode active material to obtain a mixture. The activating agent contains one or more alkali compounds and one or more alkaline earth metal compounds.

[0053] The mixing method of the positive electrode composite material and the activating agent may be either dry mixing or wet mixing, or a combination of these mixing methods, and the mixing order is not particularly limited.

[0054] During mixing, it is preferable to go through a step of pulverizing and mixing using a mixing device equipped with a mixing medium such as balls, which can improve the mixing efficiency.

[0055] As a mixing method, dry mixing is preferable in terms of easier mixing. In dry mixing, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a powder mixer equipped with stirring blades inside, a ball mill, a vibration mill, or a combination of these devices can be used.

[0056] As a mixing device used for dry mixing, a powder mixer equipped with stirring blades inside is preferable, and specifically, a Lodige mixer (manufactured by Matsubo Corporation) can be mentioned.

[0057] Hereinafter, the activating agent used in this step will be described in detail.

[0058] <Activating agent> The activating agent contains one or more alkali metal compounds. It is preferable that the activating agent contains at least one compound selected from the group consisting of potassium compounds and sodium compounds. Here, potassium and / or sodium may be referred to as alkali metal element X. The activating agent may contain an alkali metal compound containing other alkali metals such as Li in addition to the potassium compound and / or sodium compound.

[0059] When the activating agent comes into contact with the positive electrode active material, the positive electrode active material can be activated. When the alkali metal compound in the activating agent particularly contains a molten part, the contact property between the molten part and the positive electrode active material is improved, thereby further promoting the activation of the positive electrode active material.

[0060] In addition, the positive electrode composite material may contain a fluorine-containing compound derived from the binder and / or the electrolytic solution. By bringing the fluorine-containing compound into contact with the activating agent, the fluorine component is stabilized as an alkali metal fluoride, so that the generation of corrosive gases such as hydrogen fluoride can be suppressed. Note that it is desirable to prevent the generation of hydrogen fluoride because it reduces the activity of the positive electrode active material.

[0061] The ratio of the total alkali metal compounds in the activating agent is appropriately set in consideration of the type of the alkali metal compound, the type of the target positive electrode active material, etc. Usually, it is 50% by weight or more, preferably 70% by weight or more (including 100% by weight) based on the total weight of the activating 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 arbitrarily adjusted within 0 to 100 mol%, preferably 10 mol% or more, more preferably 20 mol% or more, preferably 90 mol% or less, and more preferably 80 mol% or less.

[0062] Examples of the alkali metal compounds that are 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.

[0063] Specific examples of suitable alkali metal compounds include hydroxides such as LiOH, NaOH, KOH, RbOH, CsOH; borates such as LiBO2, NaBO2, KBO2, RbBO2, CsBO2; carbonates such as Li2CO3, Na2CO3, K2CO3, RbCO3, CsCO3; oxides such as Li2O, Na2O, K2O, Rb2O, Cs2O; 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, CsCl; bromides such as LiBr, NaBr, KBr, RbBr, CsBr; vanadates such as LiVO3, NaVO3, KVO3, RbVO3, CsVO3; molybdates such as Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, CsMoO4; tungstates such as Li2WO4, Na2WO4, K2WO4, Rb2WO4, CsWO4; may be mentioned.

[0064] 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.

[0065] 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.

[0066] The activation treatment agent contains one or more alkaline earth metal compounds. 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 start temperature of the activation treatment agent. Furthermore, the alkaline earth metal compounds can reduce the internal resistance (impedance or direct current 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 compound 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 compound promotes the regeneration of the crystal structure on the surface of the positive electrode active material, thereby reducing (recovering) the reaction resistance of the battery (resistance component due to the speed limit of the chemical reaction).

