JP7559631B2 - Deactivation solution for non-aqueous secondary batteries, method for producing deactivation solution, and method for deactivating non-aqueous secondary batteries - Google Patents

Description

The present disclosure relates to a deactivating solution for non-aqueous secondary batteries, a method for producing the deactivating solution, and a method for deactivating non-aqueous secondary batteries.

Conventionally, when non-aqueous secondary batteries are recycled or disposed of, a deactivation process is performed to deactivate the recovered batteries. For example, this process can involve connecting the recovered batteries to a charge/discharge device and discharging them to 0 V, but in this case, it can take a long time to discharge them. Also, if the recovered batteries are batteries after the current interrupt mechanism (CID) has been activated, they cannot be discharged at all. Therefore, it has been proposed to add a redox shuttle agent (e.g., ferrocene) that has an oxidation-reduction potential in the range of 3.0 to 4.5 V relative to the oxidation-reduction potential of lithium to the inside of the recovered batteries (see Patent Document 1). This makes it possible to safely and quickly lower the battery voltage of the non-aqueous secondary battery to 0 V without using a charge/discharge device.

JP 2018-137137 A

However, when a non-aqueous secondary battery is deactivated using the redox shuttle agent of Patent Document 1, the negative electrode potential after deactivation is sometimes high. If the negative electrode potential is high, copper and other substances from the negative electrode current collector dissolve and precipitate at the positive electrode, which causes problems such as difficulty in removing or recovering the precipitate from the positive electrode when recycling or disposing of the non-aqueous secondary battery after deactivation. For this reason, it has been desirable to keep the negative electrode potential low, for example, below 3.0 V, when deactivating a non-aqueous secondary battery.

The present disclosure has been made to solve these problems, and has as its main objective the provision of a deactivating solution for non-aqueous secondary batteries that can maintain a low negative electrode potential when deactivating non-aqueous secondary batteries, a method for producing the deactivating solution, and a method for deactivating non-aqueous secondary batteries.

After extensive research to achieve the above-mentioned object, the inventors discovered that adding a deactivating solution containing a redox shuttle agent including a two-electron reduced form of a viologen compound and a non-aqueous solvent of at least one of an ether compound and a nitrile compound to the inside of a non-aqueous secondary battery keeps the negative electrode potential low when the non-aqueous secondary battery is deactivated, and thus completed the invention of the present disclosure.

That is, the nonaqueous secondary battery deactivation solution of the present disclosure is:
A deactivating solution for deactivating a non-aqueous secondary battery,
a redox shuttle agent including a two-electron reduced form of a viologen compound;
A non-aqueous solvent for at least one of an ether compound and a nitrile compound;
It includes.

In addition, the method for producing the inactivation solution of the present disclosure includes the steps of:
A method for producing a deactivating solution for deactivating a non-aqueous secondary battery, comprising:
a preparation step of mixing a viologen compound, a reducing agent for reducing the viologen compound, and a non-aqueous solvent for at least one of an ether compound and a nitrile compound to prepare an inactivation liquid;
It includes.

The method for deactivating a nonaqueous secondary battery according to the present disclosure further comprises the steps of:
An addition step of adding the above-mentioned inactivation liquid to the inside of the nonaqueous secondary battery;
It includes.

In the inactivation liquid for non-aqueous secondary batteries, the method for producing the inactivation liquid, and the inactivation method for non-aqueous secondary batteries disclosed herein, the negative electrode potential can be kept low when inactivating the non-aqueous secondary battery. The reason for obtaining such an effect is presumed to be, for example, as follows. For example, when the inactivation liquid is added to a non-aqueous secondary battery in a charged state, a reaction in which the reductant of the redox shuttle agent (a two-electron reductant of a viologen compound) gives electrons to the positive electrode to become an oxidant (a viologen compound) and a reaction in which the oxidant of the redox shuttle agent receives electrons from the negative electrode to become a reductant are repeated, causing the battery to discharge and become inactive. These reactions are driven by the potential difference between each electrode and the redox shuttle agent, so that when the positive electrode potential falls to the redox-reduction potential of the redox shuttle agent, the discharge of the positive electrode ends, and when the negative electrode potential rises to the redox-reduction potential of the redox shuttle agent, the discharge of the negative electrode ends. In the present disclosure, the redox shuttle agent has a low redox potential (for example, less than 3.0 V based on the Li reference potential), so the negative electrode potential can be kept low. In addition, in the present disclosure, the redox shuttle agent is a two-electron reductant, so the reduction of the positive electrode is promoted, and the discharge rate at the positive electrode is less likely to decrease even after the negative electrode potential reaches the redox potential of the redox shuttle agent. Therefore, the battery can be quickly inactivated until the battery voltage reaches near 0 V.

FIG. 2 is an explanatory diagram showing an example of an oxidation-reduction reaction of a viologen compound. FIG. 2 is a cross-sectional view showing the outline of the configuration of a nonaqueous secondary battery 20 . FIG. 2 is an explanatory diagram showing the mechanism by which a nonaqueous secondary battery is deactivated. Cyclic voltammetry measurement results of the inactivation solution of Experimental Example 1. Cyclic voltammetry measurement results of the inactivation solution of Experimental Example 2. Cyclic voltammetry measurement results of the inactivation solution of Experimental Example 3. Graph showing the discharge behavior of the battery after the inactivation solutions of Experimental Examples 1 to 3 are added.

[Deactivation solution]
First, the inactivation liquid of the present disclosure will be described. The inactivation liquid of the non-aqueous secondary battery of the present disclosure is an inactivation liquid for inactivating a non-aqueous secondary battery, and includes a redox shuttle agent containing a two-electron reduced product of a viologen compound, and a non-aqueous solvent of at least one of an ether compound and a nitrile compound. In this specification, the redox shuttle agent refers to a compound that can be oxidized and reduced and can repeatedly transport charge between a positive electrode and a negative electrode.

