Inerting agent for nonaqueous secondary battery and method for inerting nonaqueous secondary battery

Abstract

An inerting agent for inerting a nonaqueous secondary battery, which contains: a redox shuttle having a redox potential higher than a negative electrode active material of the nonaqueous secondary battery and lower than a positive electrode active material of the nonaqueous secondary battery on a Li-based potential scale; and N-methyl-2-pyrrolidone.

Description

Technical Field

[0001] This invention relates to inertizers for non-aqueous secondary batteries and inertization methods for non-aqueous secondary batteries. Background Technology

[0002] Conventionally, when recycling or discarding non-aqueous secondary batteries, an inerting process is performed to inert the batteries. This process, for example, involves connecting the recycled battery to a charge / discharge device and discharging it to 0V. However, in this case, discharging can sometimes be time-consuming. Furthermore, if the recycled battery has been deactivated by a current interruption device (CID), discharging itself is not possible. Therefore, it has been proposed to add a redox shuttle such as a 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO) compound (see Patent Document 1). This allows the battery voltage of non-aqueous secondary batteries to be safely and quickly reduced to 0V without the use of a charge / discharge device. Furthermore, it has been proposed to use a phenothiazine compound as a redox shuttle in such an inerting method (see Patent Document 2). This allows for even faster inerting of non-aqueous secondary batteries. In particular, when using inertizing agents obtained by dissolving phenothiazine in solvents with high solubility and low viscosity, such as 1,2-dimethoxyethane, inertization can be rapidly accomplished with a small amount of inertizing agent by balancing the high concentration of phenothiazine with the increased diffusion rate.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-137137

[0006] Patent Document 2: Japanese Patent Application Publication No. 2022-073888 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in Patent Document 2, although it is possible to inert non-aqueous secondary batteries quickly with a small amount of inert agent, it is desirable to inert non-aqueous secondary batteries even more quickly with an even smaller amount of inert agent.

[0009] This invention was made to solve such a problem, with the main objective of inertizing non-aqueous secondary batteries more quickly with a smaller amount of inerting agent.

[0010] Methods for solving problems

[0011] In order to achieve the above objectives, in-depth research was conducted, and as a result, the inventors discovered that when an inert agent containing a redox shuttle and N-methyl-2-pyrrolidone is added to the inside of a non-aqueous secondary battery, the non-aqueous secondary battery is rapidly inertized, thus completing the present invention.

[0012] That is, the inertizer of the non-aqueous secondary battery of the present invention is an inertizer that inertizes the non-aqueous secondary battery, which contains: an oxidation-reduction shuttle with an oxidation-reduction potential 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 as measured by a Li reference potentiometer; and N-methyl-2-pyrrolidone.

[0013] Furthermore, the inerting method for the non-aqueous secondary battery of the present invention includes an addition step of adding the inerting agent of the non-aqueous secondary battery into the interior of the non-aqueous secondary battery.

[0014] Invention Effects

[0015] According to the inerting agent and inerting method for non-aqueous secondary batteries, non-aqueous secondary batteries can be inerted more rapidly with a smaller amount of inerting agent. It is speculated that this effect is achieved because, for example, by using an inerting agent containing N-methyl-2-pyrrolidone in addition to a redox shuttle, the diffusion of the inerting agent within the battery can be suppressed, maintaining a high concentration of the redox shuttle participating in the reaction. Therefore, even with a smaller amount of inerting agent, redox shuttle proceeds smoothly, resulting in faster battery inerting. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view showing the structure of the non-aqueous secondary battery 20.

[0017] Figure 2 This is an explanatory diagram illustrating the inerting mechanism of non-aqueous secondary batteries.

[0018] Figure 3 This is a graph showing the battery voltage changes in Experiment Examples 1-3.

[0019] Figure 4 This is a graph showing the battery voltage changes in Experiments 4-6.

[0020] Figure 5 This is a graph showing the battery voltage changes in Experiments 7-9.

[0021] Figure 6 This is a graph showing the battery voltage changes in Experiment Examples 10-11. Detailed Implementation

[0022] The inerting agent for the non-aqueous secondary battery of the present invention contains a redox shuttle agent and N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and is used to inert the non-aqueous secondary battery. The non-aqueous secondary battery as the inerting target may be an unused product or a used product.

[0023] [Non-aqueous secondary battery]

[0024] First, the non-aqueous secondary battery as the inerting target will be described. The non-aqueous secondary battery includes: a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; and a non-aqueous ion-conducting medium that is interposed between the positive electrode and the negative electrode and conducts 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. Hereinafter, for convenience of description, the case where the non-aqueous secondary battery is a lithium ion secondary battery will be mainly described.

[0025] The positive electrode can be formed, for example, by mixing a positive electrode active material, a conductive material and a binder, adding an appropriate solvent to prepare a paste-like positive electrode composite material, applying the composite material to the surface of a current collector, drying the applied composite material, and compressing the composite material as needed to increase the electrode density. The positive electrode active material may be any material whose redox potential based on Li is higher than that of the redox shuttle agent contained in the inerting agent, and the redox potential is preferably 3.3 V or more based on the Li reference potential, and may be 3.4 V or more, 3.8 V or more, 4.0 V or more, 4.2 V or more, and the like. As the positive electrode active material, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, and the like can be used. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2 can be used; Li (1-x) MnO2 (0<x<1, etc., the same applies hereinafter), Li (1-x) lithium manganese composite oxides such as Mn2O4; Li (1-x) lithium cobalt composite oxides such as CoO2; Li (1-x) lithium nickel composite oxides such as NiO2; Li (1-x) Ni a Mn b O2 (a+b=1), Li (1-x) Ni a Mn b lithium nickel manganese composite oxides such as O4 (a+b=2); Li (1-x) Ni a Co b Mn c lithium nickel cobalt manganese composite oxides such as O2 (a+b+c=1); lithium vanadium composite oxides such as LiV2O3; transition metal oxides such as V2O5, and the like. In addition, Li(1-x) Olivine-type lithium manganese phosphate compounds such as MnPO4; Li (1-x) CoPO4 and other olivine-type cobalt-lithium phosphate compounds; Li (1-x) NiPO4 and other olivine-type nickel-lithium phosphate compounds; Li (1-x) Olivine-type lithium iron phosphate compounds such as FePO4. Additionally, Li can be used. (1-x) MnVO4 and other anti-spinel-type lithium manganese vanadate compounds; Li (1-x) CoPO4 and other anti-spinel-type lithium cobalt vanadate compounds; Li (1-x) NiPO4 and other anti-spinel lithium nickel vanadate compounds, etc. The positive electrode active material is preferably an oxide containing one or more of nickel, manganese, and cobalt; for example, LiCoO2, LiNiO2, LiMnO2, and LiNi are preferred. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. Alternatively, the positive electrode active material is preferably an iron-containing phosphate, preferably LiFePO4, etc.