[0067] The total content of alkaline earth metals in the activation treatment agent is 0.5 mol% or more. By the total content of alkaline earth metals in the activation treatment agent being 0.5 mol% or more, the internal resistance of a battery using the recycled cathode active material as the cathode can be reduced. When the amount of substance (unit: mol) of the alkaline earth metals (Group 2 elements) in the activation treatment agent is represented by m, and the total amount of substance of the alkali metal compounds (molecules) and alkaline earth compounds (molecules) in the activation treatment agent is represented by M, the total content of alkaline earth metals in the activation treatment agent may be represented as {100×(m / M)} mol%. The upper limit of the total content of alkaline earth metals in the activation treatment agent is not limited. For example, the total content of alkaline earth metals 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 is preferably 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 the recycled cathode active material as the cathode tend to improve. The total content of alkaline earth metals in the activation treatment agent is more preferably 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 improve. The total content of alkaline earth metals in the activation treatment agent may be 0.5 mol% or more and 14.3 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.

[0068] The alkaline earth metal contained in the alkaline earth metal compound 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 compound is preferably one or both of magnesium and calcium. Examples of the alkaline earth metal compound include hydroxides, borates, carbonates, oxides, peroxides, superoxides, nitrates, phosphates, sulfates, chlorides, vanadates, bromates, molybdates, and tungstates of alkaline earth metals. These can be used alone or in combination as components of the activation treatment agent.

[0069] Specific examples of suitable alkaline earth metal compounds include hydroxides such as Be(OH)2, Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2; borates such as Be(BO2)2, Mg(BO2)2, Ca(BO2)2, Sr(BO2)2, Ba(BO2)2; carbonates such as BeCO3, MgCO3, CaCO3, SrCO3, BaCO3; oxides such as BeO, MgO, CaO, SrO, BaO; peroxides such as Be2O3, Mg2O3, Ca2O3, Sr2O3, Ba2O3; superoxides such as BeO2, MgO2, CaO2, SrO2, BaO2; Nitrates such as Be(NO3)2, Mg(NO3)2, Ca(NO3)2, Sr(NO3)2, Ba(NO3)2; Phosphates such as Be3(PO4)2, Mg3(PO4)2, Ca3(PO4)2, Sr3(PO4)2, Ba3(PO4)2; Sulfates such as BeSO4, MgSO4, CaSO4, SrSO4, BaSO4; Chlorides such as BeCl2, MgCl2, CaCl2, SrCl2, BaCl2; Bromides such as BeBr2, MgBr2, CaBr2, SrBr2, BaBr2; Vanadates such as Be(VO3)2, Mg(VO3)2, Ca(VO3)2, Sr(VO3)2, Ba(VO3)2; Molybdates such as BeMoO4, MgMoO4, CaMoO4, SrMoO4, BaMoO4; Tungstates such as BeWO4, MgWO4, CaWO4, SrWO4, BaWO4; may be mentioned.

[0070] The activation treatment agent may optionally contain compounds other than alkali metal compounds and alkaline earth metal compounds. Further, the content of the compounds other than the alkali metal compounds in the activation treatment agent is selected within a range that does not significantly suppress the effects derived from the above-mentioned molten alkali metal compounds, and can be less than 50% by weight of the total weight of the activation treatment agent.

[0071] The addition amount of the activation treatment agent in the mixture of the positive electrode composite material and the activation treatment agent is preferably 0.001 to 100 times, more preferably 0.05 to 1 times, based on the weight of the positive electrode active material contained in the positive electrode composite material.

[0072] The number of moles of the alkali metal compound in the activation treatment agent in the mixture of the positive electrode composite material 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 when the number of moles of the positive electrode active material (for example, formula A) contained in the positive electrode composite material is 1.

[0073] By appropriately controlling the ratio of the activating agent in the mixture, the cost of recovering the cathode active material from the cathode composite material can be reduced, and the oxidation decomposition rate of the carbon-based conductive material and the binder can be increased. In addition, the effect of preventing the generation of corrosive gases in the heating process can be improved, and furthermore, the discharge capacity of the battery manufactured using the obtained cathode active material can be further increased.

[0074] Moreover, it is preferable that at least one of the alkali metal compounds contained in the activating agent is an alkali metal compound that exhibits alkalinity when dissolved in water. When an activating agent containing such an alkali metal compound is dissolved in pure water, the pH of the solution becomes greater than 7. Hereinafter, such an activating agent may be referred to as an "alkaline activating agent" in some cases.

