Regeneration method, method for manufacturing power storage device, and regeneration device

Abstract

To more easily execute regeneration of an active material of a power storage device.SOLUTION: A regeneration method of the present disclosure is a regeneration method for an active material that is used for a power storage device and occludes and discharges lithium. The method includes a regeneration step of reducing an active material in which lithium is deficient due to stoichiometric composition to supply lithium ions, in an aqueous solution including a mediator capable of oxidation reduction that is oxidized at an electrical potential for a standard hydrogen electrode (SHE) of 0.6 V or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification discloses a playback method, a method for manufacturing a power storage device, and a playback device.

Background Art

[0002] Conventionally, as a method for regenerating an active material used in a power storage device, a method has been proposed in which lithium supplementation is performed from lithium metal in 1,2-dimethoxyethane, which is a non-aqueous solvent, using a quinone derivative as a redox substance for a used ternary active material (Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2) (for example, Non-Patent Document 1). In addition, a method has been proposed in which lithium supplementation is performed by treating a used ternary active material in a 4 mol / L aqueous lithium hydroxide solution at 220°C for 4 hours (for example, Non-Patent Document 2). Further, a method has been proposed in which ethanol is added to a 4 mol / L aqueous lithium hydroxide solution for a used ternary active material and the treatment is performed at 100°C for 8 hours to perform lithium supplementation (for example, Non-Patent Document 3).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Non-Patent Document 1, since a non-aqueous solvent was used, the treatment was complicated, such as the maintenance of the solution before and after the treatment. Further, in Non-Patent Documents 2 and 3, although an aqueous solution was used, the replenishment of lithium was not sufficient, and the treatment had to be carried out at a relatively high temperature, which was still not sufficient, and further improvement was desired. Thus, a novel regeneration method capable of restoring the deteriorated capacity of the active material has been desired.

[0005] The present disclosure has been made to solve such problems, and the main object thereof is to provide a novel regeneration method, a method for manufacturing a power storage device, and a regeneration device that can more easily execute the regeneration of the active material of the power storage device.

Means for Solving the Problems

[0006] As a result of intensive studies to achieve the above-described object, the present inventors have found that when a lithium source and a mediator that undergoes oxidation-reduction at a predetermined potential are placed in an aqueous solution to obtain a treatment aqueous solution, the regeneration of the active material of the power storage device can be more easily executed, and thus the present disclosure has been completed.

[0007] That is, the regeneration method of the power storage device disclosed in the present specification is A method for regenerating an active material used in a power storage device that occludes and releases lithium, A regeneration step of reducing the active material in which lithium is deficient from the stoichiometric composition and replenishing lithium ions in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE), which includes.

[0008] The method for manufacturing a power storage device of the present disclosure is A method for manufacturing a power storage device including an electrode having an active material that occludes and releases lithium, After obtaining an active material in which the active material in which lithium is deficient from the stoichiometric composition is reduced and lithium ions are replenished in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE), a regeneration step of incorporating an electrode containing the active material is carried out. It includes the following.

[0009] The playback device of the present disclosure is a playback device for a storage device used for a rechargeable device that stores and releases lithium, and includes a regeneration unit that reduces the active material in which lithium is deficient from the stoichiometric composition and replenishes lithium ions in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE). It is equipped with the following.

Advantages of the Invention

[0010] In the regeneration method, the manufacturing method of the storage device, and the regeneration device of the present disclosure, the regeneration of the active material of the storage device can be carried out more simply. The reason for obtaining such an effect is presumed as follows. For example, when the active material in which lithium is deficient from the stoichiometric composition is immersed in an aqueous solution as a treatment solution, lithium ions present in the aqueous solution are supplied to the active material. As a counter reaction, electrons are simultaneously withdrawn from the reduced mediator, the active material is reduced, and lithium is replenished to the active material. In this regeneration method, since the treatment is carried out with an aqueous solution and the active material is only immersed in the aqueous solution, the treatment is simpler. Further, in this regeneration method, even if heating is omitted, the regeneration of the active material can be performed sufficiently efficiently.

Brief Description of the Drawings

[0011]

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Mode for Carrying Out the Invention

[0012] The reproduction method disclosed in this specification is a reproduction method of an active material used in a power storage device that stores and releases lithium, and includes a reproduction step of reducing an active material in which lithium is deficient from the electrochemically equivalent composition and replenishing lithium ions in an aqueous solution containing a mediator. The mediator is a compound that undergoes oxidation-reduction. The aqueous solution contains lithium ions. The power storage device is not particularly limited as long as it uses lithium ions as carrier ions, and may be a non-aqueous electrolyte secondary battery, or may be a metal secondary battery such as a lithium ion secondary battery or a lithium metal secondary battery. Hereinafter, as an example, the case where the power storage device is a lithium ion secondary battery will be mainly described.

[0013] (Power storage device) The power storage device includes a positive electrode, a negative electrode, and an ion conductive medium. The positive electrode may have a positive electrode active material capable of storing and releasing lithium ions. The negative electrode may have a negative electrode active material capable of storing and releasing lithium ions. The non-aqueous electrolyte may be interposed between the positive electrode and the negative electrode and conduct lithium ions.

[0014] The positive electrode may be formed by, for example, mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to obtain a paste-like positive electrode composite material, applying and drying the composite material on the surface of a current collector, and compressing it as necessary to increase the electrode density. Examples of the positive electrode active material include sulfides containing transition metal elements and composite oxides containing lithium and transition metal elements. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2, and the basic composition formula is Li (1-x) MnO2 (0 < x < 1, etc., the same below), Li (1-x) Mn2O4, etc., lithium manganese composite oxides, the basic composition formula is Li (1-x) CoO2, etc., lithium cobalt composite oxides, the basic composition formula is Li (1-x) NiO2, etc., lithium nickel composite oxides, the basic composition formula is Li (1-x) Ni a Co b Mn c O2 (a + b + c = 1), etc., lithium nickel cobalt manganese composite oxides, the basic composition formula is LiV2O3, etc., lithium vanadium composite oxides, the basic composition formula is V2O5, etc., transition metal oxides can be used. Further, the positive electrode active material may be an olivine-type compound, for example, lithium iron phosphate (LiFePO4: LFP), etc. This lithium iron phosphate may be added with additive elements such as manganese. Specifically, the positive electrode active material is, for example, LFP, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM111), LiNi 0.5 Co 0.3 Mn 0.2 O2 (NCM532), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.5 Mn 1.5Examples include O4, LiMn2O4, etc. Note that the "basic composition formula" means that other elements may be included. The positive electrode active material may have a redox potential of 3.5 V or more, or 4.0 V or more based on the Li metal standard.

[0015] In the positive electrode, as the conductive material, for example, one or a mixture of two or more of graphite such as natural graphite (scaly graphite, flaky graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to connect and hold the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resins such as fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), etc. can be used alone or as a mixture of two or more. Also, water-dispersible substances such as aqueous binders like carboxymethyl cellulose (CMC) of the cellulose type, styrene-butadiene copolymer (SBR), and polyvinyl alcohol can be used. As the solvent for dispersing the positive electrode active material, conductive material, and binder, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. Also, a dispersant, thickener, etc. can be added to water, and the active material can be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. As the coating method, for example, roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. can be mentioned, and any thickness and shape can be obtained using any of these. The basis weight of the positive electrode composite material is not particularly limited, but for example, it may be 5 mg / cm 2 or more, and may be 6 mg / cm 2 or more, and may be 7 mg / cm 2The above may be sufficient. The basis weight of the positive electrode composite material may be, for example, 20 mg / cm 2 or less. As the current collector, in addition to aluminum, titanium, stainless steel, nickel, iron, fired carbon, conductive polymer, conductive glass, etc., those obtained by treating the surface of aluminum or copper with carbon, nickel, titanium, silver, etc. can be used for the purpose of improving adhesiveness, conductivity, and oxidation resistance. For these, it is also possible to perform surface oxidation treatment. Examples of the shape of the current collector include foil-like, film-like, sheet-like, net-like, punched or expanded ones, lath bodies, porous bodies, foams, and formed bodies of fiber groups. The thickness of the current collector is, for example, 1 to 500 μm.

