JP6592228B2 - Overcharge prevention agent, electrolytic solution containing the same, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an overcharge inhibitor used in a non-aqueous secondary battery, and more particularly to an overcharge inhibitor that exhibits a current interruption effect in an overcharged state, an electrolyte containing the same, and a lithium ion secondary battery.

  A battery such as a lithium ion secondary battery is used as a power source for a mobile phone, a personal computer, a power source for an automobile, and the like. Moreover, in the battery used for such a use, research aiming at improvement of various characteristics, such as ensuring safety | security and improvement of cycling characteristics, is repeated.

  As a technology to improve the safety of the battery, a film (resistive film) is formed on the electrode by electrolytic polymerization of the compound (overcharge inhibitor) added to the electrolyte, and the battery temperature rises due to heat generation during overcharge or the battery There is a technology to suppress swelling. For example, Patent Document 1 discloses a technique in which cyclohexylbenzene, biphenyl and fluorobenzene having different oxidative decomposition potentials are used in specific amounts as an overcharge inhibitor, and Patent Document 2 discloses an overcharge inhibitor. A technique using a compound having a polymerizable functional group is disclosed.

JP 2006-261559 A JP 2012-48873 A

  However, when a film is formed on the electrode by a polymerization reaction, polymerization heat is generated. The heat generated inside the battery may cause thermal decomposition of the battery components and further thermal runaway of the battery. In addition, since the conventional overcharge inhibitor polymerizes at a voltage close to the rated charge voltage, there is a demerit that the polymerization reaction proceeds slightly even when used below the rated charge voltage, leading to a decrease in battery performance due to an increase in resistance.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is to provide a technology that can further improve the safety of a battery during overcharge by itself or in combination with an existing technology. There is to do.

The overcharge inhibitor of the present invention that has achieved the above object is an overcharge inhibitor having a current interruption effect, and is characterized in that it contains a compound represented by the following general formula (1).
(XSO ₂ ) (FSO ₂ ) NLi (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.)
The overcharge preventing agent preferably contains 500 ppm or less of water. In addition, "ppm" represents mass parts per million and indicates a mass ratio of moisture contained in the compound represented by the general formula (1). The same applies below.

  Moreover, the electrolytic solution of the present invention is characterized in that it contains an overcharge inhibitor containing the compound represented by the general formula (1). The compound represented by the general formula (1) preferably contains 500 ppm or less of water. Moreover, in the electrolyte solution of this invention, it is preferable that content of the compound represented by the said General formula (1) is 0.35 mol / L or more.

  The present invention also includes a lithium ion secondary battery including the overcharge inhibitor and a lithium ion secondary battery including the electrolytic solution.

  The overcharge preventive agent of the present invention functions as an electrolyte salt during normal use, but during overcharge, the overcharge preventive agent is decomposed by the charging current, so that the increase in voltage can be stagnated. . And when the decomposition of the overcharge inhibitor further proceeds, a current interruption effect is exhibited. In addition, the overcharge inhibitor of the present invention does not generate significant heat until the battery is overcharged and exhibits a current interruption effect. Furthermore, when using the overcharge preventive agent of the present invention in contrast to the conventional overcharge preventive agent that may increase the resistance of the battery even if it is used below the rated charge voltage and may deteriorate the battery performance. Such problems are unlikely to occur, and in addition, the overcharge inhibitor of the present invention can improve battery characteristics such as cycle life characteristics and discharge rate characteristics as the addition amount increases. Therefore, according to the overcharge preventing agent of the present invention, a battery having good battery characteristics and further improved safety during overcharge is expected.

FIG. 1 is a diagram showing the results of the overcharge test 1 of Experimental Example 1. FIG. 2 is an enlarged view of the region of the cell voltage 4.0V to 6.0V in FIG. FIG. 3 is a diagram showing the result of the overcharge test of Experimental Example 1 (up to more than 300 minutes). FIG. 4 is a diagram illustrating the relationship between the charging time, the battery voltage, and the battery surface temperature during the overcharge test in Experimental Example 1. FIG. 5 is a diagram showing the results of the overcharge test 2 of Experimental Example 4.

1. Overcharge inhibitor The overcharge inhibitor of the present invention is characterized in that it contains a compound represented by the following general formula (1) (hereinafter sometimes referred to as compound (1)).
(XSO ₂ ) (FSO ₂ ) NLi (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.)
The inventors have surprisingly studied that the function and safety of an electricity storage device such as a lithium ion secondary battery are improved, and surprisingly, the compound represented by the general formula (1) used as an electrolyte salt Was found to have a current interruption effect in an overcharged state, and the present invention was completed.

  Compound (1) decomposes when a certain voltage is exceeded. And the decomposition product produced | generated at this time reacts with a positive electrode, a passive film is formed in the positive electrode surface, and a battery becomes a resistor by this and an electric current is interrupted | blocked. In addition, since the compound (1) is preferentially decomposed after the start of the decomposition of the compound (1), the decomposition of the solvent contained in the electrolytic solution is suppressed. Therefore, when the battery includes the overcharge preventing agent of the present invention, even when the battery is overcharged, generation of gas due to decomposition of the solvent, and expansion and rupture of the battery are suppressed.