[0075] By using an alkaline activating agent, the generation of corrosive gases in the heating process can be further suppressed, so that the discharge capacity of the battery manufactured using the recovered cathode active material can be further increased. In addition, by using an alkaline activating agent, the treatment rate of the carbon-based conductive material and the binder can also be increased.

[0076] Examples of the alkali metal compound that exhibits alkalinity when dissolved in water and is contained in the alkaline activating agent include alkali metal hydroxides, carbonates, bicarbonates, oxides, peroxides, and superoxides. Specifically, LiOH, NaOH, KOH, RbOH, CsOH; Li2CO3, Na2CO3, K2CO3, RbCO3, CsCO3; LiHCO3, NaHCO3, KHCO3, RbHCO3, CsHCO3; Li2O, Na2O, K2O, Rb2O, Cs2O; Li2O2, Na2O2, K2O2, Rb2O2, Cs2O2; LiO2, NaO2, KO2, RbO2, CsO2; can be mentioned. These may be included in the activating agent alone or in combination of two or more.

[0077] Further, when the conductive material contained in the positive electrode composite material is a carbon-based conductive material, at least one of the alkali metal compounds contained in the activation treatment agent may be an alkali metal compound having an oxidizing power to oxidatively decompose the carbon-based conductive material at the temperature of the heating step. In addition, the activation treatment agent containing such an alkali metal compound may sometimes be hereinafter referred to as an "activation treatment agent having an oxidizing power".

[0078] When using such an activation treatment agent having an oxidizing power, it is particularly effective in promoting the oxidation of the carbon-based conductive material, which is a carbon material, into carbon dioxide, and promoting the oxidation of the binder, which is a hydrocarbon material, into carbon dioxide and water vapor, and can further increase the discharge capacity of the battery manufactured using the obtained positive electrode active material, and may further improve the effect of preventing the generation of corrosive gases in the heating step.

[0079] Examples of the alkali metal compound having an oxidizing power necessary for oxidizing the carbon-based conductive material and hydrocarbon into carbon dioxide and water vapor include peroxides, superoxides, nitrates, sulfates, vanadates, and molybdates of alkali metals. These may be used alone or in combination of two or more.

[0080] Specifically, Li2O2, Na2O2, K2O2, Rb2O2, Cs2O2; LiO2, NaO2, KO2, RbO2, CsO2; LiNO3, NaNO3, KNO3, RbNO3, CsNO3; Li2SO4, Na2SO4, K2SO4, Rb2SO4, Cs2SO4; LiVO3, NaVO3, KVO3, RbVO3, CsVO3; Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, CsMoO4; can be mentioned.

[0081] Details of the oxidizing power of these alkali metal compounds are described in Japanese Patent Application Laid-Open No. 2012-186150.

[0082] (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 a temperature equal to or higher than the melting start 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 start temperature of the activation treatment agent. However, the temperature of the mixture in the heating step does not necessarily have to be constantly at a temperature equal to or higher than the melting start temperature of the activation treatment agent. The mixture obtained in this heating step may be referred to as the "mixture after heating".

[0083] Note that the "melting start temperature (Tmp) of the activation treatment agent" means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase.

[0084] The melting start temperature (Tmp) of the activation treatment agent is a value obtained by differential thermal analysis (DTA). That is, 5 mg of the above mixture before heating is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10 °C / min), and the temperature at which the DTA signal shows an endothermic peak is taken as the melting start temperature (Tmp).

[0085] The melting start temperature (Tmp) of the activation treatment agent is preferably 700 °C or lower, and more preferably 600 °C or lower. There is no lower limit for the melting start temperature (Tmp) of the activation treatment agent, but for example, it may be 150 °C.

