JP7803142B2 - 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 such process involves connecting the recovered batteries to a charge/discharge device and discharging them to 0 V, but this can take a long time to discharge. Furthermore, if the recovered battery has undergone current interruption detection (CID) activation, it is not even possible to discharge it. 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.

Japanese Patent Application Laid-Open No. 2018-137137

In the deactivation process for non-aqueous secondary batteries, which involves adding a deactivator consisting of a redox shuttle agent and a non-aqueous solvent, it is necessary to add the deactivator to the limited space within the battery. However, reducing the amount of redox shuttle agent added reduces the battery's discharge rate and lengthens the deactivation time, so it is thought necessary to increase the concentration of the redox shuttle agent in the deactivator and reduce the amount of liquid added. In contrast, in Patent Document 1, the concentration of the redox shuttle agent is in the range of 0.01 to 0.1 mmol/L, requiring the addition of a relatively large amount of deactivator to the non-aqueous secondary battery. There is a need for a deactivator that can more reliably perform deactivation of non-aqueous secondary batteries.

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

After extensive research to achieve the above-mentioned objectives, the inventors discovered that using a compound having a hydroquinone structure as a redox shuttle agent can more reliably inactivate nonaqueous secondary batteries, 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 that is a hydroquinone-based compound containing a hydroquinone structure, the redox potential of which is 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 relative to a Li reference potential;
a non-aqueous solvent;
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 enable more reliable deactivation of 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. Furthermore, this disclosure uses a hydroquinone-based compound containing a hydroquinone structure as the redox shuttle agent. Hydroquinone is a two-electron reduced form of p-benzoquinone and exhibits various redox mechanisms under the influence of protons. For example, there is a reaction scheme in which a two-electron redox reaction occurs between p-benzoquinone and a dianion generated by desorbing a proton from hydroquinone, and another in which a two-electron redox reaction occurs without desorbing a proton from hydroquinone. It is believed that which mechanism predominates in the oxidation-reduction of hydroquinone depends on the composition and concentration of the coexisting solvent and supporting salt. However, because either of these oxidation-reduction reactions can occur in a variety of solvents, it is believed that non-aqueous secondary batteries can be more reliably deactivated without being affected by the type of solvent.

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 is a scheme showing an example of an oxidation-reduction reaction of a redox shuttle agent. 1 shows the discharge behavior after the deactivators of Experimental Examples 1 and 2 were added to a fully charged evaluation cell. 1 shows the discharge behavior after the deactivators of Reference Examples 1 and 2 were added to a fully charged evaluation cell.

(inactivating agent)
The deactivator for a non-aqueous secondary battery according to the present disclosure comprises a redox shuttle agent and a non-aqueous solvent. The redox shuttle agent is a hydroquinone-based compound containing a hydroquinone structure 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 a positive electrode and a negative electrode.

[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). Water-based binders such as cellulose-based binders and aqueous dispersions of 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.

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 dissolved lithium salt in the space between the positive electrode 22 and the negative electrode 23.

[Deactivating agent]
Next, the deactivator will be described. The deactivator includes a redox shuttle agent and a non-aqueous solvent. The redox shuttle agent is, for example, a hydroquinone-based compound having a hydroquinone structure. The hydroquinone structure refers to a dihydric phenol structure having a six-membered aromatic hydrocarbon skeleton and two hydroxyl groups. The hydroquinone-based compound is a compound having a hydroquinone structure, including hydroquinone and its derivatives. The hydroquinone derivative refers to a compound having a substituent other than hydrogen on a carbon atom other than the carbon atom bearing a hydroxyl group. This hydroquinone-based compound may be represented by formula (1). Here, the functional groups R ¹ to R ⁴ in formula (1) may be, for example, hydrogen, or one or more substituents selected from the group consisting of a hydrocarbon group, a carboxyl group, an alkoxy group, a nitro group, an amino group, and a halogen (F, Cl, Br, etc.). The hydrocarbon group is preferably, for example, a chain hydrocarbon group or a cyclic hydrocarbon group. The chain hydrocarbon may be linear or branched. Examples of chain hydrocarbon groups 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 halogeno group (F-, Cl-, Br-, etc.). Of these, linear alkyl groups are preferred, and unsubstituted hydrocarbon groups are preferred. Each of the hydrocarbon groups preferably has 20 or less carbon atoms, more preferably 10 or less carbon atoms, and even more preferably 6 or less carbon atoms.

