JP7803159B2 - Deactivating agents and deactivation methods - Google Patents

Description

This disclosure relates to a deactivating agent and a deactivation method.

Conventionally, when recycling or disposing of non-aqueous secondary batteries, a deactivation process is performed to inactivate the recovered batteries. For example, one possible process involves connecting the recovered batteries to a charge/discharge device and discharging them to 0 V. However, this process can take a long time. Furthermore, if the recovered battery has a current interrupt device (CID), it is not possible to discharge it at all. Therefore, it has been proposed to add a redox shuttle agent (e.g., ferrocene) that exhibits a redox potential in the range of 3.0 to 4.5 V relative to the redox potential of lithium to the recovered battery (see Patent Document 1). This allows the battery voltage of a non-aqueous secondary battery to be safely and quickly reduced to 0 V without using a charge/discharge device. Additionally, a method has been proposed in the past for removing carbon from the copper foil surface of a lithium-ion battery negative electrode sheet using an aqueous release agent (see, for example, Patent Documents 2 and 3). This method claims to significantly reduce recycling costs by recovering the copper foil and carbon using the release agent.

Japanese Patent Application Laid-Open No. 2018-137137 Japanese Patent Application Laid-Open No. 2015-26566 JP 2007-179774 A

However, while the deactivator in Patent Document 1 can deactivate non-aqueous secondary batteries, when considering the simplification and safety of processes such as deactivation and disposal of non-aqueous secondary batteries, the types of solvents that dissolve the redox shuttle agent have not yet been sufficiently studied, and a new, better deactivator has been sought.

The present disclosure has been made to solve these problems, and its main objective is to provide a new deactivating agent and deactivation method for deactivating non-aqueous secondary batteries.

After extensive research to achieve the above-mentioned objective, the inventors discovered that non-aqueous secondary batteries can be deactivated by using a carboxylic acid ester compound as the non-aqueous solvent of the deactivator, leading to the completion of the disclosed invention.

That is, the deactivating agent of the present disclosure is
A deactivator for deactivating a non-aqueous secondary battery,
a redox shuttle agent having an oxidation-reduction potential, relative to a Li reference potential, higher than that of a negative electrode active material of the nonaqueous secondary battery and lower than that of a positive electrode active material of the nonaqueous secondary battery;
a non-aqueous solvent containing a carboxylic acid ester compound;
It includes:

The inactivation method of the present disclosure also includes:
A method for deactivating a non-aqueous secondary battery, comprising:
The method includes adding the above-mentioned deactivator for non-aqueous secondary batteries to the inside of the non-aqueous secondary battery.

This deactivator and deactivation method can deactivate nonaqueous secondary batteries. The reason for this effect is believed to be as follows: When a redox shuttle agent with an oxidation-reduction potential lower than the positive electrode potential and higher than the negative electrode potential is added to a charged nonaqueous secondary battery, the potential difference between each electrode and the redox shuttle agent serves as the driving force for discharging the battery, thereby deactivating the battery. Furthermore, using a nonaqueous solvent containing a carboxylic acid ester compound can, for example, act on the electrode binder and promote separation between the current collector and the electrode composite. Furthermore, using a nonaqueous solvent containing a carboxylic acid ester compound can, for example, increase the flash point of the electrolyte used in the nonaqueous secondary battery, thereby further improving safety when disposing of the nonaqueous secondary battery.

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. 1 shows the discharge behavior after the deactivators of Experimental Examples 1 and 2 were added to a fully charged evaluation cell. Photographs showing examples of the peeled state of the electrode mixtures of Experimental Examples 3 to 5. Photographs showing the peeling state of the electrode composite after ultrasonic treatment in Experimental Examples 6 to 8.

(inactivating agent)
The non-aqueous secondary battery deactivator of the present disclosure includes a redox shuttle agent and a non-aqueous solvent. The redox shuttle agent is a compound whose oxidation-reduction potential, relative to Li, is higher than that of the negative electrode active material of the non-aqueous secondary battery and lower than that of the positive electrode active material of the non-aqueous secondary battery. In this specification, the redox shuttle agent refers to a compound that can be oxidized and reduced and that can repeatedly transport charge between the positive electrode and the negative electrode. The non-aqueous solvent includes a carboxylic acid ester compound.

[Non-aqueous secondary battery]
First, a nonaqueous secondary battery to be deactivated will be described. The nonaqueous secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous ion-conducting medium interposed between the positive electrode and the negative electrode and conducting carrier ions. Examples of carrier ions include Group 1 element ions and Group 2 element ions. Examples of Group 1 element ions include lithium ions, sodium ions, and potassium ions. Examples of Group 2 element ions include magnesium ions and calcium ions. For ease of explanation, the following description will mainly focus on a case where the nonaqueous secondary battery is a lithium-ion secondary battery in which the negative electrode active material is a carbon material.