[0026] For the positive electrode, conductive materials such as natural graphite (flake graphite, scaly graphite), artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fibers, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. For the binder, fluorinated resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber can be used; thermoplastic resins such as polypropylene and polyethylene can be used; ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR) can also be used. Additionally, aqueous binders such as cellulose-based binders and aqueous dispersions of styrene-butadiene rubber (SBR) can also be used. For the solvent, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. In addition, dispersants, thickeners, etc., can be added to the water, and the active material can be slurried using latex such as SBR. As a thickener, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or in mixtures of two or more. As for coating methods, examples include roller coating, screen coating, doctor blade coating, spin coating, and bar coating; any of these can be used to produce any thickness and shape. As a current collector, in addition to materials such as aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymers, and conductive glass, materials treated with carbon, nickel, titanium, silver, etc., can be used to improve adhesion, conductivity, and oxidation resistance. For these, surface oxidation treatment can also be performed. Regarding the shape of the current collector, examples include foil, film, sheet, mesh, shapes processed by punching or expanding mesh, plate mesh, porous body, foam, and fibrous group moldings. The thickness of the current collector can be, for example, 1–500 μm.

[0027] For example, the negative electrode can be formed by mixing a negative electrode active material, a conductive material, and a binder, adding a suitable solvent to make a paste-like negative electrode composite material, coating it on the surface of a current collector, drying it, and compressing it as needed to increase the electrode density. Alternatively, the negative electrode active material can be formed by tightly bonding it to the current collector. The negative electrode active material can be any substance whose redox potential based on Li is lower than that of the redox shuttle contained in the inert agent. Preferably, the redox potential is 3.0V or less based on Li, more preferably 2.0V or less, and even more preferably 1.0V or less. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys, and tin compounds; carbonaceous materials capable of inserting and de-intercalating lithium ions; composite oxides containing two or more elements; and conductive polymers. Examples of carbonaceous materials include coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, and carbon fibers. Examples of composite oxides include Li₄Ti₅O. 12Lithium-titanium composite oxides and lithium-vanadium composite oxides such as LiV₂O₃ are used. Carbonaceous materials such as graphite are preferred as the negative electrode active material. Furthermore, the conductive materials, binders, and solvents used in the negative electrode can be the same substances exemplified in the positive electrode. Regarding the current collector of the negative electrode, in addition to copper, nickel, stainless steel, titanium, aluminum, sintered carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., materials such as copper treated with carbon, nickel, titanium, silver, etc., can be used to improve adhesion, conductivity, and reduction resistance. For these, surface oxidation treatment can also be performed. The shape of the current collector can be the same as that of the positive electrode.

[0028] As ion-conducting media, non-aqueous electrolytes and non-aqueous gel electrolytes containing supporting salts can be used. Examples of solvents for non-aqueous electrolytes include: cyclic carbonate compounds (such as ethylene carbonate) and chain carbonate compounds (such as dimethyl carbonate); cyclic ester compounds (such as γ-butyrolactone) and chain ester compounds (such as methyl formate); ether compounds such as dimethoxyethane; nitrile compounds such as acetonitrile; furan compounds such as tetrahydrofuran; sulfolane compounds such as sulfolane; and dioxane compounds such as 1,3-dioxane. These can be used alone or in combination. 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. These can be used alone or in combination. The concentration of the salt in the electrolyte is preferably 0.1 mol / L or higher and 5 mol / L or lower, more preferably 0.5 mol / L or higher and 2 mol / L or lower. Furthermore, as the ion-conducting medium, ion-conducting polymers, inorganic solid electrolytes, or mixtures of organic polymer electrolytes and inorganic solid electrolytes, or inorganic solid powders bound together by organic binders, can be used instead of liquid ion-conducting media.

[0029] There are no particular limitations on the composition of the separator, as long as it can withstand the use of non-aqueous secondary batteries. Examples include thin microporous membranes made of polymer nonwoven fabrics such as polypropylene and olefin resins such as polyethylene. These can be used alone or in combination.

[0030] The shape of this non-aqueous secondary battery is not particularly limited; examples include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, and square shapes. Alternatively, it can be a large battery used in electric vehicles, etc. Figure 1 An example of a non-aqueous secondary battery is shown in the figure. Figure 1 This is a schematic cross-sectional view showing the structure of a coin-shaped non-aqueous secondary battery 20. (See diagram below.) Figure 1As shown, the non-aqueous secondary battery 20 includes: a cup-shaped battery casing 21; a positive electrode 22 having a positive active material and disposed at the lower part of the battery casing 21; a negative electrode 23 having a negative active material and disposed opposite to the positive electrode 22 via a separator 24; a gasket 25 formed of insulating material; and a sealing plate 26 disposed at the opening of the battery casing 21 and sealing the battery casing 21 by means of the gasket 25. The non-aqueous secondary battery 20 has an ion-conducting medium 27 in which lithium salt is dissolved in the space between the positive electrode 22 and the negative electrode 23.

[0031] [Inert agent]

[0032] The inerting agent will be explained next. The inerting agent contains a redox shuttle and NMP.