[0086] Also, the melting point of the activation treatment agent means the lowest temperature at which a part of the activation treatment agent exhibits a liquid phase when only the activation treatment agent is heated. By mixing the positive electrode composite material and the activation treatment agent, the melting start temperature (Tmp) of the activation treatment agent becomes lower than the melting point of the activation treatment agent.

[0087] The melting point of the activation treatment agent is a value obtained by differential thermal analysis (DTA). Specifically, 5 mg of the activation treatment agent is subjected to differential thermal analysis (DTA, measurement conditions: heating rate: 10 °C / min), and the temperature at which the DTA signal shows an endothermic peak is taken as the melting point of the activation treatment agent.

[0088] There is no particular limitation on the atmosphere during heating, and it may be an oxygen-containing gas such as air, nitrogen, argon, or carbon dioxide. There is no particular limitation on the pressure of the atmosphere, and it can be atmospheric pressure, but a reduced-pressure atmosphere or a pressurized atmosphere may also be used.

[0089] In step (2), by heating the mixture before heating to a temperature equal to or higher than the melting start temperature (Tmp) of the activating agent as described above, the following effects occur.

[0090] When the molten activating agent comes into contact with the positive electrode active material, deterioration of the crystal structure of the positive electrode active material can be suppressed. In some cases, a crystal structure repair effect can also be obtained.

[0091] When the molten activating agent comes into contact with the carbon-based conductive material or the binder, the rate of oxidative decomposition of the conductive material and the binder is improved. Further, when the molten activating agent comes into contact with the fluorine compound derived from the binder and the electrolyte, the fluorine component is stabilized as an alkali metal fluoride, preventing the generation of hydrogen fluoride, which is a corrosive gas, and suppressing deterioration of the crystal structure of the positive electrode active material.

[0092] Furthermore, when the activating agent contains the same alkali metal as the positive electrode active material, it becomes possible to supply the alkali metal that is deficient in the positive electrode active material.

[0093] The temperature of the heating step and the holding time at that temperature can be appropriately adjusted according to the types and combinations of the positive electrode active material, conductive material, binder, and alkali metal compounds and other compounds contained in the activating agent that make up the positive electrode composite material. Usually, the temperature is in the range of 100 to 1500 °C, and the holding time is about 10 minutes to 24 hours.

[0094] The temperature in the heating step is preferably higher than the melting point of the alkali metal compound contained in the activating agent. Note that the melting point of the alkali metal compound may be lower than the melting point of each single compound by mixing a plurality of compounds. When the activating agent contains two or more kinds of alkali metal compounds, the eutectic point is taken as the melting point of the alkali metal compound.

[0095] After the heating step, if necessary, the mixture can be cooled to an arbitrary temperature, for example, about room temperature. In this way, a heated mixture containing the heated positive electrode active material is obtained.

[0096] (Step (3): Positive electrode active material recovery step) The positive electrode active material recovery step is a step of recovering the heated positive electrode active material from the heated mixture after the heating step in step (2).

[0097] In the heated mixture, in addition to the heated positive electrode active material, components derived from the activating agent (such as alkali metal compounds), undecomposed conductive materials and binder materials, and undecomposed products of other positive electrode composite materials are included. Further, when the positive electrode composite agent contains an electrolyte containing a fluorine component, it may also contain a fluorine component derived from the electrolyte.

[0098] As a method for separating and recovering the heated positive electrode active material from the heated mixture, there are a solid-liquid separation method in which a solvent such as water is added to the mixture to form a slurry and then solid-liquid separation is performed, and a vaporization separation method in which the mixture is heated to vaporize and separate components other than the heated positive electrode active material. Hereinafter, the solid-liquid separation step of performing the solid-liquid separation method will be described.

[0099] Step (3a): Solid-liquid separation step Step (3a) is a step of bringing the heated mixture into contact with a liquid containing water to obtain a slurry containing a solid component and a liquid component, and then separating the slurry into a solid component and a liquid component.

