JP2014203748A - Nonaqueous electrolytic solution for lithium ion secondary batteries, and lithium ion secondary battery having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution for lithium ion secondary batteries which is hard to cause the corrosion of aluminum when being caused to work under the condition of 4.2 V or larger even in the case of using an imide-based alkali metal salt such as an imide lithium salt as an electrolyte, and to provide a lithium ion secondary battery including such a nonaqueous electrolytic solution.SOLUTION: A nonaqueous electrolytic solution for lithium ion secondary batteries comprises, as an electrolyte, 0.6 mol/L or more of an imide-based alkali metal salt expressed by the general formula (1), MN(RSO)(FSO) (where M represents an alkali metal ion, and R represents fluorine atom, an alkyl group with 1-6 carbon atoms, or a fluoroalkyl group with 1-6 carbon atoms); and 10 vol.% or more of fluorine-containing carbonic ester.

Description

  The present invention relates to a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery including the same.

  In recent years, since lithium ion secondary batteries have high energy density, they have been used as power sources for mobile communication devices, power sources for portable information terminals, etc., and the market has been growing rapidly with the spread of these terminals. Various studies have been conducted for the purpose of ensuring safety, improving cycle characteristics and energy density, and improving high-temperature storage characteristics.

For example, Patent Document 1 discloses a nonaqueous electrolytic solution containing a fluorinated cyclic carbonate as a solvent, LiPF ₆ as a main electrolyte, and lithium bis (fluorosulfonyl) imide (LiFSI) as an additive electrolyte. It is disclosed that charge / discharge storage characteristics in a high temperature environment have been improved.

JP 2010-129449 A (Claim 1, paragraph 0027, etc.)

  However, in a non-aqueous electrolyte containing an imide-based alkali metal salt such as LiFSI as the main electrolyte (about 50% by mass or more of the total amount of the electrolyte), when operated at a high voltage exceeding 4.2 V, the positive electrode of the lithium ion secondary battery There was a problem of corroding aluminum used as a current collector. In addition, in the said patent document 1, it does not touch at all about the problem of the corrosion originating in LiFSI.

  The present invention has been made paying attention to the above circumstances, and its purpose is to operate under a condition of 4.2 V or higher when an imide-based alkali metal salt such as an imide lithium salt is used as a main electrolyte. An object of the present invention is to provide a non-aqueous electrolyte for a lithium ion secondary battery in which aluminum corrosion hardly occurs and a lithium ion secondary battery with a high withstand voltage against corrosion.

The present invention that has achieved the above-mentioned problems
A non-aqueous electrolyte for a lithium ion secondary battery,
The non-aqueous electrolyte is an imide-based alkali metal salt represented by the general formula (1): MN (RSO ₂ ) (FSO ₂ ) as an electrolyte (in the formula (1), M represents an alkali metal ion, R Represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms) in an amount of 0.6 mol / L or more, and contains 10% by volume or more of a fluorine-containing carbonate. .

The non-aqueous electrolyte is further used as an electrolyte.
General formula (2): M′PF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2)
(In formula (2), M ′ represents an alkali metal ion)
It is preferable that the salt compound represented by these is included.

The imide-based alkali metal salt represented by the general formula (1) is preferably 50 mol% or more in 100 mol% of the electrolyte. In addition, the embodiment in which the imide-based alkali metal salt represented by the general formula (1) is lithium bis (fluorosulfonyl) imide and the embodiment in which the salt compound represented by the general formula (2) is LiPF ₆ Is also a preferred embodiment of the present invention.

The fluorine-containing carbonate is preferably a fluorinated cyclic carbonate.
The present invention also includes a lithium ion secondary battery comprising the non-aqueous electrolyte for a lithium ion secondary battery of the present invention.

  By using a fluorine-containing carbonic acid ester, even when an imide-based alkali metal salt is used as a main electrolyte, corrosion of aluminum hardly occurs. Therefore, it is considered that by using the non-aqueous electrolyte of the present invention, a lithium ion secondary battery in which deterioration of battery characteristics due to corrosion of the current collector hardly occurs even under high voltage can be obtained.

1. Nonaqueous Electrolyte The nonaqueous electrolyte for a lithium ion secondary battery of the present invention has an imide-based alkali metal salt (formula (1) represented by the general formula (1): MN (RSO ₂ ) (FSO ₂ ) as an electrolyte. ), M represents an alkali metal ion, and R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms) and a fluorine-containing carbonate. Have. Hereinafter, the non-aqueous electrolyte of the present invention will be described in detail.