[0016] The negative electrode may be formed by closely adhering a negative electrode active material and a current collector. For example, a negative electrode composite material obtained by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like material, applying and drying it on the surface of the current collector, and compressing it as necessary to increase the electrode density may also be used. Examples of the negative electrode active material include lithium, lithium alloys, inorganic compounds such as tin compounds, carbonaceous materials capable of occluding and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, suppress self-discharge when using a lithium salt as a supporting salt, and can reduce the irreversible capacity during charging, so they are preferable. Examples of the composite oxides include lithium titanium composite oxides and lithium vanadium composite oxides. Among these, carbonaceous materials are preferable as the negative electrode active material from the viewpoint of safety. In addition, as the conductive material, binder, solvent, etc. used for the negative electrode, those exemplified for the positive electrode can be used respectively. The negative electrode active material may have a redox potential of 1.0 V or less, 0.5 V or less, or 0.3 V or less based on the Li metal standard. The basis weight of the negative electrode composite material may be, for example, 3 mg / cm 2 or more, and 4 mg / cm 2The above may be sufficient. The basis weight of the negative electrode composite may be, for example, 15 mg / cm 2 The following may be sufficient. As the current collector of the negative electrode, in addition to copper, nickel, stainless steel, titanium, aluminum, fired carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., for the purpose of improving adhesion, conductivity, and reduction resistance, for example, those obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver, etc. can also be used. Regarding these, it is also possible to perform an oxidation treatment on the surface. As the shape of the current collector, the same ones as those of the positive electrode can be used.

[0017] The ion conduction medium may be, for example, a non-aqueous electrolyte containing a supporting salt and an organic solvent. Examples of the supporting salt include inorganic salts such as LiPF6, LiClO4, LiAsF6, LiBF4, and organic salts such as LiN(FSO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2. These supporting salts may be used alone or in combination of a plurality. The concentration of the supporting salt is preferably 0.1 to 2.0 M, and more preferably 0.8 to 1.2 M. As the organic solvent, for example, an aprotic organic solvent can be used. Examples of such organic solvents include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers, etc. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. Examples of cyclic esters include gamma-butyrolactone, gamma-valerolactone, etc. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, etc. Examples of chain ethers include dimethoxyethane, ethylene glycol dimethyl ether, etc. These may be used alone or in combination of a plurality. In addition, as the non-aqueous electrolyte, nitrile solvents such as acetonitrile and propylnitrile, ionic liquids, gel electrolytes, etc. may also be used. The non-aqueous electrolyte may contain additives such as a film-forming agent and a flame retardant, for example.

[0018] Alternatively, instead of the liquid ion conductive medium, a solid ion conductive polymer can also be used as the ion conductive medium. Examples of the ion conductive polymer include polymer gels composed of polymers such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and vinylidene fluoride and a supporting salt. Furthermore, an ion conductive polymer and a non-aqueous electrolyte can also be used in combination. In addition, as the ion conductive medium, in addition to the ion conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used.

[0019] The power storage device may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the usage range of the power storage device. Examples include polymer non-woven fabrics such as polypropylene non-woven fabrics and polyphenylene sulfide non-woven fabrics, and thin microporous membranes of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0020] The shape of the power storage device is not particularly limited, and examples include coin type, button type, sheet type, laminated type, cylindrical type, flat type, and square type. It may also be applied to large ones used in electric vehicles and the like. FIG. 1 is an explanatory diagram showing an example of the power storage device 20 of this embodiment. The power storage device 20 includes a positive electrode sheet 23 formed with a positive electrode composite material 22 on a current collector 21, a negative electrode sheet 26 formed with a negative electrode composite material 25 on the surface of a current collector 24, a separator 28 provided between the positive electrode sheet 23 and the negative electrode sheet 26, and an ion conductive medium 29 interposed between the positive electrode sheet 23 and the negative electrode sheet 26. In this power storage device 20, the separator 28 is sandwiched between the positive electrode sheet 23 and the negative electrode sheet 26, these are wound and inserted into a cylindrical case 32, and a positive electrode terminal 34 connected to the positive electrode sheet 23 and a negative electrode terminal 36 connected to the negative electrode sheet 26 are disposed. The ion conductive medium 29 may be a non-aqueous electrolyte.

[0021] (Treatment solution) The treatment solution is an aqueous solution containing a mediator that is a redox agent. This aqueous solution contains lithium ions as a lithium source. The mediator is a redox-capable compound that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE). The mediator preferably has a redox potential lower than the potential after lithium replenishment of the active material to be replenished with lithium. Further, the mediator preferably has a redox potential higher than the reduction decomposition potential of the active material. For example, in the case of a ternary active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, since a deoxygenation reaction from nickel oxide, manganese oxide, and cobalt oxide has been reported at less than 0.7 V vs Li / Li + (-2.3 V vs SHE) (Reference 1: Sci Rep 7, 42263 (2017)), it is preferable to use a mediator having a high redox potential of -2.3 V vs SHE or higher. This mediator preferably has a potential with respect to the standard hydrogen electrode (SHE) in the range of -2.3 V or higher and 0.6 V or lower. More preferably, this mediator has a redox potential with respect to the standard hydrogen electrode (SHE) in the range of -0.7 V or higher and 0.6 V or lower. In this range, electrolysis of the aqueous solution can be more suppressed and the regeneration of the active material can be further promoted. This mediator is not particularly limited as long as it undergoes redox within the above potential range, but for example, it may be at least one of ferricyanide and ferrocene compounds. Examples of ferricyanides include potassium ferricyanide and sodium ferricyanide. Examples of ferrocene compounds include ferrocene and its derivatives. The ferrocene derivative may have a structure in which a substituent is bonded to the cyclopentadienyl ring of ferrocene, for example. Examples of the substituent include hydrocarbon groups such as a methyl group, a hydroxyl group, an amino group, and a sulfonic acid group. Further, examples of this mediator include water-soluble anthraquinone disulfonate having a quinone skeleton.

[0022] The mediator preferably has a concentration in the aqueous solution in the range of 0.01 mol / L (M) or more and 8 mol / L or less. When the concentration of the mediator is within this range, its redox ability can be fully exerted. This concentration is preferably higher, preferably 0.1 M or more, more preferably 0.5 M or more, still more preferably 2 M or more, and even more preferably 2.5 M or more. The pH of the treatment solution is preferably alkaline for better suppression of water electrolysis, and preferably in the range of pH 9 or more and 14 or less. From the perspective of ease of handling, the pH of the aqueous solution may be lower, such as 13 or less, 12 or less, or 11 or less.

