Recovery agent, recovery method for non-aqueous electrolyte secondary battery, and manufacturing method for non-aqueous electrolyte secondary battery

Abstract

To provide a novel recovery method for a non-aqueous electrolyte secondary battery.SOLUTION: A recovery agent includes a solute having an aromatic hydrocarbon compound in a reduced state and a metal ion, a solvent that dissolves the solute, and an electrolyte. A recovery method of a non-aqueous electrolyte secondary battery includes a recovery step of injecting the recovery agent into the non-aqueous electrolyte secondary battery to recover the capacity of the non-aqueous electrolyte secondary battery.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a recovery agent, a method for recovering a nonaqueous electrolyte secondary battery, and a method for manufacturing a nonaqueous electrolyte secondary battery. [Background technology]

[0002] Conventionally, as a method for restoring the capacity of a nonaqueous electrolyte secondary battery whose capacity has deteriorated due to long-term storage or charge-discharge cycles, a method has been proposed in which a third electrode is provided in addition to a positive electrode and a negative electrode, the third electrode and the positive electrode are externally short-circuited, and carrier ions are supplied from the third electrode to the positive electrode (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-076358 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, there is a problem that the structure of the battery becomes complicated by incorporating a third electrode. For this reason, a new recovery method for a nonaqueous electrolyte secondary battery that can recover the capacity without using a third electrode has been desired.

[0005] The present disclosure has been made to solve such problems, and has as its main object to provide a novel method for restoring a non-aqueous electrolyte secondary battery. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that when a solution containing a solute having a reduced aromatic hydrocarbon compound and a metal ion and a solvent that dissolves the solute is injected into a nonaqueous electrolyte secondary battery, the capacity is restored. In particular, the present inventors have found that when the restoring agent contains, in addition to the above-mentioned solute and solvent, an electrolyte such as that used in nonaqueous electrolyte secondary batteries, the capacity of the battery after restoration is further improved, and have completed the present disclosure.

[0007] That is, the recovery agent disclosed in the present specification is A recovery agent for recovering the capacity of a non-aqueous electrolyte secondary battery having a metal ion as a carrier ion, The present invention includes a solute having a reduced aromatic hydrocarbon compound and a metal ion, a solvent for dissolving the solute, and an electrolyte. It is something.

[0008] The method for recovering a non-aqueous electrolyte secondary battery disclosed in the present specification includes the steps of: A method for recovering the capacity of a non-aqueous electrolyte secondary battery that uses metal ions as carrier ions, comprising the steps of: a recovery step of injecting the recovery agent into the nonaqueous electrolyte secondary battery to recover the capacity of the nonaqueous electrolyte secondary battery; It includes.

[0009] The method for producing a nonaqueous electrolyte secondary battery disclosed in the present specification further comprises the steps of: a battery preparation step of preparing a capacity-degraded nonaqueous electrolyte secondary battery having metal ions as carrier ions; a recovery step of recovering the capacity of the nonaqueous electrolyte secondary battery in the above-mentioned recovery method for the nonaqueous electrolyte secondary battery; It includes. Effect of the Invention

[0010] The recovery agent, the recovery method for a non-aqueous electrolyte secondary battery, and the manufacturing method for a non-aqueous electrolyte secondary battery provide a novel recovery method for a non-aqueous electrolyte secondary battery and a novel manufacturing method for a non-aqueous electrolyte secondary battery using the recovery agent. The reason why such an effect is obtained is presumed to be as follows. For example, it is presumed that a recovery agent containing a solute having an aromatic hydrocarbon compound in a reduced state and a metal ion, and a solvent that dissolves the solute, acts directly on the positive electrode by simply injecting the solute into a non-aqueous electrolyte secondary battery, and causes a recovery reaction that supplies electrons and metal ions to the positive electrode. In particular, a recovery agent containing an electrolyte in addition to the above-mentioned solute and solvent further improves the capacity of the battery after recovery. The reason for this is presumed to be as follows. For example, a recovery agent containing an electrolyte has a larger solvation with respect to the aromatic hydrocarbon compound than a recovery agent that does not contain an electrolyte, and the aromatic hydrocarbon compound in a reduced state is more likely to release the metal ion. For this reason, it is believed that the use of a recovery agent containing an electrolyte reduces the activation energy required when electrons and metal ions are supplied to the positive electrode, allowing electrons and metal ions to be supplied smoothly to the positive electrode, resulting in an efficient recovery reaction and improved battery capacity after recovery. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery 20. FIG. [Diagram 2] FIG. 2 is an explanatory diagram showing an example of a recovery reaction scheme. [Diagram 3] 1 is a graph showing the discharge capacities before and after capacity recovery in Experimental Examples 1 to 4. [Figure 4] 4 shows ESR measurement results of the electrolyte of the battery after injection of a recovery agent in Experimental Example 2. [Diagram 5] 4 shows ESR measurement results for the recovery agents of Experimental Examples 2 and 4. [Figure 6] 4 shows ESR measurement results for the recovery agents of Experimental Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The recovery agent disclosed in this specification is for recovering the capacity of a non-aqueous electrolyte secondary battery. Also, the method for recovering a non-aqueous electrolyte secondary battery disclosed in this specification is a method for recovering the capacity of a non-aqueous electrolyte secondary battery. Preferred embodiments of the recovery agent and the method for recovering a non-aqueous electrolyte secondary battery will be described below.