1-1. Electrolyte 1-1-1. Imide Alkali Metal Salt The non-aqueous electrolyte of the present invention is an imide alkali metal salt represented by the general formula (1): MN (RSO ₂ ) (FSO ₂ ) (in the formula (1), M is an alkali metal ion) R represents an imide-based alkali metal salt represented by a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms (in the general formula (1), M represents an alkali) Represents a metal ion, hereinafter referred to as an imide-based alkali metal salt (1)). As the alkali metal ion, lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion are preferable, lithium ion, sodium ion, and potassium ion are more preferable, and lithium ion is more preferable.

  The above R independently represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms. The alkyl group is preferably a linear alkyl group, and 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. The fluoroalkyl group may be linear, branched, cyclic, or a combination thereof. The fluoroalkyl group may be any group in which part of the hydrogen atoms bonded to the carbon atom is replaced with a fluorine atom. Specific examples of the fluoroalkyl group include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a fluoropropyl group, a fluoropentyl group, and a fluorohexyl group. Groups and the like. R is preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group.

  Preferred imide alkali metal salts (1) include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, potassium bis (fluoro Sulfonyl) imide, potassium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, sodium bis (fluorosulfonyl) imide, sodium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, and more preferably lithium bis (fluorosulfonyl) ) Imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide There, more preferred is lithium bisfluorosulfonylimide. As the imide-based alkali metal salt, a commercially available product may be used, or one synthesized by a conventionally known method may be used.

  The amount of the imide-based alkali metal salt (1) used is preferably such that the concentration in the nonaqueous electrolytic solution of the present invention is 0.6 mol / L or more and the saturation concentration or less. More preferably, it is 0.62 mol / L-2.0 mol / L, More preferably, it is 0.64 mol / L-1.8 mol / L, Especially preferably, it is 0.67 mol / L-1.6 mol / L Most preferably, it is 0.7 mol / L to 1.4 mol / L.

1-1-2. Other Electrolytes In addition to the imide-based alkali metal salt (1), the nonaqueous electrolytic solution of the present invention may contain another electrolyte different from this.

As other electrolytes, compounds represented by the general formula (2): M′PF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2) (hereinafter, fluorine-containing) The salt compound (referred to as salt compound (2)) is preferred. In formula (2), M ′ represents an alkali metal ion. Examples of the alkali metal ion include the same as those described above for M, preferably lithium ion, sodium ion, and potassium ion.

  By using the fluorine-containing salt compound (2) in combination, the corrosion inhibitory effect of the current collector is improved as compared with the case where the imide-based alkali metal salt (1) is used alone, and the non-aqueous electrolyte solution Since stability is improved, it is preferable. Furthermore, the ionic conductivity and mobility of the non-aqueous electrolyte are also increased.

Examples of the fluorine-containing salt compound (2) include LiPF ₆ and LiPF ₃ (C ₂ F ₅ ) ₃ , and LiPF ₆ is more preferable.

  The amount of the fluorine-containing salt compound (2) is 0 to 50 mol% when the total amount of the imide alkali metal salt (1) and the fluorine-containing salt compound (2) is 100 mol%. Preferably, it is 5 mol%-45 mol%, More preferably, it is 10 mol%-40 mol%.

  In addition, it is preferable that the density | concentration of the fluorine-containing salt compound (2) in the non-aqueous electrolyte of this invention is 0.02 mol / L-1.5 mol / L. More preferably, it is 0.05 mol / L-1.2 mol / L, More preferably, it is 0.1 mol / L-0.8 mol / L. If the amount of the fluorine-containing salt compound (2) used is too large, the viscosity of the non-aqueous electrolyte is increased, the conductivity is lowered, and the desired battery performance may not be sufficiently exhibited.

  As the fluorine-containing salt compound (2), a commercially available product may be used, or a product synthesized by a conventionally known method may be used.

The nonaqueous electrolytic solution of the present invention may contain a salt compound other than the imide-based alkali metal salt (1) and the fluorine-containing salt compound (2). Examples of the cation species constituting the salt compound other than the imide-based alkali metal salt (1) and the fluorine-containing salt compound (2) include alkali metal ions such as Li ⁺ , Na ⁺ and K ⁺ , Ca ²⁺ and Mg ^2. Examples thereof include alkaline earth metal ions such as ⁺ and onium cations, and lithium ions are particularly preferable. On the other hand, as anion species, BF ₄ ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , C [(CN) ₃ ] ⁻ , N [(CN) ₂ ] ⁻ , B [(CN) ₄ ] ⁻ , N [(SO ₂ CF ₃ ) ₂ ] ⁻ , CF ₃ (SO ₃ ) ⁻ , C [(CF ₃ SO ₂ ) ₃ ] ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ and dicyanotriazolate ion (DCTA).

