Recovery agent, recovery method, and method for manufacturing electricity storage device

Abstract

A recovery agent for recovering the capacity of an electricity storage device having a metal ion as a carrier ion, the recovery agent containing an aromatic hydrocarbon compound in a reduced state, a metal ion of the same kind as the carrier ion, and a recovery agent solvent, the aromatic hydrocarbon compound being a fluorene compound having a fluorene skeleton. The recovery method is a recovery method for recovering the capacity of an electricity storage device having a metal ion as a carrier ion, and includes a recovery step for recovering the capacity of the electricity storage device by adding the recovery agent to the electricity storage device.

Description

Technical Field

[0001] This invention relates to a recovery agent, a recovery method, and a method for manufacturing an energy storage device. Background Technology

[0002] Conventionally, as a method for restoring the capacity of non-aqueous electrolyte secondary batteries using metal ions as carrier ions, a method has been proposed that involves adding a solution containing a reduced aromatic hydrocarbon compound and metal ions of the same type as the carrier ions to the non-aqueous electrolyte secondary battery (see, for example, Patent Documents 1 and 2). As aromatic hydrocarbon compounds, polyphenylene and polystyrene are exemplified in Patent Document 1, while polyphenacene is used in Patent Document 2.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-139890

[0006] Patent Document 2: Japanese Patent Application Publication No. 2022-111519 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in patent documents 1 and 2, there are also instances where the capacity recovery is insufficient, and new recovery agents and recovery methods are desired.

[0009] This invention was made to solve such problems, and its main purpose is to provide new restorative agents and methods.

[0010] Methods for solving problems

[0011] To achieve the above objectives, the inventors discovered that a recovery agent comprising an aromatic hydrocarbon compound in a reduced state having a fluorene skeleton, a metal ion of the same kind as the carrier ion, and a recovery agent solvent can more appropriately restore capacity, thus completing the present invention.

[0012] That is, the restorer of the present invention is a restorer that restores the capacity of an energy storage device that uses metal ions as carrier ions. It comprises an aromatic hydrocarbon compound in a reduced state, a metal ion of the same kind as the carrier ion, and a restorer solvent. The aromatic hydrocarbon compound is a fluorene compound with a fluorene skeleton.

[0013] Furthermore, the recovery method of the present invention is a recovery method for restoring the capacity of an energy storage device that uses metal ions as carrier ions, which includes a recovery step of adding the above-mentioned recovery agent into the energy storage device to restore the capacity of the energy storage device.

[0014] Furthermore, the method for manufacturing the energy storage device of the present invention includes: a preparation step of preparing an energy storage device with deteriorated capacity that uses metal ions as carrier ions; and a recovery step of adding the above-mentioned recovery agent into the energy storage device to restore the capacity of the energy storage device.

[0015] Invention Effects

[0016] This invention provides a novel recovery agent and recovery method. Furthermore, it enables the manufacture of capacity-recovering storage devices using capacity-degraded storage devices. The reason for this effect is presumably as follows: For example, the recovery agent, comprising a reduced-state aromatic hydrocarbon compound and metal ions, acts directly on the positive electrode simply by being injected into a non-aqueous electrolyte secondary battery, resulting in a recovery reaction that supplies electrons and metal ions to the positive electrode. In particular, it is presumed that since the aromatic hydrocarbon compound is a fluorene series compound, its capacity can be more appropriately recovered due to suitable reducing power and low overvoltage of the capacity recovery reaction. Attached Figure Description

[0017] Figure 1 This is an explanatory diagram showing a schematic representation of the structure of a non-aqueous electrolyte secondary battery 20.

[0018] Figure 2 This is an illustrative diagram showing an example of a recovery reaction. Detailed Implementation

[0019] The recovery agent disclosed in this specification is a recovery agent that restores the capacity of energy storage devices that use metal ions as carrier ions.

[0020] (Electronic storage devices)

[0021] First, the energy storage device that is the object of restoration will be described. Examples of energy storage devices include hybrid capacitors, pseudo-double-layer capacitors, lithium or sodium alkali metal secondary batteries, alkali metal ion batteries, and air batteries. Examples of metal ions used as carrier ions include alkali metal ions such as Li, Na, and K, and Group 2 ions (alkaline earth metal ions) such as Mg, Ca, and Sr, with lithium ions being preferred. Among these, lithium secondary batteries are preferred as energy storage devices, and lithium-ion secondary batteries are particularly preferred. Here, the case where the energy storage device is a lithium secondary battery will be mainly described. The energy storage device may include, for example, a positive electrode with a positive electrode active material that absorbs and releases lithium ions, a negative electrode with a negative electrode active material that absorbs and releases lithium ions, and an ion-conducting medium sandwiched between the positive and negative electrodes and conducting lithium ions. The energy storage device may have a separator between the positive and negative electrodes.