[0013] [Non-aqueous electrolyte secondary battery] First, the non-aqueous electrolyte secondary battery to be recovered will be described. The non-aqueous electrolyte secondary battery is preferably a non-aqueous electrolyte secondary battery having metal ions as carrier ions. The non-aqueous electrolyte secondary battery may use, for example, Group 1 ions such as lithium, sodium, and potassium, or Group 2 ions such as magnesium, calcium, and strontium as carrier ions. Also, the non-aqueous electrolyte secondary battery may be an ion secondary battery such as a lithium-ion secondary battery or a metal secondary battery such as a lithium metal secondary battery. Below, as an example, the case where the non-aqueous electrolyte secondary battery is a lithium-ion secondary battery will be mainly described.

[0014] The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode may have a positive electrode active material capable of occluding and releasing lithium ions. The negative electrode may have a negative electrode active material capable of occluding and releasing lithium ions. The non-aqueous electrolyte may be interposed between the positive electrode and the negative electrode and conduct lithium ions.

[0015] 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 mixture, applying and drying it on the surface of a current collector, and compressing it as necessary 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 TiS 2 、TiS 3 、MoS 3 、FeS 2 etc., and the basic composition formula Li (1-x) MnO 2 (0 < x < 1, etc., the same below) or Li (1-x) Mn2 O 4 such as a lithium manganese composite oxide with the basic composition formula of Li (1-x) CoO 2 such as a lithium cobalt composite oxide with the basic composition formula of Li (1-x) NiO 2 such as a lithium nickel composite oxide with the basic composition formula of Li (1-x) Ni a Co b Mn c O 2 (a + b + c = 1) such as a lithium nickel cobalt manganese composite oxide with the basic composition formula of LiV 2 O 3 such as a lithium vanadium composite oxide with the basic composition formula of V 2 O 5 Transition metal oxides such as these can be used. Among these, lithium transition metal composite oxides, for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , LiV 2 O 3 etc. are preferable. Also, Li y Ni (1-x) M x O 2 (where 0 ≦ x ≦ 0.5, 0 < y < 1.20, and M is at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, and B) is also preferable, and it may be used in combination with a lithium manganese composite oxide having a spinel structure. Note that the "basic composition formula" means that other elements may be included. The positive electrode active material may have a redox potential of 3.5 V or more, 4.0 V or more, or 4.5 V or more based on the Li metal standard.

[0016] In the positive electrode, the conductive material may be, for example, one or more of graphite such as natural graphite (scale graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.), etc. Among these, from the viewpoint of electronic conductivity and coating property, carbon black and acetylene black are preferable as the conductive material. The binder plays a role of binding the active material particles and the conductive material particles, and may be, for example, fluorine-containing resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, etc., or thermoplastic resin such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), etc., used alone or as a mixture of two or more kinds. In addition, aqueous binders such as cellulose-based carboxymethylcellulose (CMC), styrene butadiene copolymer (SBR), and aqueous dispersions of polyvinyl alcohol can also be used. As a solvent for dispersing the positive electrode active material, conductive material, and binder, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. In addition, a dispersant, a thickener, and the like can be added to water, and the active material can be slurried with latex such as SBR. As a thickener, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more kinds. Examples of application methods include roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, and bar coater, and any thickness and shape can be obtained by using any of these. The basis weight of the positive electrode mixture is not particularly limited, but for example, 5 mg / cm 2 May exceed 6mg / cm 2 or more, 7 mg / cm 2The weight of the positive electrode mixture may be, for example, 20 mg / cm 2 The following may be used. As the current collector, in addition to aluminum, titanium, stainless steel, nickel, iron, baked carbon, conductive polymer, conductive glass, etc., aluminum or copper whose surface is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance can be used. The surface of these can also be subjected to oxidation treatment. The shape of the current collector can be a foil, film, sheet, net, punched or expanded one, lath, porous body, foam, fiber group formation, etc. The thickness of the current collector used is, for example, 1 to 500 μm.