Specific examples of salt compounds other than the imide-based alkali metal salt (1) and the fluorine-containing salt compound (2) preferably include LiAlO ₄ and LiAlCl ₄ . These salt compounds are preferably used as part of the fluorine-containing salt compound (2), and the amount used is other than the imide-based alkali metal salt (1), the fluorine-containing salt compound (2) and the fluorine-containing salt compound. It is preferable that it is 0.2 mass part-10 mass parts with respect to a total of 100 mass parts of this salt compound, More preferably, they are 0.5 mass part-8 mass parts, More preferably, they are 1 mass part-5 parts. Part by mass.

1-2. Solvent The nonaqueous electrolytic solution of the present invention contains a solvent for dissolving the electrolyte and additives. The solvent according to the present invention is not particularly limited as long as it contains 10% by volume or more of the fluorine-containing carbonate ester in 100% by volume of the solvent, but when the fluorine-containing carbonate ester exceeds 60% by volume, the non-aqueous electrolyte solution The viscosity of the battery increases, the conductivity decreases, and the desired battery performance may not be fully exhibited. The reason why the fluorine-containing carbonate is used as a part of the solvent in the present invention is that the corrosion of aluminum is difficult to occur, and the mechanism thereof is that the fluorine-containing carbonate reacts with aluminum and the current collector made of aluminum is used. It is considered that a corrosion-resistant film such as aluminum fluoride is formed on the body surface to suppress corrosion.

As content of the fluorine-containing carbonate contained in a solvent, 10 mass% or more is required by making the total amount of a solvent into 100 mass%. Preferably it is 15 mass% or more, More preferably, it is 20 mass% or more.
In the non-aqueous electrolyte of the present invention, the content (mass ratio) of the fluorine-containing carbonate and the imide alkali metal salt (1) is imide alkali metal salt (1) / fluorine carbonate. = 1/4 to 2/1 is preferable. More preferably, it is 1 / 3.5 to 1.5 / 1, and still more preferably 1/3 to 1.2 / 1.

  Fluorinated cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, tetrafluoroethylene carbonate, 4-fluoro-5-methylethylene carbonate; trifluoro Examples thereof include fluorinated chain carbonates such as dimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethyl methyl carbonate. Among the above, fluorinated cyclic carbonate is preferable. More preferred is fluoroethylene carbonate. These fluorine-containing carbonates may be used as a mixture of two or more.

  Other solvents used together with the fluorine-containing carbonate include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate; tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane; γ-butyrolactone, γ-valero Nonaqueous solvents such as lactones, lactones such as α-methyl-γ-butyrolactone; chain carboxylic acid esters such as methyl propionate and methyl butyrate; These nonaqueous solvents may be used as a mixture of two or more. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.

  Among these other solvents, chain carbonates are preferable as a solvent used in combination with a fluorine-containing carbonate because they are difficult to decompose upon application of voltage and are stable. When a graphite material is used for the negative electrode, lactones are easily reduced and decomposed at the negative electrode. In this case, it is preferable to use a solvent other than the lactones.

  The amount of the solvent used is preferably from 100 parts by weight to 5000 parts by weight, more preferably from 150 parts by weight to 2500 parts by weight, and even more preferably from 200 parts by weight to 2000 parts by weight with respect to 100 parts by weight of the electrolyte. is there.

1-3. Additive The non-aqueous electrolyte of the present invention may contain an additive for the purpose of improving cycle characteristics and safety.

