Method for using power storage device and dormant agent

Abstract

To enable a power storage device to be charged and discharged again after being temporarily inactivated.SOLUTION: A method for using a power storage device having a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material includes: a dormancy starting step of adding a dormant agent containing a redox shuttle agent whose oxidation-reduction potential is lower than the negative electrode material and higher than the positive electrode material and non-aqueous media to deactivate the power storage device; and a dormancy ending step of applying a current from outside to the deactivated power storage device to enable it to be charged and discharged again. The redox shuttle agent is, for example, a fluorenone-based compound having a fluorenone skeleton. Alternatively, the redox shuttle agent is a compound that is deactivated by forming a dimer during oxidation-reduction.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method of using a power storage device and a dormancy agent.

Background Art

[0002] Conventionally, when recycling or disposing of a power storage device such as a non-aqueous electrolyte secondary battery, an inactivation treatment for inactivating the recovered battery has been performed. As such a treatment, for example, it is possible to connect the recovered battery to a charge / discharge device and discharge it to 0 V, but in that case, the discharging may take time. Further, when the recovered battery is a battery after the operation of a current interruption mechanism (CID), it has not been possible to discharge the battery itself. Therefore, it has been proposed to add an inactivating agent containing a phenothiazine-based redox shuttle agent and a non-aqueous solvent to the inside of the recovered battery (see Patent Document 1). Thereby, the battery voltage of the non-aqueous secondary battery can be safely and rapidly decreased without using a charge / discharge device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when transporting or storing a power storage device, etc., it may be desired to temporarily inactivate the power storage device and keep it in a safe state. However, in Patent Document 1, although the power storage device can be inactivated, reuse of the inactivated power storage device has not been considered.

[0005] The present disclosure has been made to solve such problems, and the main object thereof is to provide a method of using a power storage device and a dormancy agent that can make the power storage device rechargeable again after being temporarily inactivated.

Means for Solving the Problem

[0006] As a result of intensive research to achieve the above object, the inventors of the present invention have found that when a solution containing a predetermined redox shuttle agent and a non-aqueous solvent is added to an electricity storage device, the electricity storage device can be temporarily inactivated and then be rechargeable again, and thus the invention of the present disclosure has been completed.

[0007] That is, the method for using the electricity storage device of the present disclosure is a method for using an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, a dormancy start step of adding a dormancy agent containing a redox shuttle agent having a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material and a non-aqueous solvent to inactivate the electricity storage device, a dormancy end step of applying an external current to the inactivated electricity storage device to make it rechargeable again, and includes the above steps.

[0008] Further, the dormancy agent of the present disclosure is a dormancy agent for dormancy of an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, and includes a redox shuttle agent which is a fluorenone-based compound having a fluorenone skeleton with a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material, and a non-aqueous solvent.

[0009] Alternatively, the dormancy agent of the present disclosure is a dormancy agent for dormancy of an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, and includes a redox shuttle agent which is a compound that forms a dimer and deactivates during redox with a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material, and a non-aqueous solvent.

Advantages of the Invention

[0010] In the method of using this power storage device and the dormancy agent, the power storage device can be temporarily inactivated simply by adding the dormancy agent, and then can be recharged and discharged again simply by applying an electric current from the outside. The reason for obtaining such an effect is presumed as follows. For example, it is presumed that the redox shuttle agent contained in the dormancy agent can receive electrons from the negative electrode and transfer the electrons to the positive electrode, thereby causing the discharge of the power storage device to proceed and reducing the capacity of the power storage device to inactivate it. Further, if the redox shuttle agent contained in the dormancy agent is a predetermined one, the redox shuttle agent is deactivated, for example, by forming a dimer while the redox reaction is frequently repeated by applying an electric current from the outside, so that the inactivation function is lost. Thereby, it is presumed that the power storage device can be recharged and discharged again.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] The method of using the power storage device of the present disclosure includes a dormancy start step and a dormancy end step. In the dormancy start step, a dormancy agent is added to the power storage device to inactivate the power storage device. In the dormancy end step, an electric current is applied from the outside to the inactivated power storage device to make it rechargeable and dischargeable again.

[0013] [Power Storage Device] First, the power storage device to be put into dormancy will be described. The power storage device includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous ion conduction medium interposed between the positive electrode and the negative electrode for conducting carrier ions. Examples of the carrier ions include Group 1 element ions and Group 2 element ions. Examples of the Group 1 element ions include lithium ions, sodium ions, and potassium ions. Examples of the Group 2 element ions include magnesium ions and calcium ions. The power storage device may be a non-aqueous electrolyte secondary battery, and may also be an ion secondary battery such as a lithium ion secondary battery or a metal secondary battery such as 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.