[0022] The positive electrode can be formed, for example, as follows: A positive electrode active material, a conductive material, and a binder material are mixed, an appropriate solvent is added, and a pasty positive electrode composite material is made. This is coated on the surface of a current collector and dried, and compression is performed as needed to increase the electrode density. 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, etc., lithium manganese composite oxides with a basic composition formula of Li

[0023] MnO2 (0 < x < 1, etc., the same below), Li (1-x) Mn2O4 and other lithium manganese composite oxides, lithium cobalt composite oxides with a basic composition formula of Li (1-x) CoO2 and other lithium cobalt composite oxides, lithium nickel composite oxides with a basic composition formula of Li (1-x) NiO2 and other lithium nickel composite oxides, lithium nickel cobalt manganese composite oxides with a basic composition formula of Li (1-x) Ni a Co b Mn c O2 (a + b + c = 1) and other lithium nickel cobalt manganese composite oxides, lithium vanadium composite oxides with a basic composition formula of LiV2O3, transition metal oxides with a basic composition formula of V2O5, etc. Among them, lithium transition metal composite oxides are preferred, such as LiCoO2, LiNiO2, LiMnO2, LiV2O3, etc. It should be noted that the "basic composition formula" means that other elements can also be included. The redox potential of the positive electrode active material can be set to 3.5 V or more, 4.0 V or more, or 4.5 V or more based on the Li metal standard.

[0023] In the positive electrode, the conductive material can be one or a mixture of two or more of the following: natural graphite (flake graphite, scaly graphite), artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.). From the viewpoint of electronic conductivity and coatability, carbon black and acetylene black are preferred as conductive materials. The binder serves to bond the active material particles and the conductive material particles. For example, fluorinated resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR) can be used alone or in mixtures of two or more. Alternatively, aqueous binders such as cellulose-based carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), and polyvinyl alcohol can also be used. As a solvent for dispersing the positive electrode active material, conductive material, and binder material, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. Alternatively, dispersants and thickeners can be added to water, and the active material can be prepared into a slurry using latex such as SBR. As a thickener, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or in mixtures of two or more. As for coating methods, examples include roller coating, screen coating, doctor blade coating, spin coating, and bar coating; any of these methods can be used to produce any thickness and shape. The weight per unit area of ​​the positive electrode composite material is not particularly limited; for example, it can be set to be greater than 5 mg / cm³. 2 It can be set to 6mg / cm 2 The above can also be set to 7 mg / cm³. 2 The above. The weight per unit area of ​​the positive electrode composite material can be set, for example, as 20 mg / cm³. 2 The following are examples of current collectors. Besides aluminum, titanium, stainless steel, nickel, iron, sintered carbon, conductive polymers, and conductive glass, current collectors made by treating the surfaces of aluminum, copper, etc., with carbon, nickel, titanium, silver, etc., can also be used to improve adhesion, conductivity, and oxidation resistance. These can also be surface-oxidized. Regarding the shape of the current collector, examples include foil, film, sheet, mesh, perforated or expanded shapes, metal mesh, porous bodies, foamed bodies, and fiber clusters. The thickness of the current collector is, for example, 1–500 μm.

[0024] The negative electrode can be formed by tightly bonding the negative electrode active material with the current collector, or it can be formed as follows: For example, a negative electrode active material, a conductive material, and a binder are mixed, a suitable solvent is added to form a paste-like negative electrode composite material, which is then coated onto the surface of the current collector and dried. It is then compressed as needed 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 absorbing / releasing lithium ions; composite oxides containing two or more elements; and conductive polymers. Examples of carbonaceous materials include coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, and carbon fibers. Among these, artificial graphite and natural graphite have operating potentials close to that of metallic lithium, enabling charging and discharging at high operating voltages. When using lithium salts as supporting salts, they can suppress self-discharge and reduce irreversible capacity during charging, making them preferred. Examples of composite oxides include lithium-titanium composite oxides and lithium-vanadium composite oxides. From a safety perspective, carbonaceous materials are preferred as negative electrode active materials. Furthermore, the conductive materials, binder materials, solvents, etc., used in the negative electrode can be the same substances exemplified in the positive electrode. The redox potential of the negative electrode active material, based on Li metal, can be set to 1.0V or less, 0.5V or less, or 0.3V or less. The weight per unit area of ​​the negative electrode composite material can, for example, be greater than 3 mg / cm³. 2 It can also be set to 4mg / cm 2 The above. The weight per unit area of ​​the negative electrode composite material can be set, for example, as 15 mg / cm³. 2 The following applies to the current collector for the negative electrode. Besides materials such as copper, nickel, stainless steel, titanium, aluminum, sintered carbon, conductive polymers, conductive glass, and Al-Cd alloys, current collectors with surfaces treated with carbon, nickel, titanium, or silver, for example, can be used to improve adhesion, conductivity, and reduction resistance. These can also be surface-oxidized. The current collector can have the same shape as the positive electrode.

