JP2013218963A - Nonaqueous electrolyte cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte cell which exhibits excellent low temperature performance, while using a flammable nonaqueous electrolyte.SOLUTION: A nonaqueous solvent contains a carbonate-based solvent, a fluorine-containing phosphate ester, and fluorine-containing ester. In the nonaqueous electrolyte, the inflammation point is not measured at 80°C or lower by an inflammation point measurement method using a Seta enclosed inflammation point measuring device specified in JISK2265-2, and the nonaqueous electrolyte boils before the inflammation point by an inflammation point measurement method using a Cleveland open inflammation point tester specified in JISK2265-4.

Description

The present invention relates to a non-flammable non-aqueous electrolyte and a non-aqueous electrolyte battery using the same.

  Conventionally, a non-aqueous electrolyte battery typified by a lithium ion secondary battery has a high voltage and a high energy density, and is therefore widely used as a power source for consumer electronic devices. Such a non-aqueous electrolyte battery is assembled by being wound around a separator between a positive electrode and a negative electrode and inserted into a battery outer package. In recent years, this type of non-aqueous electrolyte battery has been developed for use in large batteries such as electric vehicles and power storage.

  In non-aqueous electrolytes used in such non-aqueous electrolyte batteries, flammable solvents or flammable solvents are often used, but such materials are classified as dangerous materials under the Fire Service Act. When transporting and storing, handling in an explosion-proof or fire-proof facility is necessary, so there was a problem in distribution.

  Also, assuming that the outer casing of the nonaqueous electrolyte battery is damaged, it is desirable that the leaked nonaqueous electrolyte has flame retardancy or nonflammability. Specifically, for example, in a coin-type battery, since the amount of the nonaqueous electrolyte used is small, it is difficult to assume that the nonaqueous electrolyte does not leak out even if the exterior body is damaged, or even if it leaks out. . However, for example, in a medium-sized or large-sized battery of 3 Ah or more, in addition to a large amount of non-aqueous electrolyte used, in particular, in a non-aqueous electrolyte battery designed to have a long cycle life design, the pore volume of the positive electrode, the negative electrode, and the separator Since it is designed to include a large amount of non-aqueous electrolyte, the possibility of non-aqueous electrolyte leaking out and igniting increases when it is assumed that the battery outer body is damaged. Furthermore, in recent years, it has been studied to use metal resin composite films such as aluminum, aluminum alloys, and aluminum laminate films for exterior bodies (batteries) in large batteries for weight reduction. Since the mechanical strength is low, there is an increased risk of damage due to sharp object collision. Therefore, also from this viewpoint, the nonaqueous electrolyte is desired to have flame retardancy or nonflammability.

  Patent Documents 1 to 3 describe nonaqueous electrolyte batteries using a nonaqueous electrolyte containing a fluorinated phosphate ester. Patent Document 4 discloses a nonaqueous electrolytic solution in which a flame retardant containing a fluorine atom in a side chain and an additive composed of a boron compound coexist in order to obtain a nonaqueous electrolytic solution having improved flame retardancy and battery characteristics. An invention using a liquid is described. Further, in the same document, “as a flame retardant having a fluorine atom in the side chain used in the present invention, a fluorine-containing phosphate ester, a fluorine-containing phosphazene compound, a fluorine-containing ether, a fluorine-containing carbonate, a fluorine-containing ester and the like are exemplified. Is possible "(see paragraph 0018).

JP 2011-044245 A JP 2011-113822 A JP 2011-1113889 A JP 2011-222431 A

  This invention is made | formed in view of the said subject, and it aims at providing the nonaqueous electrolyte battery excellent also in low temperature performance, using the nonaqueous electrolyte which has nonflammability.

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention is a non-aqueous electrolyte comprising a non-aqueous solvent containing an alkali metal salt, wherein the non-aqueous solvent is a carbonate solvent, a fluorine-containing phosphate ester represented by Chemical Formula 1, The flash point is not measured at a temperature of 80 ° C. or less by a flash point measuring method using a setta hermetic flash point measuring instrument defined in JIS K2265-2, and JIS K2265-4 A non-aqueous electrolyte is characterized in that the non-aqueous electrolyte boils before ignition by a flash point measurement method using a Cleveland open-type flash point tester as defined in 1.