(Viologen Compounds)
Prior to the description of the redox shuttle agent, a viologen compound, which is an oxidized form of the redox shuttle agent, will be described. The viologen compound is a compound having a structure in which a hydrocarbon group is bonded to each of the two nitrogen atoms of the pyridine ring of a 4,4'-bipyridine skeleton, and has a structure of, for example, formula (v1). In formula (v1), R and R' are hydrocarbon groups which may be the same or different. The hydrocarbon group is preferably a chain-like (which may be linear or branched) hydrocarbon group or a cyclic hydrocarbon group. Examples of the chain-like hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decanyl, undecanyl, and dodecanyl; and alkenyl groups such as vinyl, propenyl, butenyl, pentenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl. Examples of the cyclic hydrocarbon group include cycloalkyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl; and aryl groups such as phenyl and naphthyl. These hydrocarbon groups may have a substituent such as a carboxyl group, an alkoxy group, a nitro group, an amino group, or a halogen (F, Cl, Br, etc.). Of these, the hydrocarbon group is preferably a linear alkyl group, and is preferably one that has no substituent. Each of the hydrocarbon groups preferably has 20 or less carbon atoms, more preferably 10 or less, and even more preferably 6 or less. The viologen compound may have a structure in which a substituent such as a hydrocarbon group, a carboxyl group, an alkoxy group, a nitro group, an amino group, or a halogen is introduced into one or more of the carbons of the 4,4'-bipyridine skeleton. Examples of the hydrocarbon group include those exemplified as the hydrocarbon group of R and R' described above. When the viologen compound has a plurality of substituents, the substituents may be bonded to each other to form a ring. The viologen compound preferably has 30 or less carbon atoms, more preferably 20 or less carbon atoms, and even more preferably 14 or less carbon atoms.

Specific examples of viologen compounds include those having the structure of formula (v1), such as methyl viologen (formula (v2)), ethyl viologen (formula (v3)), propyl viologen (formula (v4)), butyl viologen (formula (v5)), pentyl viologen (formula (v6)), hexyl viologen (formula (v7)), heptyl viologen (formula (v8)), and octyl viologen (formula (v9)). Examples of viologen compounds include those having the structure of formula (v1), such as 1,1'-dimethyl-3,3'-[methylenebis(oxy)]-4,4'-bipyridinium (formula (v10)), phenyl viologen (formula (v11)), and 1-(4-aminophenyl)-1'-methyl-4,4'-bipyridinium (formula (v12)).

The viologen compound may have, as a counter anion of the cation of formula (v1), an inorganic anion such as ^{hexafluorophosphate} anion ( _PF6- ), tetrafluoroborate anion ( _BF4- ), _{pentafluoroarsine anion (AsF6-), perchlorate anion (ClO4-} ⁾ _, ^{Br- , Cl-} , or F- ^, or an organic _{anion such as trifluoromethanesulfonate anion (CF3SO3-), bis(trifluoromethanesulfonyl)imide anion (N(CF3SO2)2-, TFSI), or tris(trifluoromethylsulfonyl)methide anion (C(CF3SO2)3- ) .} ^The _{counter anion may} ^{be the} _{same type} ^as the anion of the supporting salt of the nonaqueous secondary battery to be inactivated.

Viologen compounds exhibit, for example, the redox reaction shown in Figure 1. Viologen compounds are divalent cations that become cation radicals by one-electron reduction and neutral molecules by two-electron reduction (see J. Electrochem. Soc. 130(1983)1523).

(Redox shuttle agent)
Next, the redox shuttle agent will be described. The redox shuttle agent is a two-electron reduced product of the viologen compound described above. The two-electron reduced product of the viologen compound may be a compound having a structure in which a hydrocarbon group is bonded to each of the two pyridine ring nitrogen atoms of a 4,4'-bipyridinylidene skeleton, and may have a structure of formula (r1), for example. In formula (r1), R and R' are hydrocarbon groups which may be the same or different, and are the same as R and R' in formula (v1) described above. For example, the two-electron reduced product of methyl viologen (formula (v2)) may be 1,1'-dimethyl-4,4'-bipyridinylidene (formula (r2)).

The redox shuttle agent has an oxidation-reduction potential of, for example, less than 3.0 V based on the Li standard potential, preferably 0.5 V or more and less than 3.0 V, more preferably 1.0 V or more and less than 3.0 V, and even more preferably 1.5 V or more and 2.9 V or less. The redox shuttle agent can be determined by cyclic voltammetry. Specifically, the redox shuttle agent has an oxidation-reduction potential of E ₀ [V], which is determined by E ₀ = (E _pa + E _pc ) / 2, where E _pa [V] is the peak potential on the oxidation side determined by cyclic voltammetry, and E _pc [V] is the peak potential on the reduction side. When there are two or more oxidation-reduction potentials within the potential window, it is preferable that all the oxidation-reduction potentials are within the above-mentioned range. It is preferable to perform cyclic voltammetry on a measurement solution containing a non-aqueous solvent, a supporting electrolyte, and a redox shuttle agent. As the non-aqueous solvent of the measurement solution, a non-aqueous solvent of the inactivation liquid described later can be used. Examples of the supporting electrolyte of the measurement solution include inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , and LiC(CF ₃ SO ₂ ) ₃ , which can be used alone or in combination. The supporting electrolyte of the measurement solution may be the same as the supporting salt of the non-aqueous secondary battery to be inactivated. The concentration of the supporting electrolyte in the measurement solution may be 0.1 mol/L or more and 5 mol/L or less, or 0.5 mol/L or more and 2 mol/L or less, and may be the same as the concentration of the supporting salt in the ion conductive medium of the non-aqueous secondary battery to be inactivated. The concentration of the redox shuttle agent in the measurement solution may be 1 mmol/L or more and the solubility level or less, 30 mmol/L or more and the solubility level or less, or 50 mmol/L or more and 100 mmol/L or less. The concentration of the redox shuttle agent in the measurement solution may be the same as the concentration of the redox shuttle agent in the target inactivation solution.

The concentration of the redox shuttle agent contained in the inactivation liquid is preferably 1 mmol/L or more, more preferably 30 mmol/L or more, and even more preferably 50 mmol/L or more. This is because the higher the concentration of the redox shuttle agent, the more quickly a high-energy density battery such as that used in an electric vehicle (EV) can be discharged. The concentration of the redox shuttle agent contained in the inactivation liquid may be below the solubility or may be below 100 mmol/L.