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 as needed to increase electrode density. The positive electrode active material may have a redox potential relative to Li higher than that of the redox shuttle agent contained in the deactivator, but the redox potential may be greater than 3.0 V relative to Li, preferably 3.5 V or higher, more preferably 3.8 V or higher, and even more preferably 4.0 V or higher. Examples of the positive electrode active material that can be used include sulfides containing transition metal elements and oxides containing lithium and transition metal elements. Specifically, transition metal sulfides such as _TiS2 , _TiS3 , _MoS3 , and _FeS2 , 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), and _LiV2O Lithium vanadium composite oxides such as Li _{(1-x) MnPO4} , transition metal oxides such as _{V2O5 ,} etc. can be used. Olivine-type lithium manganese phosphate compounds such as Li(1-x) _MnPO4 , olivine-type lithium cobalt phosphate compounds such as Li _{(1-x) CoPO4} , and olivine-type lithium nickel phosphate compounds such as Li _{(1- x) NiPO4} can also be used. 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 ,} and inverse spinel-type lithium nickel vanadate compounds such as Li _{(1-x) NiPO4} can also be used. The positive electrode active material is preferably an oxide containing one or more of nickel, manganese, and cobalt, and examples thereof include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

Examples of conductive materials that can be used for the positive electrode include graphite (e.g., natural graphite (e.g., scaly graphite, flake graphite) and artificial graphite), acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (e.g., copper, nickel, aluminum, silver, and gold). Examples of binders that can be used include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, as well as thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, and natural butyl rubber (NBR). Additionally, aqueous binders such as aqueous dispersions of cellulose-based materials like carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) can also be used. Examples of solvents that can be used include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, a dispersant, thickener, or the like may be added to water, and the active material may be slurried with a latex such as SBR. Examples of thickeners include polysaccharides such as carboxymethyl cellulose and methyl cellulose, either alone or in combination. Application methods include roller coating (e.g., applicator roll), screen coating, doctor blade coating, spin coating, and bar coating. Any of these can be used to achieve any desired thickness and shape. Examples of current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, and conductive glass. For the purpose of improving adhesion, conductivity, and oxidation resistance, aluminum and copper surfaces treated with carbon, nickel, titanium, or silver can also be used. These surfaces can also be subjected to oxidation treatment. The current collector may be in the form of a foil, film, sheet, net, punched or expanded material, lath, porous material, foam, or fiber group. The current collector may have a thickness of, for example, 1 to 500 μm.

The negative electrode may be formed, for example, by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode mixture, applying it to the surface of a current collector, drying it, and compressing it to increase electrode density as needed. Alternatively, the negative electrode may be formed by closely adhering the negative electrode active material to the current collector. The redox potential of the negative electrode active material is preferably 3.0 V or less, more preferably 2.0 V or less, and even more preferably 1.0 V or less, relative to the Li reference potential. Examples of negative electrode active materials 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 carbonaceous materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Examples of composite oxides include lithium titanium composite oxides such as Li4Ti5O12 and lithium vanadium} composite oxides such as _LiV2O3 . Of these, carbonaceous materials such as graphite are preferred as the negative electrode active material. The conductive materials, binders, solvents, etc. used in the negative electrode can be the same as those exemplified for the positive electrode. For the negative electrode current collector, in addition to copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymers, conductive glass, Al—Cd alloys, etc., materials such as copper whose surfaces have been treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and reduction resistance can also be used. These surfaces can also be subjected to an oxidation treatment. The shape of the current collector can be the same as that of the positive electrode.

At least one of the positive and negative electrodes preferably contains at least SBR as a binder. When the electrode contains SBR as a binder, the addition of a deactivator allows the electrode composite to be peeled from the current collector due to the relationship with the non-aqueous solvent of the deactivator. Non-aqueous secondary batteries are disassembled and disposed of after being deactivated, but with this deactivator and electrode, the process of peeling the electrode composite can be omitted, further simplifying the disassembly process.

As the ion-conducting medium, a non-aqueous electrolyte solution containing a supporting salt or a non-aqueous gel electrolyte solution can be used. Examples of solvents for non-aqueous electrolyte solutions 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. Specific examples of carbonate compounds include cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, as well as 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 ester compounds include cyclic ester compounds such as γ-butyllactone and γ-valerolactone, and chain ester compounds such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate. Examples of ether compounds include dimethoxyethane, ethoxymethoxyethane, and diethoxyethane. Examples of nitrile compounds include acetonitrile and benzonitrile. Examples of amide compounds include dimethylacetamide (DMA) and dimethylformamide. Examples of furan compounds include tetrahydrofuran and methyltetrahydrofuran. Examples of sulfolane compounds include sulfolane and tetramethylsulfolane. Examples of oxolane compounds include 1,3-dioxolane and methyldioxolane. These compounds can be used alone or in combination. Among these, preferred solvents for non-aqueous electrolytes are mixtures of cyclic carbonate compounds and chain carbonate compounds, such as DMC-EC, DEC-EC, and DMC-EMC-EC. Examples of supporting salts include inorganic salts such as _LiPF6 , _LiBF4 , _LiAsF6 , and _LiClO4 , and _organic salts _such as _LiCF3SO3 , LiN( _CF3SO2 ) ₂ , _and LiC( _CF3SO2 ) ₃ , and these can be used alone or in combination. The concentration of the supporting salt in the electrolyte solution is preferably 0.1 mol/L or more and 5 mol/L or less, and more preferably 0.5 mol/L or more and 2 mol/L or less. In addition, instead of a liquid ion-conducting medium, an ion-conducting polymer, an inorganic solid electrolyte, 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-conducting medium.

This non-aqueous secondary battery may include a separator between the positive electrode and negative electrode. There are no particular limitations on the separator, so long as it has a composition that can withstand the range of uses for non-aqueous secondary batteries. Examples include polymer non-woven fabrics such as polypropylene non-woven fabrics, and thin microporous membranes made of olefin resins such as polyethylene. These may be used alone or in combination.