  The conventional overcharge inhibitor polymerizes near the current rated charge voltage (4.4 V), and the battery becomes a resistor. Therefore, a polymer is generated even in a normal use state, and the battery resistance is increased, so that the battery performance is gradually deteriorated. On the other hand, the overcharge inhibitor of the present invention has a high decomposition voltage and is superior to conventional overcharge inhibitors in that the rated charge voltage is less likely to cause deterioration in battery performance due to the formation of a polymer. . In addition, the overcharge inhibitor of the present invention is superior to conventional overcharge additives that generate heat during decomposition and polymerization in that no heat is generated during decomposition or film formation. Furthermore, if the overcharge inhibitor of the present invention is combined with other known safety mechanisms for battery members, the safety of the battery can be further enhanced.

  The usage method of the overcharge inhibitor of this invention is not specifically limited. For example, what is necessary is just to use it, making it melt | dissolve or disperse | distribute to a solvent with the component which comprises electrolyte solutions, such as electrolyte salt and an additive.

1-1. Compound (1)
The current interruption effect according to the present invention is derived from the compound represented by the general formula (1). In General Formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group. The alkyl group having 1 to 6 carbon atoms is preferably a linear or branched alkyl group. Examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, and a hexyl group. Examples of the fluoroalkyl group having 1 to 6 carbon atoms include those in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. Examples thereof include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, and a pentafluoroethyl group. As the substituent X, a fluorine atom, a trifluoromethyl group, and a pentafluoroethyl group are preferable. Specific compounds (1) include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (methylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoro Ethylsulfonyl) imide, lithium (fluorosulfonyl) (ethylsulfonyl) imide, and more preferably lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (penta Fluoroethylsulfonyl) imide, more preferably lithium bis (fluorosulfonyl) imide.

  As the compound (1), one type may be used alone, or two or more types may be used in combination. Compound (1) may be a commercially available product or a product synthesized by a conventionally known method.

  The compound (1) preferably contains 500 ppm or less of water. When the compound (1) contains a large amount of moisture, the compound (1) is likely to be decomposed and may not function properly as an overcharge inhibitor. Therefore, the water content in the compound (1) is more preferably 300 ppm or less, and still more preferably 100 ppm or less. The lower limit of the water content in the compound (1) is most preferably 0 ppm, but if the lower limit of the water content is about 1 ppm, and further about 10 ppm, problems such as decomposition of the compound (1) can be suppressed. . The amount of water in compound (1) can be measured by a measuring method using a Karl Fischer moisture meter.

  The amount of compound (1) contained in the overcharge inhibitor of the present invention is not particularly limited. In addition, when the other component mentioned later is contained in an overcharge inhibitor, from the viewpoint of obtaining a higher overcharge prevention effect, the amount of the compound (1) is determined from the overcharge inhibitor (compound (1) and other components). The total of the components) is preferably 10 parts by mass or more with respect to 100 parts by mass, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, and 99.99 parts by mass or less. More preferably, it is 99.90 mass parts or less, More preferably, it is 99.00 mass parts or less. As the amount of compound (1) increases, the battery characteristics (cycle life characteristics, discharge rate performance) tend to improve. Although the compound (1) functions as an electrolyte salt when used within the rated charging voltage, if the amount of the compound (1) is too large, the viscosity of the electrolytic solution increases, the ionic conductivity decreases, and the discharge load characteristics. On the other hand, if the amount is too small, it may be difficult to obtain the effect derived from the compound (1).

1-2. Other Components The overcharge inhibitor of the present invention may contain components (other components) other than the compound (1).

  Examples of the overcharge inhibitor that can be used as other components include cyclohexylbenzene, isopropylbenzene, t-butylbenzene, octylbenzene, toluene, xylene, fluorobenzene, difluorobenzene, trifluorobenzene, chlorobenzene, anisole, fluoroanisole, Examples include dimethoxybenzene, diethoxybenzene, dibutyl terephthalate, di-2-ethylhexyl phthalate, methylphenyl carbonate, butylphenyl carbonate, diphenyl carbonate, phenyl propionate, and biphenyl.

  When the overcharge inhibitor of the present invention contains other components, the content thereof is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass with respect to 100 parts by mass of the compound (1). Part or more, more preferably 1 part by weight or more, preferably 90 parts by weight or less, more preferably 85 parts by weight or less, and still more preferably 80 parts by weight or less.

  The overcharge inhibitor of the present invention preferably has a moisture content of 500 ppm or less. When the overcharge inhibitor contains a large amount of moisture, the compound (1) is likely to be decomposed and may not function properly as an overcharge inhibitor. Therefore, the amount of water in the overcharge inhibitor is more preferably 300 ppm or less, and even more preferably 100 ppm or less. The lower limit of the amount of water in the overcharge inhibitor is most preferably 0 ppm, but if the lower limit of the amount of water is about 1 ppm, and further about 10 ppm, problems such as decomposition of the compound (1) can be suppressed. . The amount of water in the overcharge inhibitor can be measured by a measuring method using a Karl Fischer moisture meter.

2. Electrolytic Solution The electrolytic solution of the present invention is characterized in that it contains an overcharge inhibitor containing a compound represented by the following general formula (1).

