JP2023128795A - Recovery method and method for manufacturing electricity storage device - Google Patents

Abstract

To perform capacity recovery of a power storage device including an olivine-type active material.SOLUTION: A recovery method for recovering the capacity of a power storage device using metal ions as carrier ions includes a recovery process of injecting a recovery agent, which is a solution containing an aromatic hydrocarbon compound in a reduced state and a metal ion of the same type as a carrier ion at a predetermined temperature range where the solution temperature is higher than room temperature, applying a constant voltage, maintaining a predetermined voltage lower than the full charge voltage, and restoring energy storage device capacity.SELECTED DRAWING: Figure 1

Description

This specification discloses a recovery method and a method for manufacturing an electricity storage device.

Conventionally, as a method to restore the capacity of electricity storage devices such as nonaqueous electrolyte secondary batteries whose capacity has deteriorated due to long-term storage or charge/discharge cycles, a third electrode is provided in addition to the positive and negative electrodes, and the third electrode and the positive electrode are connected. A method has been proposed in which carrier ions are supplied from the third electrode to the positive electrode by external short-circuiting (see, for example, Patent Document 1). Further, as a power storage device, one using olivine-type lithium iron phosphate as a positive electrode active material has been proposed (see, for example, Patent Document 2).

Japanese Patent Application Publication No. 2016-076358 Japanese Patent Application Publication No. 2009-104794

However, in Patent Document 1, there were problems such as the structure of the battery becoming complicated by incorporating the third electrode. For this reason, there has been a need to restore capacity without using a third electrode. Furthermore, there has been a desire for a novel recovery method that can recover degraded capacity for olivine-type positive electrode active materials such as those disclosed in Patent Document 2.

The present disclosure has been made to solve such problems, and the main purpose is to provide a novel recovery method for performing capacity recovery of a power storage device containing an olivine-type active material and a method for manufacturing a power storage device. shall be.

As a result of intensive research to achieve the above-mentioned object, the present inventors have found that a solution of a recovery agent containing a reduced aromatic hydrocarbon compound and a metal ion of the same type as the carrier ion of the electricity storage device is The present disclosure has been completed based on the discovery that the degraded capacity can be restored when the battery is charged into a power storage device at a temperature range of 100% and a predetermined voltage range.

That is, the recovery method for a power storage device disclosed in this specification is as follows:
A recovery method for recovering the capacity of an electricity storage device using metal ions as carrier ions,
For the electricity storage device containing an olivine-type compound as a positive electrode active material, a recovery agent, which is a solution containing an aromatic hydrocarbon compound in a reduced state and a metal ion of the same type as the carrier ion, is added at a predetermined temperature where the solution temperature is higher than room temperature. a recovery step in which the capacity of the electricity storage device is restored by injecting the electricity in a temperature range of , and maintaining a predetermined voltage lower than the full charge voltage by applying a constant voltage;
This includes:

Further, the method for manufacturing an electricity storage device disclosed in this specification includes:
A recovery step of recovering the capacity of the electricity storage device whose capacity has deteriorated using metal ions as carrier ions by the recovery method described above;
This includes:

With this recovery method and method for manufacturing an electricity storage device, it is possible to provide a novel method for recovering the capacity of an electricity storage device including a positive electrode active material of an olivine type compound. The reason why such an effect is obtained is surmised as follows. For example, a recovery agent containing a reduced aromatic hydrocarbon compound and metal ions acts directly on the positive electrode simply by being injected into the electricity storage device, causing a recovery reaction that supplies electrons and metal ions to the positive electrode. The driving force for this recovery reaction is considered to be the potential difference between the positive electrode and the recovery agent. When only injecting the recovery agent without applying a constant voltage, the potential of the positive electrode decreases as electrons and metal ions are supplied to the positive electrode, and the potential difference between the positive electrode and the recovery agent becomes small. On the other hand, when a recovery agent is injected and a predetermined voltage is maintained by applying a constant voltage, the potential of the positive electrode is kept high even if electrons and metal ions are supplied to the positive electrode, and the potential difference between the positive electrode and the recovery agent is reduced. kept high. As a result, the driving force for the recovery reaction is maintained at a high level, so that more metal ions can be supplied into the battery. In addition, in this recovery process, the recovery agent is used at a higher temperature and the recovery process is performed at a higher voltage, so the capacity can be fully recovered for the positive electrode active material of the olivine type compound, and the negative electrode etc. It is presumed that the impact is smaller.

FIG. 2 is a schematic diagram showing an example of a power storage device 20. An explanatory diagram showing an example of a recovery reaction scheme. An explanatory diagram conceptually showing a change in the potential difference ΔE _rec between the positive electrode and the recovery agent after injection of the recovery agent. Charging and discharging curves before and after recovery treatment in Experimental Examples 1 to 7. Measurement results of capacity changes after recovery processing in Experimental Examples 1 to 7.