[0017] The negative electrode may be formed by bonding a negative electrode active material and a current collector, or may be formed by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary. Examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbonaceous materials capable of absorbing and releasing lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of the carbonaceous material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, amorphous carbon, diamond-like carbon, fullerene, carbon nanotubes, and carbon nanohorns. Among these, graphites such as artificial graphite and natural graphite are preferred because they have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and can suppress self-discharge when a lithium salt is used as a supporting salt, and can reduce irreversible capacity during charging. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. Of these, carbonaceous materials are preferable as the negative electrode active material from the viewpoint of safety. The conductive material, binder, solvent, and the like used in the negative electrode can be the same as those exemplified for the positive electrode. The negative electrode active material may have an oxidation-reduction potential of 1.0 V or less, 0.5 V or less, or 0.3 V or less based on Li metal. The weight of the negative electrode composite material is, for example, 3 mg / cm. 2 May exceed 4mg / cm 2 The weight of the negative electrode mixture may be, for example, 15 mg / cm. 2 The negative electrode current collector may be made of copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., or may be made of copper or the like whose surface has been treated with carbon, nickel, titanium, silver, etc., for the purpose of improving adhesion, conductivity, and reduction resistance. The surface of these materials may also be oxidized. The shape of the current collector may be the same as that of the positive electrode.

[0018] The non-aqueous electrolyte may contain a supporting salt and an organic solvent. The supporting salt may be, for example, LiPF 6 , LiClO 4 , LiAsF 6 , LiAlCl 4 , LiBF 4 , LiSbF 6 Inorganic salts such as LiN(FSO 2 ) 2 (also called LiFSI), LiN(CF 3 SO 2 ) 2 (also called LiTFSI), LiN(C 2 F 5 SO 2 ) 2 Examples of the organic salt include organic salts such as LiBETI. These supporting salts may be used alone or in combination. The concentration of the supporting salt is preferably 0.1 to 2.0M, more preferably 0.8 to 1.2M. As the organic solvent, for example, an aprotic organic solvent can be used. Examples of such organic solvents include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers, and fluorinated derivatives thereof. Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic esters include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ethers include dimethoxyethane and ethylene glycol dimethyl ether. These may be used alone or in combination. In addition, the non-aqueous electrolyte may be a nitrile-based solvent such as acetonitrile or propylnitrile, an ionic liquid, or a gel electrolyte. The non-aqueous electrolyte may contain additives such as a film-forming agent or a flame retardant.

[0019] The non-aqueous electrolyte secondary battery may have 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 range of use of the non-aqueous electrolyte secondary battery, and examples thereof include polymer non-woven fabrics such as polypropylene non-woven fabrics and polyphenylene sulfide non-woven fabrics, and thin microporous films such as olefin resins such as polyethylene and polypropylene, and fluororesins. These may be used alone or in combination.

[0020] The nonaqueous electrolyte secondary battery may have an openable / closable electrolyte injection port in a battery case that houses the positive electrode, the negative electrode, and the nonaqueous electrolyte, allowing the recovery agent to be easily injected through the electrolyte injection port.

[0021] The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and examples thereof include coin type, button type, sheet type, laminated type, cylindrical type, flat type, and square type. The nonaqueous electrolyte secondary battery may also be applied to large batteries used in electric vehicles and the like. FIG. 1 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery 20. The nonaqueous electrolyte secondary battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and provided at the bottom of the battery case 21, a negative electrode 23 having a negative electrode active material and provided at a position facing the positive electrode 22 via a separator 24, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. In the nonaqueous electrolyte secondary battery 20, a nonaqueous electrolyte 27 is filled in the space between the positive electrode 22 and the negative electrode 23.

[0022] A non-aqueous electrolyte secondary battery has an internal resistance of 5 Ωcm when the capacity of the battery is not degraded (also called a pre-degraded battery). 2 It may be in excess of 7 Ωcm 2 It may be 10 Ωcm or more. 2In non-aqueous electrolyte secondary batteries, such as batteries for electric vehicles, in which the thickness or weight of the electrode composite is large and the internal resistance is relatively high, the capacity and cycle capacity retention rate of the battery after recovery are often low simply by injecting a recovery agent, so it is highly meaningful to apply the recovery method for non-aqueous electrolyte secondary batteries of the present disclosure. Note that the internal resistance of the battery before deterioration is 50 Ω cm 2 It may be the following:

[0023] [Recovery potion] Next, the restoring agent will be described. The restoring agent includes a solute having a reduced aromatic hydrocarbon compound and a metal ion, a solvent for dissolving the solute, and an electrolyte. The restoring agent may be a pre-prepared restoring agent, or may be prepared in the preparation step for preparing the restoring agent. In the restoring agent, the reduced aromatic hydrocarbon compound and the metal ion may be dissociated or associated.