The shape of this nonaqueous secondary battery is not particularly limited, and examples include coin, button, sheet, laminate, cylindrical, flat, and prismatic types. Larger batteries for use in electric vehicles and the like may also be used. An example of a nonaqueous secondary battery is shown in Figure 1. Figure 1 is a cross-sectional view showing the schematic configuration of a coin-type nonaqueous secondary battery 20. As shown in Figure 1, the nonaqueous secondary battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and disposed at the bottom of the battery case 21, a negative electrode 23 having a negative electrode active material and disposed opposite the positive electrode 22 via a separator 24, a gasket 25 made 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 nonaqueous secondary battery 20 includes an ionically conductive medium 27 containing a dissolved lithium salt in the space between the positive electrode 22 and the negative electrode 23. Furthermore, this nonaqueous secondary battery 20 preferably contains SBR as a binder in either the positive electrode 22 or the negative electrode 23.

[Deactivating agent]
Next, the passivating agent will be described. The passivating agent includes a redox shuttle agent and a non-aqueous solvent. The non-aqueous solvent included in the passivating agent includes a carboxylic acid ester compound. The carboxylic acid ester compound may be represented by, for example, formula (1). In formula (1), R ¹ and R ² may be the same or different and are hydrocarbon groups which may have a substituent. The hydrocarbon group may, for example, have a linear or cyclic skeleton and may further have a substituent. The hydrocarbon group preferably has 20 or fewer carbon atoms, more preferably 15 or fewer carbon atoms, and may be 12 or fewer carbon atoms. Specific examples of the hydrocarbon group include alkyl groups and aryl groups. The alkyl group may have 1 to 8 carbon atoms, may be linear or branched, or may be a halogenated alkyl group in which some or all of the hydrogen atoms are substituted with halogen. Examples of the alkyl group include a methyl group, an ethyl group, an isopropyl group, a tert-butyl group, and a trifluoromethyl group. The aryl group may have 6 to 12 carbon atoms. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a mesityl group, and a naphthyl group. Examples of the substituent include one or more of an alkyl group, an aryl group, a hydroxyl group, a sulfone group, a nitro group, an amino group, and a halogen atom.

The carboxylic acid ester compound is preferably one or more of an acetate compound, a benzoate compound, and a butyrate compound. Specifically, the carboxylic acid ester compound may be represented by, for example, formulas (2) to (12). Examples of acetate compounds include octyl acetate (formula (2)), phenyl acetate (formula (3)), menthyl acetate (formula (4)), benzyl acetate (formula (5)), amyl acetate (formula (6)), hexyl acetate (formula (7)), butyl acetate (formula (8)), and derivatives thereof. Examples of benzoate compounds include ethyl benzoate (formula (9)), butyl benzoate (formula (10)), benzyl benzoate (formula (11)), and derivatives thereof. Examples of butyrate compounds include butyl butyrate (formula (12)) and derivatives thereof. Among these, octyl acetate and phenyl acetate are preferred from the standpoint of the solubility of the redox shuttle agent and the increase in flash point.

Furthermore, it is more preferable that the non-aqueous solvent of the deactivator, when added to the electrolyte of a non-aqueous secondary battery, raises the flash point of the electrolyte. A solvent that raises the flash point even more is preferable, as it can enhance safety when deactivating a non-aqueous secondary battery. For example, the carboxylic acid ester compound preferably has a higher flash point, such as 25°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 80°C or higher. The flash point of the carboxylic acid ester compound may be, for example, 200°C or lower, or 150°C or lower. It is also preferable that the non-aqueous solvent of the deactivator raises the flash point more when added to the electrolyte of a non-aqueous secondary battery, preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher. This flash point increase refers to the temperature difference between the flash point of the mixture of the electrolyte and the deactivator and the flash point of the electrolyte. The flash points (°C) for each of the formulas (2) to (12) are listed.

The deactivator may further contain a carbonate compound in addition to the carboxylic acid ester compound. When the deactivator contains a carbonate compound, for example, it may be possible to adjust the redox power of the redox shuttle agent. Examples of carbonate compounds include the cyclic carbonate compounds and chain carbonate compounds described above. The amount of carbonate compound is preferably as small as possible, preferably 50% by volume or less, more preferably 25% by volume or less, and even more preferably 10% by volume or less, when the total amount of the carboxylic acid ester compound and the carbonate compound is taken as 100.

The redox shuttle agent is not particularly limited as long as it is a compound that can be oxidized and reduced and can repeatedly transport charge between the positive electrode and the negative electrode. Examples of redox shuttle agents include one or more of ferrocene-based compounds, TEMPO-based compounds, phenothiazine-based compounds, viologen-based compounds, and quinone-based compounds. The redox shuttle agent preferably has a redox potential of less than 3.0 V relative to the lithium potential. When the current collector is made of Cu or its alloy, a redox shuttle agent with a redox potential of less than 3.0 V relative to the lithium potential is preferred, as it can further suppress Cu elution. Depending on the materials used in the nonaqueous secondary battery, the redox shuttle agent may also have a redox potential of 3.0 V or higher relative to the lithium potential.

Ferrocene-based compounds include ferrocene and its derivatives. TEMPO-based compounds include, for example, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), N-(3,3,5,5-tetramethyl-4-oxypiperidyl)pyrene-1-carboxyamide (Pyrene-TEMPO), 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (MeO-TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxybenzoate (BzO-TEMPO), and 4-acetamido-2,2,6,6-tetramethyl-1-piperidinyloxy (Ac-TEMPO).