[0033] Redox shuttles are not particularly limited to any oxidizable and reducible compound capable of repeatedly transferring charge between the positive and negative electrodes. The redox potential of the redox shuttle, measured using a Li reference potentiometer, is higher than that of the negative electrode active material of a non-aqueous secondary battery that is to be inertized, and lower than that of the positive electrode active material of a non-aqueous secondary battery that is to be inertized. The redox potential of the redox shuttle is preferably 3.0V or higher and 4.2V or lower, more preferably 3.0V or higher and 4.0V or lower, and even more preferably 3.0V or higher and 3.8V or lower, measured using a Li reference potentiometer. The redox potential of the redox shuttle can be determined by cyclic voltammetry. Specifically, the peak potential on the oxidation side determined by cyclic voltammetry is set as Eo. pa [V], The peak potential on the reduction side is set to E. pc At [V], the redox potential of the redox shuttle is given by E0 = (E pa +E pc The value E0[V] is obtained by calculating () / 2. This redox shuttle can also have a redox potential of less than 3.0V based on a lithium reference potentiometer. When the current collector is Cu or its alloys, a redox shuttle having a redox potential of less than 3.0V based on a lithium reference potentiometer can further suppress the dissolution of Cu, and is therefore preferred.

[0034] The redox shuttle is preferably a substance with high solubility in NMP. Using a redox shuttle with high solubility in NMP allows for the preparation of inert agents containing high concentrations of the redox shuttle, thus enabling faster inertization and reducing the amount of inert agent used. With the increasing energy density of batteries, the space available for injecting inert agents often becomes smaller, therefore reducing the amount of inert agent used is desirable. The solubility of the redox shuttle in NMP can be, for example, 0.5 mol / L or more, 1 mol / L or more, or 3 mol / L or more. The solubility of the redox shuttle in NMP can be, for example, 5 mol / L or less, or 4 mol / L or less. It should be noted that the solubility in this specification refers to the solubility at 25°C.

[0035] The redox shuttle can also be set as the dispersion force D in the Hansen solubility parameter of NMP. s Polar force P s Hydrogen bond force H s And the dispersion force D in the Hansen solubility parameter of redox shuttles. p Polar force P p Hydrogen bond force H p The distance R between the NMP and the Hansen space, obtained by the following mathematical formula (1), is 10.5 MPa. 0.5 The following substances. The Hansen solubility parameter (also known as HSP), published by Charles M. Hansen, is known as an indicator of solubility between substances. The Hansen solubility parameter consists of three values: D (dispersion force of atoms), P (polar force of molecules), and H (hydrogen bonding force of molecules). These three parameters are represented as coordinates in a three-dimensional space (Hansen space) of orthogonal coordinates. The solubility between substances is inferred from the distance between the coordinates representing the HSPs of each substance; the closer the coordinates are, the easier it is to dissolve, and the farther apart they are, the more difficult it is to dissolve. Therefore, a smaller distance R between the redox shuttle and NMP in Hansen space is preferred. The aforementioned distance R for the redox shuttle can be, for example, 10.5 MPa. 0.5 The following can be 10 MPa 0.5 The following can also be 9.5 MPa. 0.5 The following should be noted: Hansen's solubility parameter is the value at 25℃.

[0036] R 2 =4×(D p -D s ) 2 +(P p -P s ) 2 +(H p -H s ) 2 …Mathematical formula (1)

[0037] As redox shuttles, one or more of the following can be listed: phenothiazine compounds, viologen compounds, quinone compounds, diazoxide compounds and fluorenone compounds, ferrocene compounds, and TEMPO compounds.

[0038] Phenothiazine compounds can be phenothiazines or their derivatives. Phenothiazines are heterocyclic compounds formed by the fusion of benzene rings at both ends of a thiazide. Phenothiazine compounds can also be compounds formed by introducing substituents onto phenothiazines. For example, a phenothiazine compound can be represented by formula (1). In formula (1), R... 1 ~R 9 Each group may have the same or different functional groups. Examples of functional groups include one or more selected from hydrogen, alkyl, aryl, acyl, alkoxy, alkylthio, hydroxyl, sulfonic acid, nitro, amino, carboxyl, and halogen. Alkyl groups may have 1 or more but less than 6 carbon atoms, and may be straight-chain or branched, or haloalkyl groups in which some or all of the hydrogen atoms are replaced by a halogen. Examples of alkyl groups include methyl, ethyl, isopropyl, tert-butyl, and trifluoromethyl. Aryl groups may have 6 or more but less than 12 carbon atoms. Examples of aryl groups include phenyl, tolyl, xylyl, mesitylene, and naphthyl. Acyl groups may have 1 or more but less than 7 carbon atoms. Examples of acyl groups include formyl, acetyl, and benzoyl. Alkoxy groups may have 1 or more but less than 6 carbon atoms. Examples of alkoxy groups include methoxy, ethoxy, and phenoxy. Alkylthio groups may have 1 or more but less than 6 carbon atoms. Examples of alkyl thio groups include methyl thio and ethyl thio. Examples of halogens include fluorine, chlorine, and bromine. In formula (1), R 1 ~R 9 Each can be independently hydrogen, alkyl, phenyl, acetyl, or halogen. Additionally, in formula (1), R can be... 1 ~R 9 More than 6 of them are hydrogen, or R 1 ~R 9 Seven or more of these compounds are hydrogen atoms. 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.

[0039]

[0040] (where R) 1 ~R 9 (These are functional groups that are the same or different.)