(XSO ₂ ) (FSO ₂ ) NLi (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.)
The other configuration of the electrolytic solution of the present invention is not particularly limited as long as it contains the overcharge preventing agent of the present invention, and can have the same configuration as the electrolytic solution provided in a known power storage device. Therefore, in addition to the overcharge inhibitor, the electrolyte solution of the present invention may contain an electrolyte salt, a solvent, and an additive as necessary. Hereinafter, the electrolytic solution of the present invention will be described.

2-1. Overcharge inhibitor The electrolytic solution of the present invention contains an overcharge inhibitor containing the compound (1). Any overcharge inhibitor may be used as long as it contains the compound (1), but the above-described overcharge inhibitor of the present invention is preferably used.

  The overcharge inhibitor is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, based on 100 parts by mass of the electrolytic solution (total of electrolyte salt, solvent and other optional components). The amount is preferably 9 parts by weight or more, preferably 28 parts by weight or less, more preferably 26 parts by weight or less, and still more preferably 24 parts by weight or less. When the amount of the overcharge inhibitor is too large, the increase in the viscosity of the electrolyte concentration becomes remarkable, the ionic conductivity is lowered, and the battery performance (discharge load characteristics and the like) may be lowered. On the other hand, when the overcharge inhibitor concentration is too low, it may be difficult to obtain an overcharge prevention effect.

  In addition, from the viewpoint of more effectively exerting the effect derived from the compound (1), the concentration of the compound (1) contained in the electrolytic solution is in a range of 0.35 mol / L or more and 1.5 mol / L or less. It is preferable to use an overcharge inhibitor (more preferably 0.4 mol / L to 1.4 mol / L, still more preferably 0.5 mol / L to 1.3 mol / L). If the concentration of the compound (1) is too high, the viscosity of the electrolytic solution may increase and the ionic conductivity may decrease. On the other hand, if the concentration of the compound (1) is too low, the effect derived from the compound (1). May be difficult to obtain.

2-2. Electrolyte Salt The electrolyte salt contained in the electrolyte solution of the present invention is not particularly limited, and any electrolyte salt used in a conventionally known non-aqueous electrolyte solution can be used. As the electrolyte salt, those having a large dissociation constant in the electrolytic solution and having an anion that is difficult to solvate with a non-aqueous solvent described later are preferable. Specific examples of the electrolyte salt include alkali metal salts and alkaline earth metal salts of trifluoromethanesulfonic acid such as LiCF ₃ SO ₃ , NaCF ₃ SO ₃ , and KCF ₃ SO ₃ ; LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ perfluoroalkanesulfonic acid imide or fluorosulfonylimide alkali metal salt or alkaline earth metal salt; LiPF ₆ , NaPF ₆ , alkali metal salt of hexafluorophosphoric acid such as KPF ₆ And alkaline earth metal salts; alkali metal perchlorates such as LiClO ₄ and NaClO ₄ and alkaline earth metal salts; tetrafluoroborate such as LiBF ₄ and NaBF ₄ ; lithium tetracyanoborate, lithium tricyanomethoxyborate, Sodium tricyanomethoxyborate, magnesium bis (tricyanomethoxyborate ), Lithium tricyanoisopropoxyborate, lithium tricyanobutoxyborate, lithium tricyanophenoxyborate, lithium tricyano (pentafluorophenoxy) borate, lithium tricyano (trimethylsiloxy) borate, lithium tricyano (hexafluoroisopropoxy) borate , lithium tricyanomethylphosphine thio borate, lithium dicyano-dimethoxy-borate, alkali metal salts of cyanoborohydride acids such as lithium cyano trimethoxy _{borate; LiAsF 6, LiI, LiSbF 6} , LiAlO 4, LiAlCl 4, LiCl, NaI, NaAsF 6, the KI or the like quaternary ammonium salts of perchloric acid such as tetraethylammonium perchlorate; alkali metal salt _{(C 2 H 5) 4 NBF} 4, (C 2 H 5) 3 (CH 3) Quaternary ammonium salts of tetrafluoroborate of BF ₄ and the like; tetraethylammonium tetracyanoborate, 1-ethyl-3-methylimidazolium tetracyanoborate, Triethylmethylammonium Tetracyanoborate, tetraethylammonium tetracyanoborate, tetraethylammonium tricyanobenzene Methoxyborate, triethylmethylammonium tricyanomethoxyborate, triethylmethylammonium tricyanoisopropoxyborate, triethylmethylammonium tricyanobutoxyborate, triethylmethylammonium tricyanophenoxyborate, triethylmethylammonium tricyano (pentafluorophenoxy) borate, triethylmethyl Ammonium tricyano (trimethylshiro Xy) borate, triethylmethylammonium tricyanomethylthioborate, triethylmethylammonium tricyano (hexafluoroisopropoxy) borate, 1-ethyl-3-methylimidazolium tricyanomethoxyborate, triethylammonium tricyanomethoxyborate, tributylammonium tricyano Ammonium salts of cyanoboric acid such as methoxyborate, triethylmethylammonium dicyanodimethoxyborate, triethylmethylammonium cyanotrimethoxyborate; quaternary ammonium salts such as (C ₂ H ₅ ) ₄ NPF ₆ ; (CH ₃ ) ₄ P · BF ₄ , quaternary phosphonium salts such as (C ₂ H ₅ ) ₄ P · BF ₄ . These electrolyte salts may be used individually by 1 type, and may be used in combination of 2 or more type.