[0025] The ion-conducting medium can be a non-aqueous electrolyte containing a supporting salt and an organic solvent. Examples of supporting salts include inorganic salts such as LiPF6, LiClO4, LiAsF6, and LiBF4, and organic salts such as LiN(FSO2)2, LiN(CF3SO2)2, and LiN(C2F5SO2)2. These supporting salts can be used alone or in combination of two or more. The concentration of the supporting salt is preferably 0.1–2.0 M, more preferably 0.8–1.2 M. Examples of organic solvents are aprotic organic solvents. Examples of such organic solvents include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, and chain ethers. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butyl carbonate, and vinylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of cyclic esters include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of chain ethers include dimethoxyethane and ethylene glycol dimethyl ether. They can be used alone or in combination of two or more. In addition, as non-aqueous electrolytes, nitrile solvents such as acetonitrile and propionitrile, ionic liquids, and gel electrolytes can also be used. Non-aqueous electrolytes may contain additives such as film-forming agents and flame retardants. The ion-conducting medium can be a solid ion-conducting polymer, an inorganic solid electrolyte, a mixture of organic polymer electrolyte and inorganic solid electrolyte, or an inorganic solid powder bonded with an organic binder.

[0026] There are no particular limitations on the composition of the separator, as long as it can withstand the use of non-aqueous electrolyte secondary batteries. Examples include thin microporous membranes made of polypropylene nonwoven fabric, polyphenylene sulfide nonwoven fabric, and olefin resins such as polyethylene and polypropylene. They can be used alone or in combination of two or more.

[0027] The energy storage device can have an openable and closable filling port on the casing that houses the positive electrode, negative electrode, and non-aqueous electrolyte. A restorative agent can be easily injected through the filling port.

[0028] There are no particular limitations on the shape of energy storage devices; examples include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, and square shapes. Furthermore, they can also be used in large objects such as electric vehicles. Figure 1This is a schematic diagram showing an example of a non-aqueous electrolyte secondary battery 20 as an energy storage device. The non-aqueous electrolyte secondary battery 20 includes a cup-shaped battery casing 21, a positive electrode 22 having a positive active material and disposed at the lower part of the battery casing 21, a negative electrode 23 having a negative active material and disposed opposite to the positive electrode 22 via a separator 24, a gasket 25 formed of insulating material, and a sealing plate 26 disposed at the opening of the battery casing 21 and sealing the battery casing 21 via the gasket 25. In this non-aqueous electrolyte secondary battery 20, the space between the positive electrode 22 and the negative electrode 23 is filled with a non-aqueous electrolyte 27.

[0029] (Recovery Agent)

[0030] Next, the recovery agent will be described. The recovery agent comprises a reduced aromatic hydrocarbon compound, a metal ion of the same type as the carrier ion in the energy storage device, and a recovery agent solvent. The aromatic hydrocarbon compound is a fluorene compound with a fluorene skeleton. In the recovery agent, the reduced aromatic hydrocarbon compound can dissociate or associate with the metal ion.

[0031] Fluorene compounds have a fluorene skeleton with two six-membered rings arranged in a manner that surrounds a five-membered ring. Fluorene compounds include fluorene and its derivatives. Fluorene derivatives may have substituents on the aromatic ring or contain heteroatoms within the aromatic ring. Examples of substituents include halogen atoms, alkyl, aryl, alkenyl, alkoxy, aryloxy, sulfonyl, amino, cyano, carbonyl, acyl, amide, and hydroxyl groups. Examples of heteroatoms include nitrogen, oxygen, and sulfur. Fluorene compounds may have a structure with two hydrogens bonded to the carbon at the 9-position of the fluorene skeleton, as shown in formula (1) below, or a structure with two substituents bonded to the carbon at the 9-position of the fluorene skeleton, as shown in formula (2) below. In addition, fluorene compounds may have one hydrogen and one substituent bonded to the carbon at the 9-position of the fluorene skeleton, as shown in 9-methyl-9H-fluorene. Aromatic hydrocarbons in their reduced state are, for example, aromatic hydrocarbons in the reduced state of the above-mentioned fluorene compounds (also called reduced forms), such as anions or free radical anions. Fluorene compounds can be fluorene represented by formula (1) without substituents or heteroatoms, or 9,9-dimethylfluorene represented by formula (2) without substituents or heteroatoms.