[0024] In the recovery agent, the aromatic hydrocarbon compound is preferably polyacene or polyphenyl. Polyacene is a compound having a structure in which a plurality of benzene rings are condensed, and examples thereof include naphthalene, anthracene, tetracene, and pentacene. Polyphenyl is a compound having a structure in which a plurality of phenyl groups are linked by single bonds, and examples thereof include biphenyl, ortho-terphenyl, meta-terphenyl, para-terphenyl, para-quaterphenyl, and para-quinquiphenyl. Polyacene and polyphenyl may have a substituent on the aromatic ring, or may contain a heteroatom in the aromatic ring. Examples of the substituent include a halogen atom, an alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, and a hydroxyl group. Examples of the heteroatom include nitrogen, oxygen, and sulfur. Examples of polyacene containing a heteroatom in an aromatic ring include quinoline, chromene, and acridine. Examples of polyphenyl containing a heteroatom in an aromatic ring include bipyridine. In addition to the above, the aromatic hydrocarbon compound is preferably a compound in which a cycloalkane is bonded to an aromatic ring, such as cyclohexylbenzene. Among the above, the aromatic hydrocarbon compound is preferably one or more of naphthalene, biphenyl, anthracene, ortho-terphenyl, and para-terphenyl, and more preferably one or more of naphthalene and biphenyl. The aromatic hydrocarbon compound may be, for example, one or more of formula (1) and formula (2). The aromatic hydrocarbon compound in a reduced state is, for example, the above-mentioned aromatic hydrocarbon compound in a reduced state (also called a reduced form), and is, for example, a radical anion. The aromatic hydrocarbon compound in a reduced state may be, for example, one or more of the reduced form of the compound of formula (1) and the reduced form of the compound of formula (2).

[0025] [ka]

[0026] In the recovery agent, the metal ion is not particularly limited, and may be, for example, the same type of metal ion as the carrier ion of the nonaqueous electrolyte secondary battery. In the recovery agent, the metal ion may be, for example, one or more of alkali metal ions such as lithium ions, sodium ions, and potassium ions, and alkaline earth metals such as magnesium ions, calcium ions, and strontium ions.

[0027] The recovery agent may contain, as a solute, one or more compounds of formula (3) and formula (4). In the compounds of formula (3) and formula (4), the radical anion portion is the above-mentioned aromatic hydrocarbon compound in a reduced state, and the metal cation portion is the above-mentioned metal ion.

[0028] [ka]

[0029] In the recovery agent, the solvent is preferably one that dissolves the above-mentioned solute and is liquid at room temperature. Examples of the solvent include aprotic solvents such as ether compounds. The ether compound may be a compound having an ether skeleton, and may be a cyclic ether or a chain ether. The ether compound is preferably one having two or more ether groups in the molecule. The solvent may be one or more of tetrahydrofuran (THF), dimethoxyethane (DME), diethoxyethane (DEE), dioxolane (DOL), and dioxane (DOX). The solvent is preferably one or more of tetrahydrofuran and dimethoxyethane.

[0030] The recovery agent may be obtained by adding an aromatic hydrocarbon compound and a metal in a metallic state, not an ion state, to a solvent. For example, the recovery agent may be obtained by one or more of formulas (5) and (6). More specifically, the recovery agent may be obtained by reacting naphthalene, diphenyl, or terphenyl with Li metal in a THF solvent, as shown in formulas (7) to (9). Also, the recovery agent may be obtained by reacting naphthalene, diphenyl, or terphenyl with Li metal in a DME solvent, according to formulas (7) to (9). In this way, a recovery agent containing a solute having an aromatic hydrocarbon compound in a reduced state and a metal ion, and a solvent that dissolves the solute, can be easily prepared. The recovery agent may be prepared by adding a metal to a precursor obtained by adding an aromatic hydrocarbon compound to a solvent. The recovery agent may be prepared under an inert atmosphere, such as an argon atmosphere or a nitrogen atmosphere. The recovery agent may be prepared under a low dew point environment, such as a dew point of -20°C or less, -40°C or less, or -60°C or less. The restoring agent may be prepared by stirring the solvent, the aromatic hydrocarbon compound, and the metal, and a stirrer may be used for this purpose. The solvent is preferably dehydrated by distillation or immersion in molecular sieves to reduce the water content to 100 ppm or less.

[0031] [ka]

[0032] [ka]

[0033] The above-described restoring agent is also referred to as a restoring agent stock solution. In the restoring agent stock solution, the concentration of the solute (which may be the concentration of each of the aromatic hydrocarbon compound in a reduced state and the metal ion) may be 0.05 mol / L or more and 1.1 mol / L or less, 0.1 mol / L or more and 1.1 mol / L or less, or 0.5 mol / L or more and 1.0 mol / L or less. This concentration may be equal to or less than the solubility. The number of moles M of the aromatic hydrocarbon compound in a reduced state contained in the restoring agent may be 0.05 mol / L or more and 1.1 mol / L or less, or 0.1 mol / L or more and 1.1 mol / L or less, or 0.5 mol / L or more and 1.0 mol / L or less. In addition, this concentration may be equal to or less than the solubility. In addition, the number of moles M of the aromatic hydrocarbon compound in a reduced state contained in the restoring agent may be equal to or less than the solubility. A (mol) and the number of moles of metal ion MB (mol) M A / M B is preferably 1 / 1, but may be 1.1 / 1.0 to 1.0 / 1.1, or may be 1.2 / 1.0 to 1.0 / 1.2.