[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 form a paste-like positive electrode composite material, applying and drying it on the surface of a current collector, and compressing it as necessary to increase the electrode density. The positive electrode active material may be one having a redox potential based on Li higher than that of the redox shuttle agent contained in the inactivator, and may be one having a redox potential exceeding 3.0 V based on the Li standard potential, preferably 3.5 V or more, more preferably 3.8 V or more, and even more preferably 4.0 V or more. As the positive electrode active material, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, etc. can be used. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, FeS2, Li (1-x) MnO2 (0 < x < 1, etc., the same hereinafter), Li (1-x) lithium manganese composite oxides such as Li (1-x) lithium cobalt composite oxides such as CoO2, Li (1-x) lithium nickel composite oxides such as NiO2, Li (1-x) Ni a Mn b O2 (a + b = 1) or Li (1-x) Ni a Mn b lithium nickel manganese composite oxides such as Li (1-x) Nia Co b Mn c Lithium nickel cobalt manganese composite oxides such as O2(a + b + c = 1), lithium vanadium composite oxides such as LiV2O3, transition metal oxides such as V2O5, etc. can be used. Also, Li (1-x) Olivine-type lithium manganese phosphate compounds such as MnPO4, Li (1-x) Olivine-type lithium cobalt phosphate compounds such as CoPO4, Li (1-x) Olivine-type lithium nickel phosphate compounds such as NiPO4, etc. can be used. Also, Li (1-x) Inverse spinel-type lithium manganese vanadate compounds such as MnVO4, Li (1-x) Inverse spinel-type lithium cobalt vanadate compounds such as CoPO4, Li (1-x) Inverse spinel-type lithium nickel vanadate compounds such as NiPO4, etc. can be used. The positive electrode active material is preferably an oxide containing one or more of nickel, manganese, and cobalt. For example, LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. are preferred.

[0015] As the conductive material for the positive electrode, for example, graphite such as natural graphite (scaly graphite, flaky graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, metals (such as copper, nickel, aluminum, silver, gold, etc.) can be used. As the binder, for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, natural butyl rubber (NBR), etc. can be used. Also, water-based binders such as carboxymethyl cellulose (CMC) which is a cellulose-based material or an aqueous dispersion of styrene butadiene rubber (SBR) can be used. As the solvent, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. 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. As the current collector, in addition to aluminum, titanium, stainless steel, nickel, iron, fired carbon, conductive polymers, conductive glass, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance, those obtained by treating the surface of aluminum or copper with carbon, nickel, titanium, silver, etc. can be used. For these, it is also possible to perform surface oxidation treatment. Regarding the shape of the current collector, foil-like, film-like, sheet-like, net-like, punched or expanded ones, lath bodies, porous bodies, foams, formed bodies of fiber groups, etc. can be mentioned. The thickness of the current collector is, for example, those of 1 to 500 μm are used.

[0016] The negative electrode may be formed by, for example, mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode composite material, applying and drying it on the surface of a current collector, and compressing it as necessary to increase the electrode density, or it may be formed by closely adhering the negative electrode active material and the current collector. The negative electrode active material preferably has a redox potential of 3.0 V or less, more preferably 2.0 V or less, and even more preferably 1.0 V or less based on the Li reference potential. Examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbon materials capable of occluding and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbon materials include cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Examples of the composite oxides include lithium titanium composite oxides such as Li4Ti5O 12 and lithium vanadium composite oxides such as LiV2O3. Among these, carbon materials such as graphites are preferred as the negative electrode active material. In addition, the conductive material, binder, solvent, etc. used for the negative electrode can be the same as those exemplified for the positive electrode. 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 with the surface of copper or the like treated with carbon, nickel, titanium, silver, etc. can also be used. It is also possible to oxidize the surface of these. The shape of the current collector can be the same as that of the positive electrode. The current collector of the negative electrode may be one containing copper among these. According to References 1 (J. Electrochem. Soc. 144 (1997) 3476-3483, J. Mater. Chem. 21 (2011) 9891-9911), since the redox potential of copper is about 3.0 - 3.5 V based on the Li reference potential, it is considered that elution of copper can be suppressed if the negative electrode potential is kept below 3.0 V during inactivation. Also, if elution of copper from the negative electrode is suppressed, it is considered that precipitation of copper at the positive electrode is also suppressed.