(Non-aqueous solvent)
Next, the non-aqueous solvent in which the redox shuttle agent is dissolved will be described. The non-aqueous solvent is at least one of an ether compound and a nitrile compound. The ether compound may be a cyclic ether compound or a chain ether compound. Examples of the cyclic ether compound include furan compounds such as tetrahydrofuran and methyltetrahydrofuran, pyran compounds such as tetrahydropyran and methyltetrahydropyran, dioxolane compounds such as 1,3-dioxolane and methyldioxolane, and dioxane compounds such as 1,4-dioxane and 1,3-dioxane. Examples of the chain ether compound include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, diglyme, triglyme, and tetraglyme. Examples of the nitrile compound include acetonitrile and benzonitrile. These compounds may have a substituent. Of these, the non-aqueous solvent is preferably an ether compound, more preferably a cyclic ether compound, and more preferably tetrahydrofuran. In at least one of the non-aqueous solvents of the ether compound and the nitrile compound, the two-electron reduced form of the viologen compound is present stably (see, for example, J. Org. Chem. 52(1987)2779-2789). For this reason, the two-electron reduced form of the viologen compound can be used as a redox shuttle agent. In addition, in at least one of the non-aqueous solvents of the ether compound and the nitrile compound, the viologen compound (oxidized form of the redox shuttle agent) is also present relatively stably, so it is considered that the redox shuttle agent shows stable oxidation-reduction. This non-aqueous solvent may be the same as or different from the solvent contained in the ion-conducting medium of the non-aqueous secondary battery to be inactivated.

(others)
The inactivating liquid may contain the above-mentioned counter anion that the viologen compound had before reduction. The inactivating liquid may also contain a metal ion of a metal capable of reducing the viologen compound. Examples of the metal ion include Group 1 ions (alkali metal ions) such as lithium, sodium, and potassium, and Group 2 ions such as magnesium, calcium, and strontium.

The inactivating liquid preferably has an open circuit potential (also referred to as an open circuit potential based on Li) of less than 2.2 V, more preferably 2.1 V or less, measured using a carbon electrode and a metal Li electrode. The inactivating liquid may have an open circuit potential of 1.9 V or more. For measuring the open circuit potential, a measurement solution containing the inactivating liquid and, if necessary, a supporting electrolyte can be used. Examples of the supporting electrolyte of the measurement solution include inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , and LiC(CF ₃ SO ₂ ) ₃ , which can be used alone or in combination. The supporting electrolyte of the measurement solution may be the same type as the supporting salt (described later) of the nonaqueous secondary battery to be inactivated. The concentration of the supporting electrolyte in the measurement solution may be 0.1 mol/L or more and 5 mol/L or less, or 0.5 mol/L or more and 2 mol/L or less, and may be the same as the concentration of the supporting electrolyte in the ion conductive medium of the nonaqueous secondary battery to be inactivated. The measurement solution may be the same as the measurement solution used to measure the oxidation-reduction potential of the redox shuttle agent.

[Method of producing the inactivation solution]
Next, a method for producing a deactivating solution according to the present disclosure will be described. This method for producing a deactivating solution for deactivating a non-aqueous secondary battery includes a preparation step of mixing a viologen compound, a reducing agent for reducing the viologen compound, and a non-aqueous solvent of at least one of an ether compound and a nitrile compound to prepare a deactivating solution. In the preparation step, for example, the above-mentioned deactivating solution may be prepared.

As the viologen compound, the viologen compound described above can be used. As the reducing agent for reducing the viologen compound, metal reducing agents such as Group 1 metals (alkali metals) such as lithium, sodium, and potassium, and Group 2 metals such as magnesium, calcium, and strontium can be used. The reducing agent may be a metal of the carrier ion of the nonaqueous secondary battery to be inactivated. For example, when the carrier ion of the nonaqueous secondary battery to be inactivated is a lithium ion, metallic lithium may be used as the reducing agent. As the reducing agent, an alkali metal is preferable, and metallic lithium is more preferable. As the nonaqueous solvent, the nonaqueous solvent described above can be used. If the nonaqueous solvent is at least one of an ether compound and a nitrile compound, a two-electron reduced product of the viologen compound can be obtained by acting the viologen compound together with a reducing agent.

In the preparation step, the inactivation liquid may be prepared by adding a viologen compound and a reducing agent to a non-aqueous solvent. The amount of the viologen compound added may be 1 mmol/L or more, 30 mmol/L or more and less than the solubility, or 50 mmol/L or more and less than 100 mmol/L. The amount of the reducing agent added is preferably an amount that can convert the viologen compound into a two-electron reduced form without waste. For example, when the reducing agent is a Group 1 metal, the amount of the reducing agent added may be 2 equivalents or more with respect to the amount of the viologen compound added, specifically, 2 mol/L or more, 60 mol/L or more and less than the solubility, or 100 mmol/L or more and less than 200 mmol/L. When the reducing agent is a Group 2 metal, the amount of the reducing agent added may be 1 equivalent or more with respect to the amount of the viologen compound added, specifically, 1 mmol/L or more, 30 mmol/L or more and less than the solubility, or 50 mmol/L or more and less than 100 mmol/L. In the preparation step, the viologen compound and the reducing agent may be added to a non-aqueous solvent and stirred. The stirring time is not particularly limited, but may be, for example, 1 hour to 300 hours, 12 hours to 200 hours, or 24 hours to 100 hours. The preparation step is preferably carried out in an inert atmosphere such as an argon atmosphere.

In the preparation step, for example, the viologen compound may be reduced to a two-electron reduced form in the following reaction formula (1). More specifically, as shown in the following reaction formula (2), methyl viologen having two equivalents of hexafluorophosphate anion relative to the cationic portion of methyl viologen may be reacted with two equivalents of metallic lithium relative to the cationic portion of methyl viologen in the presence of tetrahydrofuran to reduce methyl viologen to a two-electron reduced form. In the formulas (1) and (2), the counter anion possessed by the viologen compound and the metal ion of the metal reducing agent are assumed to form a salt after the reaction, but they may be present in any manner, and may be ionized or associated.

