KR20200135298A - Thermal runaway inhibitor - Google Patents

Abstract

An object of the present invention is to provide a non-aqueous electrolyte secondary battery that does not increase in size or significantly increases the cost, is unlikely to cause thermal runaway even when an internal short circuit occurs, and does not have a risk of ignition or rupture. The present invention is an inhibitor of thermal runaway due to an internal short circuit for a nonaqueous electrolyte secondary battery comprising a silyl ester compound, a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte. In addition, it is a method of suppressing thermal runaway due to an internal short circuit of a nonaqueous electrolyte secondary battery in which 0.01% by mass to 10% by mass of the thermal runaway inhibitor for an internal short circuit for a nonaqueous electrolyte secondary battery is blended in the nonaqueous electrolyte.

Description

Thermal runaway inhibitor

The present invention relates to an inhibitor of thermal runaway due to an internal short circuit of a nonaqueous electrolyte secondary battery, and a method of inhibiting thermal runaway due to an internal short circuit using the inhibitor.

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are small and lightweight, have high energy density, high capacity, and can be repeatedly charged and discharged, so they are widely used as power sources for portable electronic devices such as portable computers, handy video cameras, and information terminals. Is being used. In addition, from the viewpoint of environmental issues, electric vehicles using non-aqueous electrolyte secondary batteries or hybrid vehicles using electric power as part of the power have been put into practice.

The nonaqueous electrolyte secondary battery is composed of members such as an electrode, a separator, and an electrolyte. A flammable organic solvent is used as the main solvent of the electrolyte, and when large energy is released due to an internal short circuit or the like, thermal runaway occurs, and there is a risk of ignition or rupture, so various measures are being investigated. As such a countermeasure, a method of using a porous film containing polyolefin as a main component as a separator (for example, refer to Patent Documents 1 and 2), and a method of providing a porous heat-resistant layer between the anode and the cathode in addition to the separator (e.g. For example, refer to Patent Document 3), a method of coating the surface of an electrode active material with a metal oxide (for example, refer to Patent Document 4), a method of using a lithium-containing nickel oxide as a positive electrode active material (for example, Patent Document 5), a method of using an olivine-type lithium phosphate compound as a positive electrode active material (for example, refer to Patent Document 6), a method of using a spinel structure lithium titanate compound as a negative electrode active material (for example, refer to Patent Document 7 ), a method of using a non-flammable fluorine-based solvent as the main solvent of the electrolyte (for example, see Patent Documents 8 and 9), a method of using a solid electrolyte that does not use an organic solvent as an electrolyte (for example, Patent Document 10 See) and the like are known.

As a separator of a porous film containing polyolefin as a main component, it is necessary to thicken the separator in order to prevent internal short circuit.In the method of providing the porous heat-resistant layer, the battery becomes larger as the amount of the porous heat-resistant layer, and the surface of the electrode active material is covered with metal oxide. In this method, the content of the electrode active material contained in the electrode mixture layer of the electrode is relatively reduced, the capacity of the battery is reduced, and the advantages of the non-aqueous electrolyte secondary battery of small size, light weight, and high capacity are lost. High charge/discharge capacity cannot be obtained in either the method of using a lithium-containing nickel oxide or an olivine-type lithium phosphate compound as a positive electrode active material or a method of using a spinel-structure lithium titanate compound as a negative electrode active material. Further, in the method of using a fluorine-based solvent, the fluorine-based solvent is extremely expensive and needs to be used in a large amount, resulting in a significant increase in cost. In a method using a solid electrolyte, since a solid electrolyte material having no fluidity is used, internal resistance is increased, and performance is lowered than that of an electrolyte using an organic solvent.

On the other hand, for example, in a lithium ion secondary battery, a non-aqueous electrolyte obtained by dissolving a lithium salt containing a fluorine atom such as lithium hexafluoride phosphate in a carbonate ester organic solvent such as propylene carbonate or diethyl carbonate is used as an electrolyte. Carboxylic acid silyl ester compounds (for example, see Patent Documents 11 to 13), sulfuric acid silyl ester compounds (for example, see Patent Documents 4 to 5), and sulfonic acid silyl ester compounds (For example, see Patent Documents 14 and 16), phosphate silyl ester compound (for example, refer to Patent Documents 15, 17, 18), boric acid silyl ester compound (for example, refer to Patent Documents 15 and 19) A non-aqueous electrolyte to which a silyl ester compound such as) is further added is being studied. However, by using a non-aqueous electrolyte to which a silyl ester compound is added, thermal runaway is unlikely to occur even when an internal short circuit occurs, and it is not known that a non-aqueous electrolyte secondary battery without risk of ignition or rupture occurs.

US2018097256 US9923181 US7759004 Japanese Unexamined Patent Application Publication No. 2011-216300 Japanese Unexamined Patent Application Publication No. 2002-015736 US7572548 Japanese Unexamined Patent Application Publication No. 2008-159280 US2009253044 US8163422 US2016315324 Japanese Unexamined Patent Application Publication No. 2002-313416 US7410731 WO2016/013480 US7241536 Japanese Unexamined Patent Application Publication No. 2006-253086 US9112236 US6379846 Japanese Unexamined Patent Application Publication No. 2004-342607 US2002015895

An object of the present invention is to provide a non-aqueous electrolyte secondary battery that does not increase in size or significantly increases the cost, is unlikely to cause thermal runaway even when an internal short circuit occurs, and does not have a risk of ignition or rupture.

The inventors of the present invention have conducted a careful review of the above problems. Even in a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte using an organic solvent as a solvent, by mixing a silyl ester compound in the non-aqueous electrolyte, thermal runaway is difficult to occur, and ignition or rupture due to an internal short circuit. Found what can be prevented, and completed the present invention. That is, the present invention is a thermal runaway inhibitor for a nonaqueous electrolyte secondary battery having a positive electrode including a positive electrode active material made of a silyl ester compound, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte secondary battery.