[0041] Viologen compounds can be viologen or viologen derivatives. Viologen compounds are compounds with a structure in which hydrocarbon groups are bonded to the nitrogen atoms of the two pyridine rings of a 4,4'-bipyridine skeleton, for example, having the structure of formula (2). In formula (2), R... 10 and R 11 The hydrocarbon groups can be the same or different. As hydrocarbon groups, straight-chain or branched chain hydrocarbon groups and cyclic hydrocarbon groups are preferred. Examples of chain hydrocarbon groups include: alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl; alkenyl groups such as vinyl, propenyl, butenyl, pentenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl. Examples of cyclic hydrocarbon groups include: cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl and naphthyl. Furthermore, these hydrocarbon groups may also have substituents such as carboxyl, alkoxy, nitro, amino, and halogen (F, Cl, Br, etc.). Among these hydrocarbon groups, straight-chain alkyl groups are preferred, and hydrocarbon groups without substituents are preferred. The number of carbon atoms in each hydrocarbon group is preferably 20 or less, more preferably 10 or less, and even more preferably 6 or less. In formula (2), R... 12 ~R 19 Each substituent may be the same or different. For example, the functional group may be hydrogen, or it may be a substituent such as a hydrocarbon group, carboxyl group, alkoxy group, nitro group, amino group, or halogen group. As a hydrocarbon group, one or more of the hydrocarbon groups exemplified above can be listed. When a viologen compound has two or more substituents, the substituents can bond with each other to form a ring. The number of carbon atoms in the viologen is preferably 30 or less, more preferably 20 or less, and even more preferably 14 or less. Specifically, examples of such viologen compounds include methyl viologen, ethyl viologen, propyl viologen, butyl viologen, pentyl viologen, hexyl viologen, heptyl viologen, and octyl viologen. Additionally, 1,1'-dimethyl-3,3'-[methylenebis(oxy)]-4,4'-bipyridine can be listed as a viologen compound. phenyl violarin, 1-(4-aminophenyl)-1'-methyl-4,4'-bipyridine etc. Viologen compounds can possess hexafluorophosphate anions (PF6). - ), tetrafluoroborate anion (BF4) - ), pentafluoroarsenate anion (AsF6) - ), perchlorate anion (ClO4) - ), Br - Cl - F -Inorganic anions, trifluoromethanesulfonate anions (CF3SO3) - ), bis(trifluoromethanesulfonyl)imine anion (N(CF3SO2)2 - TFSI), tri(trifluoromethanesulfonyl)methyl anion (C(CF3SO2)3) - Organic anions such as ) serve as counter anions to the cations in formula (2). The counter anion can be of the same type as the anion of the supporting salt of the non-aqueous secondary battery that is being inertized, or it can be different.

[0042]

[0043] (where R) 10 and R 11 For the same or different hydrocarbon groups, R 12 ~R 19 (These are functional groups that are the same or different.)

[0044] Quinones are compounds having a structure in which the CH groups on two carbons of an aromatic hydrocarbon skeleton are replaced with C=O groups. Quinones can have an aromatic hydrocarbon skeleton with 4 to 7 members, preferably with a 6-membered ring (having a benzoquinone structure). Quinones can, for example, have the p-benzoquinone structure of formula (3) and the o-benzoquinone structure of formula (4). In formulas (3) and (4), R... 20 ~R 23 Each group may have the same or different functional groups. Examples of functional groups include one or more selected from hydrogen, alkyl, aryl, acyl, alkoxy, alkylthio, hydroxyl, sulfonic acid, nitro, amino, carboxyl, or halogen. When a quinone compound has two or more substituents, the substituents can bond with each other to form a ring. Examples of quinone compounds that form a ring by bonding substituents include naphthoquinones (1,4-naphthoquinone, 1,2-naphthoquinone, etc.), anthraquinones (9,10-anthraquinone, etc.), and their derivatives. The number of carbon atoms in a quinone compound is preferably 20 or less, more preferably 14 or less, and even more preferably 10 or less. As quinone compounds, specific examples 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.

[0045]

[0046] (where R) 20 ~R 23 (These are functional groups that are the same or different.)

[0047] Diazabenzene compounds possess a diazabenzene skeleton. Examples of diazabenzene compounds include diazabenzene skeletons with two nitrogen-substituted benzene rings, and compounds and their derivatives with naphthidine skeletons, such as those with two nitrogen-substituted carbons of naphthalene, anthracene, or other benzobenzenes, formed by further fused aromatic rings onto the diazabenzene skeleton. Examples of diazabenzene compounds include phenazine compounds and their derivatives (Formula (5)), quinoxaline compounds and their derivatives (Formula (6)), and pyrazine compounds and their derivatives (Formula (7)). In addition to the pyrazine skeleton, diazabenzene compounds also contain pyrazine skeletons and pyrimidine skeletons, which are isomers of pyrazine. Furthermore, as a naphthidine skeleton, diazabenzene compounds also contain benzopyrazine (zoline) skeletons, quinazoline skeletons, and phthalazine skeletons, which are isomers of quinoxaline, in addition to the quinoxaline skeleton. In Formulas (5) to (7), R 24 ~R 31 Each group may have the same or different functional groups. Examples of functional groups include hydrogen, alkyl, aryl, acyl, alkoxy, alkylthio, hydroxyl, sulfonic acid, nitro, amino, carboxyl, or halogen. Alkyl groups may have 1 or more but less than 12 carbon atoms, and may be straight-chain or branched, or haloalkyl groups in which some or all of the hydrogen atoms are replaced by a halogen. Examples of alkyl groups include methyl, ethyl, isopropyl, tert-butyl, and trifluoromethyl. Aryl groups may have 6 or more but less than 12 carbon atoms. Examples of aryl groups include phenyl, tolyl, xylyl, mesitylene, and naphthyl. Acyl groups may have 1 or more but less than 7 carbon atoms. Examples of acyl groups include formyl, acetyl, and benzoyl. Alkoxy groups may have 1 or more but less than 6 carbon atoms. Examples of alkoxy groups include methoxy, ethoxy, and phenoxy. Alkylthio groups may have 1 or more but less than 6 carbon atoms. Examples of alkyl thio groups include methyl thio and ethyl thio. Examples of halogens include fluorine, chlorine, and bromine. R 24 ~R 31 Each can be independently hydrogen, alkyl, phenyl, acetyl, or halogen. Additionally, it can be R. 24 ~R 31 Four or more of the atoms in the compound are hydrogen atoms. Examples of phenazine compounds, such as phenazines and their derivatives, can be listed as having a basic skeleton. Examples of quinoxaline compounds, such as quinoxalines and their derivatives, can be listed as having a basic skeleton. Examples of pyrazine compounds, such as pyrazines and their derivatives, can be listed as having a basic skeleton. When the number of aromatic rings in quinoxalines, phenazines, etc., increases, their solubility in non-aqueous solvents may sometimes decrease; therefore, quinoxalines and phenazines are preferred as redox shuttles.

[0048]

[0049] (where R) 24 ~R 31 (These are functional groups that are the same or different.)