The phenothiazine-based compound may be phenothiazine or a derivative of phenothiazine. Phenothiazine is a heterocyclic compound formed by condensing benzene rings at both ends of thiazine. The phenothiazine-based compound may be a phenothiazine with a substituent introduced therein. The phenothiazine-based compound may be, for example, a compound represented by formula (13). In formula (13), R ³ to R ¹¹ are functional groups that may be the same or different. Examples of functional groups include one or more of hydrogen, alkyl groups, aryl groups, acyl groups, alkoxy groups, alkylsulfanyl groups, hydroxyl groups, sulfonic groups, nitro groups, amino groups, carboxyl groups, and halogens. The alkyl groups may have from 1 to 6 carbon atoms, may be linear or branched, or may be halogenated alkyl groups in which some or all of the hydrogen atoms are substituted with halogens. Examples of alkyl groups include methyl groups, ethyl groups, isopropyl groups, tert-butyl groups, and trifluoromethyl groups. The aryl group may have 6 to 12 carbon atoms. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a mesityl group, and a naphthyl group. The acyl group may have 1 to 7 carbon atoms. Examples of the acyl group include a formyl group, an acetyl group, and a benzoyl group. The alkoxy group may have 1 to 6 carbon atoms. Examples of the alkoxy group include a methoxy group, an ethoxy group, and a phenoxy group. The alkylsulfanyl group may have 1 to 6 carbon atoms. Examples of the alkylsulfanyl group include a methylsulfanyl group and an ethylsulfanyl group. Examples of the halogen include fluorine, chlorine, and bromine. In formula (13), R ³ to R ¹¹ may each independently represent hydrogen, an alkyl group, a phenyl group, an acetyl group, or a halogen. In addition, in formula (13), six or more of R ³ to R ¹¹ may be hydrogen, or seven or more of R ³ to R ¹¹ may be hydrogen. Examples of phenothiazine compounds include phenothiazine, 2-trifluoromethylphenothiazine, 2-methoxyphenothiazine, 10-methylphenothiazine, 2-ethylthiophenothiazine, 2-methylthiophenothiazine, 2-chlorophenothiazine, 2-acetylphenothiazine, 10-ethylphenothiazine, 10-isopropylphenothiazine, 10-tert-butylphenothiazine, 10-acetylphenothiazine, 10-phenylphenothiazine, 3,7-dichloro-10-ethylphenothiazine, 3,7-dibromo-10-ethylphenothiazine, and 3,7-bis(trifluoromethyl)-10-ethylphenothiazine.

The viologen compound may be a viologen or a derivative of a viologen. A 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 represented by formula (14), for example. In formula (14), R ¹² and R ¹³ are hydrocarbon groups that may be the same or different. The hydrocarbon group is preferably a linear or branched chain hydrocarbon group or a cyclic hydrocarbon group. Examples of the linear 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 cyclic hydrocarbon groups 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.). Among these, linear alkyl groups are preferred, and those without a substituent are preferred. Each hydrocarbon group preferably has 20 or fewer carbon atoms, more preferably 10 or fewer carbon atoms, and even more preferably 6 or fewer carbon atoms. The viologen-based compound may have a structure in which a hydrocarbon group, a carboxyl group, an alkoxy group, a nitro group, an amino group, or a halogen atom is introduced into one or more carbon atoms of the 4,4'-bipyridine skeleton. Examples of hydrocarbon groups include one or more of the hydrocarbon groups exemplified above. When the viologen-based compound has multiple substituents, the substituents may be bonded to form a ring. The viologens preferably have 30 or less carbon atoms, more preferably 20 or less, and even more preferably 14 or less. Specific examples of the viologen compounds include methyl viologen, ethyl viologen, propyl viologen, butyl viologen, pentyl viologen, hexyl viologen, heptyl viologen, and octyl viologen. Further examples of the viologen compounds include 1,1'-dimethyl-3,3'-[methylenebis(oxy)]-4,4'-bipyridinium, phenyl viologen, and 1-(4-aminophenyl)-1'-methyl-4,4'-bipyridinium.

The viologen compound may ^have , as a counter anion to the cation of formula (14), ^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 as or different from the anion of the supporting salt of _the nonaqueous secondary battery to be passivated.

A quinone compound is a compound having a structure in which the C—H groups on two carbon atoms of an aromatic hydrocarbon skeleton are each replaced with a C═O group. The quinone compound may have a 4- to 7-membered aromatic hydrocarbon skeleton, preferably a 6-membered aromatic hydrocarbon skeleton (a benzoquinone structure). Quinones may have, for example, a p-benzoquinone structure represented by formula (15) or an o-benzoquinone structure represented by formula (16), preferably a p-benzoquinone structure represented by formula (15). In formulas (15) and (16), R ²² to R ²⁵ are functional groups that may be the same or different. Examples of functional groups include one or more of hydrogen, alkyl groups, aryl groups, acyl groups, alkoxy groups, alkylsulfanyl groups, hydroxyl groups, sulfonic groups, nitro groups, amino groups, carboxyl groups, and halogens. When a quinone compound has multiple substituents, the substituents may be bonded to form a ring. Examples of quinone compounds in which substituents are bonded to form a ring include naphthoquinones (1,4-naphthoquinone, 1,2-naphthoquinone, etc.), anthraquinones (9,10-anthraquinone, etc.), derivatives thereof, etc. The quinone compounds preferably have 20 or less carbon atoms, more preferably 14 or less, and even more preferably 10 or less. Specific examples of quinone compounds include p-benzoquinone, methyl-p-benzoquinone, 2,5-dimethyl-1,4-benzoquinone, methoxybenzoquinone, 2,5-dihydroxy-1,4-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, anthraquinone, 2-methylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 1,4-dihydroxyanthraquinone, and 1-nitroanthraquinone.