(However, R ₁ , R ₂ , and R ₃ are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms, At least one of R _{1 to} R ₃ is a fluorine-containing alkyl group.)
(Wherein, R ₄ and R ₅ are each independently a linear or branched fluorinated alkyl group having 1 to 6 carbon linear or branched alkyl group or a C 1 to 6 carbon atoms, R ₄ and At least one of R ₅ is a fluorine-containing alkyl group.)

  The present invention is also a non-aqueous electrolyte comprising a non-aqueous solvent containing an alkali metal salt, wherein the non-aqueous solvent includes a carbonate-based solvent, a fluorine-containing phosphate ester represented by Chemical Formula 1, 2 and the proportion of the carbonate-based solvent in the non-aqueous solvent is 65% by volume or less, and the fluorine-containing phosphate ester and the fluorine-containing occupying in the non-aqueous electrolyte. The nonaqueous electrolyte is characterized in that the ratio of ether is 35% by volume or more, and the volume ratio of the fluorine-containing phosphate ester to the fluorine-containing ether is 25:75 to 45:55.

  Moreover, this invention is a nonaqueous electrolyte battery provided with the positive electrode, the negative electrode, and the said nonaqueous electrolyte.

  The present inventor has studied a non-aqueous electrolyte for a non-aqueous electrolyte battery containing a carbonate-based solvent such as a cyclic carbonate or a chain carbonate. In this study, the fluorine-containing phosphate ester, the fluorine-containing phosphazene compound, the fluorine-containing ether, and the fluorine-containing carbonate are used. Non-flammable by selecting and combining specific fluorine-containing phosphate ester and specific fluorine-containing ether from various materials known as flame retardants, such as fluorine-containing esters The present inventors have found that a nonaqueous electrolyte battery having sufficient low-temperature performance can be obtained while having the above.

  In this specification, having non-flammability means that a non-aqueous electrolyte is measured at a temperature of a flash point of 80 ° C. or less by a flash point measurement method using a setter-sealed flash point measuring instrument defined in JIS K2265-2. In addition, it means that the non-aqueous electrolyte boils before ignition by the flash point measurement method using a Cleveland open-type flash point tester defined in JIS K2265-4.

  Although it is not necessarily clear about the action mechanism in which nonflammability is shown by the above-mentioned composition, the present inventors guess as follows. That is, since the non-aqueous electrolyte according to the present invention contains the fluorine-containing ether represented by Chemical Formula 2, the vapor of the fluorine-containing ether has nonflammability, so that the surface of the non-aqueous electrolyte has the vapor of the fluorine-containing ether. Covered by. For this reason, even if the above contains a flammable or flammable liquid, the fluorine-containing ether vapor reduces the flammable vapor concentration and can be controlled below the lower explosion limit. It becomes flammable. However, since the fluorine-containing ether has a low ability to dissolve the alkali metal salt, the nonaqueous electrolyte tends to cause precipitation of the alkali metal salt and the like particularly at a low temperature. For this reason, the low temperature performance of the nonaqueous electrolyte battery is inferior. However, since the non-aqueous electrolyte further contains the fluorine-containing phosphate ester represented by Chemical Formula 1, the fluorine-containing phosphate ester has a high ability to dissolve the alkali metal salt, and thus is excellent as a non-aqueous electrolyte even at a low temperature. Since the ionic conductivity can be exhibited, the excellent low temperature performance of the nonaqueous electrolyte battery can be maintained. On the other hand, the fluorine-containing phosphate ester has a high ability to dissolve an alkali metal salt and is excellent in self-extinguishing properties, so that the non-aqueous electrolyte has non-flammability even if it does not contain the fluorine-containing ether. can do. However, since the fluorine-containing phosphate ester has a high viscosity, when it does not contain the fluorine-containing ether, the low-temperature performance of the nonaqueous electrolyte battery using the fluorine-containing ether is inferior.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte which can provide the nonaqueous electrolyte battery excellent in low-temperature performance can be provided, using the nonaqueous electrolyte which has nonflammability. Moreover, according to the present invention, it is possible to provide a non-aqueous electrolyte battery excellent in low-temperature performance while using a non-flammable non-aqueous electrolyte.

