JP7569719B2 - 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 objective, the inventors discovered that the capacity of a non-aqueous electrolyte secondary battery is restored when a solution containing a reduced aromatic hydrocarbon compound and the same type of metal ion as the carrier ion of the non-aqueous electrolyte secondary battery is injected into the non-aqueous electrolyte secondary battery. In particular, they discovered that the capacity of the restored battery is further improved when the reduced aromatic hydrocarbon compound and metal ion are at a predetermined high concentration relative to the ether solvent in the recovery agent, and have completed 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,
a reduced aromatic hydrocarbon compound, a metal ion of the same type as the carrier ion, and a solvent which is an ether compound, wherein the concentrations of the reduced aromatic hydrocarbon compound and the metal ion relative to the solvent are 1.7 mol/L or more and 5.0 mol/L or less;
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.

This recovery agent and the recovery method for non-aqueous electrolyte secondary batteries can provide a new recovery method for non-aqueous electrolyte secondary batteries. The reason for such an effect is presumed to be as follows. For example, it is presumed that the recovery agent containing a reduced aromatic hydrocarbon compound and a metal ion acts directly on the positive electrode simply by 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, the recovery agent in which the concentration of each of the reduced aromatic hydrocarbon compound and the metal ion in the ether solvent is 1.7 mol/L or more and 5.0 mol/L or less improves the capacity of the battery after recovery. The reason for this is presumed to be as follows. For example, in the recovery agent in which the concentration of each of the reduced aromatic hydrocarbon compound and the metal ion in the ether solvent is 1.7 mol/L or more and 5.0 mol/L or less, the reduced aromatic hydrocarbon compound and the metal ion have high diffusibility to the positive electrode. Therefore, it is believed that adding this recovery agent to a non-aqueous electrolyte secondary battery will facilitate the smooth supply of electrons and metal ions to the positive electrode, allowing the recovery reaction to proceed efficiently and improving the capacity of the battery 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 capacity at constant voltage in Experimental Example 1. 1 is a graph showing recovery capacity in Experimental Example 1. 1 is a graph showing the relationship between the capacity at constant voltage and the recovery capacity in Experimental Examples 1 to 10. 1 is a graph showing the relationship between the concentration of naphthalene and lithium and the recovery capacity.

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 restored will be described. The nonaqueous electrolyte secondary battery is not particularly limited as long as it uses metal ions as carrier ions. For example, a lithium The non-aqueous electrolyte secondary battery may have a Group 1 ion such as sodium or potassium, or a Group 2 ion such as magnesium, calcium or strontium as a carrier ion. The non-aqueous electrolyte secondary battery may be a lithium ion secondary battery or a metal secondary battery such as a lithium metal secondary battery. In the following, as an example, the non-aqueous electrolyte secondary battery will be mainly described. explain.

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 _LiCoO2 , _LiNiO2 , _LiMnO2 , and _LiV2O3 , are preferred. 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 composite, 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, and carbon fibers. 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, the carbonaceous material is 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. For these, the surface can also be oxidized. The shape of the current collector can 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 , and LiBF ₄ , and organic salts such as LiN(FSO ₂ ) ₂ (also referred to as LiFSI), LiN(CF ₃ SO ₂ ) ₂ (also referred to as LiTFSI), and LiN(C ₂ F ₅ SO ₂ ) ₂ (also referred to as 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. Examples of the organic solvent include aprotic organic solvents. Examples of such organic solvents include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, and chain ethers. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 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 of olefin resins such as polyethylene and polypropylene. 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 recovery agent will be described. The recovery agent includes an aromatic hydrocarbon compound in a reduced state, metal ions of the same type as the carrier ions of the nonaqueous electrolyte secondary battery, and a solvent that is an ether compound. The recovery agent may be a recovery agent prepared in advance, or may be prepared in a preparation step for preparing the recovery agent. In the recovery agent, the aromatic hydrocarbon compound in a reduced state and the metal ions may be dissociated or associated. The recovery agent may include an electrolyte in addition to a recovery agent stock solution that includes an aromatic hydrocarbon compound in a reduced state, metal ions of the same type as the carrier ions of the nonaqueous electrolyte secondary battery, and a solvent that is an ether compound. The recovery agent may be a recovery agent stock solution without including an electrolyte.

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. 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 ions may be of the same type as the carrier ions in the nonaqueous electrolyte secondary battery, but are preferably one or more of alkali metal ions such as lithium ions, sodium ions, and potassium ions.