1 is a longitudinal sectional view schematically showing an example of the structure of a coin-type battery of a nonaqueous electrolyte secondary battery.
2 is a schematic diagram showing the basic configuration of a cylindrical battery of a nonaqueous electrolyte secondary battery.
3 is a perspective view showing the internal structure of a cylindrical battery of a non-aqueous electrolyte secondary battery as a sectional view.

The thermal runaway inhibitor of the present invention is characterized by comprising a silyl ester compound. Examples of the silyl ester compound include a carboxylic acid silyl ester compound, a sulfate silyl ester compound, a sulfonic acid silyl ester compound, a phosphate silyl ester compound, a phosphorous acid silyl ester compound, and a boric acid silyl ester compound.

As a carboxylic acid silyl ester compound, the carboxylic acid silyl ester compound represented by the following general formula (1) is mentioned, for example.

(In the formula, R ¹ to R ³ each independently represent a hydrocarbon group having 1 to 6 carbon atoms, and X ¹ is an a-valent hydrocarbon group having 1 to 10 carbon atoms, or a methylene group in the hydrocarbon group substituted with an oxygen atom or a sulfur atom. Represents a valent group having 1 to 10 carbon atoms, and a represents the number of 1 to 4.)

In general formula (1), R ¹ to R ³ each independently represent a hydrocarbon group having 1 to 6 carbon atoms. Hydrocarbon groups having 1 to 6 carbon atoms include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group , 1-methylbutyl group, isohexyl group, vinyl group, cyclopentyl group, cyclohexyl group, phenyl group, and the like. As R ¹ to R ³ , a methyl group, an ethyl group, and a phenyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased. All of R ¹ to R ³ may be the same group or may be a combination of 2 to 3 types of groups, but in the case of a combination of 2 to 3 types of groups, one type is preferably a methyl group.

X ¹ represents an a-valent hydrocarbon group having 1 to 10 carbon atoms, or an a-valent group having 1 to 10 carbon atoms in which the methylene group in the hydrocarbon group is substituted with an oxygen atom or a sulfur atom, and a represents the number of 1 to 4. When the number of carbon atoms of X ¹ is too large, the solubility in the non-aqueous electrolyte may decrease or the effect of inhibiting thermal runaway may decrease. Therefore, the number of carbon atoms of X ¹ is preferably 1 to 10, and more preferably 1 to 6. a is preferably a number of 2 to 3 from the viewpoint of the solubility of the carboxylic acid silyl ester compound in the non-aqueous electrolyte and the stability of the carboxylic acid silyl ester compound.

The carboxylic acid silyl ester compound represented by the general formula (1) can be obtained by silyl esterification of a carboxylic acid represented by the following general formula (1a) or an acid anhydride thereof by a known method.

(In the formula, X ¹ has the same meaning as in General Formula (1), and m represents the number of 1 to 4.)

Among the carboxylic acid silyl ester compounds represented by the general formula (1), the compounds in which a is 1 include trimethylsilyl acetate, trimethylsilyl propanoate, trimethylsilyl butanoate, trimethylsilyl pentanoate, trimethylsilyl hexanoate, trimethylsilyl heptanoate, Trimethylsilyl octanoate, trimethylsilyl nonanoate, trimethylsilyl decanoate, trimethylsilyl 2-methylpropanoate, trimethylsilyl 2-methylbutanoate, trimethylsilyl 3-methylbutanoate, trimethylsilyl tert-butanoate, 2-methylphene Trimethylsilyl carbonate, 2-ethylbutanoate trimethylsilyl, isohexanoate trimethylsilyl, 2-ethylhexanoate trimethylsilyl, isooctanoate trimethylsilyl, 3,5,5-trimethylhexanoate trimethylsilyl, acrylate trimethylsilyl, methacrylic acid Trimethylsilyl, trimethylsilyl crotonate, trimethylsilyl benzoate, trimethylsilyl toluic acid, trimethylsilyl 4-tert-butylbenzoate, trimethylsilyl naphthalenecarboxylic acid, trimethylsilyl phenylacetate, trimethylsilyl naphthyl acetate, trimethyl methoxybenzoate, 4-methoxybenzoate Silyl, trimethylsilyl methoxyacetate, trimethylsilyl ethoxyacetate, trimethylsilyl tert-butoxyacetate, trimethylsilyl phenoxyacetate, and the like.

Among the carboxylic acid silyl ester compounds represented by the general formula (1), the compounds in which a is 2 include ethane diacid bis (trimethyl silyl), propane di acid bis (trimethyl silyl), butane diacid bis (trimethyl silyl), pentane diacid bis (trimethyl Silyl), bis hexane diacid (trimethylsilyl), bis heptane diacid (trimethylsilyl), bis octane diacid (trimethylsilyl), bis nonane diacid (trimethylsilyl), bis decanoic acid (trimethylsilyl), bis fumarate (trimethylsilyl), Bis maleate (trimethylsilyl), bis citraconic acid (trimethylsilyl), bis mesaconic acid (trimethylsilyl), bis glutaconate (trimethylsilyl), bis itaconic acid (trimethylsilyl), bis muconate (trimethylsilyl), Acetylene dicarboxylic acid bis (trimethylsilyl), cyclohexanedicarboxylic acid bis (trimethylsilyl), cyclohexene dicarboxylic acid bis (trimethylsilyl), norbornane dicarboxylic acid bis (trimethylsilyl), norbornene Dicarboxylic acid bis(trimethylsilyl), adamantanedicarboxylic acid bis(trimethylsilyl), bicyclo[2.2.1]heptane-2,3-dicarboxylic acid bis(trimethylsilyl), bicyclo[2.2 .1] Hepta-5-ene-2,3-dicarboxylic acid bis(trimethylsilyl), benzenedicarboxylic acid bis(trimethylsilyl), xylenedicarboxylic acid bis(trimethylsilyl), furandicarboxylic acid Bis(trimethylsilyl), adamantanediacetate bis(trimethylsilyl), (ethylenedioxy)diacetate bis(trimethylsilyl), (phenylenedioxy)diacetate bis(trimethylsilyl), thiodiacetate bis(trimethylsilyl) , Dithiodiacetate bis (trimethylsilyl), thioacetate propionic acid bis (trimethylsilyl), thiodipropionic acid bis (trimethylsilyl), dithiodipropionic acid bis (trimethylsilyl), ethylenedithiodiacetate bis (trimethylsilyl), thiophenedicar Acid bis (trimethylsilyl), etc. are mentioned.