The recovery method disclosed in this specification is a recovery method for recovering the capacity of an electricity storage device, and includes a recovery step of recovering the capacity of the electricity storage device using a recovery agent. The power storage device is not particularly limited as long as it uses metal ions as carrier ions, and for example, it uses Group 1 ions such as lithium, sodium, and potassium, and Group 2 ions such as magnesium, calcium, and strontium as carrier ions. It may also be something to do. Further, the power storage device may be a non-aqueous electrolyte secondary battery, an ion secondary battery such as a lithium ion secondary battery, a metal secondary battery such as a lithium metal secondary battery, or the like. Below, as an example, a case where the power storage device is a lithium ion secondary battery will be mainly described.

(Electricity storage device)
The electricity storage device includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode may include a positive electrode active material that can insert and release lithium ions. The negative electrode may include a negative electrode active material capable of intercalating and deintercalating lithium ions. The non-aqueous electrolyte may be interposed between the positive electrode and the negative electrode to conduct lithium ions.

For the positive electrode, for example, a positive electrode active material, a conductive material, and a binder are mixed, an appropriate solvent is added to make a paste-like positive electrode mixture, and the mixture is applied and dried on the surface of a current collector, and then mixed as necessary. It may be formed by compression in order to increase the electrode density. This positive electrode active material may be an olivine type compound, such as lithium iron phosphate. This lithium iron phosphate may be added with an additional element such as manganese. The positive electrode active material may have an oxidation-reduction potential of 3.5 V or more, or 4.0 V or more based on Li metal.

In the positive electrode, the conductive material is, for example, graphite such as natural graphite (scaly graphite, flaky graphite) or artificial graphite, acetylene black, carbon black, Ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel), etc. , aluminum, silver, gold, etc.) or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferred as the conductive material from the viewpoint of electronic conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles, and includes, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resin such as fluororubber, or polypropylene, Thermoplastic resins such as 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. Further, an aqueous dispersion of cellulose-based carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), polyvinyl alcohol, etc., which is an aqueous binder, can also be used. Examples of solvents for dispersing the positive electrode active material, conductive material, and binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, and N,N-dimethylaminopropylamine. Organic solvents such as , ethylene oxide, and tetrahydrofuran can be used. Alternatively, the active material may be slurried with latex such as SBR by adding a dispersant, a thickener, etc. to water. 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. Application methods include, for example, roller coating using an applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Any of these methods can be used to obtain an arbitrary thickness and shape. The basis weight of the positive electrode composite material is not particularly limited, but may be, for example, more than 5 mg/cm ² , more than 6 mg/cm ² , or more than 7 mg/cm ² . The basis weight of the positive electrode composite material may be, for example, 20 mg/cm ² or less. Current collectors include aluminum, titanium, stainless steel, nickel, iron, sintered carbon, conductive polymers, conductive glass, etc., as well as aluminum, copper, etc. for the purpose of improving adhesiveness, conductivity, and oxidation resistance. It is possible to use materials whose surfaces have been treated with carbon, nickel, titanium, silver, etc. It is also possible to oxidize the surface of these materials. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded material, lath material, porous material, foam material, and fiber group formed material. The thickness of the current collector used is, for example, 1 to 500 μm.

The negative electrode may be formed by closely adhering a negative electrode active material and a current collector, or, for example, by mixing a negative electrode active material, a conductive material, and a binding material, and adding an appropriate solvent to form a paste-like negative electrode composite. The material may be applied and dried on the surface of the current collector, and if necessary, compressed to increase the electrode density. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbonaceous materials capable of intercalating and deintercalating lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of 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 operating potentials close to those of metallic lithium, and can be charged and discharged at high operating voltages.When using lithium salts as supporting salts, they suppress self-discharge. In addition, it is preferable because irreversible capacity during charging can be reduced. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. Among these, carbonaceous materials are preferable as the negative electrode active material from the viewpoint of safety. Further, as the conductive material, binding material, solvent, etc. used in the negative electrode, those exemplified for the positive electrode can be used. The negative electrode active material may have an oxidation-reduction potential of 1.0 V or less, 0.5 V or less, or 0.3 V or less based on Li metal. The basis weight of the negative electrode composite material may be, for example, more than 3 mg/cm ² or more than 4 mg/cm ² . The basis weight of the negative electrode composite material may be, for example, 15 mg/cm ² or less. The current collector of the negative electrode is made of copper, nickel, stainless steel, titanium, aluminum, fired carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as materials with improved adhesiveness, conductivity, and reduction resistance. For this purpose, for example, copper or the like whose surface is treated with carbon, nickel, titanium, silver, etc. can also be used. It is also possible to oxidize the surface of these materials. The shape of the current collector can be similar to that of the positive electrode.