[0032]

[0033] These aromatic rings may have substituents or heteroatoms in their structure.

[0034] The metal ion only needs to be the same type as the carrier ion of the energy storage device, preferably one or more of the alkali metal ions such as lithium ion, sodium ion and potassium ion.

[0035] The solvent for the restoring agent can be an organic solvent. The solvent for the restoring agent is preferably an ether compound, which can be a cyclic ether or a chain ether. The solvent for the restoring agent may contain one or more solvents selected from tetrahydrofuran (THF), dimethoxyethane (DME), diethoxyethane (DEE), dioxolane (DOL), and dioxane (DOX).

[0036] The restoring agent may contain the aforementioned aromatic hydrocarbon compounds, for example, it may contain one or more aromatic hydrocarbon compounds as described in formulas (1) and (2) above. Alternatively, the restoring agent may be a substance that reacts a metal with an aromatic hydrocarbon compound to contain a reduced aromatic hydrocarbon compound and metal ions, for example, it may be a substance obtained from one or more of formulas (3) and (4) below. It should be noted that when a metal reacts with an aromatic hydrocarbon compound having one hydrogen atom and one substituent bonded to the carbon at the 9-position of the fluorene skeleton, similar to formula (3), the hydrogen is desorbed to generate an anion of the aromatic hydrocarbon compound and a metal ion.

[0037]

[0038] These aromatic rings can have substituents and heteroatoms in their structure. x and y are arbitrary numbers, and M is a metal.

[0039] The restoring agent can be obtained by adding an aromatic hydrocarbon compound and a metal in a metallic state (not in an ionic state) to a restoring agent solvent. For example, fluorene, 9,9-dimethylfluorene, and their derivatives can be reacted with Li metal in a DME solvent as shown in formulas (5) and (6) below. Alternatively, fluorene, 9,9-dimethylfluorene, and their derivatives can be reacted with Li metal in a THF solvent according to formulas (5) and (6). In this way, a restoring agent containing a reduced aromatic hydrocarbon compound and a metal ion can be easily prepared. The restoring agent can be prepared by adding a metal to a precursor obtained by adding an aromatic hydrocarbon compound to a restoring agent solvent. The restoring agent can be prepared under an inactive atmosphere such as an argon atmosphere. The restoring agent can be prepared under low dew point environments such as below -20°C, below -40°C, or below -60°C. The restoring agent can be prepared by stirring the restoring agent solvent, the aromatic hydrocarbon compound, and the metal; in this case, a stirrer or the like can be used.

[0040]

[0041] A solution consisting of reduced aromatic hydrocarbon compounds, metal ions of the same type as the carrier ions in the energy storage device, and a restoring agent solvent is also called a restoring agent stock solution. In the restoring agent stock solution, the concentrations of the reduced aromatic hydrocarbon compounds and metal ions can be set to 0.05 mol / L or higher, 0.1 mol / L or higher, or 0.5 mol / L or higher, respectively. Furthermore, this concentration can be set below the solubility limit, below 5 mol / L, or below 2 mol / L. Additionally, the number of moles M of the reduced aromatic hydrocarbon compounds contained in the restoring agent stock solution... A (mol) and the number of moles of metal ions M B The ratio M (mol) A / M B It is preferred to set it to 1 / 1, but it can also be set to 1.1 / 1.0 to 1.0 / 1.1, or 1.2 / 1.0 to 1.0 / 1.2.

[0042] The restorer may also include an electrolyte solvent. Examples of electrolyte solvents include the aforementioned organic solvents used in the electrolytes of storage devices. The restorer may also include a supporting salt. Examples of supporting salts include the aforementioned supporting salts contained in the non-aqueous electrolytes of storage devices. Preferably, the organic solvent and supporting salt are the same as those contained in the electrolyte of the storage device to be restored. The restorer may contain an electrolyte obtained by dissolving the supporting salt in the electrolyte solvent; in this case, the electrolyte is preferably the same as the non-aqueous electrolyte of the storage device to be restored. When the restorer includes an electrolyte and an electrolyte solvent, the content of the electrolyte and electrolyte solvent can be set to 10% by volume or more, 20% by volume or more, or 30% by volume or more. Alternatively, the content of the electrolyte and electrolyte solvent can be set to 70% by volume or less, 60% by volume or less, or 50% by volume or less.