Among the electrolyte salts, alkali metal salts and / or alkaline earth metal salts are preferable. As the alkali metal salt, a lithium salt, a sodium salt, and a potassium salt are preferable, and as the alkaline earth metal salt, a calcium salt and a magnesium salt are preferable. More preferred is a lithium salt. From the viewpoint of solubility in a non-aqueous solvent and ion conductivity, LiPF ₆ , LiBF ₄ , and LiAsF ₆ are preferable.

  The concentration of the electrolyte salt in the electrolytic solution of the present invention is preferably 0.5 mol / L or more, more preferably 0.8 mol / L or more, and further preferably 1.0 mol / L or more. It is preferably 0 mol / L or less, more preferably 1.8 mol / L or less, and still more preferably 1.5 mol / L or less. If the electrolyte salt concentration is too low, it may be difficult to obtain a desired conductivity. On the other hand, if the electrolyte salt concentration is too high, ion migration may be inhibited.

  In addition, before it will be in an overcharge state, the said compound (1) will also work as electrolyte salt. Therefore, in this invention, it is preferable that the sum total of the density | concentration of a compound (1) and electrolyte salt shall be the said density | concentration range.

  The amount of the electrolyte salt used relative to the compound (1) is preferably 17.5 mol% to 95 mol%, more preferably 25 mol%, based on 100 mol% of the total of the compound (1) and the total electrolyte salt. It is -90 mol%, More preferably, it is 30 mol%-90 mol%.

2-3. Solvent The solvent that can be used in the electrolytic solution of the present invention is not particularly limited as long as it can dissolve and disperse the electrolyte salt and the overcharge inhibitor, and a non-aqueous solvent, a polymer used in place of the solvent, a polymer Any conventionally known solvent used for batteries, such as a medium such as gel, can be used.

  As the non-aqueous solvent, a solvent having a large dielectric constant, high solubility of the electrolyte salt, a boiling point of 60 ° C. or higher, and a wide electrochemical stability range is preferable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. Examples of such organic solvents include ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, Ethers such as tetraethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane; dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate, etc. Chain carbonates of ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate, butyrate , Cyclic carbonates such as vinylene carbonate and 2-vinylethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, propionic acid, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; Aromatic carboxylic acid esters such as methyl acid and ethyl benzoate; Lactones such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, triethyl phosphate Phosphoric acid esters such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, nitriles such as 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutyronitrile; N-methylformamide, N-ethylformua Amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-vinylpyrrolidone; dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4 -Sulfur compounds such as dimethylsulfolane: alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide, diethyl sulfoxide; benzonitrile, tolunitrile, etc. Aromatic nitriles; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3-methyl And ru-2-oxazolidinone.

  Among these, chain carbonic acid esters, cyclic carbonic acid esters, aliphatic carboxylic acid esters, lactones, ethers are preferable, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone and the like are more preferable. The said non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the polymer used as a solvent include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, which are homopolymers or copolymers of epoxy compounds (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.) Methacrylic polymers such as methyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluorinated polymers such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof Is mentioned. In addition, a polymer gel obtained by mixing these polymers with another organic solvent can also be used as the solvent (medium) according to the present invention. Examples of the other organic solvent include the non-aqueous solvents described above.

  When the polymer gel is used as a solvent, a solution in which an electrolyte salt is dissolved in the above-mentioned non-aqueous solvent is dropped onto a polymer film formed by a conventionally known method to impregnate and carry the electrolyte salt and the non-aqueous solvent. Method: A method in which a polymer and an electrolyte salt are melted and mixed at a temperature equal to or higher than the melting point of the polymer, and then formed into a film and impregnated with a non-aqueous solvent (the gel electrolyte); the electrolyte salt is dissolved in an organic solvent in advance. After mixing the electrolyte solution and the polymer, this is formed by casting or coating, and the organic solvent is volatilized; the polymer and electrolyte salt are melted at a temperature above the melting point of the polymer, mixed and molded. (Intrinsic polymer electrolyte);

2-4. Other Components The electrolytic solution of the present invention may contain an additive for the purpose of improving various characteristics of the battery.

  As additives, cyclic carbonates having unsaturated bonds such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC); fluoroethylene carbonate, trifluoropropylene carbonate, Carbonate compounds such as phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetra Carboxylic anhydrides such as carboxylic dianhydride and phenyl succinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methane sulfone Sulfur-containing compounds such as methyl, busulfan, sulfolane, sulfolene, dimethylsulfone, tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3- Nitrogen-containing compounds such as dimethyl-2-imidazolidinone and N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; saturated hydrocarbon compounds such as heptane, octane and cycloheptane; It is done.

  The additive is preferably used in the range of 0.1% by mass to 10% by mass in the electrolytic solution of the present invention (more preferably 0.2% by mass to 8% by mass, and still more preferably 0.3%. Mass% to 5 mass%). When the amount of the additive used is too small, it may be difficult to obtain an effect derived from the additive.On the other hand, even if another additive is used in a large amount, it is difficult to obtain an effect commensurate with the added amount. There is a possibility that the viscosity of the electrolytic solution increases and the conductivity decreases.

3. Lithium ion secondary battery The lithium ion secondary battery of the present invention includes a positive electrode and a negative electrode, and includes the electrolytic solution of the present invention (preferably, an electrolytic solution containing the overcharge inhibitor of the present invention) as an electrolytic solution. It has the characteristics in the place. More specifically, a separator is provided between the positive electrode and the negative electrode, and the electrolytic solution of the present invention is contained in an outer case together with the positive electrode, the negative electrode, and the like in a state of being impregnated in the separator.