The non-aqueous electrolyte may include a supporting salt and an organic solvent. Examples of supporting salts include inorganic salts such as LiPF ₆ , LiClO ₄ , LiAsF ₆ , and LiBF ₄ , LiN(FSO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , and LiN(C ₂ F ₅ SO ₂ ) _{2 .} Organic salts such as These supporting salts may be used alone or in combination. The concentration of the supporting salt is preferably 0.1 to 2.0M, more preferably 0.8 to 1.2M. 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, and chain ethers. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and methylethyl carbonate. Examples of the cyclic ester include gamma-butyrolactone and gamma-valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of chain ethers include dimethoxyethane and ethylene glycol dimethyl ether. These may be used alone or in combination. In addition, as the nonaqueous electrolyte, nitrile solvents such as acetonitrile and propylnitrile, ionic liquids, gel electrolytes, and the like may be used. The nonaqueous electrolyte may contain additives such as a film forming agent and a flame retardant.

The electricity 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 power storage devices, but examples include polymeric nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous membranes made of olefin resins such as polyethylene and polypropylene. can be mentioned. These may be used alone or in combination.

The shape of the power storage device is not particularly limited, and examples thereof include a coin shape, a button shape, a sheet shape, a stacked type, a cylindrical shape, a flat shape, a square shape, and the like. Further, the present invention may be applied to large-sized vehicles used in electric vehicles and the like. FIG. 1 is a schematic diagram showing an example of a power storage device 20. This electricity storage device 20 includes a cup-shaped battery case 21, a positive electrode 22 that has a positive electrode active material and is provided at the bottom of the battery case 21, and a negative electrode active material that is connected to the positive electrode 22 through a separator 24. A negative electrode 23 provided at opposing positions, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed in the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. There is. In this electricity storage device 20, the space between the positive electrode 22 and the negative electrode 23 is filled with a non-aqueous electrolyte 27.

(Recovery agent)
The recovery agent is a solution containing an aromatic hydrocarbon compound in a reduced state and metal ions of the same type as the carrier ions of the electricity storage device. The restoring agent may be a restoring agent prepared in advance, or may be prepared in the preparation process of preparing the restoring agent. In the recovery agent, the reduced aromatic hydrocarbon compound and the metal ion may be dissociated or associated. The recovery agent may contain an electrolyte solution in addition to an arenide solution containing a reduced aromatic hydrocarbon compound and metal ions of the same type as the carrier ions of the electricity storage device. The recovery agent may be an arenide solution without containing an electrolyte. The arenide solution may further contain an organic solvent.

In the recovery agent, the aromatic hydrocarbon compound is preferably polyacene or polyphenyl. Polyacene is a compound having a structure in which a plurality of benzene rings are condensed, and examples include naphthalene, anthracene, tetracene, and pentacene. Polyphenyl is a compound having a structure in which a plurality of phenyl groups are connected by single bonds, and includes biphenyl, orthoterphenyl, metaterphenyl, paraterphenyl, paraquaterphenyl, paraquinkyphenyl, and the like. Polyacene and polyphenyl may have a substituent on the aromatic ring or may contain a heteroatom within the aromatic ring. Examples of the substituent include a halogen atom, an alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, and a hydroxyl group. Examples of heteroatoms include nitrogen, oxygen, sulfur, and the like. Examples of polyacenes containing heteroatoms in the aromatic ring include quinoline, chromene, and acridine. Examples of polyphenyl containing a heteroatom in the aromatic ring include bipyridine. Among those mentioned above, the aromatic hydrocarbon compound is preferably one or more of naphthalene, biphenyl, anthracene, orthoterphenyl, and paraterphenyl, and more preferably one or more of naphthalene and biphenyl. The aromatic hydrocarbon compound may be, for example, one or more of formula (1) and formula (2). The aromatic hydrocarbon compound in a reduced state is, for example, the above-mentioned aromatic hydrocarbon compound in a reduced state (also referred to as a reduced product), and is, for example, a radical anion. The aromatic hydrocarbon compound in a reduced state may be, for example, one or more of the reduced form of the compound of formula (1) and the reduced form of the compound of formula (2).

In the recovery agent, the metal ions may be of the same type as the carrier ions of the electricity storage device, but are preferably one or more of alkali metal ions such as lithium ions, sodium ions, and potassium ions.

The recovery agent may contain one or more compounds of formula (3) and formula (4). In the compounds of formula (3) and formula (4), the radical anion part is the above-mentioned reduced aromatic hydrocarbon compound, and the metal cation part is the above-mentioned metal ion.

The recovery agent may include an organic solvent. The organic solvent is preferably a solvent having an ether skeleton, and may be a cyclic ether or a chain ether. The recovery agent may include one or more solvents among tetrahydrofuran (THF), dimethoxyethane (DME), diethoxyethane (DEE), dioxolane (DOL), and dioxane (DOX). It is preferable that the recovery agent contains one or more solvents of tetrahydrofuran and dimethoxyethane, and dimethoxyethane is more preferable from the viewpoint of suppressing deterioration of charge/discharge characteristics after the recovery treatment.