[0050] Fluorenone compounds have a fluorenone skeleton with two hydrogen atoms bonded to the 9th carbon atom of fluorene replaced by an oxo group (=O). Fluorenone compounds include fluorenones and their derivatives. Fluorenone derivatives refer to substances that have substituents other than hydrogen on carbons other than the 9th carbon with the oxo group. This fluorenone compound can be represented by formula (8). In formula (8), R 32 ~R 39 Each group may have the same or different functional groups. Examples of functional groups include hydrogen, alkyl, aryl, acyl, alkoxy, alkylthio, hydroxyl, sulfonic acid, nitro, nitrooxy, amino, carboxyl, or halogen. Alkyl groups may have 1 or more but less than 12 carbon atoms, and may be straight-chain or branched, or haloalkyl groups in which some or all of the hydrogen atoms are replaced by a halogen. Examples of alkyl groups include methyl, ethyl, isopropyl, tert-butyl, and trifluoromethyl. Aryl groups may have 6 or more but less than 12 carbon atoms. Examples of aryl groups include phenyl, tolyl, xylyl, mesitylene, and naphthyl. Acyl groups may have 1 or more but less than 7 carbon atoms. Examples of acyl groups include formyl, acetyl, and benzoyl. Alkoxy groups may have 1 or more but less than 6 carbon atoms. Examples of alkoxy groups include methoxy, ethoxy, and phenoxy. Alkylthio groups may have 1 or more but less than 6 carbon atoms. Examples of alkyl thio groups include methyl thio and ethyl thio. Examples of halogens include fluorine, chlorine, and bromine. R 32 ~R 39 Each can be independently hydrogen, alkyl, phenyl, acetyl, or halogen. Additionally, it can be R. 32 ~R 39 Four or more of them are hydrogen. Additionally, R... 32 ~R 39 Two or more of them can bond together to form a ring. Examples of fluorenone compounds include fluorenone as the basic skeleton and 2-aminofluorenone, 2,7-dihydroxyfluorenone, 2-carboxyfluorenone, 2-nitrofluorenone, 2,7-dinitrofluorenone, benzo[B]fluorenone, 2,7-dibromofluorenone, etc.

[0051]

[0052] (where R) 32 ~R 39 (These are functional groups that are the same or different.)

[0053] Ferrocene compounds include ferrocene and its derivatives. Ferrocene is a compound with a central iron ion bonded to two cyclopentadienyl groups. Ferrocene compounds can also be compounds in which substituents are introduced onto the cyclopentadienyl groups of ferrocene. Ferrocene compounds can be represented by formula (9). As functional groups, examples include those exemplified in phenothiazines. In formula (9), R 40 ~R 49 Each can be independently hydrogen, alkyl, phenyl, acetyl, amino, acyl, or halogen. Additionally, in formula (1), R can be... 40 ~R 49 More than 6 of them are hydrogen, or R 40 ~R 49 Seven or more of them are hydrogen atoms. Examples of ferrocene compounds include ferrocene, acetylferrocene, aminoferrocene, benzoylferrocene, brominated ferrocene, tert-butylferrocene, butylferrocene, and decamethylferrocene. In ferrocene compounds (e.g., formula (9)), the two cyclopentadienyl rings can be in an alternating conformation or an overlapping conformation.

[0054]

[0055] (where R) 40 ~R 49 (These are functional groups that are the same or different.)

[0056] Examples of TEMPO compounds include 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO), N-(3,3,5,5-tetramethyl-4-oxypiperidinyl)pyrene-1-carboxamide (Pyrene-TEMPO), 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxy free radical (MeO-TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxybenzoate (BzO-TEMPO), and 4-acetamido-2,2,6,6-tetramethyl-1-piperidinoxy (Ac-TEMPO).

[0057] The inerting agent preferably contains a redox shuttle at a concentration of 0.1 mol / L or higher, more preferably at a concentration of 0.5 mol / L or higher, even more preferably at a concentration of 1 mol / L or higher, and even more preferably at a concentration of 2 mol / L or higher. The inerting agent may contain a redox shuttle at a concentration of 5 mol / L or lower, or at a concentration of 4 mol / L or lower. The inerting agent may also contain a redox shuttle in an amount less than its solubility.

[0058] The inerting agent preferably does not contain solutes other than redox shuttles (e.g., supporting salts), and even if it does contain solutes other than redox shuttles, the concentration is preferably less than 0.1 mmol / L or less than 0.01 mmol / L. Examples of supporting salts include inorganic salts such as LiPF6, LiBF4, LiAsF6, and LiClO4, as well as organic salts such as LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SO2)3. The supporting salt may be the same as or different from the supporting salt contained in the ion-conducting medium of the non-aqueous secondary battery to be inertized.

[0059] The inerting agent preferably does not contain any solvent other than NMP. Even if it does contain a solvent other than NMP, it is preferably less than 50% by volume, less than 10% by volume, or less than 1% by volume of NMP. Examples of solvents include non-aqueous solvents such as carbonate compounds, ester compounds, ether compounds, nitrile compounds, amide compounds, phosphate ester compounds, furan compounds, sulfolane compounds, and dioxane compounds, which can be used alone or in combination.

[0060] [Inertization method]

[0061] Next, a method for inertizing the aforementioned non-aqueous secondary battery using the inertizing agent will be described. This inertization method includes an inertizing agent addition step of adding the inertizing agent into the interior of the non-aqueous secondary battery.

[0062] In the addition process, an inert agent is added to the interior of the non-aqueous secondary battery. Specifically, the inert agent is added in such a way that the positive and negative electrodes of the non-aqueous secondary battery come into contact with the inert agent. There are no particular limitations on the method of adding the inert agent; it can be injected after opening the non-aqueous secondary battery or injected using a syringe.