  Examples of additives include carbonate compounds such as phenylethylene carbonate and erythritan carbonate; 1,3-propane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1,4-hexane sultone, 4,6- Sulfonic esters such as heptane sultone, methyl methanesulfonate, methyl benzenesulfonate, methyl trifluoromethanesulfonate; sulfones such as sulfolane, 3-methylsulfolane, ethylmethylsulfone, diphenylsulfone, bis (4-fluorophenyl) sulfone Compound: succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinate Carboxylic anhydrides such as acid anhydrides; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methyls Nitrogen-containing compounds such as succinimide; phosphates such as monofluorophosphate and difluorophosphate; hydrocarbon compounds such as heptane, octane and cycloheptane; When these additives are used in the non-aqueous electrolyte, the concentration thereof is 0.1 parts by mass or more and 10 parts by mass or less in 100 parts by mass of the total amount of the constituent materials (electrolyte solvent and additive) of the non-aqueous electrolyte. It is preferable that

2. Lithium ion secondary battery The lithium ion secondary battery of the present invention is characterized in that the non-aqueous electrolyte for a lithium ion secondary battery of the present invention is provided as an electrolytic solution. More specifically, the secondary battery includes a positive electrode and a negative electrode. A separator is provided between the positive electrode and the negative electrode, and the positive electrode is in a state where the separator is impregnated with the non-aqueous electrolyte of the present invention. And the negative electrode together with the negative electrode.

  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 ion secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. Can do. 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. .

  Even when the non-aqueous electrolyte of the present invention uses an imide-based alkali metal salt as an electrolyte, corrosion of the aluminum current collector is difficult to occur. Therefore, it is possible to provide a lithium ion secondary battery having good battery characteristics that is unlikely to cause a significant decrease in battery performance.

2-1. The positive electrode is a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, a dispersion solvent and the like supported on a positive electrode current collector, and is usually formed into a sheet shape. .

  Examples of the method for producing the positive electrode include a method in which the positive electrode active material composition is applied to the positive electrode current collector by a doctor blade method or the like, or the positive electrode current collector is immersed in the positive electrode active material composition and then dried; A method in which a sheet obtained by kneading, molding and drying an active material composition is bonded to a positive electrode current collector via a conductive adhesive, pressed and dried; a positive electrode active material composition to which a liquid lubricant is added Examples include a method of applying or casting on an electric body to form a desired shape, removing the liquid lubricant, and then stretching in a uniaxial or multiaxial direction.

2-1-1. 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 alloy, SUS (stainless steel), and titanium can be used. Among these, aluminum is preferable from the viewpoint of being easily processed into a thin film and being inexpensive.

2-1-2. 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, lithium manganese _{acid, 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 ), A transition metal oxide such as a ternary oxide represented by Li _x Ni _y Mn _(2-y) O ₄ (0.9 ≦ x ≦ 1.1, 0 <y <1) Lithium nickel manganate, compounds having an olivine structure such as LiAPO ₄ (A = Fe, Mn, Ni, Co), and solid solution materials incorporating a plurality of transition metals (electrochemically inert layered Li ₂ MnO ₃ and As the positive electrode active material, an electrochemically active layered LiM ″ O [M ″ = transition metal such as Co and Ni]) and the like can be exemplified. These positive electrode active materials may be used alone or in combination of two or more.

2-1-3. Conductive aid Examples of the conductive aid include acetylene black, carbon black, graphite, metal powder material, single-walled carbon nanotube, multi-walled carbon nanotube, and vapor grown carbon fiber.

2-1-4. Binders As binders, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamideimide; polyethylene, polypropylene and the like Polyolefin resin; poly (meth) acrylic resin; polyacrylic acid; cellulose resin such as carboxymethylcellulose; These binders may be used alone or in combination of two or more. These binders may be dissolved in a solvent at the time of use or dispersed in a solvent.

  The blending amounts of the conductive auxiliary agent 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.

  In producing the positive electrode, examples of the solvent used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethanol, ethyl acetate, and water. 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.

2-2. Negative electrode A negative electrode is a negative electrode current collector comprising a negative electrode active material, a dispersion solvent, a binder, and a conductive auxiliary agent, if necessary. Molded.

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

2-2-2. 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.

  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.

2-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. There is no restriction | limiting in particular in a separator, In this invention, all the conventionally well-known separators can be used. Specific separators include, for example, porous sheets (for example, polyolefin microporous separators and cellulose separators) made of a polymer that can absorb and retain a nonaqueous electrolyte, nonwoven fabric separators, porous metal bodies, and the like. Can be mentioned. 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 of the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., depending on the mechanical strength required for the non-aqueous electrolyte layer. The materials exemplified above can be used alone or in combination.

2-4. Battery exterior material A battery element provided with a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte of the present invention is accommodated in a battery exterior material in order to protect the battery element from external impact, environmental degradation, etc. when the battery is 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.