  The shape of the lithium ion secondary battery according to the present invention is not particularly limited, and any conventionally known shape can be used as the shape of the lithium secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. it can. Further, when used as a high voltage power source (several tens of volts to several hundreds of volts) for mounting on an electric vehicle, a hybrid electric vehicle, etc., a battery module configured by connecting individual batteries in series can be used. .

3-1. Positive electrode The positive electrode is one in which a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder and the like is carried on a positive electrode current collector, and is usually formed into a sheet shape.

  As a method for producing the positive electrode, for example, a positive electrode active material composition in which a positive electrode mixture is dissolved or dispersed in a dispersion solvent is applied to the positive electrode current collector by a doctor blade method or the like. A method of drying after dipping in a material composition; a method of bonding a sheet obtained by kneading, molding and drying a positive electrode active material composition to a positive electrode current collector through a conductive adhesive, pressing and drying; A method in which a positive electrode active material composition to which a lubricant is added is applied or cast onto a positive electrode current collector and formed into a desired shape, then the liquid lubricant is removed, and then the film is stretched in a uniaxial or multiaxial direction. And the like.

3-1-1. Positive electrode current collector The material of the positive electrode current collector is not particularly limited, and for example, conductive metals such as aluminum, aluminum alloys, and titanium can be used. Among these, aluminum is preferable because it is easy to process into a thin film and is inexpensive.

3-1-2. Positive electrode active material As the positive electrode active material, any known positive electrode active material used in lithium ion secondary batteries may be used as long as it can occlude and release lithium ions.

Specifically, lithium cobalt acid, lithium nickel acid, LiNi _0.5 Mn _1.5 O ₄ lithium manganate, partially in LiMn ₂ O ₄ system was replaced by _{Ni, LiNi 1-xy Co x} Mn y O 2 or LiNi _{1 -xy Co x Al y O 2 (} 0 <x <1,0 <y <1,0 <x + y <1) a transition metal oxide such as ternary oxide represented by, LiAPO ₄ (a = Fe, Compounds having an olivine structure such as Mn, Ni, Co), solid solution materials incorporating a plurality of transition metals (electrochemically inactive layered Li ₂ MnO _3, and electrochemically active layered LiMO [M = Solid solution with transition metals such as Co and Ni] can be exemplified as the positive electrode active material. These positive electrode active materials may be used individually by 1 type, or may be used in combination of multiple.

  The amount of the positive electrode active material used is preferably 75 parts by mass to 99 parts by mass with respect to 100 parts by mass of the positive electrode mixture, and more preferably 85 parts by mass to 97 parts by mass.

3-1-3. Conductive aid The conductive aid is used to increase the output of the lithium ion secondary battery, and conductive carbon is mainly used as the conductive aid. Examples of the conductive carbon include acetylene black, carbon black, graphite, fullerene, metal powder material, single-walled carbon nanotube, multi-walled carbon nanotube, and vapor grown carbon fiber.

  In the case of using a conductive additive, the content of the conductive additive in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more preferably Preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 10% by mass). If the amount of the conductive assistant is too small, the conductivity is extremely deteriorated and the load characteristics and the discharge capacity may be deteriorated. On the other hand, if the amount is too large, the bulk density of the positive electrode mixture layer is increased, and it is necessary to further increase the binder content.

3-1-4. Binders As binders, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber, nitrile butadiene rubber, methyl methacrylate butadiene rubber and chloroprene rubber; polyamides such as polyamideimide Polyolefin resins such as polyethylene and polypropylene; Poly (meth) acrylic resins such as polyacrylamide and polymethylmethacrylate; Polyacrylic acid; Cellulose resins such as methylcellulose, ethylcellulose, triethylcellulose, carboxymethylcellulose, and aminoethylcellulose; And vinyl alcohol resins such as ethylene vinyl alcohol and polyvinyl alcohol. These binders may be used alone or in combination of two or more. Moreover, at the time of manufacture of the positive electrode, these binders may be dissolved in a solvent or dispersed in a solvent.

  When the binder is used, the content of the binder in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more preferably, 0.1% by mass). 5 mass% to 10 mass%, more preferably 1 mass% to 10 mass%). If the amount of the binder is too small, good adhesion cannot be obtained, and the positive electrode active material and the conductive additive may be detached from the current collector. On the other hand, if the amount is too large, the internal resistance may be increased, and the battery characteristics may be adversely affected.

  The blending amounts of the conductive assistant and the binder can be appropriately adjusted in consideration of the intended use of the battery (emphasis on output, importance on energy, etc.), ion conductivity, and the like.

  Solvents used in the positive electrode active material composition when producing the positive electrode include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carbons Examples include acid esters, phosphate esters, ethers, nitriles, and water. For example, N-methylpyrrolidone, hexamethylphosphate triamide, dimethyl sulfoxide, dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, methyl ethyl ketone, tetrahydrofuran , Acetone, ethanol, ethyl acetate and the like. These solvents may be used in combination. The amount of the solvent used is not particularly limited, and may be appropriately determined according to the production method and the material to be used.