Among the carboxylic acid silyl ester compounds represented by the general formula (1), the compounds in which a is 3 include propane tricarboxylic acid tris (trimethylsilyl), 3-carboxymuconic acid tris (trimethylsilyl), and aconitic acid tris (trimethylsilyl). ), 3-butene-1,2,3-tricarboxylic acid tris (trimethylsilyl), pentane-1,3,5-tricarboxylic acid tris (trimethylsilyl), hexane-1,3,6-tricar Acid tris (trimethylsilyl), cyclohexane tricarboxylic acid tris (trimethylsilyl), trimellitic acid tris (trimethylsilyl), trimesic acid tris (trimethylsilyl), butanetetracarboxylic acid tris (trimethylsilyl), etc. Can be lifted.

Among the carboxylic acid silyl ester compounds represented by the general formula (1), the compounds in which a is 4 include cyclobutane tetracarboxylic acid tetrakis (trimethylsilyl), cyclopentane tetracarboxylic acid tetrakis (trimethylsilyl), and tetrahydrofuran. Tetracarboxylic acid tetrakis (trimethylsilyl), pyromellitic acid tetrakis (trimethylsilyl), naphthalene tetracarboxylic acid tetrakis (trimethylsilyl), and the like.

As a silyl sulfate compound and a silyl sulfonate compound, a compound represented by the following general formula (3) is mentioned, for example.

(In the formula, R ¹¹ to R ¹⁴ each independently represent a hydrocarbon group having 1 to 6 carbon atoms, and c represents the number of 0 or 1.)

In the general formula (3), R ¹¹ to R ¹⁴ represent a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include groups exemplified by R ¹ to R ³ in General Formula (1). As R ^{11, since} industrial raw materials are readily available, a methyl group or a phenyl group is preferable, and a methyl group is more preferable. As R ¹² to R ¹⁴ , a methyl group, an ethyl group and a phenyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased.

c represents the number of 0 or 1, when c is the number of 0, the compound represented by the general formula (3) is a silyl sulfate compound, and when c is the number of 1, it is a silyl sulfonate compound.

When c in the general formula (3) is a number of 0, that is, when the compound represented by the general formula (3) is a silyl sulfate compound, preferred compounds include bis(trimethylsilyl) sulfate, bis(dimethylphenylsilyl) sulfate, And bis(methyldiphenylsilyl) sulfate and bis(triphenylsilyl) sulfate.

When c in the general formula (3) is a number of 1, that is, when the compound represented by the general formula (3) is a sulfonic acid silyl ester compound, preferred compounds include trimethylsilyl methanesulfonate, dimethylphenylsilyl methanesulfonate, and benzenesulfonate. Trimethylsilyl fonate, trimethylsilyl toluene sulfonic acid, etc. are mentioned.

The phosphoric acid silyl ester compound includes a silyl ester compound of an alkyl acid phosphate in which a part of the silyl ester group is substituted with an alkyl ester group, and the phosphorous acid silyl ester compound is an alkyl acid phosphorous acid in which a part of the silyl ester group is substituted with an alkyl ester group. The silyl ester compound of an ester is mentioned. As a phosphate silyl ester compound and a phosphorous acid silyl ester compound, the compound represented by the following general formula (4) is mentioned, for example.

(In the formula, R ¹⁵ to R ¹⁸ each independently represents a hydrocarbon group having 1 to 6 carbon atoms, d represents 0 or the number of 1 to 2, and e represents the number of 0 or 1.)

In the general formula (4), R ¹⁵ to R ¹⁸ each independently represent a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include groups exemplified by R ¹ to R ³ in General Formula (1). As R ¹⁵ , a methyl group, an ethyl group, and a butyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased. As R ¹⁶ to R ¹⁸ , a methyl group, an ethyl group, and a phenyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased.

d represents 0 or the number of 1 to 2, and e represents the number of 0 or 1. When d is a number of 1 to 2, it may be a mixture of a compound in which d is a number of 1 and a compound in which d is a number of 2. When e is a number of 1 and d is a number of 0, the compound represented by general formula (4) is a phosphate silyl ester compound, and when e is a number of 1 and d is a number of 1 to 2, silyl of an alkyl acid phosphate ester It is an ester compound. When e is the number of 0 and d is the number of 0, the compound represented by the general formula (4) is a phosphorous acid silyl ester compound, and when e is the number of 0 and d is the number of 1 to 2, the silyl of the alkyl acid phosphorous acid ester It is an ester compound. The silyl ester compound of the alkyl acid phosphoric acid ester and the silyl ester compound of the alkyl acid phosphorous acid ester have advantages in that they are easy to manufacture and excellent in storage stability as compared to the phosphate silyl ester compound and the phosphorous silyl ester compound, respectively.