[Inactivation Method]
Next, a method for inactivating a non-aqueous secondary battery according to the present disclosure will be described. The method for inactivating a non-aqueous secondary battery according to the present disclosure includes an adding step of adding a deactivating liquid to the inside of the non-aqueous secondary battery. The deactivating liquid may be the deactivating liquid described above, or may be produced by the method for producing a deactivating liquid described above.

(Non-aqueous secondary battery)
First, a non-aqueous secondary battery to be inactivated will be described. The non-aqueous secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions. Examples of the carrier ions include Group 1 element ions and Group 2 element ions. Examples of the Group 1 element ions include lithium ions, sodium ions, and potassium ions. Examples of the Group 2 element ions include magnesium ions and calcium ions. In the following, for the sake of convenience, the non-aqueous secondary battery will be mainly described as a lithium ion secondary battery.

The positive electrode may be formed by, for example, mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary. The positive electrode active material may have a redox potential based on Li higher than that of the redox shuttle agent contained in the inactivation liquid, but may have a redox potential based on Li of more than 3.0 V, preferably 3.5 V or more, more preferably 3.8 V or more, and even more preferably 4.0 V or more. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like may be used. Specifically, transition metal sulfides such as _TiS2 , _TiS3 , _MoS3 , FeS2 _, etc., lithium manganese composite oxides such as Li _{(1-x) MnO2} (0<x<1, etc., the same applies below) and Li _{(1-x) Mn2O4 ,} lithium cobalt composite oxides such as Li _{(1-x) CoO2} , lithium nickel composite oxides such as Li _{(1-x) NiO2} , _{lithium nickel} manganese composite oxides such as Li _{(1-x) NiaMnbO2 (} a+b=1) and Li _{(1-x) NiaMnbO4} (a+b ₌ 2), lithium _nickel cobalt manganese composite oxides such as Li( _{1 -x) NiaCobMncO2 (} a+b+c= ₁ ), LiV2O Lithium _vanadium composite oxides such as Li _{(1-x)MnPO4, transition metal oxides such as V2O5, etc. can be used. In addition, olivine-type lithium manganese phosphate compounds such as Li(1-x) MnPO4 ,} olivine-type _lithium cobalt phosphate compounds such as Li(1- _{x ) CoPO4} , olivine-type lithium nickel phosphate compounds such as Li(1-x) _NiPO4 , etc. can be used. In addition, inverse spinel-type lithium manganese vanadate compounds such as Li _{(1-x) MnVO4} , inverse spinel-type lithium cobalt vanadate compounds such as Li(1-x) _CoPO4 , inverse spinel-type lithium nickel vanadate compounds such as Li(1 _{- x) NiPO4} , etc. can be used. The positive electrode active material is preferably an oxide containing one or more of nickel, manganese, and cobalt, and for example, _LiCoO2 , LiNiO2, _LiMnO2 , LiNi1 _{/ 3Co1} / _{3Mn1 / 3O2} , and the like are preferable.

As the conductive material of the positive electrode, for example, graphite such as natural graphite (scale graphite, scale graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metals (copper, nickel, aluminum, silver, gold, etc.) can be used. As the binder, for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, natural butyl rubber (NBR), etc. can be used. In addition, aqueous binders such as cellulose-based and aqueous dispersions of styrene butadiene rubber (SBR) can also be used. As the solvent, for example, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. In addition, a dispersant, a thickener, and the like can be added to water, and the active material can be slurried with a latex such as SBR. As the thickener, for example, polysaccharides such as carboxymethylcellulose and methylcellulose can be used alone or as a mixture of two or more kinds. As the coating method, for example, roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like can be used, and any thickness and shape can be obtained by using any of these. As the current collector, in addition to aluminum, titanium, stainless steel, nickel, iron, baked carbon, conductive polymer, conductive glass, and the like, aluminum or copper whose surface is treated with carbon, nickel, titanium, silver, or the like 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 can be a foil, film, sheet, net, punched or expanded, lath, porous, foamed, or fibrous body. The thickness of the current collector is, for example, 1 to 500 μm.

The negative electrode may be formed by, for example, mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase the electrode density as necessary, or by bonding the negative electrode active material and the current collector together. The negative electrode active material may have a Li-based redox potential lower than that of the redox shuttle agent contained in the inactivation liquid, but the Li-based redox potential is preferably less than 1.5 V, more preferably 1.0 V or less, and even more preferably 0.5 V or less. 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. Examples of the composite oxide include lithium titanium composite oxides such as Li ₄ Ti ₅ O ₁₂ and lithium vanadium composite oxides such as LiV ₂ O _3. Of these, carbonaceous materials such as graphite are preferable as the negative electrode active material. The conductive material, binder, solvent, etc. used in the negative electrode can be the same as those exemplified for the positive electrode. In addition to copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode current collector can 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 can be the same as that of the positive electrode. Of these, it is preferable that the negative electrode current collector contains copper. Since copper has an oxidation-reduction potential of about 3.0 to 3.5 V based on Li (see, for example, J. Electrochem. Soc. 144 (1997) 3476-3483, J. Mater. Chem. 21 (2011) 9891-9911), it is believed that copper elution is suppressed if the negative electrode potential is kept below 3.0 V during inactivation, and the application of the inactivation solution and inactivation method of the present disclosure is particularly significant. When copper elution from the negative electrode is suppressed, copper precipitation at the positive electrode is also suppressed, so that when recycling or disposing of the nonaqueous secondary battery after inactivation, there is no need to remove or recover the precipitate from the positive electrode, and it is possible to recycle or dispose of the battery efficiently, which is preferable.