The concentration of the redox shuttle agent contained in the deactivator is preferably higher, preferably 1.0 mmol/L or higher, more preferably 2.0 mmol/L or higher, even more preferably 2.5 mmol/L or higher, and may be 3.0 mmol/L or higher. A higher concentration of the redox shuttle agent is preferable, as it allows high-energy density batteries, such as those used in electric vehicles (EVs), to be discharged in a shorter period of time. The concentration of the redox shuttle agent contained in the deactivator may be below the solubility limit, or may be 5.0 mol/L or lower.

The deactivator may contain solutes other than the redox shuttle agent, but preferably does not contain any solutes. Even if the deactivator contains solutes other than the redox shuttle agent, the concentration is preferably less than 0.1 mmol/L or less than 0.01 mmol/L. This is because the lower the content of solutes other than the redox shuttle agent in the deactivator, the lower the viscosity tends to be, and therefore the more rapidly the deactivation proceeds. Examples of solutes include the supporting salts mentioned above. The supporting salt may be the same as or different from the supporting salt contained in the ionically conductive medium of the nonaqueous secondary battery to be deactivated.

[Inactivation method]
Next, a method for deactivating the nonaqueous secondary battery using the deactivator described above will be described. This deactivation method includes an addition step of adding the deactivator to the interior of the nonaqueous secondary battery. Specifically, the deactivator is added so that the deactivator comes into contact with the positive and negative electrodes of the nonaqueous secondary battery. The method for adding the deactivator is not particularly limited. For example, the battery container may be opened once, the deactivator may be injected, and then resealed as needed. Alternatively, the deactivator may be injected from the outside of the battery container using a syringe and then sealed as needed. The addition step is preferably performed in an inert atmosphere such as an argon atmosphere.

In this addition step, it is preferable to add the deactivator in an amount of 0.1 mol/Ah or less relative to the capacity of the non-aqueous secondary battery. Because non-aqueous secondary batteries have limited internal space, it is preferable to add a smaller amount of deactivator. This amount may be 0.01 mol/Ah or less, or 0.005 mol/Ah or less. The amount of redox shuttle agent relative to the capacity of the non-aqueous secondary battery may be 0.001 mol/Ah or more, 0.002 mol/Ah or more, or 0.003 mol/Ah or more. Addition of an amount of 0.001 mol/Ah or more is preferable, as it further shortens the time required for deactivation.

The amount of deactivator added can be selected appropriately depending on the size of the nonaqueous secondary battery, and may be, for example, 0.01 mL to 10 mL, or 0.05 mL to 5.0 mL. The amount of deactivator added may be, for example, 0.01% to 500% or 1% to 300% of the volume [mL] of the ion conductive medium contained in the nonaqueous secondary battery to be deactivated.

The nonaqueous secondary battery containing the added deactivator may be held stationary or vibrated. The holding time may be empirically determined as the time required for complete deactivation, depending on the capacity of the nonaqueous secondary battery and the amount of deactivator added. The holding time may be, for example, 6 hours to 500 hours, 30 hours to 300 hours, or 50 hours to 200 hours, depending on the capacity of the nonaqueous secondary battery and the amount of deactivator added. Furthermore, the nonaqueous secondary battery containing the added deactivator may be subjected to ultrasonic treatment. Ultrasonic treatment is preferable because it can further shorten the time it takes for the electrode composite to peel off from the current collector. Ultrasonic treatment is preferably performed at a frequency of 10 kHz to 120 kHz, and more preferably at a frequency of 30 kHz to 80 kHz. The duration of ultrasonic treatment depends on the size of the nonaqueous secondary battery, but is preferably 10 seconds or more, more preferably 30 seconds or more, and may be 1 minute or more. The ultrasonic treatment time may also be one hour or less.

The mechanism by which this deactivation method deactivates nonaqueous secondary batteries is believed to be as follows. Figure 2 is an explanatory diagram illustrating the mechanism by which nonaqueous secondary batteries are deactivated. When a redox shuttle agent (RS in the figure) with a redox potential lower than the positive electrode potential and higher than the negative electrode potential is added to a battery, the potential difference between the positive or negative electrode and the redox shuttle agent serves as the driving force for electron transfer from the negative electrode to the redox shuttle agent and from the redox shuttle agent to the positive electrode, resulting in discharge of the battery. Specifically, the reduced form of the redox shuttle agent (RS _(red) in the figure) donates electrons to the positive electrode to become the oxidized form (RS _(ox) in the figure), and the oxidized form of the redox shuttle agent accepts electrons from the negative electrode to become the reduced form. This process repeats, resulting in discharge of the battery. When the positive or negative electrode potential becomes equal to the redox potential of the redox shuttle agent, discharge of that electrode no longer proceeds. Therefore, the positive electrode potential and the negative electrode potential eventually become equal to the potential of the redox shuttle agent, completing the deactivation. Note that "deactivation is complete" may refer to the nonaqueous secondary battery being discharged until the SOC reaches 0%. If the battery is discharged until the SOC reaches 0%, the negative electrode potential is not too low, for example, greater than 1.5 V and less than 3.0 V relative to the Li reference potential. This makes it difficult for gas to be generated due to decomposition of the electrolyte, which serves as an ion-conducting medium, and the safety of the electrode itself is also high. Therefore, recycling and disposal after deactivation can be carried out safely. The lower the battery voltage after deactivation, the less likely sparks will occur, so it is preferable. For example, it may be 3.0 V or less, and more preferably 1.2 V or less, 1.0 V or less, or 0.5 V or less.