Phosphoric acid silyl ester compounds (including silyl ester compounds of alkyl acid phosphate esters) include tris(trimethylsilyl) phosphate, methylbis(trimethylsilyl) phosphate, dimethyl phosphate (trimethylsilyl), ethyl bis phosphate (trimethylsilyl), diethyl phosphate (Trimethylsilyl), butyl bis (trimethylsilyl) phosphate, dibutyl phosphate (trimethylsilyl), etc. are mentioned. Phosphorous acid silyl ester compounds (including silyl ester compounds of alkyl acid phosphorous acid esters) include tris phosphite (trimethylsilyl), methyl bis phosphite (trimethylsilyl), dimethyl phosphite (trimethylsilyl), ethyl bis phosphite (trimethylsilyl), diethyl phosphite (Trimethylsilyl), butyl bis phosphite (trimethylsilyl), dibutyl phosphite (trimethylsilyl), and the like are mentioned.

As a boric acid silyl ester compound, the compound represented by the following general formula (5) is mentioned, for example.

(In the formula, R ¹⁹ to R ²¹ each independently represent a hydrocarbon group having 1 to 6 carbon atoms.)

In the general formula (5), R ¹⁹ to R ²¹ each independently represent a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include groups exemplified by R ¹ to R ³ in General Formula (1). As R ¹⁹ to R ²¹ , a methyl group, an ethyl group and a phenyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased. Examples of the boric acid silyl ester compound include tris boric acid (trimethylsilyl).

In the present invention, since the thermal runaway inhibiting effect is high, it is preferable to use the carboxylic acid silyl ester compound represented by the general formula (1). In addition, it is preferable that a in the general formula (1) is 2, and X ¹ is a divalent hydrocarbon group having 1 to 10 carbon atoms, or a methylene group in the hydrocarbon group has 1 to 10 carbon atoms substituted with an oxygen atom or a sulfur atom. It is preferable that the divalent group of In particular, R ¹ to R ³ in the general formula (1) is a methyl group, a is 2, and X ¹ is a divalent hydrocarbon group having 1 to 6 carbon atoms, or the number of carbon atoms in which the methylene group in the hydrocarbon group is substituted with a sulfur atom. Compounds with 1 to 6 divalent groups are preferred.

In the present invention, a silyl ester compound is blended into the non-aqueous electrolyte as a thermal runaway inhibitor. The content of the silyl ester compound in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 7% by mass, and most preferably 0.1% by mass to 5% by mass. When the content of the silyl ester compound in the non-aqueous electrolyte is too small, a sufficient suppression effect of thermal runaway cannot be obtained, and when too large, an increase effect corresponding to the blending amount cannot be obtained. Although we do not know the mechanism by which the silyl ester compound in the non-aqueous electrolyte suppresses thermal runaway due to an internal short circuit of the non-aqueous electrolyte secondary battery, the adhesion of the siloxane compound to the positive and negative surfaces of the non-aqueous electrolyte secondary battery is visible. It is presumed that the silyl ester compound is decomposed to form a siloxane compound on the electrode surface, which insulates the short-circuit current.

Non-aqueous electrolytes of non-aqueous electrolyte secondary batteries to which the present invention can be applied include, for example, a liquid electrolyte obtained by dissolving an electrolyte in an organic solvent, a polymer gel electrolyte obtained by dissolving the electrolyte in an organic solvent and gelling into a polymer, and an organic solvent. And pure polymer electrolytes in which the electrolyte is dispersed in a polymer without the need to be used. Among them, in a nonaqueous electrolyte secondary battery having a liquid electrolyte, thermal runaway is likely to occur due to an internal short circuit, and the risk of ignition or explosion is high, so that the thermal runaway inhibitor of the present invention is applied to a nonaqueous electrolyte of a nonaqueous electrolyte secondary battery having a liquid electrolyte. desirable.

As the electrolyte used in the liquid electrolyte and the polymer gel electrolyte, a conventionally known electrolyte is used. Hereinafter, when the non-aqueous electrolyte secondary battery is a lithium secondary battery, an electrolyte will be described. In the case of a sodium secondary battery, an electrolyte obtained by substituting a lithium atom with a sodium atom is used. Electrolytes used in liquid electrolytes and polymer gel electrolytes include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiB(CF ₃ SO ₃ ) ₄ , LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiSbF ₆ , LiSiF ₅ , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI, LiAlF ₄ , LiAlCl ₄ , LiPO ₂ F ₂ and derivatives thereof, etc., among them, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , and LiC(CF ₃ SO ₂ ) ₃ and derivatives of LiCF ₃ SO ₃ , and LiC It is preferable to use at least one selected from the group consisting of derivatives of (CF ₃ SO ₂ ) ₃ . The content of the electrolyte in the liquid electrolyte and the polymer gel electrolyte is preferably 0.5 mol/L to 7 mol/L, more preferably 0.8 mol/L to 1.8 mol/L.

Electrolytes used in the pure polymer electrolyte include, for example, LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(SO ₂ F) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiB(CF ₃ SO ₃ ) ₄ and LiB(C ₂ O ₄ ) ₂ are mentioned.

As the organic solvent used for the preparation of the liquid non-aqueous electrolyte used in the present invention, one type or two or more types of organic solvents commonly used for the non-aqueous electrolyte may be used. Specifically, for example, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds, etc. Can be lifted.