As the ion conductive medium, a non-aqueous electrolyte solution containing a supporting salt or a non-aqueous gel electrolyte solution can be used. Examples of the solvent for the non-aqueous electrolyte solution include carbonate compounds, ester compounds, ether compounds, nitrile compounds, amide compounds, furan compounds, sulfolane compounds, and dioxolane compounds, which can be used alone or in combination. Specifically, examples of the carbonate compound include cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, and chain carbonate compounds such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. Examples of the ester compound include cyclic ester compounds such as γ-butyl lactone and γ-valerolactone, and chain ester compounds such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate. Examples of the ether compound include dimethoxyethane, ethoxymethoxyethane, and diethoxyethane. Examples of the nitrile compound include acetonitrile and benzonitrile. Examples of the amide compound include dimethylacetamide (DMA) and dimethylformamide. Examples of the furan compound include tetrahydrofuran and methyltetrahydrofuran. Examples of the sulfolane compound include sulfolane and tetramethylsulfolane. Examples of the oxolane compound include 1,3-dioxolane and methyldioxolane. These can be used alone or in combination. Among these, the solvent for the non-aqueous electrolyte solution is preferably a mixture of a cyclic carbonate compound and a chain carbonate compound, such as DMC-EC, DEC-EC, or DMC-EMC-EC. Examples of the supporting salt include inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , and LiC(CF ₃ SO ₂ ) ₃ , which can be used alone or in combination. The supporting salt preferably has a concentration in the electrolyte of 0.1 mol/L or more and 5 mol/L or less, more preferably 0.5 mol/L or more and 2 mol/L or less. In addition, instead of a liquid ion conductive medium, an ion conductive polymer, an inorganic solid electrolyte, or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used as the ion conductive medium.

The nonaqueous 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 nonaqueous secondary battery, but examples of the separator include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and thin microporous membranes of olefin resins such as polyethylene. These may be used alone or in combination.

The shape of the non-aqueous 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. In addition, it may be a large type used in an electric vehicle or the like. An example of a non-aqueous secondary battery is shown in FIG. 2. FIG. 2 is a cross-sectional view showing an outline of the configuration of a coin-type non-aqueous secondary battery 20. As shown in FIG. 2, the non-aqueous secondary battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and provided at the bottom of the battery case 21, a negative electrode 23 having a negative electrode active material and provided at a position facing the positive electrode 22 via a separator 24, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. The non-aqueous secondary battery 20 includes an ion conductive medium 27 in which a lithium salt is dissolved in the space between the positive electrode 22 and the negative electrode 23.

(Addition process)
Next, the adding step will be described. In the adding step, the inactivating liquid is added to the inside of the non-aqueous secondary battery. Specifically, the inactivating liquid is added so that the positive electrode and the negative electrode of the non-aqueous secondary battery come into contact with the inactivating liquid. The method of adding the inactivating liquid is not particularly limited, but the battery container may be opened once and the inactivating liquid may be injected and then sealed again, or the inactivating liquid may be injected from the outside of the battery container with a syringe or the like and then sealed. The adding step is preferably performed under an inert atmosphere such as an argon atmosphere.

The amount of the deactivating liquid added may be, for example, 0.1 mL or more and less than 10 mL, or 0.5 mL or more and 5.0 mL or less. The amount of the deactivating liquid added may be, for example, 0.1% or more and 500% or less, or 10% or more and 300% or less, relative to the volume [mL] of the ion conductive medium contained in the nonaqueous secondary battery to be deactivated. The amount of the redox shuttle agent added to the nonaqueous secondary battery by adding the deactivating liquid (hereinafter also referred to as the amount of the redox shuttle agent added) may be, for example, 0.0001 mol/Ah or more and 0.1 mol/Ah or less, or 0.001 mol/Ah or more and 0.01 mol/Ah or less, per battery capacity [Ah] at full charge of the nonaqueous secondary battery to be deactivated.

This addition step is preferably carried out on a non-aqueous secondary battery having a negative electrode current collector containing copper. As described above, copper has an oxidation-reduction potential of about 3.0 to 3.5 V relative to the Li potential, so if the negative electrode potential is kept below 3.0 V during inactivation, copper elution is thought to be suppressed, making it particularly significant to add the inactivation solution of the present disclosure.

After the addition step, the nonaqueous secondary battery may be, for example, held stationary or held while being shaken. The holding time may be an empirically determined time until inactivation is complete, and may be, for example, 6 hours or more and 500 hours or less, 30 hours or more and 300 hours or less, or 50 hours or more and 200 hours or less.

The mechanism by which a non-aqueous secondary battery is inactivated by this inactivation method is presumed to be as follows. FIG. 3 is an explanatory diagram showing the mechanism by which a non-aqueous secondary battery is inactivated. When a redox shuttle agent (RS in the figure) is added to a battery, the potential difference between the positive or negative electrode and the redox shuttle agent serves as a driving force to transfer electrons from the negative electrode to the redox shuttle agent and from the redox shuttle agent to the positive electrode, and the battery is discharged. Specifically, the reductant of the redox shuttle agent (a two-electron reductant of a viologen compound, RS _(red) in the figure) gives electrons to the positive electrode to become an oxidant (a viologen compound, RS _(ox) in the figure), and the oxidant of the redox shuttle agent receives electrons from the negative electrode to become a reductant. This operation is repeated, and the battery is discharged. When the positive electrode potential or the negative electrode potential becomes equal to the redox-reduction potential of the redox shuttle agent, the discharge of that electrode does not proceed any further. Therefore, the positive electrode potential and the negative electrode potential finally become equal to the potential of the redox shuttle agent, and the inactivation is completed. In addition, "inactivation is completed" may mean that the non-aqueous secondary battery is discharged until the SOC (State of charge) is 0%. If the SOC is discharged until 0%, the negative electrode potential is not too low (for example, more than 1.5V and less than 3.0V at the Li reference potential), so gas generation due to decomposition of the ion conductive medium (electrolyte solution, etc.) is unlikely to occur, and the safety of the electrode itself is also high. Therefore, recycling and disposal after inactivation can be safely performed. The lower the battery voltage after inactivation, the less likely it is to cause sparks, so it is preferable. For example, it may be 3.0V or less, and more preferably 1.2V or less, 1.0V or less, 0.5V or less, etc.