[0023] The aqueous solution preferably has a lithium ion concentration in the range of 0.1 mol / L or more and 8 mol / L or less. In this range, it is preferable for easy replenishment of lithium ions to the active material. This concentration is more preferably 0.5 M or more, and may also be 1 M or more. Also, from the perspective of ease of handling, this concentration may be lower, preferably 5 M or less, more preferably 3 M or less, and may also be 2 M or less. Examples of the lithium salt dissolved in the aqueous solution include lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, etc., with lithium hydroxide being more preferable. The anion of the lithium salt is more preferably one that does not participate in the regeneration reaction or has little influence on the subsequent battery reaction. Also, cations other than lithium ions such as potassium ions may be present in the solution.

[0024] (Regeneration process) In the regeneration process, it is preferable to immerse the active material in an aqueous solution for a treatment time of 1 minute or more, more preferably 10 minutes or more, and it may also be 60 minutes or more. This treatment time may also be 1 second or more. When the immersion time is within this range, the regeneration treatment can be sufficiently performed. This treatment time is preferably shorter and may be 24 hours or less, but it may be determined in consideration of the regeneration efficiency and the like. Further, in this regeneration process, the regeneration treatment can be performed at a treatment temperature in the room temperature range. This treatment temperature may be, for example, in the range of 0°C or more and 40°C or less. The treatment temperature is preferably 10°C or more, more preferably 20°C or more, and may also be 25°C or more. Further, the treatment temperature may be 35°C or less, or may be 30°C or less. In addition, the treatment temperature may be 40°C or more, or may be 50°C, 60°C or more. The treatment temperature is more preferably lower from the viewpoint of the energy used, but a higher temperature can shorten the treatment time more.

[0025] In the regeneration process, the usage form of the active material is not particularly limited, and it may be such that an electrode containing the active material is immersed in an aqueous solution, or an electrode composite powder separated from the electrode or an active material powder further separated from the electrode composite powder may be immersed in an aqueous solution. In the regeneration process, after immersing the active material in an aqueous solution as a treatment solution, the active material may be washed with water and dried. The water washing treatment is preferably performed one or more times to remove the components of the treatment solution. In the drying treatment, the active material may be dried in the air at 60°C or more or 100°C or more. The drying time may be appropriately set to a good time according to the form of the active material, for example, whether it is on the electrode or in powder form, and further according to the drying temperature.

[0026] Figure 2 is an explanatory diagram showing an example of the scheme of the regeneration reaction. As shown in Figure 2, in the regeneration treatment, when a positive electrode active material lacking lithium is immersed in an aqueous solution in which a mediator, which is a water-soluble compound, is dissolved, the positive electrode active material is reduced by the mediator, and lithium ions in the aqueous solution are supplied into the positive electrode active material. At this time, the mediator, which is a reducing agent, is oxidized to an oxidized form. For example, when the mediator is a ferrocyanide, ferrocyanide ions ([Fe(CN)64- ) is oxidized to ferrocyanide ion ([Fe(CN)6] 3- ), and when the mediator is a ferrocene compound, ferrocene (Fe(C5H5)2) is oxidized to ferricenium ion ([Fe(C5H5)2] + ). By this redox reaction of the mediator, the active material can be regenerated by a simpler method using a processing solution that is easy to handle with water as the solvent and does not require heating particularly in the room temperature range.

[0027] (Regeneration device) FIG. 3 is a schematic diagram showing an example of a regeneration device 10 that executes the above-described regeneration process. This regeneration device 10 includes a regeneration unit 11 that regenerates the active material. The regeneration unit 11 performs a process of reducing the active material lacking lithium from the stoichiometric composition and replenishing lithium ions in an aqueous solution 12 containing a redox-capable mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE). The regeneration unit 11 is a container that houses the aqueous solution 12. The regeneration device 10 may be configured to immerse the positive electrode sheet 23 having the positive electrode composite material layer 22 in the aqueous solution 12 with the aqueous solution 12 contained in the housing unit 11. Alternatively, the regeneration device 10 may be configured to immerse the powder of the positive electrode composite material layer 22 or the powder of the positive electrode active material in the aqueous solution 12 with the aqueous solution 12 contained in the housing unit 11. This regeneration device 10 may include, for example, a timer that measures the processing time, a thermometer that measures the processing temperature, a temperature adjustment device that adjusts the processing temperature of the aqueous solution 12, a pH meter that measures the pH of the aqueous solution 12, and the like. Further, the regeneration device 10 may include a water washing unit that washes the active material with water and a drying unit that dries the active material after water washing.

[0028] In the method for regenerating a power storage device, the method for manufacturing a power storage device, and the regeneration device described in detail above, the regeneration of the active material of the power storage device can be carried out more simply. The reason for obtaining such an effect is speculated as follows. For example, when an active material lacking lithium from the stoichiometric composition is immersed in an aqueous solution as a treatment solution, lithium ions present in the aqueous solution are supplied to the active material. At the same time, as a counter reaction, electrons are withdrawn from the reduced mediator, the active material is reduced, and lithium is replenished to the active material. In this regeneration method, since the treatment is carried out with an aqueous solution and the active material is only immersed in the aqueous solution, the treatment is simpler. Also, in this regeneration method, the regeneration of the active material can be carried out sufficiently efficiently even without heating. Therefore, in the method for regenerating a power storage device, the method for manufacturing a power storage device, and the regeneration device of the present embodiment, the regeneration of the active material of the power storage device can be carried out more simply. Further, in this regeneration method, since the treatment is carried out with an aqueous solution using water with a small environmental load instead of an organic solvent as a solvent, it is considered that the generation of secondary waste can be suppressed and the environmental load can be further reduced.

[0029] Note that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that various embodiments can be implemented as long as they belong to the technical scope of the present disclosure.

[0030] For example, in the above-described embodiment, a method for regenerating an active material used in an energy storage device was described. In this method for regenerating the energy storage device, it is possible to regenerate the capacity-degraded active material and manufacture a new non-aqueous electrolyte secondary battery with restored capacity. Therefore, this regeneration method may also be regarded as a method for manufacturing an energy storage device. This manufacturing method may manufacture the energy storage device by executing the regeneration process in the above-described method for regenerating the energy storage device. The method for manufacturing an energy storage device may include a preparation step of preparing an active material of a capacity-degraded energy storage device using lithium ions as carrier ions, and a regeneration step of regenerating the active material by the above-described regeneration method. The active material prepared in the preparation step may be the same as the active material in which lithium in the electrode described in the above-described embodiment is deficient from the electrochemistry composition. In the regeneration step, when the electrode containing the active material is regenerated, the energy storage device may be configured using this electrode. Further, in this regeneration step, when the powder of the electrode composite material containing the active material or the powder of the active material is regenerated, an electrode may be fabricated using this powder, and the energy storage device may be configured using the electrode.

[0031] In the above-described embodiment, the regeneration method may include a recovery step of reducing the mediator oxidized in the regeneration step to restore the function of the mediator that reduces the active material, and performing the regeneration step again using the recovered mediator. By reusing the mediator, the amount of mediator used can be reduced, and the environmental load can be further reduced. The regeneration method may repeat the regeneration step and the recovery step. By repeating the regeneration step and the recovery step, the amount of mediator used can be further reduced. The regeneration method may reduce the active material in the regeneration step to supply lithium ions to the active material, and at the same time reduce the mediator in the recovery step to restore the function of the mediator.