[0034] The electrolyte may be, for example, a non-aqueous electrolyte exemplified in the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, or may contain an organic solvent exemplified in the non-aqueous electrolyte and a supporting salt exemplified in the non-aqueous electrolyte. The solvent of the electrolyte may be different from the solvent of the recovery agent stock solution, but is preferably one or more of cyclic carbonate, chain carbonate, and cyclic ester, more preferably one or more of cyclic carbonate and chain carbonate, and further preferably contains cyclic carbonate and chain carbonate. The solvent of the electrolyte may be one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt of the electrolyte may be different from the solute of the recovery agent stock solution, but is preferably LiPF 6 The electrolyte may be an inorganic salt such as LiFSI or an organic salt such as LiFSI. The electrolyte may contain additives such as a film-forming agent and a flame retardant. The composition of the electrolyte may be the same as the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery to be restored. In the recovery agent, the content of the electrolyte may be, for example, 10% by volume to 90% by volume, 20% by volume to 80% by volume, 30% by volume to 70% by volume, 30% by volume to 60% by volume, or 30% by volume to 50% by volume. When preparing a recovery agent containing an electrolyte, it is sufficient to mix the recovery agent stock solution and the electrolyte, and the recovery agent stock solution and the electrolyte may be stirred, or may be stirred using a stirrer or the like.

[0035] The redox potential of the recovery agent may be higher than that of the negative electrode and lower than that of the positive electrode. The redox potential of the recovery agent may be, for example, 0.5 V to 2.5 V, 1.0 V to 2.0 V, or 1.2 V to 1.9 V, based on Li metal.

[0036] The recovery agent may be, for example, one in which one or more signals are confirmed in the g value range of 1.996 to 2.020 measured by the electron spin resonance (ESR) method. In such a recovery agent, it is considered that the aromatic hydrocarbon compound in a reduced state exists in the form of a radical. This g value is calculated by using the resonance frequency ν (Hz) and the magnetic field strength H (mT) obtained by the ESR measurement, and is expressed as hν=gμ B H (where h is the Planck constant (6.626176×10 -34 Js), μ B is the Bohr magneton (9.274078×10 -24 JT -1 ) is derived using the formula:

[0037] [Recovery method for non-aqueous electrolyte secondary batteries] Next, a method for restoring a non-aqueous electrolyte secondary battery will be described. This method for restoring a capacity of a non-aqueous electrolyte secondary battery includes a restoring step of restoring the capacity of the non-aqueous electrolyte secondary battery using the above-mentioned restoring agent.

[0038] (Recovery process) In this process, a recovery agent is injected into the nonaqueous electrolyte secondary battery to recover the capacity of the nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery to be recovered is a battery in a state of capacity degradation (also called a degraded battery), and may be, for example, a battery in a state of capacity degradation relative to the rated capacity of the nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery to be recovered may be an unused product or a used product. Even an unused product may experience capacity degradation due to long-term storage, etc.

[0039] In this step, when injecting the recovery agent, the nonaqueous electrolyte secondary battery may be opened and the recovery agent may be injected to seal the opening, or the recovery agent may be injected into the nonaqueous electrolyte secondary battery by injection or the like to seal the perforation. When injecting the recovery agent, it may be injected under an inert atmosphere such as an argon atmosphere or a nitrogen atmosphere. The recovery agent may be injected so as to contact at least the positive electrode, but may also be mixed with the nonaqueous electrolyte. The injection amount of the recovery agent can be appropriately determined depending on the configuration of the nonaqueous electrolyte secondary battery, the degree of deterioration, and the like. The injection amount of the recovery agent may be, for example, 1% or more and 100% or less, 10% or more and 75% or less, or 25% or more and 50% or less with respect to the volume [mL] of the nonaqueous electrolyte contained in the nonaqueous electrolyte secondary battery. In this step, the capacity of the nonaqueous electrolyte secondary battery may be restored by allowing a predetermined time to pass after the injection of the recovery agent. In this case, the battery may be left to stand, shaken, or a voltage may be applied. This time period may be, for example, 1 hour or more and 48 hours or less, 6 hours or more and 36 hours or less, or 12 hours or more and 24 hours or less.