Hydroquinone-based compounds include those represented by formulas (2) to (16). Specifically, the basic skeleton includes hydroquinone (formula (2)) and its derivatives (formulas (5) to (8)), naphthohydroquinone (formula (3)) and its derivatives (formulas (9) to (12)), and anthrahydroquinone (formula 4) and its derivatives (formulas (13) to (16)). Because naphthohydroquinone and anthrahydroquinone, which contain more aromatic rings, can reduce solubility in non-aqueous solvents, hydroquinone and its derivatives (formulas (2), (5) to (8)) are more preferred as redox shuttle agents, with hydroquinone (formula (2)) being even more preferred. Formulas (5) to (16) are shown with one primary substituent—a methyl group, a methoxy group, a chloro group, or a nitro group—but the substitution position may be changed, and compounds may have two or more of the above substituents at any position.

The non-aqueous solvent contained in the deactivating agent is preferably a solvent different from the carbonate compound. Examples of carbonate compounds include the cyclic carbonate compounds and chain carbonate compounds described above. This non-aqueous solvent preferably has a higher solubility for the redox shuttle agent and can dissolve it more stably. For example, an aprotic solvent is preferred, and a polar aprotic solvent is more preferred. Examples of this non-aqueous solvent include one or more of the following: sulfoxides such as dimethyl sulfoxide (DMSO); amides such as dimethylformamide (DMF), dimethylacetamide (DMA), and hexamethylphosphoric triamide (HMPA); and ethers such as tetrahydrofuran (THF), dioxolane, dioxane, dimethyl ether (DME), diethyl ether (DEE), dimethoxyethane (G1), diglyme (G2), triglyme (G3), and tetraglyme (G4). Of these, DMSO is more preferred as the non-aqueous solvent.

The concentration of the redox shuttle agent contained in the deactivator is preferably higher, preferably 1.0 mol/L or higher, more preferably 2.0 mol/L or higher, even more preferably 2.5 mol/L or higher, and may be 3.0 mol/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, 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 may be selected appropriately depending on the size of the nonaqueous secondary battery, and may be, for example, 0.005 mL to 50 mL, 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.

After the addition step, the nonaqueous secondary battery may be held stationary or may be held while being shaken. The holding time may be an empirically determined time required for complete deactivation, depending on the capacity of the nonaqueous secondary battery and the amount of deactivator added. The holding time may vary depending on the capacity of the nonaqueous secondary battery and the amount of deactivator added, but may be, for example, 6 hours to 500 hours, 30 hours to 300 hours, or 50 hours to 200 hours.

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.

Figure 3 shows an example of an oxidation-reduction reaction of a redox shuttle agent. Figure 3A shows reaction A, in which a proton is eliminated when hydroquinone is used; Figure 3B shows reaction B, in which a proton is not eliminated when hydroquinone is used; and Figure 3C shows the oxidation-reduction scheme for reaction C, in which benzoquinone is used. Hydroquinone is a two-electron reduced form of p-benzoquinone, but exhibits various oxidation-reduction mechanisms depending on the influence of the proton. For example, reaction A shows a two-electron oxidation-reduction between p-benzoquinone and the dianion generated by the elimination of a proton from hydroquinone, while reaction B shows a two-electron oxidation-reduction without the elimination of a proton from hydroquinone. It is believed that the mechanism that predominates in the oxidation-reduction of hydroquinone depends on the composition and concentration of the coexisting solvent and supporting salt (Reference: Electrochim. Acta 81 (2012) 275-282.). For example, when a redox shuttle agent is used in a carbonate compound, which is the electrolyte of a non-aqueous secondary battery, redox reactions such as those shown in Reaction Formulas A and C may become unstable. On the other hand, when hydroquinone is used as the redox shuttle agent, other reaction mechanisms, such as Reaction Formula B, exist, and it is presumed that the redox reaction will proceed more stably even in the electrolyte of a non-aqueous secondary battery.