[0017] As the ionic conduction medium, a non-aqueous electrolyte containing a supporting salt, a non-aqueous gel electrolyte, etc. can be used. As the solvent of the non-aqueous electrolyte, for example, carbonate compounds, ester compounds, ether compounds, nitrile compounds, amide compounds, furan compounds, sulfolane compounds, dioxolane compounds, etc. can be mentioned, and these can be used alone or in combination. Specifically, as the carbonate compound, cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, etc., and chain carbonate compounds such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, etc. can be mentioned. Also, as the ester compound, cyclic ester compounds such as γ-butyrolactone, γ-valerolactone, etc., and chain ester compounds such as methyl formate, methyl acetate, ethyl acetate, methyl butyrate, etc. can be mentioned. Also, as the ether compound, dimethoxyethane, ethoxymethoxyethane, diethoxyethane, etc. can be mentioned, as the nitrile compound, acetonitrile, benzonitrile, etc. can be mentioned, as the amide compound, dimethylacetamide (DMA), dimethylformamide, etc. can be mentioned, as the furan compound, tetrahydrofuran, methyltetrahydrofuran, etc. can be mentioned, as the sulfolane compound, sulfolane, tetramethylsulfolane, etc. can be mentioned, and as the dioxolane compound, 1,3-dioxolane, methyldioxolane, etc. can be mentioned. These can be used alone or in combination. Among these, as the solvent of the non-aqueous electrolyte, for example, a mixed solution of a cyclic carbonate compound and a chain carbonate compound such as DMC-EC, DEC-EC, DMC-EMC-EC, etc. is preferable. As the supporting salt, for example, inorganic salts such as LiPF6, LiBF4, LiAsF6, LiClO4, etc., and organic salts such as LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, etc. can be mentioned, and these can be used alone or in combination.The supporting salt preferably has a concentration in the electrolyte of 0.1 mol / L or more and 5 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less. Further, as the ion conduction medium, instead of the liquid ion conduction medium, an 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.

[0018] This 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 thin microporous membranes of olefin resins such as polyethylene. These may be used alone or in combination.

[0019] The shape of this power storage device is not particularly limited. Examples include coin type, button type, sheet type, laminated type, cylindrical type, flat type, square type, etc. It may also be a large one used in electric vehicles, etc. An example of the power storage device is shown in FIG. 1. FIG. 1 is a cross-sectional view showing the schematic configuration of a coin-type power storage device 20. As shown in FIG. 1, the power storage device 20 includes a cup-shaped case 21, a positive electrode 22 having a positive electrode active material and provided at the lower part of the case 21, a negative electrode 23 having a negative electrode active material and provided at a position facing the positive electrode 22 with a separator 24 therebetween, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the case 21 and sealing the case 21 through the gasket 25. This power storage device 20 includes an ion conduction medium 27 containing carrier ions between the positive electrode 22 and the negative electrode 23.

[0020] [Dormant agent] Next, the dormant agent will be described. The dormant agent includes a redox shuttle agent and a non-aqueous solvent. The dormant agent refers to a substance that, when added to an electric energy storage device, temporarily inactivates the electric energy storage device and enables charge and discharge again by applying an external voltage thereafter. The redox shuttle agent may be a compound having a redox potential higher than that of the negative electrode active material of the non-aqueous secondary battery and lower than that of the positive electrode active material of the non-aqueous secondary battery. The redox potential may be compared with the Li reference potential. In this specification, the redox shuttle agent refers to an oxidizable and reducible compound that can repeatedly transport charges between the positive electrode and the negative electrode. The non-aqueous solvent is a solvent capable of dissolving the redox shuttle agent.

[0021] The redox shuttle agent may be, for example, a fluorenone-based compound having a fluorenone skeleton. The redox shuttle agent may be, for example, a compound that deactivates by forming a dimer during oxidation and reduction.

[0022] The redox shuttle agent preferably includes, for example, a fluorenone-based compound having a fluorenone skeleton. The fluorenone-based compound has a fluorenone skeleton in which two hydrogen atoms bonded to the 9-position carbon atom of fluorene are substituted with one oxo group (=O). The fluorenone-based compound includes fluorenone and its derivatives. The fluorenone derivative refers to a compound having a substituent other than hydrogen on a carbon other than the 9-position carbon having an oxo group. This fluorenone-based compound may be represented by formula (1). In formula (1), R 1 ~R 8are functional groups that may be the same or different from each other. Examples of functional groups include one or more of hydrogen, alkyl group, aryl group, acyl group, alkoxy group, alkylsulfanyl group, hydroxyl group, hydroxy group, sulfone group, nitro group, nitroxyl group, amino group, carboxyl group, or halogen. The alkyl group may have 1 to 12 carbon atoms, may be linear or branched, or may be a halogenated alkyl group in which part or all of the hydrogen is substituted with halogen. Examples of alkyl groups include methyl group, ethyl group, isopropyl group, tert-butyl group, and trifluoromethyl group. The aryl group may have 6 to 12 carbon atoms. Examples of aryl groups include phenyl group, tolyl group, xylyl group, mesityl group, and naphthyl group. The acyl group may have 1 to 7 carbon atoms. Examples of acyl groups include formyl group, acetyl group, and benzoyl group. The alkoxy group may have 1 to 6 carbon atoms. Examples of alkoxy groups include methoxy group, ethoxy group, and phenoxy group. The alkylsulfanyl group may have 1 to 6 carbon atoms. Examples of alkylsulfanyl groups include methylsulfanyl group and ethylsulfanyl group. Examples of halogen include fluorine, chlorine, and bromine. R 1 ~R 8 may each independently be hydrogen, an alkyl group, a phenyl group, an acetyl group, or a halogen. Also, R 1 ~R 8 may have four or more of them being hydrogen. Also, R 1 ~R 8 may have two or more of them bonded to form a ring.