Among the above organic solvents, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, and amide compounds are preferable because they have a high relative dielectric constant and thus serve to increase the dielectric constant of the nonaqueous electrolyte, and in particular, saturated cyclic carbonate compounds are preferable. . Saturated cyclic carbonate compounds include, for example, ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,1-dimethylethylene carbonate. And the like. Examples of the saturated cyclic ester compound include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone. Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene. As the sulfone compound, for example, dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also referred to as tetramethylene sulfone), 3-methylsulfolane, 3,4-dimethylsulfolane, 3, 4-diphenymethylsulfolane, sulforene, 3-methylsulforene, 3-ethylsulforene, 3-bromomethylsulforene, etc. are mentioned, and sulfolane and tetramethylsulfolane are preferable. Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

Among the organic solvents, the saturated chain carbonate compound, chain ether compound, cyclic ether compound, and saturated chain ester compound can lower the viscosity of the non-aqueous electrolyte and increase the mobility of electrolyte ions, thereby improving battery characteristics such as power density. It can be done with excellent things. In addition, since it has a low viscosity, the performance of the non-aqueous electrolyte at a low temperature can be increased, and a saturated chain carbonate compound is particularly preferable. Examples of the saturated chain carbonate compound include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl-t-butyl carbonate, diisopropyl carbonate, and t-butylpropyl carbonate. Examples of the chain ether compound or cyclic ether compound include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis (methoxycarbonyloxy) Ethane, 1,2-bis(ethoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)propane, ethylene glycolbis(trifluoroethyl)ether, propylene glycolbis(trifluoroethyl) Ether, ethylene glycol bis (trifluoromethyl) ether, diethylene glycol bis (trifluoroethyl) ether, and the like. Among these, dioxolane is preferable.

The saturated chain ester compound is preferably a monoester compound and a diester compound having a total number of carbon atoms of 2 to 8 in the molecule, and specific compounds include, for example, methyl formate, ethyl formate, methyl acetate, ethyl acetate, and acetic acid. Propyl, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate, ethyl trimethyl acetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, 3-methoxy Methyl propionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, propylene glycol diacetyl, and the like, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, And ethyl propionate are preferred.

In addition, as an organic solvent used for preparing the non-aqueous electrolyte, for example, acetonitrile, propionitrile, nitromethane, derivatives thereof, and various ionic liquids may be used.

Polymers used in the polymer gel electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, and polyhexafluoropropylene. Polymers used in the genuine polymer electrolyte include polyethylene oxide, polypropylene oxide, and polystyrene sulfonic acid. There is no restriction|limiting in particular about the compounding ratio in the gel electrolyte and the compounding method, It is possible to adopt a compounding ratio known in the art and a known compounding method.

Since the stability of the silyl ester compound is improved in the non-aqueous electrolyte, it is preferable to further contain a phenylsilane compound represented by the general formula (2).

(In the formula, R ⁴ to R ⁵ each independently represent a hydrocarbon group having 1 to 6 carbon atoms, R ⁶ to R ¹⁰ each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms, and X ² is b represents a valent hydrocarbon group, and b represents the number of 1 to 3.)

In the general formula (2), R ⁴ to R ⁵ each independently represent a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include groups exemplified by R ¹ to R ³ in General Formula (1). As R ⁴ to R ⁵ , a methyl group, an ethyl group, and a phenyl group are preferable, and a methyl group is more preferable because the effect of suppressing thermal runaway is increased.

R ⁶ to R ¹⁰ each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms. The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and iodine, and the alkyl group having 1 to 4 carbon atoms is a methyl group, ethyl group, propyl group, butyl group, isobutyl group, sec-butyl group, and tert-butyl group. Can be lifted. As R ⁶ to R ¹⁰ , a hydrogen atom is preferable because it is easy to obtain a raw material industrially.

X ² represents a b-valent hydrocarbon group, and b represents the number of 1 to 3. When the number of carbon atoms of X ² is too large, the solubility in the non-aqueous electrolyte decreases, and therefore, the number of carbon atoms of X ² is preferably 10 or less.

Preferred compounds among the phenylsilane compounds represented by the general formula (2) include trimethylphenylsilane, dimethyldiphenylsilane, methyltriphenylsilane, butyldimethylphenylsilane, dimethyloctylphenylsilane, 1,4-bis(trimethylsilyl)benzene, 1,2-bis(trimethylsilyl)benzene, 1,4-bis(dimethylphenylsilyl)benzene, 1,1,1-tris(dimethylphenylsilyl)ethane, etc. are mentioned.

Some electrolytes used in the non-aqueous electrolyte are decomposed to generate acidic substances, and the performance of the nonaqueous electrolyte secondary battery may be degraded or the silyl ester compound may be decomposed by such acidic substances. The phenylsilane compound represented by the general formula (2) captures such an acidic substance and suppresses deterioration of the performance of the nonaqueous electrolyte secondary battery and decomposition of the silyl ester compound. The amount of the phenylsilane compound represented by the general formula (2) added to the non-aqueous electrolyte is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 7% by mass, and most preferably 1% by mass to 5% by mass. Do. When the content in the non-aqueous electrolyte is too small, a sufficient effect cannot be exhibited, and when the content in the non-aqueous electrolyte is too large, the effect of increasing the amount corresponding to the added amount is not observed, but rather, the battery performance may be deteriorated.

The non-aqueous electrolyte may contain an electrode film forming agent. Examples of the electrode film forming agent include cyclic carbonate compounds having unsaturated groups such as vinylene carbonate and vinyl ethylene carbonate; Chain carbonate compounds having a propynyl group such as dipropargyl carbonate and propargyl methyl carbonate; Unsaturated diester compounds such as dimethyl maleate, dibutyl maleate, dimethyl fumarate, dibutyl fumarate, and dimethyl acetylene dicarboxylic acid; Halogenated cyclic carbonate compounds such as chloroethylene carbonate, dichloroethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; Cyclic sulfurous acid esters such as ethylene sulfite; Cyclic sulfuric acid esters, such as propane sultone and butane sultone, etc. are mentioned.