[0032] (Recovery Step) In the recovery process, the oxidized mediator may be electrochemically reduced. In the recovery process, an electrochemical cell including a working electrode chamber containing an aqueous solution containing the oxidized mediator (also referred to as a used treatment solution), a counter electrode chamber containing an electrolytic solution and separated from the working electrode chamber by an ion exchange membrane, a working electrode disposed in the working electrode chamber and contacting the used treatment solution, and a counter electrode disposed in the counter electrode chamber and contacting the electrolytic solution may be used as a recovery device to electrochemically reduce the oxidized mediator. The electrochemical cell may further include a reference electrode. Further, the electrochemical cell may omit the ion exchange membrane and the counter electrode chamber and bring the counter electrode into contact with the used treatment solution.

[0033] An aqueous solution containing the oxidized mediator is accommodated in the working electrode chamber, and the oxidized mediator is reduced. As the aqueous solution containing the oxidized mediator, for example, the used treatment solution may be used as it is, or it may be used after removing impurities by filtration or the like. In the working electrode chamber, the used treatment solution may be stirred in order to promote the diffusion of the used treatment solution and smoothly progress the reaction at the working electrode. For stirring, for example, bubbling, stirring by a magnetic stirrer, solution transport using a pump or the like, or ultrasonic irradiation can be used.

[0034] The counter electrode chamber contains an electrolytic solution. The electrolytic solution may be appropriately selected so that the electrochemical reaction in the electrochemical cell proceeds smoothly and side reactions do not occur or are less likely to occur. The electrolytic solution is preferably an aqueous electrolytic solution in which a supporting salt is dissolved in water, and more preferably a lithium ion-containing aqueous electrolytic solution. The water is preferably one from which ions have been removed, such as ion-exchanged water. Examples of the supporting salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, and lithium salts are preferred. Examples of the supporting salt include hydroxides, nitrates, sulfates, chlorides, etc., and hydroxides are preferred. The supporting salt may be the same as the lithium salt dissolved in the aqueous solution of the treatment solution, or may be lithium hydroxide. The concentration of the supporting salt in the electrolytic solution may be 0.1 mol / L (M) or more, 0.5 M or more, or 1 M or more. Also, this concentration may be 10 M or less, 5 M or less, or 3 M or less. The pH of the electrolytic solution is preferably alkaline in order to lower the oxygen evolution reaction potential due to the electrolysis of water and promote oxygen evolution, and is preferably in the range of pH 9 or more and 14 or less. The pH of the electrolytic solution may be lower for ease of handling, such as 13 or less, 12 or less, or 11 or less. In the counter electrode chamber, the electrolytic solution may be stirred to promote the diffusion of the electrolytic solution and allow the reaction at the counter electrode to proceed smoothly. For stirring, for example, bubbling, stirring with a magnetic stirrer, solution transport using a pump, etc., or ultrasonic irradiation can be used.

[0035] The counter electrode chamber is separated from the working electrode chamber by an ion exchange membrane. The ion exchange membrane suppresses, for example, the diffusion of the mediator into the counter electrode chamber. The ion exchange membrane may be a cation exchange membrane, an anion exchange membrane, or a combination of a cation exchange membrane and an anion exchange membrane such as a mosaic charged membrane, but a cation exchange membrane is preferred. Examples of the cation exchange membrane include fluorine-based polymer membranes such as Nafion (Nafion is a registered trademark), hydrocarbon-based polymer membranes such as Neosepta (Neosepta is a registered trademark) and Selemion (Selemion is a registered trademark), and solid electrolyte membranes such as cation conductive glass.

[0036] The working electrode only needs to have conductivity and alkali resistance, and examples thereof include graphite, platinum, and stainless steel. Since a reduction reaction occurs at the working electrode, in addition to the reaction in which the oxidized mediator is reduced (for example, ferricyanide ions become ferrocyanide ions), a reaction in which hydrogen is generated from protons in the aqueous solution may occur as a competing reaction. From the viewpoint of increasing the recovery efficiency of the treatment solution, it is preferable to select a working electrode in which a competing reaction does not occur or hardly occurs. For example, it is preferable to use a graphite electrode, in which hydrogen generation, which is a typical competing reaction, hardly occurs, as the working electrode. Since the selection of the material of the working electrode depends on the mediator used and the competing reaction, it is desirable to select it as appropriate. In order to promote the electrochemical reaction on the surface of the working electrode, the surface area may be increased by forming it into a felt shape or a mesh shape.

[0037] The counter electrode only needs to have conductivity and alkali resistance, and examples thereof include stainless steel such as SUS304, platinum, gold, and carbon. Since an oxidation reaction occurs at the counter electrode, oxygen is generated, for example, by the oxidation of hydroxide ions. From the viewpoint of promoting such oxygen generation, it is preferable to use stainless steel such as SUS304 or platinum, which has a low overvoltage for oxygen generation, as the counter electrode. In order to promote the electrochemical reaction on the surface of the counter electrode, the surface area may be increased by forming it into a felt shape or a mesh shape.

[0038] The reference electrode is used as the potential reference for the working electrode. As the reference electrode, a non-polarizable electrode such as an Ag / AgCl electrode can be preferably used. The reference electrode may be disposed in the working electrode chamber or the counter electrode chamber.

[0039] In the recovery process, a current is passed between the working electrode and the counter electrode while maintaining the potential of the working electrode at a potential at which the oxidized mediator can be reduced. As a result, the oxidized mediator is reduced, and the function of the mediator that reduces the active material is restored. In the recovery process, it is preferable to maintain the potential of the working electrode at a potential lower than the redox potential of the mediator and higher than the reductive decomposition potential of the mediator. For such potential control, a control device such as a potentiostat can be used, for example. The larger the difference between the potential of the working electrode and the redox potential of the mediator, the higher the recovery rate can be increased. For example, it may be 0.5 V or more, 0.7 V or more, or 1 V or more. Also, the difference between the potential of the working electrode and the redox potential of the mediator may be, for example, 2 V or less, 1.8 V or less, or 1.5 V or less. In the recovery process, the electrochemical recovery rate of the treatment solution is determined by the rate-determining elementary process among solution diffusion in the working electrode chamber and the counter electrode chamber, electrochemical reactions on the surfaces of the working electrode and the counter electrode, the migration rate of ions in the ion exchange membrane, and the like. Therefore, for example, by smoothly progressing the rate-determining elementary process by stirring the solution described above or increasing the surface area of the electrode, the electrochemical recovery rate of the treatment solution can be increased. In the recovery process, the energization time may be, for example, 1 minute or more, 5 minutes or more, or 10 minutes or more. Also, the energization time may be, for example, 5 hours or less, 1 hour or less, or 30 minutes or less.

[0040] Figure 4 is an explanatory diagram showing an example of the scheme of the recovery reaction. As shown in Figure 4, in the recovery treatment, when an aqueous solution in which an oxidized form of a mediator, which is a water-soluble compound, is dissolved is brought into contact with a working electrode held at a predetermined potential, electrons are supplied from the working electrode to the oxidized form of the mediator, the oxidized form of the mediator is reduced, and the function of the mediator that reduces the active material is restored. For example, when the mediator is a ferrocyanide, ferricyanide ions ([Fe(CN)6] 3- ) are reduced to ferrocyanide ions ([Fe(CN)6] 4- ), and when the mediator is a ferrocene compound, ferricenium ions ([Fe(C5H5)2] +) is reduced to ferrocene (Fe(C5H5)2). By this electrochemical reaction, the mediator can be recovered by a simpler method.