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

In the recovery agent, the solvent is an ether compound. The ether compound may be any compound having an ether skeleton, and may be a cyclic ether or a chain ether. 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 an aromatic hydrocarbon compound in a reduced state and a metal ion can be easily prepared. The recovery agent may be prepared by adding a metal to a precursor obtained by adding an aromatic hydrocarbon compound to a solvent. The recovery agent may be prepared under an inert atmosphere, such as an argon atmosphere. The recovery agent may be prepared 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 a solvent, an aromatic hydrocarbon compound, and a metal, and a stirrer may be used for this purpose.

The above-described restoring agent is also referred to as a restoring agent stock solution. In the restoring agent stock solution, the concentrations of the aromatic hydrocarbon compound in a reduced state and the metal ions are each 1.7 mol/L or more and 5.0 mol/L or less. This concentration may be 1.8 mol/L or more and 4.5 mol/L or less, 2.0 mol/L or more and 4.0 mol/L or less, or 2.5 mol/L or more and 3.5 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 ions 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.

When the recovery agent contains an electrolyte in addition to the recovery agent stock solution, 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, and more preferably one or more of 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. When the recovery agent contains an electrolyte, the content of the electrolyte may be 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, and the recovery agent stock solution and the electrolyte 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.

[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 process, it is preferable to inject a recovery agent into the nonaqueous electrolyte secondary battery and maintain a predetermined voltage lower than the full charge voltage by applying a constant voltage to recover the capacity of the nonaqueous electrolyte secondary battery. The predetermined voltage is preferably a voltage lower than the full charge voltage and a voltage at which the potential of the positive electrode is higher than the potential of the recovery agent. The full charge voltage may be the upper limit charging voltage set for the nonaqueous electrolyte secondary battery (pre-deterioration battery). The predetermined voltage may be appropriately determined according to the configuration of the battery to be recovered, and may be, for example, 3.0 V or more and less than 4.1 V, 3.5 V or more and 4.0 V or less, or 3.7 V or more and 4.0 V or less. If the battery is left in an open circuit state without applying a constant voltage, the positive electrode potential decreases as the recovery reaction progresses, and the potential difference between the positive electrode and the recovery agent, which is the driving force of the reaction, decreases as the recovery reaction progresses, and the effect of the recovery agent may gradually weaken. On the other hand, when the recovery agent is injected and a predetermined voltage is maintained by applying a constant voltage, the decrease in the positive electrode potential is suppressed. Therefore, even if the recovery reaction proceeds, the potential difference between the positive electrode, which is the driving force of the reaction, and the recovery agent is kept approximately constant, so that the effect of the recovery agent is unlikely to attenuate, and the capacity of the battery after recovery can be increased. In addition, the activity of the radical anions of the aromatic hydrocarbon compound is appropriately suppressed by applying a constant voltage, and the residual radical anions of the aromatic hydrocarbon compound are suppressed by effectively using the recovery agent, so that the cycle capacity retention rate of the battery after recovery is also thought to be improved.

In this step, prior to injecting the recovery agent, the voltage of the nonaqueous electrolyte secondary battery may be adjusted to the above-mentioned predetermined voltage. In this case, for example, the nonaqueous electrolyte secondary battery may be charged by constant current charging (CC charging) or constant current constant voltage charging (CCCV charging) to adjust the voltage of the nonaqueous electrolyte secondary battery. This voltage adjustment is not necessary, but it is preferable that the voltage of the nonaqueous electrolyte secondary battery to be recovered is the above-mentioned predetermined voltage.

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. The recovery agent may be injected so as to come into contact with 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, etc. 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. When applying a constant voltage, the constant voltage application may be continued before or during the injection of the recovery agent, or may be started after the injection of the recovery agent while the voltage drop of the nonaqueous electrolyte secondary battery due to the supply of metal ions to the positive electrode is negligibly small (for example, within 5 minutes, preferably within 3 minutes, more preferably within 1 minute). The constant voltage application time can be appropriately determined according to the configuration of the nonaqueous electrolyte secondary battery, the degree of deterioration, the injection amount of the recovery agent, etc. For example, the injection amount of the recovery agent may be constant, and the constant voltage application time may be adjusted according to the configuration and degree of deterioration of the nonaqueous electrolyte secondary battery. The constant voltage application time may be, for example, 1 hour or more and 48 hours or less, 6 hours or more and 36 hours or less, or 12 hours or more and 24 hours or less. In addition, when applying a constant voltage before the completion of the injection of the recovery agent, the constant voltage application time is the constant voltage application time after the injection of the recovery agent is completed.