The inactivating solution and the inactivating method described above can keep the negative electrode potential low when inactivating a non-aqueous secondary battery. The reason why such an effect is obtained is presumed to be, for example, as follows. For example, when the inactivating solution is added to a non-aqueous secondary battery in a charged state, a reaction in which the reductant of the redox shuttle agent gives electrons to the positive electrode to become an oxidant, and a reaction in which the oxidant of the redox shuttle agent receives electrons from the negative electrode to become a reductant, are repeated, causing the battery to discharge and become inactive. These reactions are driven by the potential difference between each electrode and the redox shuttle agent, so that when the positive electrode potential falls to the redox potential of the redox shuttle agent, the discharge of the positive electrode ends, and when the negative electrode potential rises to the redox potential of the redox shuttle agent, the discharge of the negative electrode ends. In the present disclosure, since the redox shuttle agent is a two-electron reductant of a viologen compound with a low redox potential, the negative electrode potential can be kept low (for example, less than 3.0 V at the Li reference potential). In addition, when this inactivation solution and inactivation method are applied to a non-aqueous secondary battery having copper as a negative electrode current collector, the elution of copper from the negative electrode current collector can be suppressed. When the elution of copper from the negative electrode current collector is suppressed, the precipitation of copper at the positive electrode is also suppressed, so that when recycling or disposing of the non-aqueous secondary battery after inactivation, there is no need to remove or recover the precipitate from the positive electrode, and the battery can be efficiently recycled or disposed of. Furthermore, in the present disclosure, since the redox shuttle agent is a two-electron reductant, the reduction of the positive electrode is promoted, and the discharge rate at the positive electrode is unlikely to decrease even after the negative electrode potential reaches the oxidation-reduction potential of the redox shuttle agent, and the battery can be quickly inactivated until the battery voltage reaches near 0 V.

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.

Below, examples of preparing a deactivating solution and deactivating a nonaqueous secondary battery are described as experimental examples. Note that experimental example 1 corresponds to an embodiment of the present disclosure, and experimental examples 2 and 3 correspond to reference examples of the present disclosure.

[Experimental Example 1]
(Preparation of inactivation solution)
First, under an argon atmosphere, methyl viologen _{hexafluorophosphate} (chemical formula: ( _{C12H14N2 )} ²⁺ ( _PF6- ) ₂ , hereinafter simply referred to as methyl viologen) and two equivalents of metallic lithium relative to methyl viologen were placed in a tetrahydrofuran (THF) solvent and stirred at room temperature for several ^days . The concentration of methyl viologen was adjusted to 0.05 mol/L. In this way, the inactivation solution of Experimental Example 1 was obtained. Hereinafter, this inactivation solution will also be referred to as "Solution A".

(Electrochemical measurement of the inactivation solution)
Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in solution A to a concentration of 1 mol/L to prepare a measurement solution for cyclic voltammetry (CV). A three-electrode H-type cell was used for the CV measurement, with glassy carbon as the working electrode, metallic lithium as the counter electrode, and metallic lithium pressed onto a nickel wire as the reference electrode. First, the potential of the working electrode relative to the reference electrode was measured without applying voltage or current. This was taken as the open circuit potential of the inactivation solution. Thereafter, the potential was raised from the open circuit potential to 3.5 V (vs. Li/Li ⁺ ), the potential sweep direction was reversed, and the potential was lowered to 1.5 V (vs. Li/ ^{Li +} ), the sweep direction was reversed again, and the potential was swept to the open circuit potential. The measurement temperature was 20° C., and the potential sweep rate was 50 mV/s. The peak potential E _pa [V] on the oxidation side and the peak potential E _pc [V] on the reduction side were then measured, and the value E ₀ [V] was calculated from E ₀ = (E _pa + E _pc )/2, which was defined as the oxidation-reduction potential of the redox shuttle agent.

(Deactivation of non-aqueous secondary batteries)
The inactivation behavior of the non-aqueous secondary battery was evaluated using solution A. As the non-aqueous secondary battery, a lithium ion battery prepared as follows was used. A positive electrode composite material in which 93 parts by weight of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , 4 parts by weight of acetylene black, and 3 parts by weight of polyvinylidene fluoride were mixed was coated on aluminum foil to prepare a positive electrode. A negative electrode composite material in which 98 parts by weight of graphite, 1 part by weight of carboxymethyl cellulose, and 1 part by weight of styrene butadiene rubber were mixed as a negative electrode composite material was coated on copper foil to prepare a negative electrode. An electrolyte solution was prepared by dissolving LiPF 6 at a concentration of 1 mol/ _L in a mixed solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC/DMC/EMC=3/4/3. A polyethylene single-layer microporous film was used as the separator. The positive and negative electrodes were opposed to each other through a separator soaked in an electrolyte solution, and the electrodes were sealed in a laminate film to prepare a lithium-ion battery. This lithium-ion battery was charged and discharged for two cycles at a voltage range of 3.0 V to 4.1 V, and then charged to 4.1 V to be fully charged. The fully charged battery was opened under an argon atmosphere, and 1.268 mL of solution A (280% inactivation agent relative to the volume [mL] of the electrolyte solution of the non-aqueous secondary battery, and 0.004 mol/Ah of redox shuttle agent per battery capacity [Ah] at full charge of the non-aqueous secondary battery) was injected, the battery was sealed again, and the voltage change was measured at a temperature of 20 ° C. The lithium-ion battery after inactivation was disassembled under an argon atmosphere, and the negative electrode was taken out. The negative electrode and metallic lithium were placed in a beaker containing an electrolyte solution prepared in the same manner as the electrolyte solution for the lithium ion battery, and the voltage between the negative electrode and the metallic lithium was measured with a tester, and this was taken as the negative electrode potential based on Li.

[Experimental Example 2]
(Preparation of inactivation solution)
Methyl viologen was dissolved in a mixed solvent of EC, DMC, and EMC in a volume ratio of EC/DMC/EMC=3/4/3 to a concentration of 0.05 mol/L, thus obtaining an inactivation solution for Experimental Example 2. Hereinafter, this inactivation solution is also referred to as "Solution B."