[0023]

Chemical formula

[0024] Examples of fluorenone-based compounds include fluorenone (formula (2)) as the basic skeleton, and its derivatives such as 2-aminofluorenone (formula (3)), 2,7-dihydroxyfluorenone (formula (4)), 2-carboxyfluorenone (formula (5)), 2-nitrofluorenone (formula (6)), 2,7-dinitrofluorenone (formula (7)), benzo[b]fluorenone (formula (8)), 2,7-dibromofluorenone (formula (9)), etc. In formulas (3) to (9), examples of having one or two substituents such as an amino group, a hydroxy group, a carboxy group, a nitro group, a benzo group, and a bromo group as the main substituents are given, but the substitution positions may be changed, or those having three or more substituents at arbitrary positions may also be used.

[0025] [Chemical formula]

[0026] The redox potential of the redox shuttle agent is preferably less than 3.0 V with respect to the Li reference potential. In addition, fluorenone-based compounds are considered to have a redox potential of less than 3.0 V with respect to the Li reference potential. The redox potential of the redox shuttle agent may be 2.9 V or less with respect to the Li reference potential. The redox potential of the redox shuttle agent may be 0.5 V or more, 1.0 V or more, or 1.5 V or more with respect to the Li reference potential. The redox potential of the redox shuttle agent can be determined by cyclic voltammetry. Specifically, when the peak potential on the oxidation side obtained by cyclic voltammetry for the redox shuttle agent is E pa [V] and the peak potential on the reduction side is E pc [V], the value E0 [V] obtained by E0 = (E pa + E pc ) / 2 is used. When there are two or more redox potentials within the potential window, it is preferable that all the redox potentials are less than 3.0 V.

[0027] The concentration of the redox shuttle agent contained in the dormancy agent is preferably higher, preferably 50 mmol / L or more, more preferably 100 mmol / L or more, still more preferably 200 mmol / L or more, and may be 500 mmol / L or more. The higher the concentration of the redox shuttle agent, the more preferably the battery with high energy density such as for an electric vehicle (EV) can be discharged in a short time. The concentration of the redox shuttle agent contained in the inactivator may be below the solubility, may be 5.0 mol / L or below, or may be 2.0 mol / L or below.

[0028] The dormancy agent may contain solutes other than the redox shuttle agent, but preferably does not contain solutes. Even if the dormancy agent contains solutes other than the redox shuttle agent, it is preferably less than 0.1 mmol / L or less than 0.01 mmol / L. In the dormancy agent, the less the solutes other than the redox shuttle agent, the lower the viscosity tends to be, so the inactivation proceeds more rapidly. Examples of the solute include the supporting salts described above. The supporting salt may be the same as or different from the supporting salt contained in the ion conductive medium of the power storage device to be inactivated.

[0029] The non-aqueous solvent contained in the dormancy agent is not particularly limited as long as it can dissolve the redox shuttle agent. It is preferable that this non-aqueous solvent has a higher solubility of the redox shuttle agent and can dissolve it more stably. For example, an aprotic solvent is preferable, and a polar aprotic solvent having polarity is more preferable. Examples of this non-aqueous solvent include ethers such as tetrahydrofuran (THF), dioxolane, dioxane, diethyl ether (DEE), dimethoxyethane (DME), diglyme (G2), triglyme (G3), and tetraglyme (G4); carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC); sulfoxides such as dimethyl sulfoxide (DMSO); and amides such as dimethylformamide (DMF), dimethylacetamide (DMA), and hexamethylphosphoric triamide (HMPA). One or more of these may be mentioned. The non-aqueous solvent may be an ether or a carbonate among these. If it is an ether or a carbonate, it is possible to inactivate the electrode while maintaining a better state of the electrode, so that charge and discharge after the end of dormancy can be preferably performed, which is preferable.

[0030] [Dormancy start process] Subsequently, the dormancy start process will be described. In the dormancy start process, a dormancy agent is added to the power storage device to inactivate the power storage device. In this specification, inactivating the power storage device may mean reducing the voltage of the power storage device to a predetermined voltage or less. The predetermined voltage can be determined empirically based on a voltage that enables safe transportation and storage. For example, it may be the voltage when the power storage device is discharged until the state of charge (SOC) becomes 0%.

[0031] The sleep start process includes an addition process of adding the above-described sleep agent inside the power storage device. Specifically, the sleep agent is added so that the positive electrode and the negative electrode of the power storage device come into contact with the sleep agent. The method of adding the sleep agent is not particularly limited. For example, after once opening the battery container and injecting the sleep agent, it may be sealed again as necessary, or after injecting the sleep agent from the outside of the battery container with a syringe, it may be sealed as necessary. The addition process is preferably carried out under an inert atmosphere such as an argon atmosphere.