[0063] The amount of inerting agent added can be, for example, 10 μL or more, 20 μL or more, 30 μL or more, or 1000 μL or less, 100 μL or less, or 50 μL or less. In the case of large batteries such as those used in automobiles, the amount of inerting agent added can be, for example, 1 mL or more, 5 mL or more, 10 mL or more, or 1000 mL or less, 100 mL or less, or 50 mL or less. Regarding the amount of inerting agent added, for example, relative to the volume of the ion-conducting medium contained in the non-aqueous secondary battery to be inertized, it can be 0.1% or more and 500% or less, or 10% or more and 300% or less. The amount of inerting agent added relative to the battery capacity of the non-aqueous secondary battery can be 0.1 μL / mAh or more, 0.5 μL / mAh or more, 1 μL / mAh or more, or 70 μL / mAh or less, 50 μL / mAh or less, 10 μL / mAh or less, or 5 μL / mAh or less. The amount of redox shuttle added to a non-aqueous secondary battery by adding an inerting agent (hereinafter also referred to as the amount of redox shuttle added) may be, for example, 0.1 μmol / mAh or more, 0.5 μmol / mAh or more, 1 μmol / mAh or more, or 7 μmol / mAh or less, or 6 μmol / mAh or less, relative to the battery capacity of the non-aqueous secondary battery.

[0064] The time elapsed from the addition of the inert agent in the addition process until the battery voltage of the non-aqueous secondary battery drops below 0.5V is preferably 30 hours or less, more preferably 25 hours or less, and even more preferably 20 hours or less.

[0065] The mechanism by which this inerting method inertizes non-aqueous secondary batteries is hypothesized as follows. Figure 2 This is an explanatory diagram illustrating the inerting mechanism of non-aqueous secondary batteries. Figure 2 As an example, we will explain the case where the redox shuttle is phenothiazine. The phenothiazine contained in the inerting agent exists in the electrolyte (the ion-conducting medium of a non-aqueous secondary battery + the non-aqueous solvent of the inerting agent) in the form of neutral molecules or cationic free radicals, and functions as a redox shuttle that shuttles back and forth between free radicals and neutrals by utilizing electron donation and acceptance between the positive and negative electrodes.

[0066] Specifically, when an inert agent is added to a non-aqueous secondary battery, phenothiazine, existing in neutral molecular form, donates electrons to the positive electrode and transforms into a cationic free radical. Figure 2 (1) and the anions (PF6) from the supporting salts contained in the electrolyte. - Stabilization (etc.) Figure 2 (2) When electrons are supplied from the negative electrode to the cation radical, phenothiazine becomes a neutral molecule. Figure 2(3)). Li ions and electrons are simultaneously released from the negative electrode, and the Li ions migrate from the membrane to the positive electrode. Figure 2 (4)). By repeating the above process, the potential difference between the positive and negative electrodes eventually disappears, the battery voltage approaches 0V, and inertization is completed.

[0067] The inerting agent and inerting method described above enable more rapid inerting of non-aqueous secondary batteries with a smaller amount of inerting agent. It is speculated that this effect is achieved because, for example, by using an inerting agent containing NMP in addition to a redox shuttle, the diffusion of the inerting agent within the battery can be suppressed, maintaining a high concentration of the redox shuttle participating in the reaction. Therefore, even with a smaller amount of inerting agent, redox shuttle proceeds smoothly, resulting in more rapid inerting of the battery.

[0068] It should be noted that the present invention is not limited to any of the above embodiments. As long as it falls within the technical scope of the present invention, it can be implemented in various ways, which is self-evident.

[0069] The present invention may also be the content shown in any of the following [1] to [6].

[0070] [1] An inertizing agent for non-aqueous secondary batteries, comprising: an inertizing agent whose redox potential, measured by a Li reference potentiometer, 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; and N-methyl-2-pyrrolidone.

[0071] [2] The inert agent of the non-aqueous secondary battery according to [1], wherein the redox shuttle is a ferrocene compound or a phenothiazine compound.

[0072] [3] The inertizer of the non-aqueous secondary battery according to [1] or [2] contains more than 0.5 mol / L of the above redox shuttle.

[0073] [4] An inerting method for a non-aqueous secondary battery, comprising an adding step of adding an inerting agent for a non-aqueous secondary battery as described in any one of [1] to [3] into the interior of the non-aqueous secondary battery.

[0074] [5] The inerting method for a non-aqueous secondary battery according to [4], wherein, in the above-mentioned addition step, the inerting agent is added in such a way that the amount of the inerting agent added is less than 10 μL / mAh relative to the battery capacity of the non-aqueous secondary battery.

[0075] [6] The inerting method for the non-aqueous secondary battery according to [4] or [5], wherein the time elapsed from the addition of the inerting agent in the above-mentioned addition step until the battery voltage of the non-aqueous secondary battery becomes 0.5V or less is 30 hours or less.

[0076] Example

[0077] Hereinafter, examples of the inerting agent used in the non-aqueous secondary battery of the present invention will be described as embodiments. It should be noted that experimental examples 1-2, 7-8, and 10 are equivalent to the embodiments, and experimental examples 3-6, 9, and 11 are equivalent to the comparative examples.

[0078] [Experimental Example 1]

[0079] (1) Non-aqueous secondary battery

[0080] As a non-aqueous secondary battery, a lithium secondary battery with a voltage of 4.1V and a capacity of 17mAh is prepared as follows. LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode composite material obtained by mixing O2 (redox potential of 4.2V at full charge using a Li reference potentiometer), acetylene black, and polyvinylidene fluoride (PVdF) in a mass ratio of 93:4:3 was coated onto an aluminum current collector foil and vacuum dried at 120°C to obtain the positive electrode. Separately, a negative electrode composite material obtained by mixing graphite (redox potential of 0.1V at full charge using a Li reference potentiometer), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 98:1:1 was coated onto a copper current collector foil and vacuum dried at 120°C to obtain the negative electrode. An ion-conducting medium was prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of approximately 3:4:3, and adding LiPF6 as a lithium salt to achieve a concentration of 1 mol / L. A polyethylene membrane was sandwiched between the obtained positive and negative electrodes, and 0.45 mL of the ion-conducting medium was impregnated into the membrane before being sealed within a laminated film. The battery obtained in this way is charged to 4.1V after two charge-discharge cycles at a temperature of 25℃ and a voltage range of 3.0 to 4.1V, thus reaching a fully charged state.

[0081] (2) Inert agent

[0082] An inert solution (inert agent) was prepared by dissolving phenothiazine in N-methyl-2-pyrrolidone (NMP) to achieve a concentration of 1.0 mol / L.