Furthermore, for example, when a nonaqueous secondary battery has electrodes using styrene butadiene rubber (SBR) as a binder, this deactivator can achieve peeling between the electrode composite and the current collector. The structure of styrene butadiene rubber (SBR) is shown in formula (17). As shown in formula (17), SBR is presumed to have high solubility in solvents containing linear alkyl or phenyl groups. Furthermore, the carboxylic acid ester used as the nonaqueous solvent for the deactivator is a solvent containing linear alkyl or phenyl groups, such as octyl acetate (formula (2)) or phenyl acetate (formula (3)), and is presumed to affect the binding strength of the SBR. It is presumed that the SBR dissolves in the nonaqueous solution of the deactivator, weakening the binding strength of the electrode composite, resulting in the electrode composite peeling from the current collector.

The deactivator and deactivation method described above can deactivate nonaqueous secondary batteries. The reason for this effect is believed to be as follows: When a redox shuttle agent with a redox potential lower than the positive electrode potential and higher than the negative electrode potential is added to a charged nonaqueous secondary battery, the potential difference between each electrode and the redox shuttle agent serves as the driving force for battery discharge, thereby deactivating the battery. In this case, a carboxylic acid ester compound sufficiently dissolves the redox shuttle agent and is chemically stable, allowing the redox shuttle agent to function more reliably. Furthermore, using a nonaqueous solvent containing a carboxylic acid ester compound can, for example, act on the electrode binder (e.g., SBR) and promote the separation of the current collector from the electrode composite. Therefore, when disassembling the electrode components during disposal of a nonaqueous secondary battery, a separate solution can be prepared, eliminating the need for a separation process for the electrode composite, further simplifying the process. Furthermore, by using a non-aqueous solvent containing a carboxylic acid ester compound, it is possible to increase the flash point of the electrolyte used in the non-aqueous secondary battery, thereby further improving safety when disposing of the non-aqueous secondary battery.

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

For example, in the above-described embodiment, the nonaqueous secondary battery to be deactivated was described as a lithium ion secondary battery, but this is not particularly limited, and the battery may also be a hybrid capacitor, a pseudo-electric double layer capacitor, a lithium or sodium alkali metal secondary battery, an alkali metal ion battery, etc.

Below, experimental examples are described that specifically examine the deactivators and deactivation methods for nonaqueous secondary batteries disclosed herein. Experimental Examples 1, 4, 5, 7, and 8 correspond to working examples of the present disclosure, while Experimental Examples 2, 3, and 6 correspond to comparative examples.

(Experimental Example 1)
The deactivator was prepared by dissolving the redox shuttle agent phenothiazine in octyl acetate (formula (2)) at a concentration of 0.05 mol/L. The deactivation behavior of the battery due to the addition of the deactivator was evaluated. A lithium-ion battery was fabricated as an evaluation cell, consisting of a negative electrode using graphite as _the negative electrode active material and _{a positive electrode using LiNiCoMnO2} as the positive electrode active material. The negative electrode was prepared by coating a copper foil with a slurry mixture containing graphite, flaky graphite, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) in a mass ratio of 93.1:4.9:1:1 and then vacuum drying at 120°C. The positive electrode was a slurry mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ : acetylene black : polyvinylidene fluoride (PVdF) in a mass ratio of 93:4:3, coated on aluminum foil, and vacuum dried at 120 ° C. The nonaqueous electrolyte solution was a 1 mol/L solution of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 3:4:3). A polyethylene single-layer microporous membrane was used as the separator. The positive electrode and negative electrode were placed opposite each other with a separator impregnated with the electrolyte interposed between them and enclosed in a laminate film to form an evaluation cell. This cell was subjected to two charge/discharge cycles at a temperature of 20°C and a voltage range of 3.0 to 4.1 V, and then charged to 4.1 V to be fully charged. The battery capacity of this evaluation cell was 17 mAh. At room temperature of 25°C in an inert atmosphere (Ar), 1.2 mL of the prepared deactivator was injected all at once into this evaluation cell by injection, and the injection hole was sealed. The evaluation cell was placed in a thermostatic chamber at 20°C while maintaining the positive electrode composite, separator, and negative electrode composite in close contact, and deactivation was performed while recording the change in voltage over time.

(Experimental Example 2)
The deactivator was prepared by dissolving 4-methoxy-2,2,6,6-tetramethylpiperidine 1-oxyl (MeO-TEMPO), a redox shuttle agent, in a solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, at a concentration of 0.1 mmol/L. As in Experimental Example 1, the deactivator of Experimental Example 2 was injected into the evaluation cell, and the evaluation cell was placed in a thermostatic chamber at 20°C while maintaining the positive electrode composite, separator, and negative electrode composite in close contact, and deactivation was performed while recording the change in voltage over time.