3-2. Negative electrode The negative electrode is formed by supporting a negative electrode active material, a binder, and, if necessary, a negative electrode mixture containing a conductive auxiliary agent on a negative electrode current collector, and is usually formed into a sheet shape.

  As a manufacturing method of the negative electrode, a method similar to the manufacturing method of the positive electrode can be employed. In addition, the same conductive auxiliary agent, binder, and material dispersing solvent as used in the positive electrode are used in the production of the negative electrode.

3-2-1. Negative Electrode Current Collector As a material for the negative electrode current collector, a conductive metal such as copper, iron, nickel, silver, and stainless steel (SUS) can be used. From the viewpoint of easy processing into a thin film, copper is preferable.

3-2-2. Negative electrode active material As the negative electrode active material, a conventionally known negative electrode active material used in lithium ion secondary batteries can be used as long as it can occlude and release lithium ions. Specifically, graphite materials such as artificial graphite and natural graphite, mesophase fired bodies made from coal and petroleum pitch, carbon materials such as non-graphitizable carbon, Si-based negative electrode materials such as Si, Si alloy, and SiO, Sn An Sn-based negative electrode material such as an alloy, or a lithium alloy such as lithium metal or a lithium-aluminum alloy can be used.

  The amount of the negative electrode active material used is preferably 80 parts by mass to 99 parts by mass, and more preferably 90 parts by mass to 99 parts by mass with respect to 100 parts by mass of the negative electrode mixture.

3-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. The separator is not particularly limited, and any conventionally known separator can be used in the present invention. Specific examples of the separator include a porous sheet made of a polymer that absorbs and retains a nonaqueous electrolytic solution (for example, a polyolefin-based microporous separator or a cellulose-based separator), a nonwoven fabric separator, a porous metal body, and the like. It is done. Among these, a polyolefin-based microporous separator is preferable because it has a property of being chemically stable to an organic solvent.

  Examples of the material for the porous sheet include polyethylene, polypropylene, and a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene.

  Examples of the material for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, and the like. Or in combination of two or more.

3-4. Battery Exterior Material A battery element including a positive electrode, a negative electrode, a separator, an electrolytic solution, and the like is accommodated in a battery exterior material in order to protect the battery element from external impact, environmental degradation, and the like when using a lithium ion secondary battery. In the present invention, the material of the battery exterior material is not particularly limited, and any conventionally known exterior material can be used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

1. Preparation of Electrolyte Solution In a nonaqueous solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at 3: 7 (volume ratio), lithium hexafluorophosphate ( LiPF ₆ , manufactured by Kishida Chemical Co., Ltd., electrolyte salt) and / or lithium bis (fluorosulfonyl) imide (LiFSI, manufactured by Nippon Shokubai Co., Ltd., overcharge inhibitor / electrolyte salt, water content 120 ppm) are dissolved in the electrolyte solution. 1-6 were prepared.

  For comparison, the electrolyte 7 has the same composition as the electrolyte 3 except that the overcharge inhibitor is biphenyl (BP, 3% by mass in the electrolyte) and the water content of LiFSI is 600 ppm. Electrolytic solution 3 ′ was prepared.

2. Manufacture of Laminate Type Lithium Ion Secondary Battery 1 A positive electrode active material (lithium cobaltate), a conductive additive (acetylene black) and a binder (polyvinylidene fluoride, PVdF) are mixed in a mass ratio of 92: 4: 4. The positive electrode mixture slurry dispersed in (N-methylpyrrolidone) was coated on an aluminum foil (positive electrode current collector) and dried to prepare a positive electrode sheet.

  A negative electrode active material (spherical processed natural graphite), a conductive additive (carbon black), and a binder (a mixture of 1.2 parts by mass of styrene-butadiene rubber and 2.0 parts by mass of carboxymethyl cellulose) were 96.3 / 0.5. The negative electrode mixture slurry mixed at a mass ratio of /3.2 was coated on a copper foil (negative electrode current collector) and dried to prepare a negative electrode sheet.

  The positive electrode sheet, polyethylene separator (thickness 20 mm) and negative electrode sheet were laminated in this order. At this time, it laminated | stacked so that a positive electrode and a negative electrode active material layer might oppose. Next, this laminate is sandwiched between two aluminum laminate films (a three-layer structure of polyethylene resin layer / aluminum layer / polyethylene resin layer), and the periphery is thermally welded in a bag shape with a heater at 165 ° C. After filling the inside with each electrolyte solution placed, it was sealed in a vacuum state.

  Using a charge / discharge test apparatus (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the battery was charged and discharged once at a charge / discharge rate of 0.2 C (constant current mode) at 3.5 to 4.2 V, and then the battery Was opened and sealed again in a vacuum state. Under the same conditions, charging / discharging was repeated 5 times to produce a laminated lithium ion secondary battery 1 (length 50 mm, width 40 mm, thickness 1 mm).

3. Production of Laminate Type Lithium Ion Secondary Battery 2 Lithium iron phosphate (LiFePO ₄ ) as a positive electrode active material, acetylene black and graphite as a conductive assistant, and polyvinylidene fluoride (PVdF) as a binder 89: 3: 3: 5 The positive electrode mixture slurry mixed at a mass ratio of (= LiFePO ₄ : acetylene black: graphite: PVdF) and dispersed in a solvent (N-methylpyrrolidone) was applied onto an aluminum foil (positive electrode current collector) and dried. Thus, a positive electrode sheet was produced.