In this step, when the recovery agent is injected, for example, a recovery reaction as shown in FIG. 2 occurs. FIG. 2 is an explanatory diagram showing an example of a scheme of the recovery reaction, 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 compound containing a radical anion of an aromatic hydrocarbon compound (Are·- in FIG. 2) 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 particular, in a recovery agent in which the concentration of a compound (reducing agent) containing a radical anion of an aromatic hydrocarbon compound and a metal ion in an ether solvent is 1.7 mol/L or more and 5.0 mol/L or less, the diffusibility of the reducing agent to the positive electrode is high. Therefore, it is believed that when this recovery agent is added to a non-aqueous electrolyte secondary battery, the supply of metal ions to the positive electrode is smoothly carried out without being hindered by factors such as diffusion rate limitation, the recovery reaction proceeds efficiently, and the capacity of the battery after recovery is improved. In this way, the capacity of the non-aqueous electrolyte secondary battery is restored, and a non-aqueous electrolyte secondary battery with restored capacity (also called a restored battery) 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 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 new recovery method that does not require a third electrode. Furthermore, in this 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 in which the concentrations of the reduced aromatic hydrocarbon compound and the metal ion relative to the ether solvent are 1.7 mol/L or more and 5.0 mol/L or less.

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 non-aqueous electrolyte secondary battery disclosed herein is described as an example. Experimental Examples 1 to 4 correspond to working examples, and Experimental Examples 5 to 10 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 2.0 mol/L, and then 2.0 mol/L of lithium metal was added and stirred, and a dark green radical anion liquid composition (lithium naphthalenide + THF) was prepared as a recovery agent stock solution by the reaction shown in the above formula (7). In addition, lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved 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 to prepare an electrolyte solution. Then, the recovery agent stock solution and the electrolyte solution were mixed to a volume ratio of 5:5 to prepare a recovery agent.

(Recovery of degraded batteries)
The deteriorated battery was CC-charged at 0.9 mA to adjust the cell voltage to 4.0 V (adjustment process), a part of the deteriorated battery was opened under an argon atmosphere, 0.5 mL of the recovery agent was injected with a pipette, the opening was sealed, and immediately (within 3 minutes of the injection of the recovery agent in the experimental example), a constant voltage of 4.0 V was applied to the deteriorated battery, and the constant voltage application was continued for 24 hours (recovery process). In this way, the deteriorated battery was restored to obtain a restored battery. During the application of the constant voltage, the current density [mA/cm ² ] was measured, and the charge capacity [mAh] (also referred to as the capacity at constant voltage) obtained during the application of the constant voltage was derived (see FIG. 3).

(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 was measured. The recovery capacity was calculated by subtracting the discharge capacity of the deteriorated battery from the discharge capacity of the recovered battery (see FIG. 4).

[Experimental Examples 2 to 3]
Experimental Example 2 was the same as Experimental Example 1, except that the concentrations of naphthalene and lithium in the THF solvent were changed to 3.0 mol/L. Experimental Example 3 was the same as Experimental Example 1, except that the concentrations of naphthalene and lithium in the THF solvent were changed to 4.0 mol/L.

[Experimental Example 4]
Experimental Example 4 was the same as Experimental Example 1, except that in the recovery agent, dimethoxyethane (DME) solvent was used instead of THF solvent, and the supporting salt of the electrolyte was changed from LiFSI to _LiPF6 .

[Experimental Example 5]
Experimental Example 5 was the same as Experimental Example 1, except that the concentration of naphthalene and lithium in the THF solvent in the recovery agent was changed to 1.0 mol/L.

[Experimental Example 6]
Experimental Example 6 was the same as Experimental Example 5, except that in the recovery agent, the supporting salt of the electrolyte was changed from LiFSI to _LiPF6 .

[Experimental Examples 7 to 9]
Experimental Example 7 was the same as Experimental Example 5, except that in the recovery agent, the supporting salt concentration of the electrolyte was changed to 1.5 M. Experimental Example 8 was the same as Experimental Example 5, except that in the recovery agent, the supporting salt concentration of the electrolyte was changed to 2.0 M. Experimental Example 9 was the same as Experimental Example 5, except that the supporting salt concentration of the electrolyte was changed to 3.0 M.