[0032] In this addition process, it is preferable to add the sleep agent in a range where the amount of the redox shuttle agent with respect to the capacity of the power storage device is 0.1 mol / Ah or less. Since the power storage device has a limited internal space, it is preferable that the addition amount of the sleep agent is smaller. This addition amount may be in a range of 0.01 mol / Ah or less, or may be in a range of 0.005 mol / Ah or less. The amount of the redox shuttle agent with respect to the capacity of this power storage device may be in a range of 0.001 mol / Ah or more, or may be in a range of 0.002 mol / Ah or more, or may be in a range of 0.003 mol / Ah or more. When this addition amount is in a range of 0.001 mol / Ah or more, the time required for inactivation can be further shortened, which is preferable.

[0033] The addition amount of the sleep agent may be appropriately selected according to the size of the power storage device, etc. For example, it may be 0.01 mL or more and 10 mL or less, or may be 0.05 mL or more and 5.0 mL or less. The addition amount of the sleep agent may be, for example, 0.01% or more and 500% or less, or 1% or more and 300% or less, with respect to the volume [mL] of the ion conductive medium contained in the power storage device to be inactivated.

[0034] This addition process may be carried out for a power storage device having a negative electrode current collector containing copper. Since copper has a redox potential of about 3.0 to 3.5 V with respect to the Li reference potential as described above, elution of copper can be suppressed if the negative electrode potential is kept below 3.0 V during inactivation.

[0035] The power storage device added with a dormancy agent may be held, for example, while being stationary or while being vibrated. The holding time may be determined empirically as the time until inactivation is completed according to the capacity of the power storage device and the added amount of the dormancy agent. The holding time depends on the capacity of the power storage device and the added amount of the inactivation agent, but may be, for example, 5 hours or more, 10 hours or more, or 20 hours or more. Also, the holding time may be, for example, 100 hours or less, 50 hours or less, or 20 hours or less.

[0036] By performing the above-described dormancy start process, the power storage device can be inactivated. The mechanism by which the power storage device is inactivated in the dormancy start process is presumed as follows. FIG. 2 is an explanatory diagram showing the mechanism by which the power storage device is inactivated. When a redox shuttle agent (RS in the figure) having a redox potential lower than the positive electrode potential and higher than the negative electrode potential is added to the battery, electron transfer from the negative electrode to the redox shuttle agent and from the redox shuttle agent to the positive electrode proceeds using the potential difference between the positive electrode or the negative electrode and the redox shuttle agent as a driving force, and the battery discharges. Specifically, the reduced form of the redox shuttle agent (RS in the figure) (red) ) gives electrons to the positive electrode to become an oxidized form (RS in the figure) (ox)As a result, the operation in which the oxidized form of the redox shuttle agent receives electrons from the negative electrode and becomes the reduced form repeats, and the battery discharges. When the positive electrode potential or the negative electrode potential becomes equal to the redox potential of the redox shuttle agent, the discharge of that electrode no longer proceeds. Therefore, the positive electrode potential and the negative electrode potential ultimately become equal to the potential of the redox shuttle agent, and inactivation is completed. Note that "inactivation is completed" may mean that discharge has occurred until at least the SOC of the non-aqueous secondary battery becomes 0%. If discharge has occurred until the SOC becomes 0%, for example, since the negative electrode potential is not too low, such as exceeding 1.5 V and less than 3.0 V based on the Li standard potential, gas generation due to decomposition of the electrolytic solution, which is an ion conduction medium, is less likely to occur, and the safety of the electrode itself is high. Therefore, transportation and storage after inactivation can be performed safely. The battery voltage after inactivation may be, for example, 3.0 V or less, 2.0 V or less, 1.5 V or less, 1.0 V or less, etc. Further, FIG. 3 is an explanatory diagram showing the redox reaction of fluorenone as a redox shuttle agent. According to Reference 2 (Tetrahedron Letters 40 (1999) 7347-7350), when fluorenone is reduced, it becomes a ketyl radical in the first step as shown in FIG. 3, and is further reduced to a dianion. It is considered that the discharge reaction of the power storage device proceeds by this reaction and inactivation occurs, resulting in a dormant state. Although the dianion is generally unstable, since the five-membered ring of fluorenone has aromaticity, it is considered to be stabilized and the discharge reaction necessary for inactivation proceeds sufficiently.

[0037] [Dormancy Ending Process] In the sleep termination process, an external current is applied to the inactivated power storage device to make it chargeable and dischargeable again. In the sleep termination process, the power storage device may be connected to an external power source for charging. In the sleep termination process, the power storage device may be charged up to a predetermined voltage. In the sleep termination process, the power storage device may be charged until the state of charge (SOC) thereof reaches 50% or more, 70% or more, 90% or more, or even until it reaches 100%. In the sleep termination process, for example, charging and discharging may be performed at a current of 0.05C or more, 0.1C or more, or charging and discharging may be performed at a current of 1C or less, 0.5C or less. In the sleep termination process, it is also possible that an electrochemical reaction is caused by applying an external current to the power storage device to deactivate the redox shuttle agent. Note that the sleep termination process may be performed independently of subsequent charging and discharging, or may be performed as a series of charging and discharging operations without being distinguished from subsequent charging and discharging.

