JP7680858B2 - Recovery agent, recovery method for non-aqueous electrolyte secondary battery, and manufacturing method for non-aqueous electrolyte secondary battery - Google Patents

Description

The present disclosure relates to a recovery agent, a recovery method for a nonaqueous electrolyte secondary battery, and a manufacturing method for a nonaqueous electrolyte secondary battery.

As a method for restoring the capacity of a non-aqueous 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 the positive and negative electrodes, the third electrode is externally short-circuited with the positive electrode, and carrier ions are supplied from the third electrode to the positive electrode (see, for example, Patent Document 1).

JP 2016-076358 A

However, in Patent Document 1, there was a problem that the incorporation of a third electrode made the battery structure complicated. For this reason, there was a need for a new recovery method for non-aqueous electrolyte secondary batteries that could recover capacity without using a third electrode.

This disclosure has been made to solve these problems, and its main objective is to provide a new method for restoring non-aqueous electrolyte secondary batteries.

After extensive research to achieve the above-mentioned object, the inventors discovered that injecting a solution containing a solute having a reduced aromatic hydrocarbon compound and a metal ion, and a solvent that dissolves the solute, into a non-aqueous electrolyte secondary battery restores the capacity. In particular, they discovered that if the restoring agent contains, in addition to the above-mentioned solute and solvent, an electrolyte such as that used in non-aqueous electrolyte secondary batteries, the capacity of the battery after restoration is further improved, leading to the completion of the present disclosure.

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.

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.

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.

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 new recovery method for a non-aqueous electrolyte secondary battery and a new 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, 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, is presumed to act directly on the positive electrode by simply injecting it into a non-aqueous electrolyte secondary battery, causing 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 greater 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 using a recovery agent containing an electrolyte reduces the activation energy required to supply electrons and metal ions to the positive electrode, allowing the supply of electrons and metal ions to the positive electrode to proceed smoothly, leading to an efficient recovery reaction and improved battery capacity after recovery.

1 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery 20. FIG. FIG. 2 is an explanatory diagram showing an example of a recovery reaction scheme. 1 is a graph showing the discharge capacity before and after capacity recovery in Experimental Examples 1 to 4. 13 shows ESR measurement results of the electrolyte of the battery after injection of a recovery agent in Experimental Example 2. 4 shows ESR measurement results for the recovery agents of Experimental Examples 2 and 4. 4 shows ESR measurement results of the recovery agents of Experimental Examples 1 and 2.

The recovery agent disclosed in this specification recovers the capacity of a nonaqueous electrolyte secondary battery. The recovery method for a nonaqueous electrolyte secondary battery disclosed in this specification is a method for recovering the capacity of a nonaqueous electrolyte secondary battery. Preferred embodiments of the recovery agent and the recovery method for a nonaqueous electrolyte secondary battery are described below.

[Nonaqueous electrolyte secondary battery]
First, the nonaqueous electrolyte secondary battery to be recovered will be described. The nonaqueous electrolyte secondary battery is preferably a nonaqueous electrolyte secondary battery having a metal ion as a carrier ion. The nonaqueous electrolyte secondary battery may have, for example, a Group 1 ion such as lithium, sodium, or potassium, or a Group 2 ion such as magnesium, calcium, or strontium as a carrier ion. The nonaqueous 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. In the following, as an example, a case where the nonaqueous electrolyte secondary battery is a lithium ion secondary battery will be mainly described.

The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode may have a positive electrode active material capable of absorbing and releasing lithium ions. The negative electrode may have a negative electrode active material capable of absorbing and releasing lithium ions. The nonaqueous electrolyte may be interposed between the positive electrode and the negative electrode and conduct the lithium ions.

The positive electrode may be formed, for example, by 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 it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as _TiS2 , _TiS3 , _MoS3 , and _FeS2 , lithium manganese composite oxides having a basic composition formula such as Li _{(1-x) MnO2} (0<x<1, etc., the same applies below) and Li _{(1-x) Mn2O4} , lithium cobalt composite oxides having a basic composition formula such as Li _{(1-x) CoO2 ,} lithium nickel composite oxides having a basic composition formula such as Li( _{1-x ) NiO2} , lithium _{nickel cobalt} manganese composite oxides having a basic composition formula such as _Li (1-x) _NiaCobMncO2 (a+b+c=1 ₎ , lithium vanadium composite oxides having a basic composition formula such as _LiV2O3 , and transition metal oxides having a basic composition _formula such as _V2O5 can be used. Among these, lithium transition metal composite oxides, such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiV ₂ O ₃ are preferred. Li _y Ni _(1-x) M _x O ₂ (where 0≦x≦0.5, 0<y<1.20, M is at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, and B) is also preferred, and may be used in combination with a lithium manganese composite oxide having a spinel structure. The term "basic composition formula" means that other elements may be included. The positive electrode active material may have an oxidation-reduction potential of 3.5 V or more, 4.0 V or more, or 4.5 V or more based on Li metal.