[0100] In the mixture after heating, in addition to the positive electrode active material after heating, components derived from the activation treatment agent (such as alkali metal compounds and alkaline earth metal compounds), undecomposed conductive materials, binder materials, and undecomposed materials of other positive electrode composite materials are included. Further, when the positive electrode composite material contains an electrolytic solution containing a fluorine component, it may also contain a fluorine component derived from the electrolyte.

[0101] In order to separate and recover the positive electrode active material after heating from the mixture after heating, a liquid (liquid) containing water is added to the mixture to make it into a slurry, and then solid-liquid separation is performed to separate it into a solid component and a liquid component.

[0102] 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 increase the solubility of the water-soluble components or increase the treatment rate, and the pH may be adjusted. Preferable examples of the liquid containing water include pure water and alkaline cleaning liquids. Examples of the alkaline cleaning liquid include aqueous solutions of one or more anhydrides and hydrates thereof selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate. Further, ammonia can also be used as the alkali.

[0103] 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. The liquid component contains an alkali metal component, an alkaline earth metal component derived from the activation treatment agent, and / or a fluorine component derived from the binder material and the electrolytic solution.

[0104] The amount of the liquid added to the mixture is appropriately determined in consideration of the amount of the positive electrode active material after heating contained in the mixture and the amount of each of the water-soluble components other than the positive electrode active material.

[0105] In step (3a), it is preferable to stir the mixture after heating and a liquid containing water to obtain a slurry. Thereby, the dissolution of the water-soluble component is promoted. The peripheral speed of the tip of the stirring blade is preferably 0.1 to 0.9 m / s.

[0106] The slurry formed in the slurrying step is then subjected to solid-liquid separation. Solid-liquid separation is a step of separating the slurry into a liquid component and a solid component. As a method of solid-liquid separation, a conventionally known method may be used, and examples thereof include filtration and centrifugation.

[0107] In step (3a), after solid-liquid separation, rinsing of the obtained solid component may be performed. Rinsing is an operation of bringing a liquid containing water into contact with the obtained solid component again to obtain a slurry, and then separating the slurry into a solid component and a liquid component again. In step (3a), rinsing may be performed a plurality of times. The slurry concentration in rinsing can also be the same as described above.

[0108] (Step (4): Drying step) In step (4), the solid component obtained in step (3a) is exposed to a heating and / or reduced-pressure environment to remove water from the solid component.

[0109] The heating temperature is preferably 100°C or higher in order to remove water. In order to more sufficiently remove water, it is preferably 150°C or higher. In particular, at a temperature of 250°C or higher, the discharge capacity of the battery manufactured using the obtained positive electrode active material is further increased, which is preferable. The temperature in the drying step may be constant, or may be changed stepwise or continuously. The temperature range reached by heating can be, for example, 10°C or higher and less than 900°C.

[0110] The reduced-pressure range reached can be, for example, 1.0×10 -10 ~1.0×10 3 Pa.

[0111] (Step (5): Annealing (re-firing) step) Step (5) is preferably a step of heat-treating the solid component after the step (4) at a temperature below 900°C.

[0112] Although there is no limitation on the atmosphere for the heat treatment, it is preferably carried out in an oxygen-containing atmosphere such as air. Also, the heat treatment temperature can be 100°C or higher. Further, the holding time of the heat treatment can be from 1 minute to 24 hours. In particular, it is preferably heated at a holding temperature of 350°C or higher for 0.1 hour or more and 5 hours or less.

[0113] By using the method for producing a recycled positive electrode active material of the present invention, the recycled positive electrode active material obtained from the battery composite material can be reused in the same manner as an unused active material. Methods for manufacturing a positive electrode and a battery using the recycled positive electrode active material are well known.

[0114] Finally, the discharge capacity of the recycled positive electrode active material according to the embodiment of the present invention can be 150 mAh / g or more.

Examples

[0115] Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples unless the gist thereof is changed.

[0116] (Example 1) 100 parts by mass of LiNi 0.6 Co 0.2 Mn 0.2 O2 (positive electrode active material), 5 parts by mass of carbon black (conductive material), and 3 parts by mass of PVdF (binder) were mixed to prepare a simulated composite material (positive electrode composite material).