(Electrochemical measurement of the inactivation solution)
_LiPF6 was dissolved in solution B to a concentration of 1 mol/L to prepare a CV measurement solution. A three-electrode H-type cell similar to that in Experimental Example 1 was used for the CV measurement, and the open circuit potential of the inactivation solution and the redox potential of the redox shuttle agent were obtained. The measurement temperature, potential sweep rate, and potential range were the same as in Experimental Example 1, and only the potential sweep direction was reversed. That is, the potential was lowered from the open circuit potential to 1.5 V (vs. Li/Li ⁺ ), the potential sweep direction was reversed, the potential was raised to 3.5 V (vs. Li/Li ⁺ ), the sweep direction was reversed again, and the potential was swept to the open circuit potential.

(Deactivation of non-aqueous secondary batteries)
The deactivation behavior of the nonaqueous secondary battery was evaluated in the same manner as in Experimental Example 1, except that solution B was used instead of solution A, and the negative electrode potential after deactivation was determined.

[Experimental Example 3]
(Preparation of inactivation solution)
A deactivation solution was prepared in the same manner as in Experimental Example 1, except that a mixed solvent of EC, DMC, and EMC in a volume ratio of EC/DMC/EMC=3/4/3 was used instead of THF. Hereinafter, this deactivation solution is also referred to as "Solution C."

(Electrochemical measurement of the inactivation solution)
The open circuit potential of the inactivating solution and the oxidation-reduction potential of the redox shuttle agent were determined in the same manner as in Experimental Example 1, except that solution C was used instead of solution A.

(Deactivation of non-aqueous secondary batteries)
The deactivation behavior of the nonaqueous secondary battery was evaluated in the same manner as in Experimental Example 1, except that Solution C was used instead of Solution A.

[Experimental Results]
When the negative electrode potential of the batteries after deactivation in Experimental Examples 1 and 2 was confirmed, it was about 2.4 V based on the Li reference potential in Experimental Example 1 and about 2.7 V based on the Li reference potential in Experimental Example 2, and it was confirmed that the negative electrode potential was less than 3.0 V as expected. From this, it was inferred that the negative electrode potential in Experimental Example 3 would also be less than 3.0 V, and it was inferred that Solutions A to C in Experimental Examples 1 to 3 can suppress the elution of copper from the negative electrode current collector foil when used as a deactivation solution for a battery.

4 to 6 show the CV measurement results of the inactivation solutions (solutions A, B, and C) of Experimental Examples 1 to 3. As shown in Fig. 5, in the inactivation solution of Experimental Example 2 using non-reduced methyl viologen (solution B), the open circuit potential was around 3.3 V (vs. Li/Li ⁺ ), and two peaks indicating a two-stage oxidation reaction were confirmed around 2.1 V (vs. Li/Li ⁺ ) and 2.6 V (vs. Li/Li ⁺ ).

As shown in Fig. 4, the open circuit potential of solution A, which is the inactivation liquid of Experimental Example 1, was 2.0 V (vs. Li/Li ⁺ ), which was a lower value than the open circuit potential of solution B. Furthermore, when the potential of solution A was gradually increased from the open circuit potential, two peaks corresponding to the two-stage oxidation reaction of methyl viologen were confirmed at around 2.1 V (vs. Li/ ^{Li +} ) and 2.6 V (vs. ^Li /Li + ). Since the open circuit potential was lower than that of solution B and the two-stage oxidation reaction proceeded when the potential was increased from the open circuit potential, it was inferred that methyl viologen exists as a two-electron reduced form in solution A in the open circuit state. Moreover, when the potential was increased to 3.5 V (vs. Li/Li ⁺ ) and then the potential sweep direction was reversed to gradually decrease the potential, two peaks corresponding to the two-step reduction reaction of methyl viologen were observed at approximately 2.5 V (vs. Li/ ^{Li +} ) and 2 V (vs. Li/Li ⁺ ). Therefore, it was inferred that the redox potential of the two-electron reduced form of the viologen compound was equal to the redox potential of the viologen compound (in the oxidized state).

As shown in FIG. 6, the open circuit potential of solution C, which is the inactivation liquid of Experimental Example 3, was 2.5 V (vs. Li/Li ⁺ ), which was lower than that of solution B, but higher than that of solution A. Furthermore, when the potential of solution C was gradually increased from the open circuit potential, no peak corresponding to the oxidation reaction of methyl viologen was observed. Furthermore, when the potential was gradually decreased after reaching 3.5 V (vs. Li/Li ⁺ ), two peaks corresponding to the reduction reaction of methyl viologen were observed at around 2.5 V (vs. Li/Li ⁺ ) and 2.0 V (vs. Li/Li ⁺ ). From the above, it was inferred that in solution C, methyl viologen was partially reduced by one electron, but most of it was present in an oxidized state.

As mentioned above, the reduction products of methyl viologen were different between Experimental Example 1, which used THF (an ether compound) as the solvent, and Experimental Example 3, which used a mixed solvent of EC, DMC, and EMC (all carbonate compounds). This is presumed to be because the stability of methyl viologen and the reduced form of methyl viologen differs due to differences in the interactions between the solvent and methyl viologen or the reduced form of methyl viologen. According to J. Org. Chem. 52 (1987) 2779-2789, it was presumed that the two-electron reduced form of the viologen compound would be stable even if a nitrile compound was used as the solvent in addition to an ether compound.

Figure 7 shows the discharge behavior of the battery using the inactivation solutions (solutions A, B, and C) in Experimental Examples 1 to 3. In Experimental Example 1, which used solution A, the battery discharge progressed after the addition, and 44 hours later the SOC (State of Charge) reached 0%, and 57 hours later the battery voltage reached 0V. On the other hand, in Experimental Examples 2 and 3, which used solutions B and C, the discharge progressed in the same way as with solution A, but the discharge rate dropped sharply once the battery voltage reached 1V. From the above, it was found that solutions A to C function as inactivation solutions for batteries, but when solution A was used, the discharge rate at the end of discharge was faster than with solutions B and C, and the battery could be quickly discharged to near 0V.