[0043] The redox potential of the restoring agent can be a substance with a redox potential higher than that of the negative electrode and lower than that of the positive electrode. For example, the redox potential of the restoring agent can be set to 0.7V or higher, 0.8V or higher, or 1.0V or higher, based on Li metal reference. Alternatively, the redox potential of the restoring agent can be set to 2.5V or lower, 2.0V or lower, 1.5V or lower, or 1.2V or lower, based on Li metal reference.

[0044] (Recovery methods and manufacturing methods for energy storage devices)

[0045] Next, the recovery method and the manufacturing method of the energy storage device will be described. The recovery method and the manufacturing method of the energy storage device may include: a preparation step of preparing a capacity-degraded energy storage device; and a recovery step of adding a recovery agent to the energy storage device to restore its capacity. By performing the recovery step, the capacity of the capacity-degraded energy storage device can be restored, thereby enabling the manufacture of a capacity-restored energy storage device using the capacity-degraded energy storage device.

[0046] In the preparation process, energy storage devices with degraded capacity are prepared. Examples of energy storage devices include those described above. A degraded energy storage device can be one whose capacity has deteriorated relative to its rated capacity. Degraded energy storage devices can be either unused or used. Even unused devices may experience capacity degradation due to prolonged storage.

[0047] In the recovery process, the aforementioned recovery agent is added to the degraded energy storage device. When adding the recovery agent, it can be added after the energy storage device has been opened and the opening sealed, or the recovery agent can be added to the energy storage device by injection and the perforation sealed. The recovery agent can be added under an inactive atmosphere such as argon. The recovery agent should be added only in a manner that ensures it is in contact with at least the positive electrode, or it can be mixed into the non-aqueous electrolyte of the energy storage device. The amount of recovery agent can be appropriately determined based on the composition and degree of degradation of the energy storage device. For example, the amount of recovery agent relative to the volume of the non-aqueous electrolyte contained in the energy storage device can be set to 1% or more and 100% or less, 10% or more and 75% or less, or 25% or more and 50% or less.

[0048] In the recovery process, the recovery agent can also be added to the energy storage device and kept in an open-circuit state. The retention time can be set to, for example, more than 1 hour and less than 48 hours, more than 6 hours and less than 36 hours, or more than 12 hours and less than 24 hours.

[0049] During the recovery process, a specified voltage lower than the full-charge voltage can be maintained by applying a constant voltage while adding a recovery agent to the energy storage device. The specified voltage is preferably a voltage lower than the full-charge voltage, and more preferably a voltage where the potential of the positive electrode is higher than the potential of the recovery agent. The full-charge voltage can also be set as the upper limit charging voltage for the energy storage device. The specified voltage can be appropriately determined based on the configuration of the energy storage device, for example, it can be set to 3.0V or higher and less than 4.1V, 3.5V or higher and less than 4.0V, or 3.7V or higher and less than 4.0V. The constant voltage can be applied continuously before adding the recovery agent, during the addition of the recovery agent, or after adding the recovery agent when the voltage drop of the energy storage device caused by the supply of metal ions to the positive electrode is negligible (e.g., within 5 minutes, preferably within 3 minutes, more preferably within 1 minute). The application time of the constant voltage can be appropriately determined based on the configuration of the energy storage device, the degree of degradation, the amount of recovery agent, etc. The application time of constant voltage can be set to, for example, more than 1 hour and less than 48 hours, more than 6 hours and less than 36 hours, or more than 12 hours and less than 24 hours.

[0050] During the recovery process, voltage adjustment to bring the energy storage device to the specified voltage can be performed before adding the recovery agent. In this case, for example, the voltage adjustment can be performed by charging with constant current charging (CC charging) or constant current constant voltage charging (CCCV charging). This voltage adjustment may not be performed, but it is preferable that the voltage of the energy storage device is the specified voltage described above.

[0051] It is believed that when the restoring agent is injected during the restoration process, for example, if such a situation occurs... Figure 2 The recovery reaction is shown. Figure 2 This is an explanatory diagram illustrating an example of a recovery reaction, and an explanatory diagram illustrating a reaction where the positive electrode active material is a lithium transition metal complex oxide. For example... Figure 2 As shown, the restorative agent contains anions of aromatic hydrocarbon compounds and free radical anions ( Figure 2 The middle is Are ·- ) and metal ions ( Figure 2 Li + The compound functions as a reducing agent that supplies electrons, thus acting on the deteriorated positive electrode ( Figure 2 Li n-y MeO2), thus, electrons and metal ions can be supplied from the reducing agent to the positive electrode, thereby restoring capacity.