[0038] By performing the above-described sleep termination process, the power storage device can be made rechargeable again. The mechanism by which the power storage device becomes rechargeable again in the sleep termination process is presumed as follows, for example. According to Reference 3 (Angew. Chem. Int. Ed. 54 (2015) 8684-8687), a part of the ketyl radical of fluorenone dimerizes to form a dimer. Since this dimer does not undergo reversible oxidation-reduction, fluorenone is deactivated by the formation of this dimer and no longer functions as a redox shuttle agent. When an external current is applied to the power storage device, the reduction product of fluorenone shown in Fig. 4 (the ketyl radical which is a one-electron reduction product) dimerizes as oxidation-reduction is frequently repeated, and it is presumed that the power storage device loses its function as a redox shuttle agent as a whole. Although dimerization also occurs slightly in the sleep start process, it is presumed that the rate of dimerization is extremely low due to the small number of repetitions of oxidation-reduction in the state where no current is applied. In view of the above mechanism of action, it is presumed that the redox shuttle agent functions as a sleep agent even if a redox shuttle agent other than the fluorenone compound is used, as long as it is a compound that deactivates by forming a dimer during oxidation-reduction. Note that the redox shuttle agent should have durability against oxidation-reduction to such an extent that the power storage device can be brought into a desired discharged state in the sleep start process.

[0039] The discharge capacity [Ah] of the power storage device after sleep termination is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more of the discharge capacity [Ah] of the power storage device before sleep start. The discharge capacity of the power storage device after sleep termination may be 90% or less of the discharge capacity of the power storage device before sleep start.

[0040] In the method of using the power storage device and the dormancy agent described above, by simply adding the dormancy agent, the power storage device can be temporarily inactivated to achieve a dormant state in which transportation and storage can be performed safely, and it can be made rechargeable again only by applying a voltage from the outside thereafter. The reason for obtaining such an effect is speculated as follows. For example, it is speculated that the redox shuttle agent contained in the dormancy agent can receive electrons from the negative electrode and transfer electrons to the positive electrode, thereby causing the discharge of the power storage device and reducing the capacity of the power storage device to make it inactive. Further, if the redox shuttle agent contained in the dormancy agent is a predetermined one, the redox shuttle agent is deactivated, for example, by forming a dimer while redox is frequently repeated by applying an external current, so that the inactivation function is lost. Thereby, it is speculated that the power storage device can be made rechargeable again. As a method of putting the power storage device into dormancy, a method of lowering the battery voltage using a charge and discharge device is also conceivable. However, in that case, the battery voltage may increase during transportation and storage after discharge. Also, with the method of lowering the battery voltage using a charge and discharge device, it was not possible to make the power storage device in which lithium was deposited into a safe state.

[0041] In particular, it is speculated that it is preferable to use a compound having a fluorenone skeleton as the redox shuttle agent. It is speculated that the fluorenone-based compound can show reversible and stable redox in the battery and can rapidly discharge the battery because the dianion generated by reduction on the negative electrode surface is stabilized by the aromaticity of the five-membered ring. Further, the compound having a fluorenone skeleton has a redox potential of 3V vs. Li / Li + For the following reasons, the negative electrode potential after discharge is 3V vs. Li / Li +It becomes possible to maintain the following, and thereby it is presumed that elution of copper can be suppressed when copper is used for the negative electrode current collector. In addition, since the compound having a fluorenone skeleton has a relatively high solubility in various non-aqueous solvents, it is presumed that the concentration of the redox shuttle agent in the dormant agent can be increased, and the power storage device can be inactivated with a relatively small amount of the dormant agent. Further, since the compound having a fluorenone skeleton forms a dimer and is inactivated during oxidation-reduction and loses its inactivation function, it is presumed that charge and discharge become possible again.

[0042] Note that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that the present disclosure can be implemented in various modes as long as it belongs to the technical scope of the present disclosure.

[0043] For example, in the above-described embodiment, the power storage device to be inactivated was described as a lithium-ion secondary battery, but it is not particularly limited thereto, and it may be a hybrid capacitor, a pseudo electric double layer capacitor, an alkali metal secondary battery such as lithium or sodium, an alkali metal ion battery, or the like.

[0044] The present disclosure may also be as shown in any one of the following [1] to [8]. [1] A method of using a power storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, the method comprising a dormancy start step of adding a dormancy agent containing a redox shuttle agent having a redox potential lower than the negative electrode active material and higher than the positive electrode active material and a non-aqueous solvent to inactivate the power storage device, and a dormancy end step of applying an external current to the inactivated power storage device to make it chargeable and dischargeable again. [2] The method of using a power storage device according to [1], wherein the redox shuttle agent is a fluorenone-based compound having a fluorenone skeleton. [3] The method of using a power storage device according to [2], wherein the fluorenone-based compound is represented by formula (1).