The increase in the discharge rate at the end of discharge when solution A was used was presumably related to the fact that the decrease in battery voltage at the end of discharge was mainly due to the decrease in the positive electrode potential caused by the discharge of the positive electrode. As shown in reaction formula (3) below, the redox shuttle agent in a reduced state is the reactant in the discharge reaction of the positive electrode. Therefore, it was presumed that the use of solution A containing the two-electron reduced form of methyl viologen as the inactivating solution increased the discharge rate of the positive electrode, and thus the discharge rate at the end of discharge.

In Experiment 3, which used solution C, the discharge rate decreased toward the end of the discharge, similar to Experiment 2, which used solution B. This was presumably because, although methyl viologen was partially reduced in solution C, most of it remained in an oxidized state.

Table 1 summarizes the state of methyl viologen, redox potential, open circuit potential, performance as a deactivating solution, and negative electrode potential after deactivation for solutions A to B of Experimental Examples 1 to 3. In all cases, the negative electrode potential is kept low, but from the viewpoint of increasing the discharge rate at the end of discharge and quickly discharging to 0 V, it was found that it is desirable for the methyl viologen contained in the deactivating solution to be reduced by two electrons. It was presumed that the redox state of methyl viologen contained in the deactivating solution can be evaluated from the open circuit potential of the deactivating solution. And, when the open circuit potential of the deactivating solution is around 2.0 V (vs. Li/Li ⁺ ), it was presumed that the two-electron reduced form of methyl viologen exists in the solution, and therefore it is possible to quickly discharge to 0 V when used as a deactivating solution for a battery.

Furthermore, as shown by CV measurement, solution A exhibits an oxidation-reduction potential of 3.0 V (vs. Li/Li ⁺ ) or less, and therefore it was found that when used as a passivation solution, it can suppress the dissolution of copper from the negative electrode current collector foil. From the above, it was found that solution A containing a two-electron reduced form of methyl viologen can rapidly discharge a battery to 0 V and simultaneously suppress the dissolution of copper during passivation when used as a passivation solution.

In addition to the methyl viologen used in Experimental Examples 1 to 3, there are also other viologen compounds having various hydrocarbon groups as R and R' in formula (v1). All of these compounds become neutral molecules through two-stage reduction, similar to methyl viologen. In Reference Example 1 below, it was confirmed that the viologen compounds exhibit redox potentials of about 2.5 V (vs. Li/Li ⁺ ) and 2.0 V (vs. Li/Li ⁺ ), regardless of the structures of R and R' in formula (v1). As described above, it was presumed that the redox potential of the two-electron reduced form of the viologen compound coincides with the redox potential of the viologen compound. Therefore, it was presumed that the two-electron reduced form of the viologen compound exhibits the same effect as the two-electron reduced form of methyl viologen, regardless of the structures of R and R'.

[Reference Example 1]
The redox potentials of various viologen compounds (cations) were calculated by density functional theory. The Gibbs free energy of the oxidized form (ΔG _OX ) and the Gibbs free energy of the reduced form (ΔG _RED ) were calculated, and the redox potential E _abs of the target was calculated as an absolute potential from the following formula (1) assuming one-electron reduction.
E _abs = (ΔG _OX - ΔG _RED )/F ... Formula (1)
In formula (1), F is the Faraday constant, 96485 C/mol.

From the obtained absolute potential, the oxidation-reduction potential E _RedOx relative to the lithium electrode was calculated using the following formula (2).
E _RedOx [V vs. Li ⁺ /Li] = E _abs -1.4 ... Formula (2)

The free energy was calculated using density functional theory. The Gaussian09 Revision E package was used with B3LYP and 6-311++GG(d,p) as functionals and basis functions, and the solvation effect was taken into account with a dielectric constant of the solvent of 29.11 using the continuum polarization model.

Table 2 shows the calculation results of the redox potential at the Li reference potential in Reference Example 1. Note that Table 2 shows only the redox potential of the second stage (low potential side). The calculation results of the redox potential of methyl viologen were generally consistent with the experimental results of Experimental Example 2 (Figure 5). From the calculation results of Reference Example 1, it was inferred that the redox potential shows similar values regardless of the structure of R or R'. Table 3 shows the redox potential of the viologen compounds disclosed in J. Mater. Chem. A, 7 (2019) 23337-23360. The redox potentials in Table 3 were all less than 3.0 V when converted to a Li reference potential. From the above, it was inferred that the redox potential of a viologen compound or its two-electron reduced product is less than 3.0 V regardless of the structure of R or R'.

This invention can be used in the battery industry.

20 nonaqueous secondary battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 ion conductive medium.

Claims (9)

A deactivating solution for deactivating a non-aqueous secondary battery,
a redox shuttle agent including a two-electron reduced form of a viologen compound;
A non-aqueous solvent for at least one of an ether compound and a nitrile compound;
Including,
A non-aqueous secondary battery deactivation solution. The non-aqueous solvent is tetrahydrofuran.
The non-aqueous secondary battery deactivation solution according to claim 1 . The viologen compound is methyl viologen.
The non-aqueous secondary battery deactivation solution according to claim 1 or 2. The inactivation solution has an open circuit potential of less than 2.2 V measured using a carbon electrode and a metal Li electrode.
The non-aqueous secondary battery deactivation solution according to any one of claims 1 to 3. The redox shuttle agent is contained at 1 mmol/L or more.
The non-aqueous secondary battery deactivation solution according to any one of claims 1 to 4. A method for producing a deactivating solution for deactivating a non-aqueous secondary battery, comprising:
a preparation step of mixing a viologen compound, a reducing agent for reducing the viologen compound, and a non-aqueous solvent for at least one of an ether compound and a nitrile compound to prepare an inactivation liquid;
Including,
Method for producing the inactivation solution. In the preparation step, an alkali metal is used as the reducing agent.
A method for producing the inactivation solution according to claim 6 . An addition step of adding the inactivation solution according to any one of claims 1 to 5 to the inside of the nonaqueous secondary battery;
Including,
A method for deactivating a non-aqueous secondary battery. The method for inactivating a non-aqueous secondary battery according to claim 8, wherein the addition step is performed on the non-aqueous secondary battery having a negative electrode current collector containing copper.

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