The recovery agent may be obtained by adding an aromatic hydrocarbon compound and a metal in a metallic state rather than an ionic state into a solvent. For example, it may be obtained by one or more of formula (5) and formula (6). More specifically, as shown in formulas (7) to (9), naphthalene, diphenyl, or terphenyl may be reacted with Li metal in a THF solvent. Further, according to formulas (7) to (9), naphthalene, diphenyl, terphenyl and Li metal may be reacted in a DME solvent. In this way, a recovery agent containing a reduced aromatic hydrocarbon compound and metal ions can be easily prepared. The recovery agent may be prepared by adding a metal to a precursor obtained by adding an aromatic hydrocarbon compound to a solvent. The recovery agent may be prepared under an inert atmosphere such as an argon atmosphere. The recovery agent may be prepared in a low dew point environment such as a dew point of -20°C or lower, -40°C or lower, or -60°C or lower. The recovery agent may be prepared by stirring a solvent, an aromatic hydrocarbon compound, and a metal, and in this case, a stirrer or the like may be used.

The solution containing the aromatic hydrocarbon compound in the reduced state, the metal ion, and the organic solvent described above is also referred to as an arenide solution. This arenide solution may be used as a recovery agent in its original form, or may be mixed with an electrolyte solution to adjust its reducing power and used as a recovery agent. In the arenide solution, the concentration of the aromatic hydrocarbon compound and the metal ion in the reduced state may be 0.05 mol/L or more and 1.1 mol/L or less, and 0.1 mol/L or more and 1.1 mol/L or less, respectively. The amount may be 0.5 mol/L or more and 1.0 mol/L or less. Further, this concentration may be lower than the solubility. In addition, the ratio M A /MB of the number of moles M _A (mol) _of the aromatic hydrocarbon compound in the reduced form contained in the recovery agent and the number M _B ( _mol ) of moles of the metal ion is 1/1. The ratio is preferably 1.1/1.0 to 1.0/1.1, or 1.2/1.0 to 1.0/1.2.

When the recovery agent contains an electrolytic solution in addition to the arenide solution, the electrolytic solution may be, for example, a non-aqueous electrolytic solution as exemplified as a non-aqueous electrolytic solution for a power storage device, and a battery solvent as exemplified as a non-aqueous electrolytic solution, It may also contain a supporting salt exemplified as a non-aqueous electrolyte. The battery solvent contained in the electrolytic solution may be different from the organic solvent of the arenide solution, but is preferably one or more of cyclic carbonates, chain carbonates, and cyclic esters, and preferably one or more of cyclic carbonates, chain carbonates, and cyclic esters. More preferably 1 or more. The battery solvent may be one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt of the electrolyte may be different from the solute of the arenide solution, but it may be an inorganic salt such as LiPF ₆ or lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(fluorosulfonyl)imide. (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which contain imide-based anions, and the like, and those containing imide-based anions are more preferable. The electrolyte may contain additives such as film forming agents and flame retardants. The composition of the electrolytic solution may be the same as or different from the non-aqueous electrolytic solution of the electricity storage device to be recovered. When the recovery agent contains an electrolyte, the content of the electrolyte may be 30 volume% or more and 70 volume% or less, 30 volume% or more and 60 volume% or less, or 30 volume% or more and 50 volume% or less. good. When preparing a recovery agent containing an electrolytic solution, the arenide solution and the electrolytic solution may be mixed, and it is more preferable to use the recovery agent immediately after mixing. Immediately after mixing the arenide solution and the electrolytic solution, the solution temperature rises to a range of, for example, 36° C. or higher and 45° C. or lower, which is preferable for capacity recovery of the electricity storage device.

The recovery agent may have a redox potential higher than that of the negative electrode and lower than that of the positive electrode. The oxidation-reduction potential of the recovery agent may be, for example, 0.5 V or more and 2.5 V or less, 1.0 V or more and 2.0 V or less, or 1.2 V or more and 1.9 V or less based on Li metal, for example. .

(Recovery process)
In this process, the recovery agent is injected into the energy storage device at a predetermined temperature range where the solution temperature of the recovery agent is higher than room temperature, and a predetermined voltage lower than the full charge voltage is maintained by applying a constant voltage to the energy storage device. Perform processing to restore capacity. The power storage device to be recovered is a battery whose capacity has deteriorated (also referred to as a degraded battery), and may be, for example, a battery whose capacity has deteriorated relative to the rated capacity of the power storage device. The power storage device to be recovered may be an unused product or a used product. Even if the product is unused, its capacity may deteriorate due to long-term storage.