[0052] The recovery agents and recovery methods detailed above can restore the capacity of energy storage devices. Furthermore, the manufacturing method of energy storage devices allows for the production of capacity-recovered energy storage devices from those with capacity degradation. The reasons for this effect are speculated as follows: For example, a recovery agent containing reduced aromatic hydrocarbon compounds and metal ions acts directly on the positive electrode simply by being injected into a non-aqueous electrolyte secondary battery, resulting in a recovery reaction that supplies electrons and metal ions to the positive electrode. In particular, the aromatic hydrocarbon compounds are fluorene compounds, which have suitable reducing power, thus preventing the reduction and decomposition of the positive electrode caused by the reduced aromatic hydrocarbon compounds, and allowing for appropriate capacity recovery. Furthermore, this allows for appropriate capacity recovery even without adding electrolyte solvents, and also reduces the time and cost of adding electrolyte solvents, achieving capacity recovery with a small amount of recovery agent. The internal volume of a battery cell in an energy storage device is limited, but if a recovery agent that can restore capacity with a small amount is used, it is easier to add the required amount of recovery agent into the battery cell. Furthermore, since aromatic hydrocarbons are fluorene compounds, the overvoltage of the capacity recovery reaction accompanying the reduction at the positive electrode is low. Therefore, even if the potential at the positive electrode decreases as the reaction proceeds, the potential difference required for the reaction with the recovery agent can be adequately maintained, thus enabling suitable capacity recovery. In addition, this allows for suitable capacity recovery even without applying a constant voltage, and also reduces the effort and cost associated with applying a constant voltage.

[0053] It should be noted that the present invention is not limited to any of the above-described embodiments. As long as it falls within the technical scope of the present invention, it can of course be implemented in various ways.

[0054] The present invention can be as shown in [1] to [6] below.

[0055] [1] A recovery agent is a recovery agent that restores the capacity of an energy storage device that uses metal ions as carrier ions, comprising an aromatic hydrocarbon compound in a reduced state, a metal ion of the same kind as the carrier ion and a recovery agent solvent, wherein the aromatic hydrocarbon compound is a fluorene compound having a fluorene skeleton.

[0056] [2] The restorative agent according to [1], wherein the aromatic hydrocarbon compound is fluorene or a fluorene derivative.

[0057] [3] The restorative agent according to [1] or [2], wherein the aromatic hydrocarbon compound is fluorene or 9,9-dimethylfluorene.

[0058] [4] The recovery agent according to any one of [1] to [3], wherein the solvent of the recovery agent is an ether compound.

[0059] [5] The restorer according to any one of [1] to [4], wherein the restorer does not contain the electrolyte solvent of the electrolyte used in the above-mentioned energy storage device.

[0060] [6] A recovery method for restoring the capacity of an energy storage device that uses metal ions as carrier ions, comprising a recovery step of adding the recovery agent described in any one of [1] to [5] into the energy storage device to restore the capacity of the energy storage device.

[0061] [7] According to the recovery method described in [6], in the above recovery process, the above recovery agent is added into the above energy storage device and kept directly in an open circuit state.

[0062] [8] A method for manufacturing an energy storage device, comprising: a preparation step of preparing an energy storage device with metal ions as carrier ions and whose capacity has deteriorated; and a recovery step of adding the recovery agent described in any one of [1] to [5] into the energy storage device to restore the capacity of the energy storage device.

[0063] It should be noted that the present invention is not limited to any of the above embodiments. As long as it falls within the technical scope of the present invention, it can be implemented in various ways.

[0064] Example

[0065] The following examples illustrate the restoration of lithium-ion batteries using the restorer of the present invention. It should be noted that Examples 1 to 5 are all equivalent to the embodiments.

[0066] [Experimental Example 1]

[0067] (Basic components of a battery)

[0068] LiNi will be used as a positive electrode composite material 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode composite material, consisting of 92% O2, 5% acetylene black, and 3% polyvinylidene fluoride, was coated onto aluminum foil to form the positive electrode. A negative electrode composite material, consisting of 98% graphite, 1% carboxymethyl cellulose, and 1% styrene-butadiene rubber, was coated onto copper foil to form the negative electrode. An electrolyte was prepared by dissolving LiPF6 in a mixed solvent containing 30% vol% ethylene carbonate (EC), 40% vol% dimethyl carbonate (DMC), and 30% vol% ethyl methyl carbonate (EMC) at a concentration of 1 mol / L. A polyethylene monolayer microporous membrane was used as the separator. It should be noted that the battery contains approximately 1 mL of electrolyte.