  Examples of the fluorine-containing phosphate ester represented by Chemical Formula 1 contained in the solvent included in the non-aqueous electrolyte according to the present invention include tris phosphate (2,2-difluoroethyl) and tris phosphate (2,2,2- Trifluoroethyl), tris phosphate (2,2,3,3-tetrafluoropropyl), tris phosphate (2,2,3,3,3-pentafluoropropyl), bis (2,2-difluorophosphate) Ethyl) 2,2,2-trifluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2 , 3,3-tetrafluoropropyl, bis (2,2,2-trifluoroethyl) methyl phosphate, bis (2,2,2-trifluoroethyl) ethyl phosphate and bis (2,2,3 phosphate) , 3-Tetrafluoropropyl Pills) 2,2,2-trifluoroethyl and the like.

  The fluorine-containing phosphate ester is required to have incombustibility, flame retardancy, or non-flammability, and particularly excellent solubility in alkali metal salts. From this viewpoint, among the above, bis (2,2,2-trifluoroethyl) phosphate 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl) methyl phosphate, bis (2 , 2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl is preferred, and bis (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate is particularly preferred. preferable.

  In the fluorine-containing ether represented by Chemical Formula 2 contained in the solvent included in the nonaqueous electrolyte according to the present invention, R4 is 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3. , 3-tetrafluoropropyl group and 2,2,3,3,3-pentafluoropropyl group, and R5 is a difluoromethyl group, 1,1,2,2 -One or more selected from the group consisting of a tetrafluoroethyl group and a 1,1,2,3,3,3-hexafluoropropyl group is preferred.

  The fluorine-containing ether is particularly required to have non-flammability, flame retardancy, or non-flammability and a vapor pressure that is not too low. Accordingly, those having a large proportion of fluorine atoms contained in the molecule are preferred, and those having a molecular weight not too large are preferred. Moreover, what the said fluorine-containing ether itself does not have flammability is preferable. When a fluorine-containing ether having a small proportion of fluorine atoms is used, it is necessary to increase the mixing ratio of the fluorine-containing ether in order to provide non-flammability, but the fluorine-containing ether has low solubility in alkali metal salts. Therefore, it is not preferable in terms of the low temperature performance of the nonaqueous electrolyte battery. From this point of view, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (molecular weight: 232, weight ratio of fluorine atoms in the molecule: 65%) or 1,1, 2,2-tetrafluoro-2,2,2-trifluoroethyl ether (molecular weight: 200, weight ratio of fluorine atoms in the molecule: 66%) is preferable, 1,1,2,2-tetrafluoro-2, 2,2-trifluoroethyl ether is most preferred.

  It may be conceivable to use a fluorine-containing ester or a fluorine-containing carbonate as a flame retardant. However, a fluorine-containing ester or a fluorine-containing carbonate having a molecular weight that is not too large has flammability itself. Therefore, when a fluorine-containing ester or a fluorine-containing carbonate is used instead of the fluorine-containing ether in the present invention, the content ratio of the fluorine-containing phosphate ester is increased in order to make the nonaqueous electrolyte nonflammable. It is necessary to do. However, when the content ratio of the fluorine-containing phosphate is increased, the viscosity of the non-aqueous electrolyte increases, so that the low-temperature performance of the non-aqueous electrolyte battery becomes inferior. Therefore, a fluorine-containing ester or a fluorine-containing carbonate cannot be used in place of the fluorine-containing ether in the present invention.

  As the carbonate solvent contained in the solvent provided in the nonaqueous electrolyte according to the present invention, a cyclic carbonate is preferably used, and a cyclic carbonate and a chain carbonate may be mixed and used. Here, the volume ratio of the carbonate-based solvent contained in the solvent included in the non-aqueous electrolyte according to the present invention is 65% by volume or less because the non-aqueous electrolyte is non-flammable. However, in order to make the performance of the nonaqueous electrolyte battery using this sufficient, it is preferably 50% by volume or more, and more preferably 55% by volume or more.

  As the cyclic carbonate, it is preferable to use propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, or a mixture of two or more thereof. Among them, propylene carbonate and / or ethylene carbonate is selected. More preferably, it is used.