The electrode film forming agent forms a protective film called SEI (Solid Electrolyte Interface) on the electrode surface, and improves the charging/discharging efficiency, cycle characteristics, and safety of the battery. If the content of the electrode film-forming agent is too small, a sufficient effect cannot be exerted, and if the content of the electrode film-forming agent is too large, not only the increasing effect corresponding to the content is not obtained, but rather, it may have an adverse effect. The content of is preferably 0.005% by mass to 10% by mass, more preferably 0.02% by mass to 5% by mass, and most preferably 0.05% by mass to 3% by mass in the non-aqueous electrolyte.

The non-aqueous electrolyte may further contain other known additives, such as an antioxidant, a flame retardant, an overcharge inhibitor, etc., in order to improve battery life, improve safety, and the like.

In the non-aqueous electrolyte secondary battery to which the present invention is applied, the positive electrode including the positive electrode active material is an electrode in which an electrode mixture layer including the positive electrode active material is formed on a current collector, and, for example, a positive electrode active material, a binder, and a conductive aid are used in an organic solvent or What has been slurried with water is applied to a current collector, and dried to form a sheet.

As the positive electrode active material of the positive electrode, a known positive electrode active material may be used. Hereinafter, when the non-aqueous electrolyte secondary battery is a lithium secondary battery, an electrolyte will be described. In the case of a sodium secondary battery, a cathode active material in which a lithium atom is substituted with a sodium atom is used.

Known cathode active materials in the case of lithium secondary batteries include, for example, lithium transition metal complex oxides, lithium-containing transition metal phosphate compounds, lithium-containing silicate compounds, lithium-containing transition metal sulfuric acid compounds, sulfur, and sulfur-containing compounds. have. The transition metal of the lithium transition metal composite oxide is preferably vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and the like. Specific examples of lithium transition metal complex oxides include lithium cobalt complex oxides such as LiCoO ₂ , lithium nickel complex oxides such as LiNiO ₂ , lithium manganese complex oxides such as LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ MnO ₃ , and these lithium transitions. Some of the transition metal atoms, which are the main body of the metal complex oxide, are substituted with other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, etc. Can be lifted. As a lithium transition metal complex oxide in which a part of the main transition metal atom is replaced with another metal, for example, Li _1.1 Mn _1.8 Mg _0.1 O ₄ , Li _1.1 Mn _1.85 Al _0.05 O ₄ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.80 Co _0.17 Al _0.03 O ₂ , LiNi _0.80 Co _0.15 Al _0.05 O ₂ , Li(Ni _1/3 Co _1/3 Mn _1/3 ) O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiNi _0.5 Mn _1.5 O ₄ , Li ₂ MnO ₃ -LiMO ₂ (M=Co, Ni, Mn), and the like. The transition metal of the lithium-containing transition metal phosphate compound is preferably vanadium, titanium, manganese, iron, cobalt, nickel, and the like, and specific examples include, for example, LiFePO ₄ , LiMn _x Fe _1-x PO ₄ (0 < Iron phosphate compounds such as x<1), cobalt phosphate compounds such as LiCoPO _4, and some of the transition metal atoms that are the main bodies of these lithium transition metal phosphate compounds are aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, Substituting other metals such as lithium, nickel, copper, zinc, magnesium, gallium, zirconium and niobium, and vanadium phosphate compounds such as Li ₃ V ₂ (PO ₄ ) _3, and the like. Examples of the lithium-containing silicate compound include Li ₂ FeSiO ₄ . Examples of the lithium-containing transition metal sulfuric acid compound include LiFeSO ₄ and LiFeSO ₄ F. These may be used alone or in combination of two or more.

The thermal runaway inhibitor of the present invention can be suitably used for a non-aqueous electrolyte secondary battery having a large charge/discharge capacity. Positive electrode active materials with large charge/discharge capacity include LiCoO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , LiNi _X Co _Y Mn _Z O ₂ (X+Y+) Z=1, 0≤X≤1, 0≤Y≤1, 0≤Z≤1), LiNiO ₂ , Li ₂ MnO ₃ -LiMO ₂ (M=Co, Ni, Mn) of the present invention. The thermal runaway inhibitor can be suitably used for a non-aqueous electrolyte secondary battery having these positive active materials.

As a binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR) ), styrene-isoprene copolymer, polymethylmethacrylate, polyacrylate, polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), carboxymethylcellulose sodium (CMCNa), methylcellulose (MC), starch, polyvinyl Pyrrolidone, polyethylene (PE), polypropylene (PP), polyethylene oxide (PEO), polyimide (PI), polyamideimide (PAI), polyacrylonitrile (PAN), polyvinyl chloride (PVC), poly Acrylic acid and polyurethane. The amount of the binder used is usually about 1% by mass to 20% by mass, preferably 2% by mass to 10% by mass based on the positive electrode active material.

Conductive aids include, for example, carbon black, kecheon black, acetylene black, channel black, furnace black, lamp black, thermal black, carbon nanotube, vapor grown carbon fiber (VGCF), graphene, fullerene, Carbon materials such as needle coke; Metal powders such as aluminum powder, nickel powder, and titanium powder; Conductive metal oxides such as zinc oxide and titanium oxide; Sulfides, such as La ₂ S ₃ , Sm ₂ S ₃ , Ce ₂ S ₃ , and TiS ₂ , are mentioned. The particle size of the conductive aid is preferably 0.0001 µm to 100 µm, more preferably 0.01 µm to 50 µm, as for the average particle size.

As the solvent to be slurried, an organic solvent or water that dissolves a binder is used. As an organic solvent, for example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene Oxide, tetrahydrofuran, etc. are mentioned. The amount of the solvent used is usually about 10% by mass to 400% by mass, preferably 20% by mass to 200% by mass based on the positive electrode active material.