(Peel test)
A peeling test of the negative electrode composite was conducted using the negative electrode of the evaluation cell described above and a passivator. A test specimen was prepared by sandwiching a polyethylene separator between a pair of negative electrodes and cut into a 20 mm x 5 mm piece. The test specimen was immersed in a test solution such as a passivator and left to stand for 72 hours, or after leaving to stand for 72 hours, ultrasonic treatment was performed for 30 seconds, and the state of peeling between the current collector and the negative electrode composite layer was visually confirmed. The ultrasonic treatment was performed using a USK-3R ultrasonic wave blaster manufactured by AS ONE Corporation at a frequency of 40 kHz.

(Experimental Examples 3 and 6)
The above test specimen was immersed in a solution (Solution 1) prepared by dissolving 1 mol/L _LiPF6 in a solvent in which EC, DMC, and EMC were mixed in a volume ratio of 3:4:3, and left to stand, which was used as Experimental Example 3. Furthermore, the test specimen was immersed in the solution of Experimental Example 3 and then subjected to ultrasonic treatment for 30 seconds, which was used as Experimental Example 6.

(Experimental Examples 4 and 7)
The test specimen was immersed in a solution in which octyl acetate and Solution 1 were mixed in a volume ratio of 1:1 and allowed to stand, which was used as Experimental Example 4. Furthermore, the test specimen was immersed in Experimental Example 4 and then subjected to ultrasonic treatment for 30 seconds, which was used as Experimental Example 7.

(Experimental Examples 5 and 8)
The test specimen was immersed in a solution in which phenyl acetate and Solution 1 were mixed in a volume ratio of 1:1 and allowed to stand, which was used as Experimental Example 5. Furthermore, the test specimen was immersed in Experimental Example 5 and then subjected to ultrasonic treatment for 30 seconds, which was used as Experimental Example 8.

(Flash point calculation)
The flash point was calculated by the following procedure.
1. The vapor pressures of DMC and octyl acetate at their flash points were calculated using the Antoine equation.
2. The molar ratio of DMC to octyl acetate was changed and the partial vapor pressures of DMC and octyl acetate at each temperature were calculated.
3. The partial vapor pressure of DMC for each composition below the flash point of octyl acetate was calculated, and compared with the vapor pressure at the flash point of DMC, to calculate the composition with the equivalent vapor pressure, which was then used as the flash point of that composition.

(Results and Discussion)
Figure 3 shows the discharge behavior after adding the passivators of Experimental Examples 1 and 2 to fully charged evaluation cells. Figure 4 is a photograph showing an example of the peeling state of the electrode composite in Experimental Examples 3 to 5. Figure 5 is a photograph showing the peeling state of the electrode composite after ultrasonic treatment in Experimental Examples 6 to 8. As shown in Figure 3, Experimental Example 2 showed a voltage of 4 V or higher even after the passage of time, indicating little progress in passivation, whereas Experimental Example 1 reached 0 V, indicating sufficient progress in passivation. Also, as shown in Figure 4, in Experimental Example 3, a black electrode composite was formed on the copper foil even after 72 hours of standing, indicating no progress in peeling of the electrode composite. On the other hand, in Experimental Examples 4 and 5, black electrode composite was observed in the solution, indicating progress in peeling of the electrode composite. Also, as shown in Figure 5, in Experimental Example 6, peeling of the electrode composite did not progress even after standing and ultrasonic treatment. On the other hand, in Experimental Examples 7 and 8, peeling of the electrode composite progressed more rapidly after standing and ultrasonic treatment. In this way, it was found that the use of a deactivator containing a redox shuttle agent and a carboxylic acid ester compound can deactivate the secondary battery and accelerate the peeling of the electrode mixture.

Considering the delamination of the electrode composite, as shown in equations (2), (3), and (17), the molecular shapes of SBR, octyl acetate, and phenyl acetate suggest that SBR has high solubility in solvents containing linear alkyl or phenyl groups. Therefore, it is presumed that delamination occurred as a result of SBR dissolving in the solution and weakening the binding strength of the active material. In a lithium-ion battery constructed using a similar negative electrode composite, the negative electrode composite faces the positive electrode composite across the separator, and they are in close contact. Therefore, it is presumed that it takes longer for the added solution to penetrate and mix with the electrolyte present before deactivation to form a homogeneous solution. However, once mixed, the state is similar to that in this delamination experiment, and therefore it is presumed that a similar delamination effect can be obtained. Additionally, carboxylic acid ester compounds, such as acetic acid-based solvents, include compounds with linear chains of varying lengths, such as ethyl acetate and amyl acetate, and compounds with cyclic carbon chains, such as menthyl acetate. It was hypothesized that similar stripping effects would be achieved when these solvents were used as deactivator solvents (formulas (2) to (12)).