In the positive electrode, the conductive material can be, for example, one or more mixtures of graphite such as natural graphite (scale graphite, flake graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, 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 can be, for example, fluorine-containing resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or thermoplastic resin such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), etc., 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 may 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 of these can be used to form an arbitrary thickness and shape. The basis weight of the positive electrode composite is not particularly limited, but may be, for example, more than 5 mg/cm ² , 6 mg/cm ² or more, or 7 mg/cm ² or more. The basis weight of the positive electrode composite may be, for example, 20 mg/cm ² or less. As the current collector, in addition to aluminum, titanium, stainless steel, nickel, iron, baked carbon, conductive polymer, conductive glass, etc., those in which the surface of aluminum or copper is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance can be used. It is also possible to oxidize the surface of these. The shape of the current collector includes foil, film, sheet, net, punched or expanded, lath, porous body, foam, fiber group formation, etc. The thickness of the current collector is, for example, 1 to 500 μm.

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 have an operating potential close to that of metallic lithium, are capable of charging and discharging at a high operating voltage, and when a lithium salt is used as a supporting salt, self-discharge can be suppressed and the irreversible capacity during charging can be reduced, which is preferable. 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. In addition, the conductive material, binder, solvent, etc. used in the negative electrode can be the same as those exemplified in 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 basis weight of the negative electrode mixture may be, for example, more than 3 mg/cm ² or 4 mg/cm ² or more. The basis weight of the negative electrode mixture may be, for example, 15 mg/cm ² or less. In addition to copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode current collector may also be one in which the surface of, for example, copper, etc. is treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and reduction resistance. It is also possible to oxidize the surface of these. The shape of the current collector may be the same as that of the positive electrode.

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

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, but examples 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.

The non-aqueous electrolyte secondary battery may have an openable and closable electrolyte injection port in the battery case that contains the positive electrode, the negative electrode, and the non-aqueous electrolyte. The recovery agent can be easily injected through the electrolyte injection port.

The shape of the nonaqueous electrolyte secondary battery is not particularly limited, but examples thereof include coin type, button type, sheet type, laminated type, cylindrical type, flat type, and square type. It 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. This 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 opposite 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 this nonaqueous electrolyte secondary battery 20, the space between the positive electrode 22 and the negative electrode 23 is filled with a nonaqueous electrolyte 27.

The nonaqueous electrolyte secondary battery may have an internal resistance of more than 5 Ωcm ² , 7 Ωcm 2 or more, or 10 Ωcm ² or ^more in a battery in a state where the capacity is not degraded (also referred to as a pre-degraded battery). In a nonaqueous electrolyte secondary battery having a large thickness or weight of an electrode mixture and a relatively large internal resistance, such as a battery for an electric vehicle, the capacity and cycle capacity retention rate of the battery after recovery are often low by simply injecting a recovery agent, so that the application of the recovery method for a nonaqueous electrolyte secondary battery of the present disclosure is highly significant. The internal resistance of the pre-degraded battery may be 50 Ωcm ² or less.

[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.

In the recovery agent, the aromatic hydrocarbon compound is preferably polyacene or polyphenyl. Polyacene is a compound having a structure in which multiple benzene rings are condensed, and examples thereof include naphthalene, anthracene, tetracene, and pentacene. Polyphenyl is a compound having a structure in which multiple 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 the aromatic ring include quinoline, chromene, and acridine. Examples of polyphenyl containing a heteroatom in the 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. Of 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 reduced aromatic hydrocarbon compound 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 reduced aromatic hydrocarbon compound may be, for example, one or more of the reduced form of the compound of formula (1) and the reduced form of the compound of formula (2).

In the recovery agent, the metal ion is not particularly limited, but 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.

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

In the recovery agent, the solvent dissolves the above-mentioned solute and is preferably 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 preferably has 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.

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, as shown in 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 recovery agent may be prepared by stirring the solvent, aromatic hydrocarbon compound, and metal, and a stirrer may be used. The solvent is preferably dehydrated by distillation or immersion in molecular sieves to reduce the moisture content to 100 ppm or less.