In general, aluminum, stainless steel, nickel plated steel, or the like is used for the current collector of the positive electrode. The shape of the current collector includes a foil shape, a plate shape, a mesh shape, and the like, and a foil shape is preferable. In the case of a foil shape, the thickness of the foil is usually 1 μm to 100 μm.

In the non-aqueous electrolyte secondary battery to which the present invention is applied, the negative electrode including the negative electrode active material is an electrode in which an electrode mixture layer including the negative electrode active material is formed on a current collector, and, for example, a negative electrode active material, a binder, and a conductive aid are used in an organic solvent or What has been slurried with water is applied to a current collector, and dried to form a sheet.

As the negative active material of the negative electrode, a known negative active material may be used. Hereinafter, an electrolyte in the case where the non-aqueous electrolyte secondary battery is a lithium secondary battery will be described.In the case of a sodium secondary battery, a negative active material in which a lithium atom is substituted with a sodium atom of a negative active material having a lithium atom among the negative active materials is used.

Known negative active materials include carbonaceous materials, lithium, lithium alloy, silicon, silicon alloy, silicon oxide, tin, tin alloy, tin oxide, phosphorus, germanium, indium, copper oxide, antimony sulfide, titanium oxide, iron oxide, manganese oxide. , Cobalt Oxide, Nickel Oxide, Lead Oxide, Ruthenium Oxide, Tungsten Oxide, Zinc Oxide, and other complex oxides such as LiVO ₂ , Li ₂ VO ₄ , Li ₄ Ti ₅ O ₁₂ , conductive polymer, yellow-modified polyacrylonitrile, etc. Can be lifted. The carbonaceous material is not particularly limited, but natural graphite, artificial graphite, fullerene, graphene, graphite fiber chop, carbon nanotubes, graphite whiskers, highly oriented pyrolytic graphite, crystalline carbon such as kish graphite, non-graphitized carbon, Graphitized carbon, petroleum coke, coal-based coke, petroleum pitch carbide, coal-based pitch carbide, phenol resin, crystalline cellulose, and other resin carbides, and carbon materials obtained by partially carbonizing these, furnace black, acetylene Black, pitch-based carbon fiber, and polyacrylonitrile-based carbon fiber. On the other hand, when the positive electrode active material is yellow-modified polyacrylonitrile, a negative electrode active material other than yellow-modified polyacrylonitrile is used as the negative electrode active material.

Examples of the binder, the conductive aid, and the solvent to be slurried include the same as those of the positive electrode. The amount of the binder used is usually about 1% by mass to 30% by mass, and preferably about 2% by mass to 15% by mass based on the negative electrode active material. In addition, the amount of the solvent is usually about 10% by mass to 400% by mass, and preferably 20% by mass to 200% by mass, based on the negative electrode active material.

Usually, copper, nickel, stainless steel, nickel plated steel, aluminum, etc. are used for the current collector of the negative electrode. Examples of the shape of the current collector include a foil shape, a plate shape, and a mesh shape, and a foil shape is preferable. In the case of a foil shape, the thickness of the foil is usually 1 μm to 100 μm.

In the non-aqueous electrolyte secondary battery to which the present invention is applied, a separator is used between a positive electrode and a negative electrode, and a polymer microporous film that is usually used may be used without particular limitation. Films include, for example, polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, Polyimide, polyethers such as polyethylene oxide and polypropylene oxide, various celluloses such as carboxymethyl cellulose and hydroxypropyl cellulose, poly(meth)acrylic acid and various esters thereof, etc. And films made of these copolymers or mixtures. These films are sometimes coated with ceramic materials such as alumina and silica, magnesium oxide, aramid resin, or polyvinylidene fluoride. On the other hand, when the non-aqueous solvent electrolyte is a pure polymer electrolyte, the separator may not be included in some cases.

The nonaqueous electrolyte secondary battery to which the present invention is applied is a single battery, a stacked battery in which a positive electrode and a negative electrode are stacked in multiple layers through a separator, or a long sheet-shaped separator, and a positive electrode and a negative electrode are wound. Although it does not matter in any form, such as a single-wound battery, since the battery has a high charge/discharge capacity and thermal runaway due to an internal short circuit is likely to occur, the present invention is preferably applied to a stacked nonaqueous electrolyte secondary battery or a wound nonaqueous electrolyte secondary battery. Do.

Example

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention. On the other hand, "parts" and "%" in Examples are by mass unless otherwise noted.

[Preparation of non-aqueous electrolyte A]

LiPF ₆ was dissolved in a mixed solvent comprising 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate to a concentration of 1.0 mol/L to obtain a non-aqueous electrolyte A.

〔Preparation of non-aqueous electrolytes B~E〕

Non-aqueous electrolytes B to G were obtained by dissolving the additives shown in Table 1 in the non-aqueous electrolyte A so that the concentrations described were.

[Production of anode 1]

90.0 parts by mass of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ as a positive electrode active material (manufactured by Nippon Chemical Industry Co., Ltd., brand name: NCM111), 5.0 parts by mass of acetylene black (manufactured by Denki Chemical Co., Ltd.) , 5.0 parts by mass of polyvinylidene fluoride (Kureha product) as a binder was mixed with 90 parts by mass of N-methylpyrrolidone, and dispersed using a rotating/revolution mixer to prepare a slurry. This slurry composition was continuously applied to both surfaces of a roll-shaped aluminum foil (20 µm in thickness) current collector by a comma coater method, and dried at 90°C for 3 hours. This roll was cut into 50 mm long and 90 mm wide, and the electrode mixture layer on one side of the horizontal side (short side) was removed 10 mm from the end, and the current collector was exposed, followed by vacuum at 150°C for 2 hours. Drying was performed, and the positive electrode 1 was produced.