[0041] In the recovery step, lithium ions decreased from the treatment solution in the regeneration step may be replenished. When there are sufficient lithium ions in the treatment solution, it may not be necessary to replenish the lithium ions. The replenishment of lithium ions may be, for example, a process of externally adding a lithium salt to the treatment solution. The addition of the lithium salt may be performed on the used treatment solution, or may be performed on the treatment solution during or after recovery. The lithium salt to be added preferably contains ions of the same kind as the substance consumed in the reaction at the counter electrode, and lithium hydroxide is preferable, for example. The lithium salt to be added may be used as a supporting salt for the electrolytic solution accommodated in the counter electrode chamber. Also, as long as the addition of the lithium salt does not become rate-determining for lithium replenishment, it may be a compound containing cations other than lithium and ions other than those consumed at the counter electrode. The lithium salt may be added to the solution on the working electrode chamber side or the solution on the counter electrode chamber side. However, when a cation exchange membrane is used as the diaphragm, it is preferable to add it to the solution on the counter electrode chamber side. When an anion exchange membrane is used as the diaphragm, it is desirable to add the lithium salt to the solution on the working electrode chamber side.

[0042] (Recovery section) FIG. 5 is a schematic diagram showing an example of a recovery unit 50 that executes the above-described recovery process. This recovery unit 50 includes a working electrode chamber 60 that houses an aqueous solution (used treatment solution) 13 containing a mediator oxidized in the playback unit 11 of the playback device 10, a counter electrode chamber 70 that houses an electrolytic solution 76 and is separated from the working electrode chamber 60 by an ion exchange membrane 54, a working electrode 62 disposed in the working electrode chamber 60 and in contact with the aqueous solution 13, a counter electrode 72 disposed in the counter electrode chamber 70 and in contact with the electrolytic solution 76, and a reference electrode 74 disposed in the counter electrode chamber 70. It is configured as an electrochemical cell. The working electrode chamber 60 is one side that partitions the inside of the container 52 with the ion exchange membrane 54, and the counter electrode chamber 70 is the other side that partitions the inside of the container 52 with the ion exchange membrane 54. The working electrode 62, the counter electrode 72, and the reference electrode 74 are connected to a control device 80, and a current flows between the working electrode 62 and the counter electrode 72 while maintaining the potential of the working electrode 62 at a predetermined potential with reference to the reference electrode 74. A bubbling nozzle 64 is disposed in the aqueous solution 13 housed in the working electrode chamber 60 to promote the diffusion of the mediator. The playback device 10 may have this recovery unit 50 in addition to the playback unit 11. The playback unit 11 and the working electrode chamber 60 of the recovery unit 50 may be connected, for example, by a liquid feed pipe (not shown) that sends the aqueous solution 13, which is a used treatment solution, to the working electrode chamber 60 of the recovery unit 50, or by a liquid return pipe (not shown) that returns the aqueous solution 12 containing the mediator recovered in the recovery unit to the playback unit 11. The liquid feed pipe and the liquid return pipe may be used in combination to timely feed the aqueous solution 13 and return the aqueous solution 12, or the aqueous solutions 12 and 13 may be circulated between the playback unit 11 and the working electrode chamber 60 without using them in combination. Further, the playback device 10 may use the working electrode chamber 60 of the recovery unit 50 as the playback unit 11. For example, while replenishing the active material with lithium ions in the working electrode chamber 60, the mediator may be electrochemically regenerated at the same time.

[0043] The present disclosure may be as shown in any of the following [1] to

[16] . [1] A method for regenerating an active material used in a power storage device and capable of occluding and releasing lithium, In an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE), a regeneration step of reducing the active material in which lithium is deficient from the stoichiometric composition and replenishing lithium ions. A regeneration method comprising the above. [2] The regeneration method according to [1], wherein the mediator has a redox potential with respect to the standard hydrogen electrode (SHE) in the range of -2.3 V or more and 0.6 V or less. [3] The regeneration method according to [1] or [2], wherein the concentration of the aqueous solution of the mediator is in the range of 0.01 mol / L or more and 8 mol / L or less. [4] The regeneration method according to any one of [1] to [3], wherein the mediator is at least one of a ferrocyanide and a ferrocene compound. [5] The regeneration method according to any one of [1] to [4], wherein the aqueous solution has a pH in the range of 9 or more and 14 or less. [6] The regeneration method according to any one of [1] to [5], wherein the concentration of lithium ions in the aqueous solution is in the range of 0.1 mol / L or more and 8 mol / L or less. [7] In the regeneration step, the active material is immersed in the aqueous solution for a treatment time in the range of 1 second or more. The regeneration method according to any one of [1] to [6]. [8] The active material has a stoichiometric composition of LiFePO4, LiMO2 (where M is one or more of Ni, Co, and Mn), LiM a A b O2 (where A is Al and a + b = 1). The regeneration method according to any one of [1] to [7]. [9] The regeneration method according to any one of [1] to [8], comprising a recovery step of reducing the mediator oxidized in the regeneration step to restore the function of the mediator for reducing the active material, and using the recovered mediator to perform the regeneration step again.

[10] In the recovery step, the mediator oxidized in the regeneration step is further electrochemically reduced. The regeneration method according to [9].

[11] In the recovery step, an electrochemical cell including a working electrode chamber containing the aqueous solution including the mediator oxidized in the regeneration step, a counter electrode chamber containing an electrolytic solution and separated from the working electrode chamber by an ion exchange membrane, a working electrode disposed in the working electrode chamber, a counter electrode disposed in the counter electrode chamber, and a reference electrode is used to electrochemically reduce the mediator oxidized in the regeneration step, which is the regeneration method described in

[10] .

[12] In the recovery step, a lithium ion-containing aqueous electrolytic solution is used for the electrolytic solution, a cation exchange membrane is used for the ion exchange membrane, graphite is used for the working electrode, stainless steel is used for the counter electrode, and an Ag / AgCl electrode is used for the reference electrode, which is the regeneration method described in

[11] .

[13] In the recovery step, the lithium ions decreased from the aqueous solution in the regeneration step are replenished, which is the regeneration method described in any one of [9] to

[12] .

[14] A method for manufacturing a power storage device including an electrode having an active material that occludes and releases lithium, In an aqueous solution including a redox mediator that oxidizes at a potential of 0.6 V or less with respect to a standard hydrogen electrode (SHE), after reducing the active material in which lithium is deficient from the stoichiometric composition and supplying lithium ions to obtain an active material, a regeneration step of incorporating an electrode including the active material, A method for manufacturing a power storage device including the above.

[15] A regeneration device for an active material that is used in a power storage device and occludes and releases lithium, A regeneration unit that reduces the active material in which lithium is deficient from the stoichiometric composition and supplies lithium ions in an aqueous solution including a redox mediator that oxidizes at a potential of 0.6 V or less with respect to a standard hydrogen electrode (SHE), A regeneration device including the above.

[16] The regeneration device described in

[15] , including a recovery unit that reduces the mediator oxidized in the regeneration unit and restores the function of the mediator that reduces the active material.

Example

[0044] The following describes, as an example, a case where the active material of the lithium-ion battery electrode was regenerated by the method for regenerating the active material of the power storage device of the present disclosure. Note that Experimental Examples 1 to 5 correspond to Examples, and Experimental Example 6 corresponds to a Comparative Example. Also, Experimental Example 7 corresponds to an Example, and Experimental Example 8 corresponds to a Comparative Example. The present disclosure is not limited to the following examples, and it goes without saying that it can be implemented in various modes as long as it belongs to the technical scope of the present disclosure.