[0040] In this step, when the recovery agent is injected, a recovery reaction such as that shown in FIG. 2 is thought to occur. FIG. 2 is an explanatory diagram showing an example of a recovery reaction scheme, and is an explanatory diagram showing a scheme in which the positive electrode active material is a lithium transition metal composite oxide. As shown in FIG. 2, the recovery agent reacts with the radical anion of an aromatic hydrocarbon compound (Are·- in FIG. 2) and a metal ion (Li + ) acts as a reducing agent that donates electrons, and the deteriorated positive electrode (Li in Figure 2) n-y MeO 2 ), electrons and metal ions are donated from the reducing agent to the positive electrode, and the capacity can be restored. It is believed that a zero-valent complex of an electrically neutral aromatic hydrocarbon compound and a lithium atom behaves like metallic lithium. Therefore, when the aforementioned zero-valent lithium complex comes into contact with a deteriorated positive electrode, it supplies electrons and metal ions to the positive electrode, and is incorporated into the positive electrode in a state that retains battery activity, which is believed to restore the capacity of the battery. Metal ions are then added to LiPF 6Even if the electrolyte is brought into contact with a deteriorated positive electrode in a salt state such as the above, such a capacity recovery effect cannot be obtained.

[0041] In this process, since a recovery agent containing an electrolyte is used in addition to the above-mentioned solute and solvent, the capacity of the battery after recovery is improved. The reason for this is presumed to be as follows. For example, a recovery agent containing an electrolyte has a larger solvation with respect to the aromatic hydrocarbon compound than a recovery agent not containing an electrolyte, and the radical anion of the aromatic hydrocarbon compound is more likely to release electrons and metal ions. For this reason, when a recovery agent containing an electrolyte is used, the activation energy when the electrons and metal ions of the solute are supplied to the positive electrode is reduced, the supply of metal ions to the positive electrode is smooth, the recovery reaction proceeds efficiently, and the capacity of the battery after recovery is improved. In addition, when a recovery agent not containing an electrolyte is injected into a non-aqueous electrolyte secondary battery, there is a concern that the ionic conductivity of the non-aqueous electrolyte may decrease and the polarization overvoltage may increase, but it is believed that the use of a recovery agent containing an electrolyte can suppress the decrease in ionic conductivity and the increase in polarization overvoltage. In this way, the capacity of the non-aqueous electrolyte secondary battery is restored, and a non-aqueous electrolyte secondary battery (also called a restored battery) with restored capacity is obtained.

[0042] In the recovery agent and the recovery method for a non-aqueous electrolyte secondary battery described above, the capacity of the non-aqueous electrolyte secondary battery can be recovered by injecting the recovery agent into the non-aqueous electrolyte secondary battery. This recovery agent and the recovery method for a non-aqueous electrolyte secondary battery can provide a novel recovery method that does not require a third electrode. In addition, in the recovery agent and the recovery method for a non-aqueous electrolyte secondary battery, the recovery agent containing an electrolyte is used, thereby further improving the capacity of the battery after recovery.

[0043] It goes without saying that the present disclosure is in no way limited to the above-described embodiment, and can be embodied in various forms as long as it falls within the technical scope of the present disclosure.

[0044] For example, in the above-mentioned embodiment, the method for recovering a nonaqueous electrolyte secondary battery has been described, but in this method for recovering a nonaqueous electrolyte secondary battery, a new nonaqueous electrolyte secondary battery with recovered capacity can be manufactured using a nonaqueous electrolyte secondary battery with deteriorated capacity. Therefore, the method for recovering a nonaqueous electrolyte secondary battery can also be said to be a method for manufacturing a nonaqueous electrolyte secondary battery. A nonaqueous electrolyte secondary battery may be manufactured using the above-mentioned method for recovering a nonaqueous electrolyte secondary battery. The method for manufacturing a nonaqueous electrolyte secondary battery may include a battery preparation step of preparing a capacity-deteriorated nonaqueous electrolyte secondary battery using a metal ion as a carrier ion, and a recovery step of recovering the capacity of the nonaqueous electrolyte secondary battery using the above-mentioned method for recovering a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery prepared in the battery preparation step may be the same as the deteriorated battery described in the above-mentioned embodiment. EXAMPLES

[0045] Hereinafter, an example of recovering a lithium ion battery using the method for recovering a non-aqueous electrolyte secondary battery according to the present disclosure will be described as an embodiment. Note that Experimental Examples 2 and 4 correspond to working examples, and Experimental Examples 1 and 3 correspond to reference examples. The present disclosure is not limited to the following examples, and it goes without saying that the present disclosure can be implemented in various forms as long as it falls within the technical scope of the present disclosure.