[0117] In step (1), a mixture was obtained by mixing an activation treatment agent with the above-described simulated composite material. The activation treatment agent consisted of a Li replenishing material, activator 1, and activator 2. The Li replenishing material was Li2CO3, activator 1 was K2SO4, and activator 2 was Mg(OH)2. The blending amounts of the Li replenishing material, 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. The "amount of substance of the positive electrode active material" in Table 1 below means the amount of substance of the positive electrode active material in the simulated composite material. The "ratio of the Li replenishing material" in Table 1 below means the ratio of the Li replenishing material to 100 mol% of the positive electrode active material (the positive electrode active material in the simulated composite material). The "ratio of activator 1" in Table 1 below means the ratio of activator 1 to 100 mol% of the positive electrode active material (the positive electrode active material in the simulated composite material). The "ratio of activator 2" in Table 1 below means the ratio of activator 2 to 100 mol% of the positive electrode active material (the positive electrode active material in the simulated composite material).

[0118] In step (2) following step (1), 5 g of the above mixture was placed in an alumina boat-shaped container and installed 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 start temperature of the activation treatment agent. After the heated mixture was cooled to room temperature by natural cooling, the heated mixture was taken out of the gas furnace.

[0119] 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% by mass. After stirring the slurry, decantation of the slurry was performed. After decantation, the solid phase was separated and recovered from the slurry by filtration of the slurry. The recovered solid phase was rinsed with water.

[0120] In step (4) following step (3), vacuum drying of the solid phase was performed at 100 °C.

[0121] In step (5) following step (4), the solid phase in the air was heated at 700 °C for 1 hour.

[0122] By the above manufacturing method, the recycled positive electrode active material of Example 1 was obtained.

[0123] <Manufacture of Positive Electrode> The recycled positive electrode active material of Example 1, a binder solution, and a conductive material were kneaded using a rotation and revolution mixer (ARE-310 manufactured by Shinchi Co., Ltd.) to produce a positive electrode mixture paste. The weight ratio of the recycled positive electrode active material: binder: conductive material was adjusted to 92:3:5. As the binder solution, NMP (N-methyl-2-pyrrolidone) in which PVdF (#1100 manufactured by Kuraray Co., Ltd.), which is a binder, was dissolved was used. 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 mixture paste was 50% by weight. As the conductive material, acetylene black (product number: Denka Black HS100, manufactured by Denki Kagaku Kogyo Co., Ltd.) was used.

[0124] 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 adjusted to 3.0 ± 0.1 mg / cm 2 The current collector coated with the positive electrode mixture 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 aluminum foil (1085 manufactured by Nippon Foil Co., Ltd.). The thickness of the current collector was 20 μm.

[0125] <Manufacture of Battery> The above positive electrode, electrolyte, separator, and negative electrode were combined to manufacture a non-aqueous electrolyte type lithium ion secondary battery (coin type battery) of Example 1. The battery assembly was performed inside a glove box in an argon atmosphere.

[0126] As the electrolyte in the electrolytic solution, LiPF6 was used. The concentration of LiPF6 in the electrolytic solution was adjusted to 1.0 mol / L. As the solvent of the electrolytic solution, a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used. The volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was adjusted to 30:35:35.

[0127] As the separator, a laminated film separator in which a heat-resistant porous layer was laminated on a porous polyethylene film was used. Also, as the negative electrode, metallic lithium was used.