[0045] 1. Regeneration of Active Material As an evaluation cell, a lithium-ion battery composed of a Cu foil negative electrode and a LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 positive electrode was fabricated. As the positive electrode, a slurry of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 / acetylene black / polyvinylidene fluoride (mass ratio 90:5:5) was coated on a stainless steel foil and vacuum dried at 120 °C. Also, as the electrolyte, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 3:4:3) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L was used. A polyethylene single-layer microporous membrane was used as the separator. The positive electrode and the negative electrode were opposed to each other through a separator impregnated with the electrolyte, and a stainless steel (SUS) half cell was fabricated. The amount of the positive electrode mixture at this time was 17 mg. This cell was charged to a charged state at a current value that would result in full charge in 10 hours at a temperature of 25 °C up to a voltage of 3.8 V. The battery charged up to 3.8 V was opened in an argon atmosphere to take out the positive electrode and washed with DMC.

[0046] [Experimental Example 1] Lithium hydroxide was dissolved in ion-exchanged water to a concentration of 1 mol / L (1 M), and potassium ferricyanide trihydrate was dissolved to a concentration of 0.087 mol / L (0.087 M) to prepare a lithium replenishing solution. 50 mL of this replenishing solution was prepared, and the charged positive electrode cut in half was immersed for 180 minutes. The immersed positive electrode was washed twice with ion-exchanged water and dried. X-ray diffraction images (XRD) were obtained for the sample before immersion and the sample after washing and drying, and composition analysis was performed by inductively coupled plasma method (ICP). XRD was measured by the reflection method using a CuKα ray source.

[0047] [Experimental Examples 2 - 4] Lithium hydroxide was dissolved in ion-exchanged water to a concentration of 1 M, and potassium ferricyanide trihydrate was dissolved to a concentration of 0.1 M to prepare a lithium replenishing solution. 3 mL of this lithium replenishing solution was prepared, and the charged positive electrode was immersed for 60 to 180 minutes. The immersed positive electrode was washed twice with ion-exchanged water and dried. XRD was obtained for the sample after washing and drying.

[0048] [Experimental Example 5] As an evaluation cell, a lithium-ion battery composed of a lithium foil negative electrode and a LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 positive electrode was fabricated. As the positive electrode, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A slurry of O₂ / acetylene black / polyvinylidene fluoride (weight ratio 90:5:5) was applied to a stainless-steel foil and vacuum-dried at 120 °C. As the electrolyte, a mixture of EC / DMC / EMC (volume ratio 3:4:3) with 1 M lithium hexafluorophosphate (LiPF₆) dissolved in it was used. A single-layer polyethylene microporous membrane was used as the separator. The positive electrode and the negative electrode were opposed to each other through a separator impregnated with the electrolyte to fabricate a stainless-steel half-cell. The amount of the composite material of the positive electrode at this time was 17 mg. This cell was charged and discharged at a current value that would result in a full charge in 10 hours within the temperature range of 25 °C and the voltage range of 4.1 to 3 V. After that, it was charged to a charged state at a current value that would result in a full charge in 10 hours up to the voltage range of 3.8 V. The battery charged up to 3.8 V was opened in an argon atmosphere to take out the positive electrode, which was then washed with DMC. Similar to Experimental Examples 2 to 4, 3 mL of a lithium replenishing solution was prepared, and the charged positive electrode was immersed for 180 minutes. The immersed positive electrode was washed twice with ion-exchanged water and dried. XRD was obtained for the sample after washing and drying.

[0049] [Experimental Example 6] A solution was prepared by dissolving a reagent in ion-exchanged water so that lithium hydroxide was 1 M. 3 mL of this solution was prepared, and the charged positive electrode was immersed for 180 minutes. XRD was obtained for the sample before immersion and the sample after washing and drying.

[0050] (X-ray diffraction (XRD) measurement) Before and after the regeneration treatment, the XRD patterns of the positive electrode were measured to examine the state of the active material of the positive electrode. Using an XRD device (Ultima IV manufactured by Rigaku Corporation), the X-ray was set as CuKα ray, and XRD measurement was performed under the measurement conditions of a voltage of 40 kV, a current of 40 mA, and a scan rate of 10 ° / min. The obtained XRD patterns were analyzed with XRD analysis software (JADE Pro).

[0051] (ICP measurement) The composition of the active material of Experimental Example 1 was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, PS3520UVDDII II manufactured by Hitachi High-Technologies Corporation).

[0052] (Results and Discussion) The charged composite material weights, the compositions of the treatment aqueous solutions used for the regeneration treatment, the treatment solution volumes, the pH of the treatment solutions, and the treatment times of Experimental Examples 1 to 6 are summarized in Table 1. The composition analysis results of Experimental Example 1 are shown in Table 2. FIG. 4 shows the XRD measurement results before and after the regeneration treatment of Experimental Example 1. FIG. 5 is an enlarged view of the XRD measurement results before and after the regeneration treatment of Experimental Example 1. FIG. 6 shows the XRD measurement results before and after the regeneration treatment of Experimental Examples 2 to 6. FIG. 7 is an enlarged view of the XRD measurement results before and after the regeneration treatment of Experimental Examples 2 to 6.

[0053] As shown in Table 2, when the lithium content when the total composition of nickel, cobalt, and manganese was set to 1 was denoted as Li / NCM, the Li / NCM after coating, after charging, and after the immersion treatment were 1.07, 0.78, and 1.00, respectively. This indicates that the ratio of the lithium amount in the positive electrode increased due to the immersion treatment of the positive electrode in the treatment aqueous solution. That is, the active material was regenerated by immersing the electrode in the treatment aqueous solution containing the mediator. Further, after the regeneration treatment with the aqueous solution, K and Fe, which are components of the mediator, were not detected in the washed and dried electrode.

[0054] The XRD chart shown in FIG. 4 indicates that there is no change in the XRD peak width due to charging and the immersion treatment. FIG. 5 is an enlarged view of the range of 2θ = 64 to 70° of the XRD in FIG. 4. As shown in FIG. 5, the peak shifted from after coating to after charging. Further, from after charging to after the immersion treatment, the peak moved in the reverse direction, and the peak positions after the immersion treatment and after coating showed the same position. From the composition analysis results and the change in the XRD peak position, it was inferred that lithium in the active material was deficient due to charging, and lithium returned to the active material by the immersion treatment in the treatment aqueous solution. The fact that Li / NCM was 1.07 after coating indicates that excessive lithium was present in the positive electrode in addition to the active material. As shown in FIGS. 6 and 7, from the XRD measurement results of Experimental Examples 2 to 4, all the peaks that had shifted due to charging returned to the positions after coating, similar to Experimental Example 1. Also, it was found that in Experimental Example 5, all the peaks that had shifted due to charging returned to the positions after coating, similar to Experimental Examples 1 to 4. On the other hand, in Experimental Example 6, different from the other Experimental Examples 1 to 5, a peak appeared at a position different from that of the unused positive electrode.