The solution temperature when the recovery agent is added is in a predetermined temperature range higher than normal temperature (20°C, etc.), and preferably in a temperature range of 36°C or higher and 45°C or lower, for example. When the solution temperature is 36° C. or higher, precipitation and gelation of substances contained in the recovery agent can be further suppressed, and when the solution temperature is 45° C. or lower, deterioration of the recovery agent can be further suppressed, which is preferable. In addition, when the recovery agent is a mixed solution of an arenide solution and an electrolyte solution, it is preferable to add it to the electricity storage device immediately after mixing the arenide solution and the electrolyte solution. This is because when these solutions are mixed, the temperature increases and the temperature falls within the vapor temperature range. Immediately after mixing may be any time before the solution temperature drops to room temperature, and includes, for example, within 5 minutes, 3 minutes, or 2 minutes after mixing.

In the recovery step, the predetermined voltage for maintaining a constant voltage may be a voltage lower than the full charge voltage, but it is preferably a voltage such that the potential of the positive electrode is higher than the potential of the recovery agent. The full charge voltage may be the upper limit charge voltage set for the power storage device (battery before deterioration). The predetermined voltage may be determined as appropriate depending on the configuration of the battery to be recovered, but may be, for example, 3.6 V or more and less than 4.1 V, 3.8 V or more, 3.9 V or more, or 4. It may be set to .0V or less. Capacity recovery can be sufficiently performed when the constant voltage is maintained in a range of 3.6 V or more and less than 4.1 V.

In this step, prior to injecting the recovery agent, voltage adjustment may be performed to bring the electricity storage device to the above-mentioned predetermined voltage. In that case, for example, the voltage of the power storage device may be adjusted by charging with constant current charging (CC charging) or constant current constant voltage charging (CCCV charging). Although it is not necessary to perform this voltage adjustment, it is preferable that the voltage of the electricity storage device to be recovered is the above-mentioned predetermined voltage.

In this step, when injecting the recovery agent, the power storage device may be unsealed, the recovery agent may be injected, and the unsealed portion may be closed, or the recovery agent may be injected into the power storage device and the perforation may be closed. When injecting the recovery agent, it may be injected under an inert atmosphere such as an argon atmosphere. The recovery agent may be injected so as to be in contact with at least the positive electrode, but it may be mixed with the non-aqueous electrolyte. The injection amount of the recovery agent can be determined as appropriate depending on the configuration of the electricity storage device, the degree of deterioration, and the like. The injection amount of the recovery agent may be, for example, 1% or more and 100% or less, 10% or more and 75% or less, or 25% or more with respect to the volume [mL] of the non-aqueous electrolyte contained in the electricity storage device. It may be 50% or less. The constant voltage application may be continued before or during the injection of the recovery agent, or after the recovery agent is injected, the voltage drop in the electricity storage device due to the supply of metal ions to the positive electrode is so small that it can be ignored. (for example, within 5 minutes, preferably within 3 minutes, more preferably within 1 minute). The constant voltage application time can be appropriately determined depending on the configuration of the electricity storage device, the degree of deterioration, the amount of recovery agent injected, and the like. For example, the injection amount of the recovery agent may be constant, and the constant voltage application time may be adjusted depending on the configuration and degree of deterioration of the electricity storage device. The constant voltage application time may be, for example, 1 hour or more and 48 hours or less, 6 hours or more and 36 hours or less, or 12 hours or more and 24 hours or less. In addition, when applying a constant voltage before the injection of the recovery agent is completed, the constant voltage application time after the injection of the recovery agent is completed is defined as the constant voltage application time.

In this step, when a recovery agent is injected, a recovery reaction as shown in FIG. 2, for example, is thought to occur. FIG. 2 is an explanatory diagram showing an example of a recovery reaction scheme, and is an explanatory diagram showing a scheme when the positive electrode active material is an olivine-type compound such as lithium iron phosphate. FIG. 3 is an explanatory diagram conceptually showing a change in the potential difference ΔE _rec between the positive electrode and the restoring agent after the restoring agent is injected, and FIG. 3A is an estimated diagram when the restoring agent is left in an open circuit state after the restoring agent is injected. , FIG. 3B is an estimated diagram when a predetermined voltage is maintained by applying a constant voltage while injecting a restoring agent. In FIG. 2, the metal ion is described as Li ⁺ , the radical anion as Are·-, and the olivine type compound as Li _ny MePO ₄ . As shown in Figure 2, in the recovery agent, a compound containing a radical anion of an aromatic hydrocarbon compound and a metal ion functions as a reducing agent that donates electrons. Electrons and metal ions are donated to the positive electrode, allowing the capacity to be restored. If the recovery agent is simply injected and left in an open circuit state without applying a constant voltage, the positive electrode potential will decrease as the recovery reaction progresses, as shown in Figure 3A, and the reaction will slow down. It is considered that the potential difference ΔE _rec between the positive electrode and the recovery agent, which serves as a driving force, decreases as the recovery reaction progresses to ΔE _rec.1 > ΔE _rec.2 > ΔE _rec.3 . Therefore, it is thought that the effect of the recovery agent gradually diminishes. On the other hand, when a recovery agent is injected and a predetermined voltage is maintained by applying a constant voltage, as shown in FIG. It is considered that the potential difference △E _rec between the positive electrode and the recovery agent, which acts as a force, is kept approximately constant as △E _rec.1 ≒△E _rec.2 ≒△E _rec.3 even as the recovery reaction progresses. At this time, the electrons donated from the recovery agent to the positive electrode are immediately sent to the negative electrode by applying a constant voltage, and the metal ions supplied to the positive electrode also move to the negative electrode. There exists an empty orbit that accepts It is thought that this makes it possible to maintain a high reaction driving force while recovering the battery capacity (while increasing the amount of metal ions in the battery) even when using an electrode with relatively high resistance. Therefore, it is considered that the recovery agent can be used effectively and the capacity of the battery after recovery is further improved. In addition, the activity of radical anions of aromatic hydrocarbon compounds can be moderately suppressed by applying a constant voltage, and the residual radical anions of aromatic hydrocarbon compounds can be suppressed by effectively using a recovery agent. It is thought that the deterioration of charge-discharge characteristics after recovery is further suppressed. In this way, the capacity of the electricity storage device is recovered, and an electricity storage device (also referred to as a recovery battery) whose capacity has been recovered is obtained.