[0128] <Charge and Discharge Test> The initial charge capacity and the 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 and discharge were carried out under the following conditions. Charge maximum voltage: 4.3 V, charge rate: 0.2C, constant current constant voltage charging Discharge minimum voltage: 2.5 V, discharge rate: 0.2C, constant current discharge

[0129] From the initial discharge capacity of the battery of Example 1 (the battery using the recycled positive electrode active material), the initial discharge capacity recovery rate was calculated. When the initial discharge capacity of the battery using the recycled positive electrode active material was X mAh / g and the discharge capacity (standard value) in the initial charge and discharge at 0.2C of the battery using the unused simulated composite material as the positive electrode material (Reference Example 1) was Y mAh / g (=179 mAh / g), the initial discharge capacity recovery rate was calculated by the following formula (a). Initial discharge capacity recovery rate (%) = X / Y × 100 (a)

[0130] Following the initial charge and discharge, the discharge capacity in each of the following charge and discharge cycles was measured. The temperature of the battery during the measurement was maintained at 25°C. The discharge minimum voltage in each charge and discharge cycle was 2.5 V. Second cycle (charge rate: 0.2C, discharge rate: 0.2C) Third 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 of the 5th cycle (2C) by the discharge capacity of the 2nd cycle (0.2C).

[0131] <Internal resistance measurement> The internal resistance (charge transfer resistance) of the battery of Example 1 at 100% SOC (State Of Charge) was measured by the following alternating current impedance method. Constant current constant voltage charging of the battery was performed at a maximum charging voltage of 4.3V and a charging current of 0.2C. A Cole-Cole plot was created by sweeping the frequency in the range of 1MHz to 0.1Hz using an alternating current impedance measuring device. The vertical axis of the Cole-Cole plot is the imaginary part of the complex impedance, and the horizontal axis of the Cole-Cole plot is the real part of the complex impedance. Subsequently, in the Cole-Cole plot, the arc portion included in 100Hz to 1Hz was fitted with a circle to identify the diameter of the circle, that is, the charge transfer resistance. As the alternating current impedance measuring device, a frequency response analyzer solartron1260 and a potentiostat / galvanostat solartron1287 were used.

[0132] The above measurement results are shown in Table 2 below.

[0133] (Examples 2 to 4) The blending amounts of the Li replenisher, activator 1, and activator 2 in the activation treatment agent of each 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 agent of each of Examples 2 to 4 was adjusted to the values shown in Table 1 below. Except for the above matters, the recycled cathode active materials and batteries of Examples 2 to 4 were prepared in the same manner as in Example 1. Measurements were carried out using the batteries of Examples 2 to 4 in the same manner as in Example 1. The measurement results of Examples 2 to 4 are shown in Table 2 below.

[0134] (Examples 5 to 8) In Examples 5 to 8, Activator 2 contained in the activation treatment agent was Ca(OH)2 instead of Mg(OH)2. The blending amounts of the Li replenishing material, Activator 1, and Activator 2 in the activation treatment agent of each 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 agent of each of Examples 5 to 8 was adjusted to the value shown in Table 1 below. Except for the above matters, the recycled cathode active materials and batteries of Examples 5 to 8 were prepared 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.

[0135] (Comparative Example 1) In the production of the recycled cathode active material of Comparative Example 1, Activator 2 was not used. Except for the above matters, the recycled cathode active material and battery of Comparative Example 1 were prepared in the same manner as in Example 1. Measurements were carried out using the battery of Comparative Example 1 in the same manner as in Example 1. The measurement result of Comparative Example 1 is shown in Table 2 below.

[0136] (Reference Example 1) In the production of the battery of Reference Example 1, a simulated composite material was used instead of the cathode material containing the recycled cathode active material. Except for the above matters, the battery of Reference Example 1 was prepared in the same manner as in Example 1. Measurements were carried out using the battery of Reference Example 1 in the same manner as in Example 1. The measurement result of Reference Example 1 is shown in Table 2 below.

[0137]

Table 1

[0138]

Table 2

Claims

1. including the following steps, (1) A step of mixing an activating 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) A step of heating the mixture to a temperature equal to or higher than the melting start temperature of the activating agent to obtain a heated mixture; (3) A step of recovering a heated positive electrode active material from the heated mixture; the activating agent further contains one or more alkaline earth metal compounds, the total content of alkaline earth metals in the activating agent is 0.5 mol% or more, A method for producing a recycled positive electrode active material.

2. the total content of alkaline earth metals in the activating agent is less than 14.3 mol%, The method for producing a recycled positive electrode active material according to Claim 1.

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