[0046] [Experimental Example 1] (Non-aqueous electrolyte secondary battery (battery before deterioration)) The positive electrode is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 The positive electrode composite material, which contains 92 wt% of ethylenediaminetetraacetate (NCM, manufactured by Toda Kogyo Co., Ltd.), 5 wt% of acetylene black (manufactured by Denka Co., Ltd.), and 3 wt% of polyvinylidene fluoride (manufactured by Kureha Co., Ltd.), is placed in a 7 mg / cm2 coating. 2 The negative electrode was made of a negative electrode composite material containing 98 wt% graphite (OMAC1.5s, Osaka Gas Chemicals), 1 wt% carboxymethyl cellulose (Daicel), and 1 wt% styrene butadiene rubber (JSR), with a weight of 4 mg / cm. 2The electrolyte was a mixture of 30 vol% ethylene carbonate, 40 vol% dimethyl carbonate, and 30 vol% ethyl methyl carbonate, dissolved in LiPF 6 The electrolyte was dissolved to a concentration of 1.1M. A polypropylene separator impregnated with 1mL of electrolyte was sandwiched between the positive and negative electrodes to prepare a laminate cell. This was used as the pre-degradation battery. The electrode area of ​​the cell was 10 cm2 for both the positive and negative electrodes. 2 When the resistance of the battery before deterioration was measured with a digital multimeter, the cell resistance was 10 Ω cm 2 In this nonaqueous electrolyte secondary battery, the lower limit discharge voltage was 3.0V and the upper limit charge voltage was 4.1V, which are determined according to the battery configuration.

[0047] (Deteriorated battery) The laminated cell thus produced was charged to a capacity (SOC=50%) equivalent to 50% of the electric capacity of the cell in the voltage range of 3.0V to 4.1V, and Li was extracted from the positive electrode to obtain a positive electrode with a simulated reduced capacity (also called a degraded positive electrode). The cell was then disassembled, and the degraded positive electrode was removed. A laminated cell was then produced in the same manner as the pre-degraded battery, except that the degraded positive electrode was used as the positive electrode. This was used as a degraded battery. The degraded battery was CC-charged at 0.9 mA to 4.1V, and then CC-discharged at 0.9 mA to 3.0V, and the discharge capacity was measured.

[0048] (Recovery Agent) Under an inert atmosphere, naphthalene was dissolved in tetrahydrofuran (THF) solvent to a concentration of 1.0 mol / L, and then 1.0 mol / L of lithium metal was added and stirred to prepare a dark green radical anion liquid composition (lithium naphthalenide + THF) as a recovery agent stock solution by the reaction shown in the above formula (7), which was used as the recovery agent.

[0049] (Recovery of degraded batteries) A part of the deteriorated battery was opened under an argon atmosphere, 0.5 mL of the recovery agent was injected using a pipette, the opened part was sealed, and the battery was left as it was for 24 hours (recovery treatment). In this way, the deteriorated battery was restored, and a restored battery was obtained.

[0050] (Recovery battery evaluation) The recovered battery was CC-charged at 0.9 mA in the voltage range of 3.0 V to 4.1 V, and then CC-discharged at 0.9 mA to 3.0 V, and the discharge capacity at that time was measured.

[0051] [Experimental Example 2] Experimental Example 2 was the same as Experimental Example 1, except that a recovery agent was used that was prepared by mixing the recovery agent (undiluted recovery agent) of Experimental Example 1 with the following electrolyte solution in a volume ratio of 5:5. The electrolyte solution was prepared by dissolving LiFSI to a concentration of 1.1 M in a mixed solvent containing 30 vol% ethylene carbonate, 40 vol% dimethyl carbonate, and 30 vol% ethyl methyl carbonate.

[0052] [Experimental Examples 3 and 4] Experimental Example 3 was the same as Experimental Example 1, except that the solvent of the recovery agent stock solution was changed from THF to dimethoxyethane (DME). Experimental Example 4 was the same as Experimental Example 2, except that the solvent of the recovery agent stock solution was changed from THF to DME.

[0053] [ESR measurement] Electron spin resonance (ESR) measurements were performed on various samples using an ESR device manufactured by Bruker, ELEXSYS-E500. Measurements were performed by placing 50 μL of sample in a quartz ESR cell for measuring aqueous solutions under the conditions shown in Table 1. As samples, the electrolyte extracted from the battery immediately after injection of the recovery agent in Experimental Example 2, the electrolyte extracted from the battery after leaving it for 5 days after injection of the recovery agent in Experimental Example 2, the recovery agent in Experimental Example 1, the recovery agent in Experimental Example 2, and the recovery agent in Experimental Example 4 were used. The fact that lithium naphthalenide exhibits activity in electron spin resonance has been reported, for example, in J. Am. Chem. Soc. 1954, 76, 13, 3367-3369.