[0055] In order to supply lithium to a lithium-deficient cathode, it is necessary for lithium ions and electrons to contact the lithium-deficient cathode simultaneously. When electrons are supplied through an external circuit, it is necessary to be constantly connected to the external circuit while performing the lithium supply process to the lithium-deficient cathode. On the other hand, when using a reductant of a mediator, which is a water-soluble compound, as an electron supply source, the lithium-deficient cathode only needs to be in contact with a solution in which both lithium ions and the reductant of the water-soluble compound are dissolved, and there is no particular need to connect to an external circuit. This indicates that in implementing the lithium supply process of the present disclosure, the state of the lithium-deficient cathode does not depend on the presence or absence of a current collector, a binder, or a conductive material. Also, when the reductant of the water-soluble compound is oxidized by the lithium-deficient cathode, electron donation to the lithium-deficient cathode occurs. Therefore, when the oxidation potential of the reductant of the water-soluble compound is higher than that of the lithium-deficient cathode, it is presumed that electron donation to the lithium-deficient cathode does not occur, and thus reduction of the lithium-deficient cathode does not occur. This shows that when the lithium-deficient cathode is reduced until it reaches the oxidation potential of the water-soluble compound, the lithium supply reaction stops, and the lithium-deficient cathode is not overly reduced. Also, in the examples, since there was no separation of the XRD peaks and the full width at half maximum was equivalent to that of the unused cathode, it was inferred that lithium supply to the lithium-deficient cathode was performed homogeneously. As mediators presumed to have a similar function, considering their potential and solubility in water, etc., for example, water-soluble anthraquinone disulfonate having a quinone skeleton can be mentioned. On the other hand, in Experimental Example 6 without a mediator, the XRD peaks did not return to the range of the unused composite material. Although there are reports that lithium can be replenished by heating such as in the hydrothermal method even during immersion in a lithium hydroxide solution as in Experimental Example 6 (Reference 2: Adv. Energy Mater. 2022, 2203093.), it was presumed that although the lithium supply reaction itself can occur at room temperature, the reaction is extremely slow.

[0056] The mediator used was potassium ferrocyanide, which is a ferrocyanide. Its redox potential against the standard hydrogen electrode (SHE) is 0.48 V, and it was speculated to be favorable for the reduction of the lithium-deficient positive electrode active material and the addition of lithium. Considering the redox potential, the mediator was speculated to be preferably a ferrocene compound including ferrocene and its derivatives, etc., whose redox potential against the SHE is in the range of -0.7 V to 0.6 V. It was speculated that the mediator preferably has a redox potential of 0.6 V or less against the standard hydrogen electrode (SHE), and is in the range of -0.7 V or more and 0.6 V or less. Also, from the viewpoint of suppressing water decomposition at this redox potential, the aqueous solution is preferably alkaline, and is preferably in the range of pH 9 or more and 14 or less. Also, considering the relationship between the regeneration function of the mediator to the active material and solubility, it was speculated that the concentration of the aqueous solution is preferably in the range of 0.01 mol / L or more and 8 mol / L or less. Also, considering the relationship of lithium replenishment, it was speculated that the concentration of lithium ions in the aqueous solution is preferably in the range of 0.1 mol / L or more and 8 mol / L or less.

[0057]

Table 1

[0058]

Table 2

[0059] 2. Recovery of the mediator and regeneration of the active material As an evaluation cell, a lithium-ion battery composed of a Cu foil negative electrode and a LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 positive electrode was fabricated. As the positive electrode, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A slurry of O2 / acetylene black / polyvinylidene fluoride (mass ratio 90:5:5) was coated on a stainless steel foil and vacuum dried at 120 °C for use. As the electrolyte, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 3:4:3) with lithium hexafluorophosphate (LiPF6) dissolved at a concentration of 1 mol / L was used. A polyethylene single-layer microporous membrane was used as the separator. The positive and negative electrodes were opposed to each other through a separator immersed in the electrolyte to fabricate a half cell made of stainless steel (SUS). The amount of the composite material of the positive electrode at this time was 17 mg. This cell was charged to a charged state (a state where the positive electrode was oxidized) at a current value that would result in a full charge in 10 hours at a temperature of 25 °C up to a voltage of 3.8 V. The battery charged up to 3.8 V was opened in an argon atmosphere to take out the positive electrode and washed with DMC. This charged positive electrode was separated from the composite material and the aluminum foil using a plastic spatula and used in the state of the composite material (also referred to as a lithium-deficient composite material or a charged composite material).

[0060] When performing the mediator recovery treatment (lithium replenishing solution recovery treatment), an acrylic cell was used. A connected cell with a cation exchange membrane was prepared with an working electrode chamber and a counter electrode chamber such that lithium ions could permeate through the cation exchange membrane. A graphite sheet, SUS304 mesh, an Ag / AgCl electrode, and nafion were used as the working electrode, counter electrode, reference electrode, and cation exchange membrane, respectively. The reference electrode was set on the counter electrode chamber side. Also, a nozzle for air bubbling was set on the working electrode side. Fig. 10 shows the state of the recovery treatment in Experimental Example 7. Fig. 10A is a schematic diagram showing the state of the experiment, Fig. 10B is a photograph showing the state of the experiment, and Fig. 10C is an explanatory diagram explaining the configurations of the working electrode chamber side and the counter electrode chamber side.

[0061] [Experimental Example 7] Lithium hydroxide was dissolved in ion-exchanged water to a concentration of 1 mol / L, and potassium ferricyanide (the oxidized form of potassium ferrocyanide) was dissolved to a concentration of 0.04 mol / L to prepare a lithium replenishing solution. 3 ml of this lithium replenishing solution was injected into the working electrode chamber side of the recovery device shown in Fig. 10, and 6 ml of a 1 mol / L aqueous lithium hydroxide solution was injected into the counter electrode chamber side. After starting air bubbling on the working electrode chamber side at 10 ml / min, electrolysis was carried out for 20 minutes while maintaining the working electrode at -1.0 V with respect to the reference electrode (recovery process). In another acrylic cell, about 70 mg of the charged composite material and a stirrer were placed, and 2.5 ml of the lithium replenishing solution after completion of electrolysis collected from the working electrode chamber was dropped. This solution was stirred at room temperature for 18 minutes and then allowed to stand for 2 minutes (regeneration process). Then, the supernatant after standing was collected and returned to the working electrode chamber again. Thereafter, the series of operations of electrolysis, collection, stirring, standing, and collection were performed 3 times. Thereafter, 3 ml of ion-exchanged water was injected into the cell containing the composite material, stirred for 2 minutes, allowed to stand for 2 minutes, and 3 ml of the supernatant was drained. Thereafter, the series of operations of ion-exchanged water injection, stirring, standing, and drainage were repeated 4 times. The wet powder remaining in the acrylic cell was vacuum dried overnight to obtain a dry powder. XRD measurement of the obtained dry powder was carried out.

[0062] [Experimental Example 8] Lithium hydroxide was dissolved in ion-exchanged water to a concentration of 1 mol / L, and potassium ferricyanide (the oxidized form of potassium ferrocyanide) was dissolved to a concentration of 0.1 mol / L to prepare a lithium replenishing solution. About 20 mg of the charged composite material and a stirrer were placed in an acrylic cell, and 3 ml of the lithium replenishing solution (without the recovery process) was dropped. This solution was stirred at room temperature for 60 minutes. After stopping the stirring and allowing it to stand for 2 minutes, 2.5 ml of the supernatant was drained. Thereafter, 3 ml of ion-exchanged water was injected into the cell containing the composite material, stirred for 2 minutes, allowed to stand for 2 minutes, and 3 ml of the supernatant was drained. Subsequently, the series of operations of ion-exchanged water injection, stirring, standing, and drainage were repeated 4 times. The wet powder remaining in the acrylic cell was vacuum dried overnight to obtain a dry powder. XRD measurement of the obtained dry powder was carried out.