  A laminate type lithium ion battery 2 was prepared in the same manner as the laminate type lithium ion secondary battery 1 except that the obtained positive electrode sheet was used. In addition, the electrolyte solutions 1 and 6 were used as electrolyte solution.

4). Battery Evaluation Experimental Example 1: Overcharge test 1
A change in voltage and a change in battery surface temperature were observed when each of the laminated lithium ion secondary batteries 1 was charged to an overcharged state.

  As a test method, a constant current / constant voltage power source (“PMC-35-2A”, manufactured by Kikusui Electronics Co., Ltd.) was used, and the current value was 1 C (constant current mode) from 2.75 V to 12 V in an atmosphere at 25 ° C. The overcharge test was conducted under the conditions of Moreover, the temperature change of the laminated battery at this time was measured with the thermocouple affixed on the cell surface.

  1 to 3 show the relationship between the charging time, voltage, and current during the overcharge test, and the relationship between the charging time (horizontal axis), battery voltage (vertical axis), and battery temperature (vertical axis) during the overcharge test. It shows in FIG. The thickness of the battery after the overcharge test is also shown in Table 2.

From FIG. 1, FIG. 2 (enlargement of the 4.0 V to 6.0 V region of FIG. 1) and FIG. 3 (result when the charging time is extended to over 300 minutes for Experimental Example 1), in the voltage range up to about 5 V Although no difference was observed in the voltage increasing tendency between the batteries, when the voltage exceeded about 5.2 V and became an overcharged state, the batteries using the electrolytes 2 to 6 containing the overcharge inhibitor of the present invention were used. Then, compared with the electrolyte solution 1 which does not contain an overcharge inhibitor, it became difficult to raise a voltage. This phenomenon occurs at a lower voltage as the amount of the overcharge preventing agent increases. For example, in the electrolytic solution 6 (LiFSI concentration: 1.2 mol / L), the electrolytic solution 5 (LiFSI concentration: 1). (0.0 mol / L), the voltage increase started to stagnate at about 5.6V. In addition, the electrolyte solution with a larger amount of the overcharge prevention agent has a shorter time until the current is cut off. The electrolyte solution 6 is about 149 minutes after the start of charging, and the electrolyte solution 5 is about 177 minutes after the start of charging. In Fig. 3, current interruption occurred about 195 minutes after the start of charging (Figs. 2 and 3).

  Thus, when the overcharge inhibitor of this invention is used, it is thought that the rise in voltage stagnates because electric energy is used for the decomposition reaction of an overcharge inhibitor. Moreover, since the overcharge inhibitor concentration in the vicinity of the positive electrode increases as the amount of the overcharge inhibitor increases, it is considered that the formation of the passive film, the resistance of the positive electrode, and the interruption of the current occurred early.

  Under the conditions of the overcharge test, the currents were not cut off even when the electrolytes 1 and 2 continued to be charged for 300 minutes or longer. In addition, although the interruption | blocking of the electric current did not occur in the electrolyte solution 2, the voltage at which the voltage increase stagnates in the overcharged state is lower than the electrolyte solution 1 (FIG. 2), and the cell thickness after the test is also the electrolyte solution 1 (Table 2). From this result, in the electrolyte solution 2, the overcharge prevention effect by the compound (1) was exhibited, and as a result of the consumption of the current for the decomposition of the overcharge inhibitor, the generation of gas was suppressed and the safety of the battery was maintained. It is considered a thing.

  Further, the cell thickness after the overcharge test tended to be thicker as the amount of the overcharge inhibitor was small (not included) (Table 2). That is, in the electrolytic solution containing the overcharge inhibitor of the present invention, the decomposition reaction of this overcharge inhibitor is preferentially decomposed. As a result, the decomposition reaction of the solvent and the generation of gas due to this decomposition reaction are suppressed. On the other hand, when the overcharge preventive agent of the present invention is not included, the current is not consumed for the decomposition of the overcharge preventive agent, so that the cell thickness increases as the decomposition of the solvent proceeds (electrolyte solution) (Refer to Table 1 and Table 2). If the overcharged state continues further, the decomposition reaction of the solvent further proceeds, and the amount of gas generation increases accordingly, so that there is a possibility that the cell may eventually rupture.

  Further, as shown in Table 3 and FIG. 4, in the electrolytes 2 to 6, no remarkable heat generation was observed in the battery in the vicinity of 4.4 V, which is close to the current rated charging voltage. On the other hand, in the battery using the electrolytic solution 7 containing the conventional overcharge inhibitor, heat generation due to polymerization of the overcharge inhibitor was confirmed from around 4.4V. From these results, it is considered that the conventional overcharge inhibitor polymerizes near the current rated charge voltage, and therefore the battery resistance increases even during normal use, resulting in deterioration of battery performance. It is done. On the other hand, the overcharge inhibitor of the present invention does not generate heat even in the vicinity of 4.4 V and does not cause a polymerization reaction. Therefore, even when used at a voltage close to the rated charge voltage, the overcharge inhibitor It is considered that the battery performance is not easily deteriorated. Moreover, the overcharge inhibitor of this invention is excellent also in the point that heat_generation | fever like the conventional overcharge inhibitor is not confirmed.