In the method for recovering an electricity storage device detailed above, the capacity of the electricity storage device can be recovered by injecting a predetermined recovery agent. In this recovery method, by injecting a recovery agent and maintaining a predetermined voltage by applying a constant voltage, the capacity of the battery after recovery can be further improved. The reason why such an effect is obtained is surmised as follows. For example, a recovery agent containing a reduced aromatic hydrocarbon compound and metal ions acts directly on the positive electrode simply by being injected into the electricity storage device, causing a recovery reaction that supplies electrons and metal ions to the positive electrode. The driving force for this recovery reaction is considered to be the potential difference between the positive electrode and the recovery agent. When only injecting the recovery agent without applying a constant voltage, the potential of the positive electrode decreases as electrons and metal ions are supplied to the positive electrode, and the potential difference between the positive electrode and the recovery agent becomes small. On the other hand, when a recovery agent is injected and a predetermined voltage is maintained by applying a constant voltage, the potential of the positive electrode is kept high even if electrons and metal ions are supplied to the positive electrode, and the potential difference between the positive electrode and the recovery agent is reduced. kept high. As a result, the driving force for the recovery reaction is maintained at a high level, so that more metal ions can be supplied into the battery. Furthermore, in this recovery treatment, since the recovery treatment is performed using the recovery agent at a temperature higher than room temperature, it is possible to further suppress fluidity reduction due to gelation of the recovery agent and precipitation of contained components such as supporting salts. Therefore, it is presumed that a higher recovery effect can be obtained by further increasing the dispersibility of the recovery agent. Furthermore, in this recovery process, since the recovery process is performed at a higher voltage, it is possible to sufficiently recover the capacity of the positive electrode active material of the olivine type compound, and it is presumed that there is less impact on the negative electrode etc. .

It goes without saying that the present disclosure is not limited to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

For example, in the embodiment described above, a method for recovering an electricity storage device has been described, but in this method for recovering an electricity storage device, a new non-aqueous electrolytic secondary battery with recovered capacity is manufactured using an electricity storage device whose capacity has been degraded. I can do it. Therefore, this recovery method may be a method for manufacturing a power storage device. In this manufacturing method, the power storage device may be manufactured by performing the recovery step in the above-described power storage device recovery method. The method for manufacturing a power storage device may include a preparation step of preparing a power storage device with degraded capacity using metal ions as carrier ions, and a recovery step of restoring the capacity of the power storage device using the above-described power storage device recovery method. good. The electricity storage device prepared in the preparation step can be the same as the degraded battery described in the embodiment described above.

Hereinafter, an example in which a lithium ion battery is recovered using the power storage device recovery method of the present disclosure will be described as an example. Note that Experimental Examples 4 to 7 correspond to Examples, and Experimental Examples 1 to 3 correspond to Comparative Examples. It goes without saying that the present disclosure is not limited to the following examples in any way, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

[Experiment example 1]
(Electricity storage device (battery before deterioration))
The positive electrode contained 92% by mass of LiFePO ₄ (LFP, synthetic product) as a positive electrode active material, 5% by mass of acetylene black (manufactured by Denka Corporation) as a conductive material, and polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder. ) was formed on one side of an aluminum current collector foil to have a basis weight of 7 mg/cm ² . The negative electrode contained 98% by mass of graphite (OMAC1.5s, manufactured by Osaka Gas Chemicals) as a negative electrode active material, 1% by mass of carboxymethyl cellulose (manufactured by Daicel) as a binder, and styrene-butadiene rubber (as a binder). A negative electrode composite material containing 1% by mass of (manufactured by JSR) was used, which was formed on one side of a copper current collector foil so that the basis weight was 4 mg/cm ² . The electrolyte was prepared by dissolving LiPF ₆ to a concentration of 1.1M in a mixed solvent containing 30% by volume of ethylene carbonate, 40% by volume of dimethyl carbonate, and 30% by volume of ethyl methyl carbonate. was used. A laminate cell was prepared by sandwiching a polypropylene separator impregnated with 1 mL of electrolyte between the positive electrode and the negative electrode. This was used as a battery before deterioration. The electrode area of the cell was 10 cm ² for both the positive and negative electrodes. When the resistance of the battery before deterioration was measured using a digital multimeter, the cell resistance was 10 Ωcm ² . In this electricity storage device, the discharge lower limit voltage determined according to the battery configuration was 3.0V, and the charge upper limit voltage was 4.1V.