[Production of anode 2]

In the same procedure as in the preparation of positive electrode 1, except that Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ was used instead of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ as the positive electrode active material, Li(Ni A positive electrode 2 was prepared using _0.8 Co _0.15 Al _0.05 ) O ₂ as a positive electrode active material.

[Manufacture of cathode 1]

92.0 parts by mass of lump-shaped artificial graphite as an electrode active material, 3.5 parts by mass of acetylene black (manufactured by Denki Chemical Industries) and 1.5 parts by mass of carbon nanotubes (VGCF: manufactured by Showa Denko) as a conductive aid, and 1.5 parts by mass of styrene as a binder Butadiene rubber (aqueous dispersion, manufactured by Nippon Xeon) and 1.5 parts by mass of sodium carboxymethylcellulose (manufactured by Daiseru Fine Chemical) were mixed with 100 parts by mass of water, and dispersed using a rotating/revolution mixer to prepare a slurry. This slurry composition was continuously applied to both surfaces of a roll-shaped copper foil (10 µm thick) current collector by a comma coater method, and dried at 90°C for 3 hours. This roll was cut into 55 mm long and 95 mm wide, and 10 mm of the electrode mixture layer on either side of the horizontal side (short side) was removed from the end, and the current collector was exposed, followed by vacuum drying at 150°C for 2 hours. Then, the cathode 1 was produced.

[Production of cathode 2]

A negative electrode 2 was produced by the same procedure as that of the negative electrode 1 except that 87.0 parts by mass of agglomerated artificial graphite and 5.0 parts by mass of silicon oxide (average particle diameter 5 µm) were used instead of 92.0 parts by mass of agglomerated artificial graphite as an electrode active material.

[Production of laminated laminate battery]

The positive electrode and the negative electrode were stacked through a separator (Cellgard Corporation product, brand name: Celgard 2325) so as to have the battery capacity shown in Table 2, and positive and negative terminals were provided on the positive and negative electrodes, respectively, to obtain a laminate. The obtained laminate and the non-aqueous electrolytes A to G were accommodated in a flexible film to obtain a laminated laminate battery of Examples 1 to 8 and Comparative Examples 1 to 6.

[Charging method]

In a 30° C. constant temperature bath, the charging end voltage was set to 4.2 V and the discharge end voltage was set to 2.75 V, charging and discharging was performed once at a charge rate of 0.1 C and a discharge rate of 0.1 C, and gas removal treatment was performed. Further, charging and discharging cycles under the same conditions were performed 5 times, and after charging to 4.2 V at a charging rate of 0.1 C, it was used for a test.

〔Method of nailing test〕

The battery was fixed on a phenolic resin plate with a hole having a diameter of 10 mm, and an iron nail having a diameter of 3 mm and a length of 65 mm was pierced perpendicularly to the surface of the battery at a speed of 1 mm/s in the center of the hole. After passing through 10 mm and holding for 10 minutes, the nail was pulled out. Table 3 shows the surface temperature (°C) of the battery immediately before nailing to the battery, 30 seconds after nailing, and 5 minutes after nailing. On the other hand, as for the surface temperature of the battery, the temperature of the battery surface 10 mm away from the nailing portion was measured using a thermocouple.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that does not increase in size or significantly increases cost, has a small size, is light weight, has a high capacity, is unlikely to cause thermal runaway even when an internal short circuit occurs, and does not have a risk of ignition or rupture.

1: positive electrode 1a: positive electrode current collector
2: negative electrode 2a: negative electrode current collector
3: non-aqueous electrolyte 4: anode case
5: cathode case 6: gasket
7: separator 10: coin-type non-aqueous electrolyte secondary battery
10': cylindrical non-aqueous electrolyte secondary battery 11: negative electrode
12: negative electrode current collector 13: positive electrode
14: positive electrode current collector 15: non-aqueous electrolyte
16: separator 17: positive terminal
18: negative terminal 19: negative plate
20: negative lead 21: positive plate
22: positive lead 23: case
24: insulation plate 25: gasket
26: safety valve 27: PTC element

Claims (6)

A thermal runaway inhibitor made of a silyl ester compound due to an internal short circuit for a nonaqueous electrolyte secondary battery having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a nonaqueous electrolyte. The method of claim 1,
The thermal runaway inhibitor, wherein the silyl ester compound is a carboxylic acid silyl ester compound represented by the following general formula (1).

(In the formula, R ¹ to R ³ each independently represent a hydrocarbon group having 1 to 6 carbon atoms, and X ¹ is an a-valent hydrocarbon group having 1 to 10 carbon atoms, or a methylene group in the hydrocarbon group substituted with an oxygen atom or a sulfur atom. Represents a valent group having 1 to 10 carbon atoms, and a represents the number of 1 to 4.) A method for suppressing thermal runaway due to internal short circuit of a nonaqueous electrolyte secondary battery, wherein 0.01% by mass to 10% by mass of the thermal runaway inhibitor according to claim 1 or 2 is blended in a nonaqueous electrolyte. The method of claim 3,
A method for suppressing thermal runaway due to an internal short circuit, wherein the non-aqueous electrolyte is a non-aqueous electrolyte using an organic solvent as a solvent. The method according to claim 3 or 4,
A method for suppressing thermal runaway due to an internal short circuit, wherein the non-aqueous electrolyte further contains a phenylsilane compound represented by the following general formula (2).

(In the formula, R ⁴ to R ⁵ each independently represent a hydrocarbon group having 1 to 6 carbon atoms, R ⁶ to R ¹⁰ each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms, and X ² is b represents a valent hydrocarbon group, and b represents the number of 1 to 3.) The method according to any one of claims 3 to 5,
The positive electrode active material is at least one selected from the group consisting of a lithium transition metal composite oxide, a lithium-containing transition metal phosphate compound, and a lithium-containing silicate compound.

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