  In addition, when the said overcharge test was implemented using electrolyte solution 3 '(The same composition as electrolyte solution 3 except that the moisture content of LiFSI is 600 ppm), an electric current does not interrupt | block and an overcharge prevention effect Could not be confirmed. The battery thickness at this time was 16.39 mm (Table 2).

Experimental Example 2: Cycle Characteristic Test Using a charge / discharge test apparatus (manufactured by Asuka Electronics Co., Ltd.) in an environment at a temperature of 25 ° C. for a laminated lithium battery, predetermined charging conditions (1C, 4.2V, constant current constant) Under the voltage mode, 0.02C cut) and the discharge conditions (1C, final voltage 2.75V, constant current mode), a cycle characteristic test was performed with a charge / discharge time of 10 minutes during each charge / discharge. Table 4 shows the ratio of the capacity in each cycle when the capacity in the first cycle is 100.

  From Table 4, it can be seen that the higher the overcharge inhibitor concentration, the less likely the cycle characteristics at 25 ° C. to deteriorate. In addition, it is considered that the deterioration of the cycle performance in Experimental Example 2-5 is due to the clogging of the separator due to the generation of the polymer derived from the overcharge inhibitor and the increase in the resistance of the positive electrode.

Experimental Example 3: Discharge rate characteristic test The dependency of the discharge rate characteristic on the overcharge inhibitor concentration was confirmed. As in Experimental Example 2, the discharge capacity of the laminated lithium battery was measured using a charge / discharge test apparatus (manufactured by Asuka Electronics Co., Ltd.) in an environment at a temperature of 25 ° C. After charging under predetermined charging conditions (1C, 4.2V, constant current and constant voltage mode, 0.02C cut), the discharge capacity was measured with a discharge end voltage of 2.75V, 0.2C and constant current discharge. Then, after charging again under predetermined charging conditions (1C, 4.2V, constant current and constant voltage mode, 0.02C cut), the discharge capacity was measured with a discharge end voltage of 2.75V, 3C and constant current discharge. . The discharge capacity was measured in the same manner as described above except that the current during discharge was changed from 0.2 to 10C. In addition, a 10 minute rest period was provided at each charge / discharge. Table 5 shows the ratio of the capacity at each rate when the battery capacity at a current of 0.2 C is 100.

  From Table 5, the discharge rate characteristics of Experimental Example 3-5 using the conventional overcharge inhibitor were lower than those of Experimental Examples 3-2 to 3-4 using the overcharge inhibitor of the present invention. It was. Moreover, it turns out from the example containing an overcharge inhibitor that a favorable discharge rate characteristic is acquired, so that an overcharge inhibitor concentration is high.

  From the above results, the overcharge inhibitor of the present invention containing the compound (1) functions as an electrolyte salt during normal use and exhibits excellent battery performance, while blocking the current in an overcharged state. It can be seen that Moreover, it turns out that the electric current interruption effect is acquired early, so that there are many amounts of overcharge inhibitors of this invention.

Experimental Example 4: Overcharge test 2
A change in voltage and a change in battery surface temperature were observed when each of the laminated lithium ion secondary batteries 2 was charged to an overcharged state.

  As a test method, a constant current / constant voltage power source (“PMC-35-2A”, manufactured by Kikusui Electronics Co., Ltd.) was used, and the current value was 1 C (constant current mode) from 2.75 V to 12 V in an atmosphere at 25 ° C. The overcharge test was conducted under the conditions of Moreover, the temperature change of the laminated battery at this time was measured with the thermocouple affixed on the cell surface.

  FIG. 5 shows the relationship between the charging time, voltage, current, and battery temperature during the overcharge test, and the relationship between the charging time, voltage, and battery temperature during the overcharge test, and the battery thickness after the overcharge test. This is also shown in FIG.

  5 and Table 6, when the electrolytic solution 6 containing the overcharge inhibitor of the present invention was used, current interruption occurred at a relatively early stage after entering the overcharge state. In addition, in the battery using the electrolytic solution 6, even when the battery is overcharged, the increase in voltage and the increase in battery temperature are suppressed as compared with the electrolytic solution 1 that does not contain an overcharge inhibitor. Further, the battery using the electrolytic solution 6 produced less gas than the battery thickness after the test. From this result, it can be seen that the overcharge inhibitor of the present invention can exert a current interruption effect in an overcharged state regardless of the type of the positive electrode active material.

Claims (2)

An electrolytic solution containing an overcharge inhibitor containing a compound represented by the general formula (1) and a non-aqueous solvent,
The concentration of the compound represented by the general formula (1) is 0.35 mol / L or more, and the moisture contained in the compound represented by the general formula (1) is 500 ppm (parts per million by mass) or less. ,
By including the above-mentioned overcharge inhibitor , when an overcharge test is performed under the condition of a current value of 1 C (constant current mode) from 2.75 V to 12 V in an atmosphere at 25 ° C., 4.4 V close to the rated charge voltage. not observed heat generation in the vicinity of the voltage when the voltage becomes overcharged more than about 5.2V, characterized in that hardly rises, electrolyte (excluding electrolyte containing lactone as a non-aqueous solvent) .
(XSO ₂ ) (FSO ₂ ) NLi (1)
(In general formula (1), X represents a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.)   A lithium ion secondary battery comprising the electrolytic solution according to claim 1.