(Deteriorated battery)
In the produced laminate cell, Li was removed from the positive electrode by charging it to a capacity (SOC = 50%, 6mAh) corresponding to 50% of the cell's electric capacity (12mAh) in a voltage range of 3.0V to 3.65V. By pulling it out, a positive electrode with a simulated capacity reduction was obtained (also referred to as a degraded positive electrode). Thereafter, the cell was disassembled and the degraded positive electrode was taken out, and then a laminate cell was produced in the same manner as in the production of the battery before degradation, except that this degraded positive electrode was used as the positive electrode. This was used as a degraded battery.

(Recovery agent)
Under an inert atmosphere, naphthalene is dissolved in dimethoxyethane (DME) solvent to a concentration of 1.0 mol/L, and then lithium metal corresponding to 1.0 mol/L is added and stirred to form the above formula ( A dark green radical anion liquid composition (lithium naphthalenide/DME), which is an arenide solution, was prepared by the reaction shown in 7). Thereafter, the arenide solution and the electrolytic solution were mixed at a volume ratio of 5:5 to prepare a recovery agent. In addition to LiPF ₆ , lithium bis(fluorosulfonyl)imide (LiFSI) was used as the supporting salt contained in the electrolytic solution. Further, a radical anion liquid composition (lithium naphthalenide/THF) was prepared by performing the same treatment as described above except that tetrahydrofuran (THF) was used instead of DME as the solvent for the arenide solution.

(Recovery of deteriorated battery)
Adjust the degraded battery prepared above to the cell voltage shown in Table 1, inject the recovery agent prepared above with a 0.5 mL pipette, and perform recovery treatment under constant voltage maintenance or open circuit conditions at the cell voltage shown in Table 1. was carried out for 24 hours. The increase in capacity before and after treatment was calculated from the capacity before and after treatment. In addition, after the recovery process, a charge/discharge test was performed at 1.2 mA in the voltage range of 3.0 V to 3.65 V above, and the discharge capacity was measured. The change in capacity with respect to the capacity before charging (recovery capacity: mAh) I asked for

[Experiment Examples 1 to 3]
In the above test, the solvent of the arenide solution was DME, the supporting salt of the electrolyte contained in the recovery agent was LiPF ₆ , the arenide solution and the electrolyte were mixed and left to stand, the temperature of the recovery agent was 25°C, and the voltage was 3. Experimental example 1 was obtained by maintaining a constant voltage of 6V. Further, Experimental Example 2 was prepared in the same manner as Experimental Example 1 except that the supporting salt of the electrolyte contained in the recovery agent was LiFSI and the recovery treatment was performed in an open circuit after the recovery agent was added. Further, Experimental Example 3 was the same as Experimental Example 1 except that the supporting salt of the electrolytic solution contained in the recovery agent was LiFSI.

[Experiment Examples 4 to 7]
In the above test, the solvent of the arenide solution was DME, the supporting salt of the electrolyte contained in the recovery agent was LiFSI, and immediately after mixing the arenide solution and the electrolyte, the recovery agent was put into the cell at a temperature of 40°C, and the voltage was Experimental example 4 was one in which the voltage was maintained at a constant voltage of 3.6V. Further, Experimental Example 5 was the same as Experimental Example 4 except that the voltage was maintained at a constant voltage of 4.0V. Further, Experimental Example 6 was prepared in the same manner as Experimental Example 4 except that the supporting salt of the electrolyte contained in the recovery agent was LiPF ₆ . Experimental Example 7 was the same as Experimental Example 4 except that THF was used as the solvent for the arenide solution.

[Results and discussion]
The composition of the arenide solutions of Experimental Examples 1 to 7, the supporting salt of the electrolyte added to the recovery agent, the mixing ratio thereof, the timing of introducing the recovery agent into the deteriorated cell and the solution temperature of the recovery agent at the time of injection, the voltage conditions of recovery treatment, Table 1 summarizes the voltage treatment conditions and the capacitance changes after the recovery treatment. FIG. 4 shows the charge/discharge curves before and after the recovery treatment for Experimental Examples 1 to 7, and FIGS. 4A to 4G are for Experimental Examples 1 to 7, respectively. FIG. 5 shows the measurement results of the capacitance changes after the recovery treatment in Experimental Examples 1 to 7.