[Experimental Example 10]
Experimental Example 10 was the same as Experimental Example 4, except that the concentration of naphthalene and lithium in the DME solvent in the recovery agent was changed to 1.5 mol/L. In addition to Experimental Example 10, an attempt was made to prepare a recovery agent in which the concentration of naphthalene and lithium in the DME solvent was changed to 3.0 mol/L, but some of the recovery agent did not dissolve and remained undissolved. No such undissolved residue was present in the recovery agents of Experimental Examples 1 to 10.

The results of Experimental Examples 1 to 10 are summarized in Table 1. The relationship between the capacity at constant voltage and the recovery capacity for Experimental Examples 1 to 10 is summarized in Figure 5. As shown in Figure 5, it was found that the recovery capacity is roughly proportional to the capacity at constant voltage. As shown in Table 1 and Figure 5, Experimental Examples 1 to 4, in which the concentrations of naphthalene and lithium were 2 mol/L or more and 4 mol/L or less, showed high recovery capacity. On the other hand, in Experimental Examples 5 and 7 to 9, the supporting salt concentration of the electrolyte contained in the recovery agent was increased, but the recovery capacity was hardly improved, and when the supporting salt concentration was about 2 mol/L, the recovery capacity decreased. From this, it was found that the recovery capacity can be improved by adjusting the concentration of naphthalene and lithium in the recovery agent relative to the solvent, which is an ether compound.

The reason why the high recovery capacity was shown in Experimental Examples 1 to 4 was presumed to be as follows. The anion radical of allenes such as naphthalene and biphenyl containing Li ⁺ functions as a reducing agent that donates electrons, and it was presumed that by acting on a deteriorated positive electrode, electrons and Li ⁺ are donated from the reducing agent to the positive electrode, thereby recovering the capacity. In particular, it was presumed that by increasing the concentration of the anion radical of allenes such as naphthalene and biphenyl containing Li ⁺ , the diffusibility of the anion radical of allenes such as naphthalene and biphenyl containing Li ⁺ that provides the recovery effect is improved, and recovery proceeds efficiently, resulting in a high recovery capacity.

The preferred range of the naphthalene and lithium concentrations was examined using Figure 6. As shown in Figure 6, it was inferred that if the naphthalene and lithium concentrations were 1.7 mol/L or more and 5.0 mol/L or less, the recovery capacity would be, for example, 1.2 mAh or more in both cases where the solvent was THF and DME, and this would be preferable. As mentioned above, it was difficult to dissolve naphthalene and lithium at 3.0 mol/L or more in the case where the solvent was DME. For this reason, it was inferred that, for example, it would be more preferable to set the naphthalene and lithium concentrations to 1.7 mol/L or more and below the solubility in the case where the solvent was DME.

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 (9)

A recovery agent for recovering the capacity of a non-aqueous electrolyte secondary battery having a metal ion as a carrier ion,
a reduced aromatic hydrocarbon compound, a metal ion of the same type as the carrier ion, and a solvent which is an ether compound, wherein the concentrations of the reduced aromatic hydrocarbon compound and the metal ion relative to the solvent are 1.7 mol/L or more and 5.0 mol/L or less;
Recovery agent. The recovery agent has a concentration of the reduced aromatic hydrocarbon compound and the metal ion in the solvent of 2.0 mol/L or more and 4.0 mol/L or less.
The recovery agent according to claim 1. The restoring agent contains, as the reduced aromatic hydrocarbon compound, at least one of a reduced product of a compound of formula (1) and a reduced product of a compound of formula (2).
The recovery agent according to claim 1 or 2.

The recovery agent includes one or more of tetrahydrofuran and dimethoxyethane as the solvent;
The recovery agent according to any one of claims 1 to 3. The recovery agent includes a recovery agent stock solution containing the aromatic hydrocarbon compound in a reduced state, metal ions of the same type as the carrier ions, and the solvent, and an electrolyte solution.
The recovery agent according to any one of claims 1 to 4. 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 5 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. In the recovery step, the recovery agent is injected into the nonaqueous electrolyte secondary battery, and a predetermined voltage lower than a full charge voltage is maintained by applying a constant voltage.
The method for restoring a nonaqueous electrolyte secondary battery according to claim 6 . In the recovery process, the predetermined voltage is set to 3.0 V or more and 4.0 V or less.
The method for restoring a nonaqueous electrolyte secondary battery according to claim 7 . 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 any one of claims 6 to 8, comprising:
The method for producing a non-aqueous electrolyte secondary battery includes the steps of:

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