[0083] (3) Inertization process

[0084] A non-aqueous secondary battery, initially in a fully charged state (4.1V), was opened under an argon atmosphere, and 31.7 μL of inerting solution was added. After adding the inerting solution, the battery was resealed, and the battery voltage change was measured at 25°C. In Example 1, the amount of inerting solution added relative to the battery capacity (17mAh) was 1.9 μL / mAh, and the amount of phenothiazine added relative to the battery capacity was 1.9 μmol / mAh.

[0085] [Experimental Example 2]

[0086] The inerting solution was prepared by dissolving phenothiazine in NMP to achieve a concentration of 3.0 mol / L, otherwise the procedure was the same as in Example 1. In Example 2, the amount of inerting solution added was 1.9 μL / mAh relative to the battery capacity, and the amount of phenothiazine added was 5.6 μmol / mAh relative to the battery capacity.

[0087] [Experiment Example 3]

[0088] Inertizing solution was prepared by dissolving phenothiazine in 1,2-dimethoxyethane (DME) to achieve a concentration of 1.0 mol / L, otherwise the procedure was the same as in Example 1. In Example 3, the amount of inertizing solution added was 1.9 μL / mAh relative to the battery capacity, and the amount of phenothiazine added was 1.9 μmol / mAh relative to the battery capacity.

[0089] [Experiment Example 4]

[0090] Inertizing solution was prepared by dissolving phenothiazine in DME to achieve a concentration of 0.1 mol / L. The amount of inertizing solution added was set to 1.268 mL, and the battery voltage change was measured at 20 °C. Otherwise, the procedure was the same as in Example 1. In Example 4, the amount of inertizing solution added relative to the battery capacity was 74.6 μL / mAh, and the amount of phenothiazine added relative to the battery capacity was 7.5 μmol / mAh.

[0091] [Experiment Example 5]

[0092] Inertizing solution was prepared by dissolving phenothiazine in triethylene glycol dimethyl ether (TGDE) to achieve a concentration of 0.1 mol / L. The amount of inertizing solution added was set to 1.268 mL, and the battery voltage change was measured at 20 °C. Otherwise, the procedure was the same as in Example 1. In Example 5, the amount of inertizing solution added relative to the battery capacity was 74.6 μL / mAh, and the amount of phenothiazine added relative to the battery capacity was 7.5 μmol / mAh.

[0093] [Experiment Example 6]

[0094] Inertizing solution was prepared by dissolving phenothiazine in tetraethylene glycol dimethyl ether (TEGED) to achieve a concentration of 0.1 mol / L. The amount of inertizing solution added was set to 1.268 mL, and the battery voltage change was measured at 20 °C. Otherwise, the procedure was the same as in Example 1. In Example 6, the amount of inertizing solution added relative to the battery capacity was 74.6 μL / mAh, and the amount of phenothiazine added relative to the battery capacity was 7.5 μmol / mAh.

[0095] [Results and Investigation]

[0096] Figure 3 The diagram shows the battery voltage changes in Experiments 1-3. Figure 4 Table 1 shows the battery voltage changes in Experiments 4-6. In Experiments 1-6, after adding inerting solution, the battery voltage dropped below 0.1V, indicating that the inerting solution functioned effectively. Table 1 summarizes the elapsed time from the addition of inerting solution to the battery voltage reaching 0.5V in Experiments 1-6.

[0097] The results of comparing Experiment 1 and Experiment 3 show that the battery in Experiment 1 discharged more rapidly. All experimental conditions were identical in Experiment 1 and Experiment 3 except for the solvent used in the inerting solution; therefore, it can be inferred that the difference in discharge rate is due to the different solvents. When comparing the viscosity of the solvents, the viscosity of NMP used in Experiment 1 was 1.65 cP, which is more than four times greater than the viscosity of DME used in Comparative Example 1 (0.41 cP). According to the Stokes-Einstein equation, the diffusion rate of phenothiazine decreases when using NMP as the solvent, suggesting a decrease in the battery's discharge rate. Regarding this point, the results of experiments 4-6 confirm that when using DME (viscosity 0.41 cP), triethylene glycol dimethyl ether (viscosity 1.96 cP), and tetraethylene glycol dimethyl ether (viscosity 3.3 cP) as the inerting solution solvent, the discharge rate tends to decrease with increasing solvent viscosity. Therefore, it can be inferred that the increased discharge rate of the battery due to the use of NMP as the inerting solvent is caused by a different mechanism than the increased diffusion rate of phenothiazine caused by the use of a low-viscosity solvent in Patent Document 2. The mechanism for the increased discharge rate due to the use of NMP is believed to be the localized increase in phenothiazine concentration resulting from the suppression of inerting agent diffusion within the battery. It is speculated that the diffusion suppression of the inerting agent caused by the use of NMP is due to the high viscosity of NMP and the low wettability of NMP with the separator. It should be noted that this mechanism for increased discharge rate is speculated to be caused by the different solvents, and the same effect can be obtained even if the redox shuttle is not a phenothiazine compound, as confirmed by experimental examples 7-11 described later.

[0098] Furthermore, NMP can increase the concentration of phenothiazine to over 3 mol / L. As Experimental Example 2, a 3 mol / L phenothiazine / NMP solution was studied, and the results are as follows... Figure 3 As shown, compared with a 1 mol / L phenothiazine / NMP solution (Experimental Example 1), it was confirmed that the discharge rate could be further increased with increasing phenothiazine concentration.