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. Furthermore, the ratio M _A /M _B of the number of moles M _A (mol) of the aromatic hydrocarbon compound in a reduced state contained in the restoring agent to the number of moles M _B (mol) of the metal ion 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.

The electrolyte may be, for example, a nonaqueous electrolyte exemplified in the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery, or may contain an organic solvent exemplified in the nonaqueous electrolyte and a supporting salt exemplified in the nonaqueous 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 more 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 may be an inorganic salt such as LiPF ₆ , or may be 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 non-aqueous electrolyte of the non-aqueous electrolyte secondary battery to be recovered. In the recovery agent, the content of the electrolyte may be, for example, 10% by volume or more and 90% by volume or less, 20% by volume or more and 80% by volume or less, 30% by volume or more and 70% by volume or less, 30% by volume or more and 60% by volume or less, or 30% by volume or more and 50% by volume or less. When preparing a recovery agent containing an electrolyte, it is sufficient to mix the recovery agent stock solution and the electrolyte solution, and the recovery agent stock solution and the electrolyte solution may be stirred, or may be stirred using a stirrer or the like.

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

The recovery agent may be one in which, for example, one or more signals are confirmed in the g-value range of 1.996 to 2.020 as measured by electron spin resonance (ESR). 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 derived using the resonance frequency ν (Hz) and magnetic field strength H (mT) obtained by ESR measurement, using the formula hν=gμ _B H (where h is Planck's constant (6.626176×10 ⁻³⁴ Js) and μ _B is Bohr magneton (9.274078×10 ⁻²⁴ JT ⁻¹ )).

[Method for restoring a non-aqueous electrolyte secondary battery]
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.

(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 capacity degraded state (also called a degraded battery), and may be, for example, a battery in a capacity degraded state 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.

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 according to 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, relative 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. At that time, it may be left to stand, may be shaken, or a voltage may be applied. This time may be, for example, 1 hour or more and 48 hours or less, 6 hours or more and 36 hours or less, or 12 hours or more and 24 hours or less.

In this step, when the recovery agent is injected, for example, a recovery reaction as shown in FIG. 2 is considered 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 the case where the positive electrode active material is a lithium transition metal composite oxide. As shown in FIG. 2, in the recovery agent, a solute having a radical anion (Are.- in FIG. 2) of an aromatic hydrocarbon compound and a metal ion (Li ⁺ in FIG. 2) functions as a reducing agent that donates electrons, so that by acting on a deteriorated positive electrode (Li _ny MeO ₂ in FIG. 2), electrons and metal ions are donated from the reducing agent to the positive electrode, and the capacity can be restored. In addition, a zero-valent complex of an electrically neutral aromatic hydrocarbon compound and a lithium atom is considered to behave like metallic lithium. Therefore, when the above-mentioned zero-valent complex of lithium comes into contact with a deteriorated positive electrode, it is taken into the positive electrode in a state of having battery activity by supplying electrons and metal ions to the positive electrode, and it is considered that the capacity of the battery can be restored. Even if metal ions are brought into contact with a deteriorated positive electrode in the form of a salt such as _LiPF6 , such a capacity recovery effect cannot be obtained.

In this process, a recovery agent containing an electrolyte in addition to the above-mentioned solute and solvent is used, so that 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 greater solvation with respect to the aromatic hydrocarbon compound than a recovery agent that does not contain 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 that does not contain 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 also 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.

In the recovery agent and the recovery method for a non-aqueous electrolyte secondary battery described above, the capacity of a non-aqueous electrolyte secondary battery can be restored by injecting a 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 new recovery method that does not require a third electrode. Furthermore, in the recovery agent and the recovery method for a non-aqueous electrolyte secondary battery, the capacity of the battery after recovery can be further improved by using a recovery agent containing an electrolyte.

It goes without saying that the present disclosure is in no way limited to the above-described embodiments, and may be implemented in various forms as long as they fall within the technical scope of the present disclosure.

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 degraded 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-degraded nonaqueous electrolyte secondary battery that uses metal ions as carrier ions, 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 degraded battery described in the above-mentioned embodiment.

Below, an example of recovering a lithium ion battery using the method for recovering a nonaqueous electrolyte secondary battery disclosed herein is described as an example. 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 it can be implemented in various forms as long as it falls within the technical scope of the present disclosure.