As shown in Table 1 and Figures 4 and 5, in the recovery treatment at a cell voltage of 3.6V in which the temperature of the recovery agent was low in Experimental Examples 1 to 3, the capacity did not recover, and some even decreased. This was presumed to be because under the recovery condition of 3.6V, unreacted substances of the solution of the recovery agent that had been introduced remained and deteriorated the negative electrode member. On the other hand, in Experimental Example 4 in which the temperature of the recovery agent was higher, it was found that the capacity could be recovered although the recovery width was small. Furthermore, it was found that higher recovery capacity could be obtained by constant voltage treatment at 4.0 V in Experimental Examples 5 and 6. By maintaining the constant voltage cell voltage at a higher voltage of 4.0 V during the recovery process, the introduced lithium naphthalenide supplies electrons and Li ⁺ to the LFP positive electrode, and at the same time unreacted It is assumed that this is because by decomposing the lithium naphthalenide, capacity recovery and subsequent side reactions could be prevented. Furthermore, from the results of Experimental Examples 5 and 6, it was found that the higher the solution temperature of the recovery agent, the less the influence of the type of supporting salt of the electrolytic solution on the capacity recovery effect. Moreover, from the results of Experimental Example 7, it was found that a good recovery capacity can be obtained even when the solvent of the arenide solution is DME or THF. In addition, the recovery agent. It was confirmed that when the solution temperature was lower than 36° C., precipitates were formed and the fluidity decreased.

As shown in Experimental Examples 1 to 3, under the same treatment conditions as layered rock salt type LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM), etc. In the recovery treatment, a sufficient recovery effect could not be obtained in a power storage device using olivine-type LiFePO ₄ as a positive electrode active material. On the other hand, as shown in Experimental Examples 4 to 7, in a power storage device using LiFePO ₄ as a positive electrode active material, the solution temperature of the recovery agent is set to 36°C or higher, or even 40°C or higher, and the temperature is relatively high from the time of adding the recovery agent. It has become clear that the capacity recovery can be sufficiently performed by performing a recovery process that maintains a constant voltage at a high voltage of 3.6V to 4.0V. Further, it was inferred that it is more preferable for the electrolytic solution to be mixed with the recovery agent to contain the same type of battery solvent as that used in the electricity storage device, and to have a supporting salt containing an imide-based anion. In this regard, since the layered rock salt type positive electrode active material has low resistance, it is presumed that the recovery effect can be obtained regardless of the state of the recovery agent. On the other hand, since olivine-type positive electrode active materials have higher resistance than layered rock salt-type positive electrode active materials, they are affected by the state of the recovery agent, and the same treatment as for layered rock-salt-type positive electrode active materials has no recovery effect. This is thought to be because it is difficult to obtain.

20 electricity storage device, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 non-aqueous electrolyte.

Claims (8)

A recovery method for recovering the capacity of an electricity storage device using metal ions as carrier ions,
For the electricity storage device containing an olivine-type compound as a positive electrode active material, a recovery agent, which is a solution containing an aromatic hydrocarbon compound in a reduced state and a metal ion of the same type as the carrier ion, is added at a predetermined temperature where the solution temperature is higher than room temperature. a recovery step in which the capacity of the electricity storage device is restored by injecting the electricity in a temperature range of , and maintaining a predetermined voltage lower than the full charge voltage by applying a constant voltage;
Recovery methods including. The recovery method according to claim 1, wherein in the recovery step, the recovery agent having the temperature range of 36°C or more and 45°C or less is injected. The recovery method according to claim 1 or 2, wherein in the recovery step, a constant voltage is applied at the predetermined voltage in a range of 3.6V or more and less than 4.1V. In the recovery step, the recovery agent containing one or more of the reduced form of the compound of formula (1) and the reduced form of the compound of formula (2) is used as the aromatic hydrocarbon compound in the reduced state;
The recovery method according to any one of claims 1 to 3.

In the recovery step, an arenide solution containing the aromatic hydrocarbon compound in a reduced state, a metal ion of the same type as the carrier ion, and an organic solvent, and an electrolyte solution containing a battery solvent and a supporting salt used in the electricity storage device. The recovery method according to any one of claims 1 to 4, wherein the recovery agent is a mixture of the following. 6. The recovery step uses the recovery agent containing the organic solvent which is one or more of dimethoxyethane (DME) and tetrahydrofuran (THF), and the supporting salt containing an imide anion. How to recover. 7. The recovery method according to claim 1, wherein in the recovery step, the recovery agent is introduced into the electricity storage device immediately after mixing the arenide solution and the electrolytic solution. A recovery step of recovering the capacity of the electricity storage device whose capacity has deteriorated using metal ions as carrier ions by the recovery method according to any one of claims 1 to 7;
A method for manufacturing a power storage device including:

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