<Measurement method of corrosion withstand voltage>
CR2032-type coin cells were produced using the non-aqueous electrolytes (1) to (4) prepared in the following examples and comparative examples. Specifically, it was as follows.

Production of Battery The positive electrode used was an aluminum foil (1085 material) punched out to a diameter of 12 mm. A lithium foil (φ13 mm) having a thickness of 0.5 mm was used for the negative electrode. A polyethylene cell separator is impregnated with 70 μL of non-aqueous electrolyte, and a coin cell is produced by crimping with a caulking machine using CR2032 coin-type battery parts (negative electrode cap, wave washer, spacer, positive electrode cap manufactured by Hosen Co., Ltd.). did.

  The coin cell was subjected to a constant voltage application test using a charge / discharge test apparatus (ACD-01, manufactured by Asuka Electronics Co., Ltd.). A continuous test at a temperature of 25 ° C. for 12 hours was measured every 0.1 V, and the occurrence of corrosion of the aluminum foil was determined by the presence or absence of an increase in the amount of flowing current and the appearance inspection.

Example 1
In a non-aqueous solvent in which fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) are mixed at 3: 7 (volume ratio), lithium bis (fluorosulfonyl) imide (concentration is 1.2 mol / L). A non-aqueous electrolyte (1) was prepared by dissolving imide-based alkali metal salt (1) manufactured by Nippon Shokubai Co., Ltd. In the measurement of the withstand voltage of corrosion of the battery using this non-aqueous electrolyte (1), no corrosion was observed up to 4.3 V, but corrosion occurred at 4.4 V, and the withstand voltage of corrosion was 4. It was 3V.

Comparative Example 1
A nonaqueous electrolytic solution (2) was prepared in the same manner as in Example 1 except that ethylene carbonate was used instead of FEC. In the measurement of the withstand voltage of corrosion of the battery using this non-aqueous electrolyte (2), no corrosion was observed up to 4.2 V, but corrosion occurred at 4.3 V, and the withstand voltage of corrosion was 4. 2V.

Example 2
A nonaqueous electrolytic solution (3) was prepared in the same manner as in Example 1 except that the lithium bis (fluorosulfonyl) imide and LiPF ₆ were used as the electrolyte and each was dissolved by 0.6 mol / L. In the measurement of the withstand voltage of corrosion of the battery using this non-aqueous electrolyte (3), no corrosion was observed up to 5V, and the withstand voltage of corrosion was 5V or more.

Comparative Example 2
A nonaqueous electrolytic solution (4) was prepared in the same manner as in Example 2 except that ethylene carbonate was used instead of FEC. In the measurement of the withstand voltage of corrosion of the battery using this nonaqueous electrolyte (4), no corrosion was observed up to 4.6V, but corrosion occurred at 4.7V, and the withstand voltage of corrosion was 4. 6V.

  The nonaqueous electrolytic solution of the present invention is used for a lithium ion secondary battery.

Claims (7)

A non-aqueous electrolyte for a lithium ion secondary battery,
The non-aqueous electrolyte is an imide-based alkali metal salt represented by the general formula (1): MN (RSO ₂ ) (FSO ₂ ) as an electrolyte (in the formula (1), M represents an alkali metal ion, R Represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms) in an amount of 0.6 mol / L or more, and contains 10% by volume or more of a fluorine-containing carbonate. Nonaqueous electrolyte for lithium ion secondary batteries. The non-aqueous electrolyte is further used as an electrolyte.
General formula (2): M′PF _a (C _m F _{2m + 1} ) _6-a (0 ≦ a ≦ 6, 1 ≦ m ≦ 2)
(In formula (2), M ′ represents an alkali metal ion)
The non-aqueous electrolyte for lithium ion secondary batteries according to claim 1, comprising a salt compound represented by:   The non-aqueous electrolyte for a lithium ion secondary battery according to claim 2, wherein the imide-based alkali metal salt represented by the general formula (1) is 50 mol% or more in 100 mol% of the electrolyte.   The non-aqueous electrolyte for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the imide-based alkali metal salt represented by the general formula (1) is lithium bis (fluorosulfonyl) imide. The general formula (2) salt compound represented by a LiPF ₆ lithium ion secondary battery nonaqueous electrolytic solution according to any one of claims 2-4.   The non-aqueous electrolyte for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the fluorine-containing carbonate is a fluorinated cyclic carbonate.   A lithium ion secondary battery comprising the non-aqueous electrolyte for a lithium ion secondary battery according to claim 1.