The above mechanism can be considered using the Hansen Solubility Parameter (HSP), which quantifies molecular similarity. HSP is a parameter used as an indicator of a compound's solubility. The dispersion force δD, polarization force δP, and hydrogen bonding force δH are determined experimentally or by calculation for each core substance, and the solubility is estimated or determined based on the distance between compounds in Hansen space, a three-dimensional orthogonal space centered on the δD, δP, and δH axes. The HSP of a mixed solvent is represented by the volume average of each solvent mixed. The HSP of SBR, for example, is δD = 18.0 MPa ^1/2 , δP = 2.9 MPa ^1/2 , and δH = 2.3 MPa ^1/2 , as described in Reference 1 (Polym.Test., 81, (2020), 106253.). On the other hand, with reference to Reference 2 (Solubility Science; Principles and Practice, Version 1.0.2.1a, March 2021, Steven Abbott.), carbonate solvents used in lithium-ion secondary batteries have δD = 15.5 MPa ^1/2 , δP = 8.6 MPa ^1/2 , and δH = 9.7 MPa ^1/2 for DMC, and δD = 18.0 MPa ^1/2 , δP = 21.7 MPa ^1/2 , and δH = 5.1 MPa ^1/2 for EC. Considering the solubility and dissociation of lithium salts, these solvents have higher δP and δH than SBR. On the other hand, octyl acetate had δD = 15.8 MPa ^1/2 , δP = 2.9 MPa ^1/2 , and δH = 5.1 MPa ^1/2 , suggesting that adding it to the electrolyte can lower both δP and δH. Thus, adding a deactivator to the electrolyte is thought to cause the HSPs of the SBR and the mixed solution to become closer in the Hansen space, resulting in swelling or dissolution of the SBR and weakening the binding strength of the electrode composite. Furthermore, phenyl acetate had δD = 19.8 MPa ^1/2 , δP = 5.2 MPa ^1/2 , and δH = 6.4 MPa ^1/2 , suggesting that it can be expected to have the same effect as octyl acetate.

Table 1 summarizes the calculated flash points of mixed solvents of DMC (molecular weight 90 g/mol, density 1.07 g/cm ³ ) and octyl acetate (molecular weight 172.3 g/mol, density 0.87 g/cm ³ ). Octyl acetate has a flash point of 86°C, and the mixed solvents of DMC and octyl acetate at temperatures below 60°C in Table 1 always exhibited higher values than the flash point of DMC. Furthermore, regardless of the mixing ratio, the flash point increased monotonically with decreasing DMC content. When DMC and octyl acetate were mixed in equal volumetric ratios, an increase of approximately 10°C was expected compared to the flash point of DMC (16°C). This was comparable to the approximately 10°C difference between the flash point of DMC reported in Reference 3 (J. Electrochem. Soc. 162 A3084.) and the flash point when DMC and EC were mixed in a 1:1 volumetric ratio, and was therefore reasonable. Furthermore, for example, if a solvent containing a 3:4:3 mixture of EC, DMC, and EMC is used as the electrolyte, and an amount of deactivator equal to the amount of electrolyte present inside the battery is added, the volume ratio of DMC, which has the lowest flash point among the solutions present inside the battery, will be 20% or less or 15% or less, and it is estimated that the flash point will be 30°C or higher or 40°C or higher.

From the above, it was found that using a carboxylic acid ester compound as the non-aqueous solvent of the deactivator can more reliably deactivate non-aqueous secondary batteries, further promoting the exfoliation of the electrode composite, and increasing the flash point of the electrolyte, thereby improving safety. Regarding the exfoliation of the electrode composite, it is preferable to use electrodes containing styrene butadiene rubber (SBR) as a binder, and it is presumed that ultrasonic treatment of non-aqueous secondary batteries is preferable. Furthermore, it is presumed that similar effects can be achieved with carboxylic acid ester compounds, such as benzoic acid ester compounds and butyric acid ester compounds, in addition to acetate ester compounds. Furthermore, it is presumed that similar effects can be achieved with redox shuttle agents, such as phenothiazine-based compounds, ferrocene-based compounds, TEMPO-based compounds, viologen-based compounds, and quinone-based compounds. It is also presumed that the deactivator may further contain a carbonate compound in addition to the carboxylic acid ester compound.

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

This invention can be used in the battery industry.

20 Non-aqueous secondary battery, 21 Battery case, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Ion conductive medium.

Claims (7)

A deactivator for deactivating a non-aqueous secondary battery,
a redox shuttle agent having an oxidation-reduction potential, relative to a Li reference potential, higher than that of a negative electrode active material of the nonaqueous secondary battery and lower than that of a positive electrode active material of the nonaqueous secondary battery;
a non-aqueous solvent containing a carboxylic acid ester compound ;
The carboxylic acid ester compound is a deactivating agent represented by any one of formulas (1) to (11) .
The deactivator according to claim 1 , wherein the non-aqueous solvent increases the flash point of the electrolyte solution of the non-aqueous secondary battery when added to the electrolyte solution. The deactivator according to claim 1 or 2 , wherein the redox shuttle agent is one or more of a ferrocene-based compound, a TEMPO-based compound, a phenothiazine-based compound, a viologen-based compound, and a quinone-based compound. The deactivating agent according to any one of claims 1 to 3 , further comprising a carbonate compound in addition to the carboxylic acid ester compound. A method for deactivating a non-aqueous secondary battery, comprising:
an addition step of adding the deactivator for a non-aqueous secondary battery according to any one of claims 1 to 4 to the inside of the non-aqueous secondary battery;
An inactivation method comprising: The deactivation method according to claim 5 , wherein the adding step adds the deactivator to the nonaqueous secondary battery having electrodes containing styrene-butadiene rubber as a binder. The deactivation method according to claim 5 or 6 , wherein the adding step comprises subjecting the nonaqueous secondary battery to an ultrasonic treatment.