The deactivator and deactivation method described above can more reliably 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. Furthermore, this embodiment uses a hydroquinone-based compound containing a hydroquinone structure as the redox shuttle agent. Hydroquinone is a two-electron reduced form of p-benzoquinone and exhibits various redox mechanisms under the influence of protons. For example, there is Reaction Formula A (Figure 3A), in which a two-electron redox reaction occurs between p-benzoquinone and the dianion generated by the desorption of a proton from hydroquinone. There is also Reaction Formula B (Figure 3B), in which a two-electron redox reaction occurs without the desorption of a proton from hydroquinone. It is believed that which mechanism predominates in the oxidation-reduction of hydroquinone depends on the composition and concentration of the coexisting solvent and supporting salt. However, because either of these oxidation-reduction reactions can occur in a variety of solvents, it is believed that non-aqueous secondary batteries can be more reliably deactivated without being affected by the type of solvent.

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 deactivator and deactivation method for nonaqueous secondary batteries disclosed herein. Experimental Example 1 corresponds to an example of the present disclosure, and Experimental Example 2 corresponds to a comparative example.

(Experimental Example 1)
The deactivation behavior of batteries due to the addition of a 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 of graphite, carboxymethyl cellulose, and styrene butadiene rubber (mass ratio 98:1:1) and vacuum drying at 120°C. The positive electrode was prepared by coating an aluminum foil with a slurry mixture of _LiNiCoMnO2 , _{acetylene black} , _and polyvinylidene fluoride (mass ratio 93:4:3) and vacuum drying at 120°C. The nonaqueous electrolyte solution used 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 single-layer microporous polyethylene membrane was used as the separator. The positive and negative electrodes were opposed to each other via a separator impregnated with the electrolyte and sealed 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 fully charge. The battery capacity of this evaluation cell was 17 mAh. The fully charged battery (voltage 4.1 V) was opened under an argon atmosphere, and a deactivator consisting of hydroquinone dissolved in dimethyl sulfoxide (DMSO) at a concentration of 2.5 mol/L was prepared. The amount of hydroquinone added relative to the battery capacity was 0.003 mol/Ah, which corresponds to a solution volume of 0.021 mL of the deactivator relative to the battery capacity (17 mAh) used in Experimental Example 1. After adding the deactivator, the evaluation cell was sealed again, and the change in battery voltage was measured at a temperature of 20°C.

(Experimental Example 2)
The battery deactivation evaluation was carried out under the same conditions as in Experimental Example 1, except that p-benzoquinone dissolved in DMSO at a concentration of 2.5 mol/L was used as the deactivator.

(Reference example 1)
Battery deactivation evaluation was carried out under the same conditions as in Experimental Example 1, except that hydroquinone dissolved in DMSO at a concentration of 0.05 mol/L was used as a deactivator and the amount of hydroquinone added relative to the battery capacity was 0.004 mol/Ah.

(Reference example 2)
Battery deactivation evaluation was carried out under the same conditions as in Experimental Example 1, except that p-benzoquinone dissolved in DMSO at a concentration of 0.05 mol/L was used as a deactivator and the amount of p-benzoquinone added relative to the battery capacity was 0.004 mol/Ah.

(Results and Considerations)
FIG. 4 shows the discharge behavior after the deactivators of Experimental Examples 1 and 2 were added to a fully charged evaluation cell. FIG. 5 shows the discharge behavior after the deactivators of Reference Examples 1 and 2 were added to a fully charged evaluation cell. Table 1 summarizes the concentrations and amounts of deactivators added for Experimental Examples 1 and 2 and Reference Examples 1 and 2, as well as the deactivation time required for the cell voltage to reach 1.0 V. As shown in FIG. 4, in Experimental Example 1, in which a small amount of a high-concentration deactivator was added to the evaluation cell, the battery voltage gradually decreased from 4.1 V after the addition of the deactivator, reaching 3.0 V after 80 hours, 1.0 V after 120 hours, and nearly 0 V after 440 hours. In contrast, in Experimental Example 2, the discharge rate was very slow, and the battery voltage only decreased to 3.6 V 440 hours after addition. Furthermore, as shown in FIG. 5, when a large amount of a low-concentration deactivator was added to the evaluation cell, in both Reference Examples 1 and 2, the battery voltage gradually decreased from 4.1 V after the addition of the deactivator and reached 1.0 V or less after 25 hours, and no difference was observed between hydroquinone and p-benzoquinone.