[Experimental Example 1]
(Non-aqueous electrolyte secondary battery (battery before deterioration))
The positive electrode used was a positive electrode composite material containing 92 wt% LiNi1 _{/3Co1 / 3Mn1/ 3O2} (NCM, Toda Kogyo Co., Ltd.), 5 wt% acetylene black (Denka Co., Ltd.), and 3 wt% polyvinylidene fluoride (Kureha Co., Ltd.), formed on one side of an aluminum current collector foil to a weight of 7 mg/ ^cm2 . The negative electrode used was a negative electrode composite material containing 98 wt% graphite (OMAC1.5s, Osaka Gas Chemicals Co., Ltd.), 1 wt% carboxymethylcellulose (Daicel Co., Ltd.), and 1 wt% styrene butadiene rubber (JSR Co., Ltd.), formed on one side of a copper current collector foil to a weight of 4 mg/ ^cm2 . The electrolyte was prepared by dissolving _LiPF6 in a mixed solvent containing 30 vol% ethylene carbonate, 40 vol% dimethyl carbonate, and 30 vol% ethyl methyl carbonate to a concentration of 1.1 M. A polypropylene separator impregnated with 1 mL of electrolyte was sandwiched between the positive and negative electrodes to prepare a laminate cell. This was used as a pre-degraded battery. The electrode area of the cell was 10 ^cm2 for both the positive and negative electrodes. When the resistance of the pre-degraded battery was measured with a digital multimeter, the cell resistance was ¹⁰ Ωcm2. In this non-aqueous electrolyte secondary battery, the lower limit discharge voltage determined according to the battery configuration was 3.0 V and the upper limit charge voltage was 4.1 V.

(Deteriorated battery)
In the laminated cell thus produced, charging was performed to a capacity (SOC = 50%) equivalent to 50% of the electric capacity of the cell in the voltage range of 3.0 V to 4.1 V, and Li was extracted from the positive electrode to obtain a positive electrode in a state in which the capacity was reduced in a simulated manner (also referred to as a degraded positive electrode). The cell was then disassembled, and the degraded positive electrode was taken out. Then, a laminated cell was produced in the same manner as the production of 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 4.1 V, and then CC discharged at 0.9 mA to 3.0 V, and the discharge capacity at that time was measured.

(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), and this was used as a recovery agent.

(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).

(Evaluation of recovery batteries)
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.

[Experimental Example 2]
Experimental Example 2 was the same as Experimental Example 1, except that a recovery agent prepared by mixing the recovery agent (recovery agent stock solution) of Experimental Example 1 with the following electrolyte solution in a volume ratio of 5:5 was used. 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.

[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.

[ESR Measurement]
Electron spin resonance (ESR) measurements were performed on various samples using an ELEXSYS-E500 electron spin resonance device manufactured by Bruker. 50 μL of the sample was placed in a quartz ESR cell for measuring aqueous solutions, and the measurements were performed 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.

[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 capacity before and after the capacity recovery is 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 using a recovery agent containing an electrolyte. In addition, when comparing Experimental Examples 1 and 2 in which the solvent of the recovery agent stock solution is THF, Experimental Example 2 using a recovery agent containing an electrolyte had a larger recovery capacity, and when comparing Experimental Examples 3 and 4 in which the solvent of the recovery agent stock solution is DME, Experimental Example 4 using a recovery agent containing an electrolyte had a larger recovery capacity. 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.

Figure 4 shows the ESR measurement results of the electrolyte extracted from the battery immediately after injection of the recovery agent in Experimental Example 2, and the electrolyte extracted from the battery after leaving it for 5 days after injection of 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 g = 2.001. This is presumably because, 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.

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

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

Figure 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. It was presumed that this indicates that the recovery agent of Experimental Example 2 had a larger solvation of naphthalenide than the recovery agent of Experimental Example 1 by adding an electrolyte. It was presumed that if the solvation of naphthalenide is large, lithium naphthalenide is more likely to release lithium ions and electrons, so the activation energy when lithium is compensated for at the positive electrode is smaller. As a result, in Experimental Example 2, lithium ions are smoothly supplied to the positive electrode, recovery proceeds efficiently, and the battery capacity after recovery is improved compared to Experimental Example 1, in which no electrolyte is added.

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 (8)

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.
The solute has the same metal ion as the carrier ion.
The recovery agent according to claim 1. The solvent comprises one or more of tetrahydrofuran and dimethoxyethane;
The recovery agent according to claim 1 or 2. The electrolyte contains a cyclic carbonate and a chain carbonate.
The recovery agent according to any one of claims 1 to 3. 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. 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. 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. 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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