Chemical formula

Examples

[0045] Examples of specifically examining the method for using an electricity storage device and the dormancy agent of the present disclosure are described below as experimental examples. Experimental Examples 1 to 2, 4 to 5 correspond to the examples of the present disclosure, and Experimental Example 3 corresponds to a comparative example.

[0046] [Experimental Example 1] Using fluorenone as a redox shuttle agent, the dormancy behavior of a lithium-ion battery was evaluated. As a dormancy agent, a solution prepared by dissolving 1.0 mol / L of fluorenone in dimethoxyethane (DME) was prepared. The lithium-ion battery used for the evaluation was fabricated as follows. LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A positive electrode composite containing 93% by mass of O2, 4% by mass of acetylene black, and 3% by mass of polyvinylidene fluoride was applied to an aluminum foil to fabricate a positive electrode. A negative electrode composite containing 98% by mass of graphite, 1% by mass of carboxymethyl cellulose, and 1% by mass of styrene-butadiene rubber was applied to a copper foil to fabricate a negative electrode. LiPF6 was dissolved in a mixed solvent (hereinafter also referred to as an electrolytic solution solvent) containing 30% by volume of ethylene carbonate (EC), 40% by volume of dimethyl carbonate (DMC), and 30% by volume of ethyl methyl carbonate (EMC) at a concentration of 1.0 mol / L to prepare an electrolytic solution. A polyethylene single-layer microporous membrane was prepared as a separator. The positive electrode and the negative electrode were opposed to each other through a separator impregnated with the electrolytic solution and sealed in a laminate film. The lithium-ion battery was assumed to have a capacity of about 17 mAh and contain about 1 mL of the electrolytic solution (the same applies to Experimental Examples 2 and 3 described later). The lithium-ion battery thus fabricated was charged and discharged for 2 cycles in a voltage range of 3 to 4.1 V. Thereafter, it was charged up to 4.1 V to obtain a fully charged state. The fully charged battery was opened in an argon atmosphere, 0.127 mL of the above-mentioned dormancy agent was injected, the battery was sealed again, and maintained at a temperature of 25°C. The voltage change at this time was measured, and it was confirmed that the voltage became stable at 1.0 V or less (entered the dormant state). Thereafter, charging and discharging were performed again for 2 cycles at 3 to 4.1 V. In this charging and discharging, the first cycle was performed at a current of 0.2 C (3.6 mA), the second cycle was charged at 0.1 C and then discharged at 0.05 C, and the discharge behavior at that time was confirmed.

[0047] [Experimental Example 2] Evaluation was carried out in the same manner as in Experimental Example 1, except that a solution in which 1.0 mol / L of fluorenone was dissolved in the above-mentioned electrolytic solution solvent was used as the dormancy agent.

[0048] [Experimental Example 3] Evaluation was carried out in the same manner as in Experimental Example 1, except that a solution in which 1.0 mol / L of phenothiazine was dissolved in dimethoxyethane was used as the dormancy agent.

[0049] [Experimental Example 4] Fluorenone, a redox shuttle agent, was evaluated by cyclic voltammetry using an H-type cell. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in N,N-dimethylacetamide (DMA) at a concentration of 1.0 mol / L as a supporting electrolyte, and fluorenone was dissolved at a concentration of 50 mmol / L as a redox shuttle agent to prepare a measurement solution. A glassy carbon was used as the working electrode, metallic lithium was used as the counter electrode, and a nickel wire with metallic lithium crimped thereon was used as the reference electrode. The measurement temperature was 20 °C, and the potential range was 1.0 - 4.0 V vs. Li / Li + , and the potential sweep rate was 50 mV / sec.

[0050] [Experimental Example 5] The redox potential of the fluorenone derivative was calculated by the density functional method. The Gibbs free energy (ΔG OX ) of the oxidized form and the Gibbs free energy (ΔG RED ) of the reduced form were calculated respectively. Assuming a two-step one-electron reduction, the target redox potential E abs was calculated as the absolute potential from the following formula (A). Here, F is the Faraday constant 96485 C / mol. E abs =(ΔG OX - ΔG RED ) / F ··· (A) From the obtained absolute potential, the redox potential E RedOx with respect to the lithium electrode was calculated using the following formula (B). E RedOx [V vs. Li + / Li] = E abs - 1.4 ··· (B) The free energy was calculated using the density functional method. The B3LYP and 6-311++G(d,p) were used for the functional and basis functions in the Gaussian09 Revision E package, and the solvent effect was incorporated with the dielectric constant of the solvent being 29.11 by the continuous polarization model.