From the above, it was found that when a hydroquinone/DMSO solution was used as a passivating agent, it was possible to rapidly discharge the battery to a voltage near 0 V, regardless of the hydroquinone concentration or amount added. This effect was particularly pronounced when the hydroquinone concentration was increased and the amount of passivating agent solution was reduced. The reason for this effect is thought to be the influence of the solvent composition and protons. For example, in the presence of Li ⁺ , p-benzoquinone exhibits stable redox in DMSO solvent, whereas it does not exhibit reversible redox in the carbonate solvent of a non-aqueous electrolyte. Therefore, in Experimental Example 2, in which the amount of passivating agent solution was reduced by increasing the concentration of p-benzoquinone, it is presumed that the influence of the carbonate solvent in the electrolyte reduced the reversibility of the redox reaction of p-benzoquinone, thereby slowing the battery discharge rate. Meanwhile, hydroquinone exhibits a redox reaction similar to that of p-benzoquinone (Figure 3A) as well as a redox reaction involving protons (Figure 3B). Hydroquinone is a two-electron reduced form of p-benzoquinone, but exhibits various redox mechanisms due to the influence of protons. For example, there is Reaction A, in which a two-electron redox reaction occurs between p-benzoquinone and the dianion generated by the elimination of a proton from hydroquinone, and Reaction B, in which a two-electron redox reaction occurs without the elimination of a proton from hydroquinone. It is presumed that the mechanism that prevails in the oxidation-reduction of hydroquinone varies depending on the composition and concentration of the coexisting solvent and supporting salt. In the hydroquinone/DMSO solution of Experimental Example 1, the amount of DMSO decreases as the amount of deactivator solution decreases, presumably reducing the reversibility of Reaction A. On the other hand, in Experimental Example 1, when the solution volume is reduced by increasing the concentration of hydroquinone, the proton-involving redox reaction of hydroquinone of Reaction B prevails, presumably enabling the battery to be discharged to 0 V more quickly and reliably.

As described above, it was found that a deactivator using a hydroquinone-based redox shuttle agent can more reliably deactivate non-aqueous secondary batteries, regardless of the redox shuttle agent concentration. Furthermore, because the capacity of non-aqueous secondary batteries to which liquid agents can be added is limited, it is inferred that a higher concentration of the redox shuttle agent in the deactivator is preferable, with the hydroquinone-based compound content being 1 mol/L or more, more preferably 2 mol/L or more, and even more preferably 2.5 mol/L or more. Furthermore, because the capacity of non-aqueous secondary batteries to which liquid agents can be added is limited, it is inferred that a smaller amount of redox shuttle agent in the deactivator is preferable, with the amount of redox shuttle agent relative to the capacity of the non-aqueous secondary battery being 0.1 mol/Ah or less, more preferably 0.01 mol/Ah or less, and even more preferably 0.005 mol/Ah or less. Furthermore, it is believed that the same effects as described above can be achieved if the redox shuttle agent has a hydroquinone structure, and that it may have any functional group as a substituent.

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 that is a hydroquinone-based compound containing a hydroquinone structure, the redox potential of which is 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 relative to a Li reference potential;
a non- aqueous solvent ;
The hydroquinone-based compound is a deactivator represented by formula (1) .
The deactivator according to claim 1, wherein the hydroquinone-based compound is represented by any one of formulas (2) to (16).
The deactivator according to claim 1 or 2, containing the hydroquinone compound at 1 mol/L or more. The deactivating agent according to any one of claims 1 to 3, wherein the non-aqueous solvent is a solvent different from the carbonate 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 in the addition step, the deactivator is added in an amount of the redox shuttle agent relative to the capacity of the nonaqueous secondary battery of 0.1 mol/Ah or less. 7. The deactivation method according to claim 5, wherein the amount of the redox shuttle agent added in the adding step is 0.001 mol/Ah or more relative to the capacity of the nonaqueous secondary battery.