[0099] [Experiment Example 7]

[0100] (1) Non-aqueous secondary battery

[0101] As a non-aqueous secondary battery, a lithium secondary battery with a voltage of 3.75V and a capacity of 10mAh is prepared as follows. A slurry-like positive electrode composite material obtained by mixing LiFePO4 (redox potential of 3.85V at full charge using a Li reference potentiometer), acetylene black, and polyvinylidene fluoride (PVdF) in a mass ratio of 92:5:3 is coated onto aluminum foil and vacuum dried at 120°C to obtain the positive electrode. Separately, a slurry-like negative electrode composite material obtained by mixing graphite (redox potential of 0.1V at full charge using a Li reference potentiometer), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 98:1:1 is coated onto copper foil and vacuum dried at 120°C to obtain the negative electrode. An electrolyte is prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3 and dissolving lithium hexafluorophosphate (LiPF6) as a lithium salt to achieve a concentration of 1.0 mol / L. A single-layer microporous polyethylene membrane was prepared as the separator. The positive and negative electrodes were placed face to face, separated by the separator which was impregnated with approximately 0.45 mL of electrolyte, and then sealed inside the laminated membrane. For this battery, after two charge-discharge cycles at a temperature of 25°C and a voltage range of 3.0–3.75V, it was charged to 3.75V, reaching a fully charged state.

[0102] (2) Inert agent

[0103] An inert solution (inert agent) was prepared by dissolving phenothiazine in N-methyl-2-pyrrolidone (NMP) to achieve a concentration of 1.0 mol / L.

[0104] (3) Inertization process

[0105] The battery, to be fully charged (3.75V), was opened under an argon atmosphere, and 18.7 μL of inerting solution was added. After adding the inerting solution, the battery was sealed again, and the battery voltage change was measured at 25°C. In Example 7, the amount of inerting solution added relative to the battery capacity (10mAh) was 1.9 μL / mAh, and the amount of phenothiazine added relative to the battery capacity was 1.9 μmol / mAh.

[0106] [Experiment Example 8]

[0107] The inerting solution was prepared by dissolving phenothiazine in NMP to achieve a concentration of 3.0 mol / L, otherwise the procedure was the same as in Example 7. In Example 8, the amount of phenothiazine added was 5.6 μmol / mAh relative to the battery capacity.

[0108] [Experiment Example 9]

[0109] The inerting solution was prepared by dissolving phenothiazine in 1,2-dimethoxyethane (DME) to achieve a concentration of 1.0 mol / L, otherwise the procedure was the same as in Example 7. In Example 9, the amount of phenothiazine added was 1.9 μmol / mAh relative to the battery capacity.

[0110] [Experiment Example 10]

[0111] The inerting solution was prepared by dissolving ferrocene in NMP to achieve a concentration of 0.5 mol / L, otherwise the procedure was the same as in Example 7. In Example 10, the amount of ferrocene added was 0.9 μmol / mAh relative to the battery capacity.

[0112] [Experimental Example 11]

[0113] The inerting solution was prepared by dissolving ferrocene in DME to achieve a concentration of 0.5 mol / L, otherwise the procedure was the same as in Example 7. In Example 11, the amount of ferrocene added was 0.9 μmol / mAh relative to the battery capacity.

[0114] [Results and Investigation]

[0115] Figure 5 The changes in battery voltage in Experiments 7-9 are shown in the figure. Figure 6 Table 2 shows the battery voltage changes in Experiments 10-11. In the batteries using LiFePO4 as the positive electrode active material and the batteries using ferrocene as the redox shuttle, the battery voltage dropped below 0.1V after the addition of inerting solution, indicating that the inerting solution effectively functioned. Table 2 summarizes the elapsed time from the addition of inerting solution to the battery voltage reaching 0.5V in Experiments 7-11.

[0116] A comparison of Experimental Examples 7 and 9 shows that, like batteries using ternary cathodes, the discharge rate of batteries using LiFePO4 cathodes is increased by using NMP as the inerting solvent. Furthermore, as shown in Experimental Example 8, using NMP solvent allows for a high concentration of phenothiazine up to 3 mol / L, which in turn further increases the discharge rate.

[0117] A comparison of Experimental Example 10 and Experimental Example 11 shows that, like the battery using ferrocene as the redox shuttle, the battery using phenothiazine as the redox shuttle also has an increased discharge rate by using NMP as the solvent for the inert liquid.

[0118] The above demonstrates that by using NMP as a solvent, both a high concentration of redox shuttle and an increased battery discharge rate can be achieved, enabling more rapid inerting of non-aqueous secondary batteries with a smaller amount of inerting agent. Furthermore, it shows that the aforementioned effects can be obtained regardless of the type of positive electrode active material or redox shuttle, using NMP as a solvent.

[0119] In addition, as a supplement, the flash points of the solvents (DME, tetrahydrofuran, N,N-dimethylacetamide, N,N-dimethylformamide) of the inerting liquid proposed in the aforementioned Patent Document 2 are -2°C, -14.5°C, 64°C, and 58°C, respectively. In contrast, the flash point of NMP used in this invention is as high as 86°C. Therefore, it is speculated that the inerting process and the safety of the battery after treatment can also be improved.

[0120] [Table 1]

[0121] [Table 2]

[0122] This application is based on Japanese Patent Application No. 2024-068889, filed on April 22, 2024, the entire contents of which are incorporated herein by reference.

[0123] Industrial availability

[0124] This invention can be applied to the battery industry.

[0125] Symbol Explanation

[0126] 20 Non-aqueous secondary battery, 21 Casing, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Ion conducting medium.

Claims

1. An inert agent for a non-aqueous secondary battery, comprising: A redox shuttle with a redox potential 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, measured using a Li reference potentiometer; and N-Methyl-2-pyrrolidone.

2. The inert agent for a non-aqueous secondary battery according to claim 1, wherein, The redox shuttle is a ferrocene compound or a phenothiazine compound.

3. The inerting agent for the non-aqueous secondary battery according to claim 1 or 2, wherein it contains more than 0.5 mol / L of the redox shuttle.

4. An inerting method for a non-aqueous secondary battery, comprising an addition step of adding an inerting agent for a non-aqueous secondary battery as described in claim 1 or 2 into the interior of the non-aqueous secondary battery.

5. The inerting method for non-aqueous secondary batteries according to claim 4, wherein, In the addition process, the inert agent is added in such a way that the amount of inert agent added is less than 10 μL / mAh relative to the battery capacity of the non-aqueous secondary battery.

6. The inerting method for non-aqueous secondary batteries according to claim 4, wherein, The time elapsed from the addition of the inert agent in the above-mentioned addition process until the battery voltage of the non-aqueous secondary battery drops below 0.5V is less than 30 hours.

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