  As the chain carbonate, it is preferable to use dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate in combination of one or more, and it is more preferable to use diethyl carbonate and / or ethyl methyl carbonate. preferable.

  The solvent provided in the non-aqueous electrolyte according to the present invention may contain a solvent other than those described above as long as the effects of the present invention are exhibited. For example, cyclic esters such as γ-butyrolactone and γ-valerolactone Chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl jig Ethers such as lime; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof may be included. Moreover, additives, such as antioxidants represented by vinylene carbonate, 1, 3- propane sultone, a radical scavenger, surfactant, etc., may be contained.

Examples of the alkali metal salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, Inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K) such as NaBr, KClO ₄ , KSCN, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C _{4 H 9) 4, NClO 4} , (n-C 4 H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N Organic ionic salts such as -phthalate, lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate and the like can be mentioned, and these ionic compounds can be used alone or in combination of two or more. Furthermore, it is also preferable to use a mixture of LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ .

  The concentration of the alkali metal salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to obtain a non-aqueous electrolyte battery having high battery characteristics. 2.5 mol / l.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The shape of the nonaqueous electrolyte battery is not limited, and examples thereof include a cylindrical battery, a square battery, and a flat battery.

The positive electrode active material is not limited. For example, lithium iron phosphate (LiFePO ₄ ), lithium iron manganese phosphate (eg, LiFe _0.9 Mn _0.1 PO ₄ ), lithium titanate (Li ₄ Ti) ₅ O ₁₂ ), tungstic acid (WO ₃ ), and lithium transition metal composite oxide are represented by spinel type lithium manganese oxide represented by LiMn ₂ O ₄ , LiNi _1.5 Mn ₀₅ O _4, etc. Lithium transition metal oxides having a spinel crystal structure typified by spinel type lithium nickel manganese oxide, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _{1.1 Co 2/3 Ni 1/6 Mn 1/6 O 2} , LiMeO 2 type with alpha-NaFeO ₂ structure represented by equal (M The transition metal) lithium transition metal composite oxide, LiMePO ₄ (transition metal Me is containing Co or _{Mn), Li 3 V 2 (} PO 4) transition metal phosphate lithium compound such as _3, and the like. Alternatively, a so-called “lithium-excess” lithium transition metal composite oxide that can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0) may be used. Here, the Li / Me ratio is preferably 1.25 to 1.6. If the Li / Me ratio is β, β = (1 + α) / (1−α). For example, when Li / Me is 1.5, α = 0.2.

The negative electrode material is not limited, and any negative electrode material that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  The exterior body (battery) is not limited, and a metal battery case made of stainless steel or aluminum can be used. Moreover, you may use metal resin composite films, such as a lightweight aluminum alloy and an aluminum laminate film.

  Note that these metal alloy composite films such as aluminum alloys and aluminum laminate films have low mechanical strength, so that there is an increased risk of breakage due to sharp object collision. Therefore, when the present invention is applied to a battery using a metal resin composite film such as aluminum, an aluminum alloy, and an aluminum laminate film, the effect of the present invention is suitably achieved.

  In addition, a medium or large battery of 3 Ah or more uses a large amount of nonaqueous electrolyte. Therefore, when the present invention is applied to a non-aqueous electrolyte battery having a rated capacity of 3 Ah or more, the effects of the present invention are suitably achieved.

  In addition, among non-aqueous electrolyte batteries having a long cycle life design among medium-sized or large-sized batteries of 3 Ah or more, the non-aqueous electrolyte is designed to have a larger amount of non-aqueous electrolyte than the pore volume of the positive electrode, the negative electrode, and the separator. Therefore, when it is assumed that the battery outer body is damaged, the risk of non-aqueous electrolyte leakage and ignition is increased. Therefore, when the present invention is applied to a nonaqueous electrolyte battery including a nonaqueous electrolyte in an amount larger than the pore volume of the positive electrode, the negative electrode, and the separator, the effect of the present invention is suitably achieved.