[0069] (The manufacture of degraded batteries)

[0070] First, a positive electrode simulating a reduced capacity is fabricated following these steps: A separator immersed in electrolyte is sandwiched between a copper foil and the positive electrode, and the cells are sealed in a laminate to fabricate a laminated battery cell. The fabricated laminated battery cell is charged at 25°C until it reaches 50% of its capacity (SOC=50%), equivalent to a voltage range of 3.0V–4.1V. This causes Li to be extracted from the positive electrode, resulting in a positive electrode simulating a reduced capacity (also called a degraded positive electrode). The battery cell is then disassembled, and the degraded positive electrode is removed. An electrolyte-immersed separator is placed between the negative electrode and the resulting degraded positive electrode, and the cells are sealed in a laminate to fabricate a laminated battery cell, which serves as the degraded battery.

[0071] (Evaluation of degraded batteries)

[0072] For the degraded batteries obtained, constant current (CC) charging at 2.0mA was performed until 4.1V, followed by constant current discharging at 2.0mA until 3.0V. Then, constant current constant voltage (CCCV) charging was performed, charging to 4.1V at 2.0mA and maintaining a constant voltage for 2 hours. Finally, constant current discharging at 1.0mA until 3.0V was performed, and the discharge capacity at this point was measured. It should be noted that the charge / discharge and open-circuit potential measurements were performed at 25℃ (the same applies below).

[0073] (Preparation of the recovery agent)

[0074] Fluorene was dissolved in a non-reactive atmosphere at a concentration of 1.0 mol / L relative to dimethoxyethane (DME) solvent. Then, 1.0 mol / L lithium metal was added and stirred to prepare the stock solution of the restoring agent. It should be noted that the reaction between fluorene and lithium metal is presumably represented by the above formula (5). The stock solution of the restoring agent was a deep orange solution. Then, an equal volume of electrolyte was added and stirred to prepare the restoring agent. The electrolyte was prepared by dissolving LiPF6 in a mixed solvent (electrolyte solvent) containing 30% by volume EC, 40% by volume DMC, and 30% by volume EMC at a concentration of 1 mol / L. The restoring agent was a pale yellow solution.

[0075] (Restoration of degraded batteries)

[0076] The degraded battery was charged at a constant current of 1.0 mA until it reached 4.0 V, thus adjusting the voltage to 4.0 V. Then, a portion of the degraded battery was opened under an argon atmosphere, and 0.5 mL of restoring agent was injected using a pipette to seal the opening. It was then charged at a constant current of 1.0 mA until it reached 4.0 V, and then maintained at a constant voltage for 25 hours. This process restored the degraded battery, yielding a restored battery.

[0077] (Evaluation of battery recovery)

[0078] For recovered batteries, the discharge capacity is measured in the same manner as for degraded batteries, and the ratio of the discharge capacity of the recovered battery to that of the degraded battery (capacity ratio) is calculated.

[0079] [Experimental Example 2]

[0080] Except for the following restoration procedures for the degraded battery, the process is the same as in Example 1. In the restoration of the degraded battery, the voltage of the battery was first adjusted to 4.0V, just as in Example 1. Then, a portion of the degraded battery was opened under an argon atmosphere, and 0.5 mL of a restoration agent containing electrolyte was injected using a pipette to seal the opening. The battery was then left in an open-circuit state for 25 hours without charging or discharging.

[0081] [Experiment Example 3]

[0082] In preparing the restorer, the unmixed restorer stock solution was used directly as the restorer, and otherwise the same procedure was followed as in Experimental Example 1.

[0083] [Experiment Example 4]

[0084] In preparing the restorer, the unmixed restorer stock solution was used directly as the restorer, and otherwise the same procedure was followed as in Experimental Example 2.

[0085] [Experiment Example 5]

[0086] In preparing the restorer, 9,9-dimethylfluorene was used instead of fluorene, and otherwise the process was the same as in Experimental Example 4. It should be noted that the reaction between 9,9-dimethylfluorene and lithium metal is presumably represented by the above formula (6). The restorer (restorer stock solution) was a deep blue solution.