[0054] [Table 1]

[0055] [Experimental Results] The results of Experimental Examples 1 to 4 are summarized in Table 2. In addition, for Experimental Examples 1 to 4, the discharge capacities before and after the capacity recovery are summarized in the graph of FIG. 3. As shown in Table 2 and FIG. 3, it was found that the capacity was recovered in both Experimental Examples 2 and 4, which used a recovery agent containing an electrolyte. In addition, when Experimental Examples 1 and 2, in which the solvent of the recovery agent stock solution was THF, were compared, the recovery capacity of Experimental Example 2, which used a recovery agent containing an electrolyte, was larger, and when Experimental Examples 3 and 4, in which the solvent of the recovery agent stock solution was DME, the recovery capacity of Experimental Example 4, which used a recovery agent containing an electrolyte, was larger. From this, it was found that the capacity of the battery after recovery was further improved when a recovery agent containing an electrolyte was used. The reasons for such effects were considered using the ESR measurement results.

[0056] Figure 4 shows the ESR measurement results of the electrolyte extracted from the battery immediately after injecting the recovery agent in Experimental Example 2 and the electrolyte extracted from the battery after leaving it for 5 days after injecting the recovery agent in Experimental Example 2. As shown in Figure 4, in both electrolytes, a signal thought to be a naphthalenide anion radical was confirmed at the position of g = 2.001. This was presumed to indicate that in lithium naphthalenide, although the 2s1 electron, which is the outermost electron of lithium, is transferred to the naphthalenide ligand, the naphthalenide ligand side is not a simple anion but an anion radical.

[0057] As shown in Figure 4, the signal thought to be from the naphthalenide anion radical showed a large decrease in amplitude (intensity) after being left for five days compared to immediately after the recovery agent was injected. This was presumed to indicate that the electrons of the naphthalenide anion radical were converted into the 2s1 electrons of lithium, and that the lithium was inserted into the positive electrode active material, resulting in a decrease in the naphthalenide anion radical.

[0058] Figure 5 shows the ESR measurement results of the recovery agents of Experimental Examples 2 and 4. The signal of Experimental Example 2 ((1) in the figure) using THF solvent was larger in amplitude (intensity) than the signal of Experimental Example 4 ((2) in the figure) using DME solvent. This was presumed to indicate that the solvation of naphthalenide was greater in Experimental Example 4 using DME solvent.

[0059] FIG. 6 shows the ESR measurement results of the recovery agents of Experimental Examples 1 and 2. However, the recovery agent of Experimental Example 1 was adjusted to a low solute concentration of 10 mmol / L for the convenience of the measurement. The signal of Experimental Example 1 had a larger amplitude (intensity) than the signal of Experimental Example 2, and the hyperfine structure was clearer. This is presumed to indicate that the recovery agent of Experimental Example 2 has a larger solvation of naphthalenide than the recovery agent of Experimental Example 1 by adding an electrolyte. It is presumed that if the solvation of naphthalenide is large, lithium naphthalenide is likely to release lithium ions and electrons, so that the activation energy when lithium is compensated for at the positive electrode is small. As a result, in Experimental Example 2, lithium ions are smoothly supplied to the positive electrode, recovery proceeds efficiently, and it is presumed that the battery capacity after recovery is improved compared to Experimental Example 1, in which no electrolyte is added.

[0060] [Table 2] [Explanation of symbols]

[0061] 20 nonaqueous electrolyte secondary battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 nonaqueous electrolyte.

Claims

1. A recovery agent for recovering the capacity of a non-aqueous electrolyte secondary battery having a metal ion as a carrier ion, The present invention includes a solute having a reduced aromatic hydrocarbon compound and a metal ion, a solvent for dissolving the solute, and an electrolyte, the solute has, as the reduced aromatic hydrocarbon compound, at least one of a reduced form of a compound of formula (1) and a reduced form of a compound of formula (2), the compound of formula (2) being naphthalene; The electrolyte includes an electrolyte solute different from the solute and an electrolyte solvent different from the solvent; Recovery agent. 【Chemistry 1】

2. The solute has the same metal ion as the carrier ion. The recovery agent according to claim 1.

3. The solvent comprises one or more of tetrahydrofuran and dimethoxyethane; The recovery agent according to claim 1 or 2.

4. The electrolyte contains a cyclic carbonate and a chain carbonate. The recovery agent according to any one of claims 1 to 3.

5. The electrolyte contains the same electrolyte as the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery. The recovery agent according to any one of claims 1 to 4.

6. The electrolyte is contained in the range of 10% by volume to 90% by volume. The recovery agent according to any one of claims 1 to 5.

7. A method for recovering the capacity of a non-aqueous electrolyte secondary battery that uses metal ions as carrier ions, comprising the steps of: A recovery step of injecting the recovery agent according to any one of claims 1 to 6 into the nonaqueous electrolyte secondary battery to recover the capacity of the nonaqueous electrolyte secondary battery; Including, A method for recovering a non-aqueous electrolyte secondary battery.

8. a battery preparation step of preparing a capacity-degraded nonaqueous electrolyte secondary battery having metal ions as carrier ions; The method for recovering a capacity of a nonaqueous electrolyte secondary battery according to claim 7, further comprising: The method for producing a non-aqueous electrolyte secondary battery includes the steps of:

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