[0051] [Results and Discussion] Figure 5 shows the evaluation results of Experimental Examples 1 to 3. Figure 5A is a graph showing the change in battery voltage after adding the dormancy agent, and Figure 5B is a graph showing the discharge behavior of the second cycle in charge and discharge after dormancy. Figure 5B also shows the discharge behavior of the power storage device before charge and discharge for reference. In Experimental Example 1, the SOC (State of Charge) of the battery became 0% (voltage 3V) 6 hours after adding the dormancy agent, and the battery discharged to around 1V 20 hours after adding it (Figure 5A). After that, when the dormant cell was charged, the voltage reached 4.1V, and it was confirmed that it had the function of a battery (Figure 5B). The discharge capacity after dormancy was 75% of the discharge capacity before dormancy. In Experimental Example 2, the SOC of the battery became 0% about 10 hours after adding the dormancy agent, and the battery discharged to around 1V about 20 hours after adding it (Figure 5A). After that, when the dormant cell was charged, the voltage reached 4.1V, and it was confirmed that it had the function of a battery (Figure 5B). The discharge capacity after dormancy was 73% of the discharge capacity before dormancy. In Experimental Example 3, the SOC of the battery became 0% about 30 hours after adding the dormancy agent, and the battery discharged to around 0V about 90 hours after adding it (Figure 5A). When the dormant cell was charged, the voltage reached 4.1V. However, it was confirmed that the function of the battery deteriorated significantly (Figure 5B).

[0052] Figure 6 shows the cyclic voltammogram of Experimental Example 4. At this time, two pairs of redox peaks were confirmed. These peaks were presumed to be due to the redox of fluorenone. From the peak potentials E pa , E pc , the standard redox potential E0 is calculated by the following formula (C). E0=(E pa +E pc ) / 2···(C) Using the above formula (C), the standard redox potential E0 of fluorenone was determined to be 2.08V vs.Li / Li + and 1.52V vs.Li / Li + .

[0053] The calculation results of the redox potentials of fluorenone (the above formula (2)) and fluorenone derivatives (the above formulas (3) to (9)) in Experimental Example 5 are shown in Table 1. Compared with the experimental results of Experimental Example 4, the calculated redox potential of fluorenone was about 0.3 V lower. However, regardless of the type of substituent, the first redox potential was 2.7 V vs. Li / Li + or lower and the second redox potential was 0.5 V vs. Li / Li + or higher. In addition, the first-step redox potential of the fluorenone derivative was taken as the value reported in Reference 4 (J. Phys. Org. Chem, 24 (2011) 1119-1128) and Reference 5 (ECS Transactions, 89 (1) (2019) 49-59). From the above, for any fluorenone derivative, the first redox potential was 3.0 V vs. Li / Li + or lower and the second redox potential was 0.5 V vs. Li / Li + or higher. It was speculated that

[0054] From the above, it was found that by adding a dormancy agent containing fluorenone to the battery, the battery can be chemically short-circuited internally to temporarily lose its function as a battery, and then the charge-discharge performance can be restored by applying an external current, and the battery can be reused again. In addition, compounds having a fluorenone skeleton have a structure very similar to that of fluorenone and a redox potential similar to that of fluorenone, so it was speculated that the same effect as when using fluorenone can be obtained. Furthermore, from its mechanism of action, it was speculated that the same effect as when using fluorenone can also be obtained when using a redox shuttle agent that forms a dimer and deactivates during redox.

[0055]

Table 1

[0056] It should be noted that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that the present disclosure can be implemented in various aspects as long as it belongs to the technical scope of the present disclosure.

Industrial Applicability

[0057] The present disclosure is applicable in the field of the battery industry.

Description of Reference Numerals

[0058] 20 Energy storage device, 21 Case, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Ion conductive medium.

Claims

1. A method for using an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, comprising: a dormancy start step of adding a dormancy agent including a redox shuttle agent having a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material and a non-aqueous solvent to inactivate the electricity storage device; a dormancy end step of applying an external current to the inactivated electricity storage device to make it rechargeable again; A method for using an electricity storage device including these steps.

2. The method for using an electricity storage device according to Claim 1, wherein the redox shuttle agent is a fluorenone-based compound having a fluorenone skeleton.

3. The method for using an electricity storage device according to Claim 2, wherein the fluorenone-based compound is represented by formula (1). 【Chemical 1】

4. The method for using an electricity storage device according to Claim 1, wherein the redox shuttle agent is a compound that forms a dimer and deactivates during redox.

5. The method for using an electricity storage device according to any one of Claims 1 to 4, wherein the non-aqueous solvent includes ethers or carbonates.

6. The method for using an electricity storage device according to any one of Claims 1 to 4, wherein the redox shuttle agent is dissolved in the non-aqueous solvent in a range of 50 mmol / L or more and 5 mol / L or less.

7. A dormancy agent for dormancy of an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, comprising: a redox shuttle agent which is a fluorenone-based compound having a fluorenone skeleton with a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material, and a non-aqueous solvent; A dormancy agent.

8. A dormancy agent for dormancy of an electricity storage device including a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, comprising: a redox shuttle agent which is a compound that forms a dimer and deactivates during redox with a redox potential lower than that of the negative electrode active material and higher than that of the positive electrode active material, and a non-aqueous solvent; A dormancy agent.

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