[0087] [Experimental Results]

[0088] The results of Experiments 1-5 are summarized in Table 1. In Experiment 1, a recovery effect was confirmed. This is presumably because the recovery agent acts directly on the positive electrode, resulting in a recovery reaction that supplies electrons and metal ions to the positive electrode. It should be noted that, to date, polyphenylene, polyphenylene, and polyphenanthrene have been reported to react with lithium to form free radical anions. In contrast, fluorene reacts with lithium to form anions, rather than free radical anions (e.g., see Reference 1: CAN Journal CHEM 38(1960)2450-2456). This shows that organic anionic molecules also function as recovery agents.

[0089] In Experiment 2, no constant voltage was applied, and the circuit was kept open, yet a recovery effect was observed. However, as shown in Patent Document 1 above, a naphthyllithium liquid composition prepared using THF solvent was used as a recovery agent, and its performance was improved by applying a constant voltage. The reasoning is presumably that by applying a constant voltage, the potential of the positive electrode remains high, thus maintaining a high potential difference between the positive electrode and the recovery agent, which is the driving force of the recovery reaction. In contrast, it is presumed that in the fluorene-lithium liquid composition, the overvoltage of the reaction between the reduced fluorene and the positive electrode is small. Therefore, even if the reaction proceeds and the potential of the positive electrode decreases, the potential difference between the positive electrode and the recovery agent, which is the driving force of the reaction, is maintained. Thus, capacity can be adequately recovered even without applying a constant voltage.

[0090] In Experiment 3, the unmixed electrolyte concentrate of the restoring agent was used directly as the restoring agent, and a restoring effect was observed. However, as shown in Patent Document 1 above, a naphthyllithium liquid composition prepared using THF solvent was used as the restoring agent, and its performance was improved by adding an electrolyte. The reason for this is presumably that the naphthyllithium liquid composition prepared using THF solvent exhibits a high reducing power of 0.64 V based on Li metal, but when the naphthyllithium liquid composition is mixed with an electrolyte in a 5:5 ratio, the reducing power is moderated to 1.2 V to 1.9 V based on Li metal. In contrast, for the fluorene lithium liquid composition, the potential measured without mixing with an electrolyte is 1.1 V based on Li metal, indicating a moderate reducing power. Therefore, it is presumed that even without mixing with an electrolyte to moderate the reducing power, the capacity can be adequately restored.

[0091] In Experiment 4, the recovery agent without electrolyte was used directly, and constant voltage charging was not performed, but a recovery effect was observed.

[0092] In Experiment 5, 9,9-dimethylfluorene, formed by replacing two protons of the five-membered ring of the fluorene molecule with methyl groups, was used instead of fluorene. The recovery agent, without mixing with the electrolyte, was applied directly, and no constant voltage was applied, yet a recovery effect was observed. This suggests that the 9,9-dimethylfluorene lithium liquid composition also possesses reducing power suitable for capacity recovery.

[0093]

[0094] This application is based on Japanese Patent Application No. 2023-177149, filed on October 13, 2023, the entire contents of which are incorporated herein by reference.

[0095] Industrial availability

[0096] This invention can be applied to the field of energy storage devices.

[0097] Symbol Explanation

[0098] 20 Non-aqueous electrolyte secondary battery, 21 Battery casing, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Non-aqueous electrolyte.

Claims

1. A capacity restorer for a storage device that uses metal ions as carrier ions, comprising a reduced aromatic hydrocarbon compound, a metal ion of the same kind as the carrier ion, and a capacity restorer solvent, wherein the aromatic hydrocarbon compound is a fluorene compound having a fluorene skeleton.

2. The restorative agent according to claim 1, wherein, The aromatic hydrocarbon compound is fluorene or a fluorene derivative.

3. The restorative agent according to claim 1, wherein, The aromatic hydrocarbon compound is fluorene or 9,9-dimethylfluorene.

4. The restorative agent according to any one of claims 1 to 3, wherein, The solvent for the restorative agent is an ether compound.

5. The restorative agent according to any one of claims 1 to 3, wherein, The restorer does not contain the electrolyte solvent used in the storage device.

6. A recovery method for restoring the capacity of an energy storage device using metal ions as carrier ions, comprising: A recovery process in which the capacity of a storage device is restored by adding the recovery agent as described in any one of claims 1 to 3 into the storage device.

7. The recovery method according to claim 6, wherein, In the recovery process, the recovery agent is added to the energy storage device and kept directly in an open-circuit state.

8. A method for manufacturing an energy storage device, comprising: Preparation steps for energy storage devices that use metal ions as carrier ions and have deteriorated capacity. and A recovery process in which the capacity of a storage device is restored by adding the recovery agent as described in any one of claims 1 to 3 into the storage device.

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