[0063] (Results and Discussion) Figure 11 shows the XRD measurement results before and after the reproduction process of Experimental Examples 7 to 8. Figure 12 is an enlarged view of the XRD measurement results before and after the reproduction process of Experimental Examples 7 to 8. As shown in Figure 11, there were no peaks different from the unused active material in each state of Experimental Example 7 and Experimental Example 8, and it was found that no heterogeneous phase was generated. Also, as shown in Figure 12, in Experimental Example 7, the peak that had shifted in the charged state returned to the peak position equivalent to that of the unused active material after the lithium replenishment treatment. Similarly, in Experimental Example 8, although a peak shift was observed after the lithium replenishment treatment for the peak that had shifted in the charged state, it did not return to the position equivalent to that of the unused active material. It is known that there is a clear correlation between the XRD peak position and the lithium amount in the active material (Reference 3: J. Am. Chem. Soc. 2019, 141, 5097 - 5101.), and for Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 it is known that when x of O2 ranges from 0.5 to 1.0, the lattice constants a and c change monotonically. Therefore, it was estimated that the lithium amount in the active material after the lithium replenishment treatment in Experimental Example 7 had returned to about x = 1.0. Also, in Experimental Example 8, since the peak was slightly shifted toward the peak position of the unused active material, it was estimated that some lithium had been replenished, but the replenishment amount was insufficient compared to Experimental Example 7. Comparing Experimental Example 7 and Experimental Example 8, in Experimental Example 7, the water-soluble compound was in contact with the lithium-deficient cathode in the reduced state, while in Experimental Example 8, the water-soluble compound was in contact with the lithium-deficient cathode in the oxidized state. From this, it was found that even a water-soluble compound in the oxidized state can be used as a lithium replenishing solution if an operation of contacting the lithium-deficient cathode after electrochemically reducing it is performed.

[0064] Table 3 shows a comparison of the amounts of substances (however, estimated values calculated from the amounts used during the production of the positive electrode and the XRD peak positions) in each state of Experimental Examples 7 to 8. The charged states of Experimental Examples 7 to 8 were estimated from the peak positions of XRD to be states in which lithium was deficient up to about x = 0.77. When comparing the amount of lithium required to replenish lithium to the lithium-deficient positive electrode up to x = 1.00 and the amount of water-soluble compound contained in the lithium replenishing solution, the amount of water-soluble compound was less in Experimental Example 7 and more in Experimental Example 8. From Experimental Example 8, it was speculated that the function of replenishing lithium to the lithium-deficient positive electrode was insufficient even when the water-soluble compound was present in excess in the oxidized state. In Experimental Example 7, the water-soluble compound was present as a reduced form when in contact with the lithium-deficient positive electrode. However, since the ferricyanide ion used this time can only return one electron to the lithium-deficient positive electrode per molecule, the water-soluble compound was insufficient to replenish lithium up to x = 1.00. However, since the ferricyanide ion in the oxidized state became a reduced form during the energization operation in the working electrode chamber, lithium could be replenished to the lithium-deficient positive electrode again, and it was speculated that lithium could be replenished to the lithium-deficient positive electrode up to the lithium amount corresponding to x = 1.00 corresponding to XRD.

[0065]

Table 3

Explanation of Symbols

[0066] 10 Recycling device, 11 Recycling section, 12 Aqueous solution, 13 Aqueous solution, 20 Energy storage device, 21 Current collector, 22 Positive electrode composite layer, 23 Positive electrode sheet, 24 Current collector, 25 Negative electrode composite layer, 26 Negative electrode sheet, 28 Separator, 29 Ion conduction medium, 32 Cylindrical case, 34 Positive electrode terminal, 36 Negative electrode terminal, 50 Recovery section, 52 Container, 54 Ion exchange membrane, 60 Working electrode chamber, 62 Working electrode, 64 Nozzle, 70 Counter electrode chamber, 72 Counter electrode, 74 Reference electrode, 76 Electrolyte solution, 80 Control device.

Claims

1. A method for regenerating an active material used in a power storage device that stores and releases lithium, comprising: a regeneration step of reducing the active material lacking lithium from the stoichiometric composition and replenishing lithium ions in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE); A regeneration method comprising the above.

2. The regeneration method according to claim 1, wherein the mediator has a redox potential with respect to the standard hydrogen electrode (SHE) in the range of -2.3 V or more and 0.6 V or less.

3. The regeneration method according to claim 1 or 2, wherein the mediator is in the range where the concentration of the aqueous solution is 0.01 mol / L or more and 8 mol / L or less.

4. The regeneration method according to claim 1 or 2, wherein the mediator is at least one of a ferrocyanide and a ferrocene compound.

5. The regeneration method according to claim 1 or 2, wherein the aqueous solution has a pH in the range of 9 or more and 14 or less.

6. The regeneration method according to claim 1 or 2, wherein the aqueous solution has a lithium ion concentration in the range of 0.1 mol / L or more and 8 mol / L or less.

7. The regeneration method according to claim 1 or 2, wherein in the regeneration step, the active material is immersed in the aqueous solution for a treatment time in the range of 1 second or more.

8. The active material has a dualistic chemical composition of LiFePO 4 , LiMO 2 (where M is one or more of Ni, Co, and Mn), LiM a A b O 2 (where A is Al and a + b = 1), and is one or more of the above, the regeneration method according to claim 1 or 2.

9. A regeneration method according to claim 1 or 2, comprising: a recovery step of reducing the mediator oxidized in the regeneration step to restore the function of the mediator that reduces the active material; using the recovered mediator to perform the regeneration step again; A regeneration method.

10. The regeneration method according to claim 9, wherein in the recovery step, the mediator oxidized in the regeneration step is electrochemically reduced.

11. In the recovery step, an electrochemical cell is used that includes a working electrode chamber containing the aqueous solution containing the mediator oxidized in the regeneration step, a counter electrode chamber containing an electrolytic solution and separated from the working electrode chamber by an ion exchange membrane, a working electrode disposed in the working electrode chamber and in contact with the aqueous solution, a counter electrode disposed in the counter electrode chamber and in contact with the electrolytic solution, and a reference electrode, to electrochemically reduce the mediator oxidized in the regeneration step. The regeneration method according to claim 10.

12. In the recovery step, a lithium ion-containing aqueous electrolytic solution is used for the electrolytic solution, a cation exchange membrane is used for the ion exchange membrane, graphite is used for the working electrode, stainless steel is used for the counter electrode, and an Ag / AgCl electrode is used for the reference electrode. The playback method according to claim 11.

13. The playback method according to claim 9, wherein in the recovery step, lithium ions decreased from the aqueous solution in the playback step are further replenished.

14. A method for manufacturing a power storage device including an electrode having an active material that stores and releases lithium, a regeneration step of obtaining an active material in which lithium ions are replenished by reducing the active material in which lithium is deficient from the stoichiometric composition in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE), and then incorporating an electrode containing the active material; A method for manufacturing a power storage device including the above.

15. A regeneration device for an active material that stores and releases lithium and is used in a power storage device, a regeneration unit that reduces the active material in which lithium is deficient from the stoichiometric composition in an aqueous solution containing a redox mediator that oxidizes at a potential of 0.6 V or less with respect to the standard hydrogen electrode (SHE) and replenishes lithium ions; A regeneration device including the above.

16. The regeneration device according to claim 15, including a recovery unit that reduces the mediator oxidized in the regeneration unit and restores the function of the mediator that reduces the active material. A regeneration device.

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