(Invention electrolyte 1)
Cyclic carbonate ethylene carbonate (EC), chain carbonate ethyl methyl carbonate (EMC), fluorine-containing phosphate ester bis (2,2,2-trifluoroethyl) 2, 2,1,3-tetrafluoropropyl and 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether, which is a fluorine-containing ether represented by Chemical Formula 2, are 30/30/15 / A non-aqueous solvent was prepared by mixing at a volume ratio of 25. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

(Comparative electrolyte 1)
Ethylene carbonate which is a cyclic carbonate, ethyl methyl carbonate which is a chain carbonate, and bis (2,2,2-trifluoroethyl) phosphate 2,2,3 which is a fluorine-containing phosphoric acid ester represented by Chemical Formula 1. 3-tetrafluoropropyl was mixed at a volume ratio of 35/35/30 to prepare a non-aqueous solvent. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

(Comparative electrolyte 2)
Ethylene carbonate which is cyclic carbonate, ethyl methyl carbonate which is chain carbonate, and 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether which is fluorine-containing ether represented by Chemical formula 2 A non-aqueous solvent was prepared by mixing at a volume ratio of 30/35/35. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

(Comparative electrolyte 3)
Ethylene carbonate which is cyclic carbonate, ethyl methyl carbonate which is chain carbonate, and 1,1,2,2-tetrafluoro-2,2,2-trifluoroethyl ether which is fluorine-containing ether represented by Chemical formula 2 A non-aqueous solvent was prepared by mixing at a volume ratio of 40/40/20. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

(Comparative electrolyte 4)
70/30 of ethylene carbonate, which is a cyclic carbonate, and bis (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate, which is a fluorine-containing phosphate represented by Chemical Formula 1. Were mixed at a volume ratio of 2 to prepare a non-aqueous solvent. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

(Comparative electrolyte 5)
A non-aqueous solvent was prepared by mixing ethylene carbonate as a cyclic carbonate and ethyl methyl carbonate as a chain carbonate in a volume ratio of 50/50. LiPF ₆ as an alkali metal salt was added to the non-aqueous solvent at a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.

<Flammability test>
About the said electrolyte 1 of this invention and the comparative electrolytes 1-6, the flash point measurement by the setta sealing type flash point measuring device was performed. As a result, the flash point was not shown about this invention electrolyte 1 and comparative electrolytes 2-4. Next, the flash point of the present invention electrolyte 1 and comparative electrolytes 2 to 4 was measured with a Cleveland open flash point tester. As a result, flash point was not shown about this invention electrolyte 1, the comparative electrolyte 2, and the comparative electrolyte 4. FIG.

<Coagulation test>
The electrolyte 1 of the present invention and the comparative electrolytes 1 to 6 were each set to −20 ° C. and visually observed. As a result, the battery 1 of the present invention and the comparative electrolytes 1, 3 and 5 were kept transparent, but the comparative electrolyte 2 and the comparative electrolyte 4 were partially or wholly solidified. Therefore, since it is obvious that the comparative electrolyte 2 and the comparative electrolyte 4 are inferior in low-temperature performance even when they are used in a battery, the subsequent tests were not performed.

<Production of nonaqueous electrolyte battery>
(Preparation of positive electrode plate)
Mass of 87: 5: 8 of positive electrode active material represented by composition formula LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , acetylene black as a conductive agent and polyvinylidene fluoride (PVdF) as a binder A positive electrode paste containing N-methyl-2-pyrrolidone (NMP) as a solvent was prepared. The positive electrode paste was applied to both sides of a 20 μm-thick belt-shaped aluminum foil current collector as a positive electrode current collector, dried, and then pressed. In this way, a positive electrode plate according to Example 1 was produced.

(Preparation of negative electrode plate)
A negative electrode paste containing artificial graphite as a negative electrode material and PVdF as a binder in a mass ratio of 94: 6 and using N-methyl-2-pyrrolidone (NMP) as a solvent was prepared. The negative electrode paste was applied to both surfaces of a strip-shaped copper foil current collector having a thickness of 10 μm, dried, and then subjected to press working to obtain a negative electrode plate.

  The positive electrode plate and the negative electrode plate were wound through a separator made of a polypropylene microporous film having a thickness of 25 μm to prepare a power generation element. The power generation element was inserted into a battery case having a height of 48 mm, a width of 30 mm, and a thickness of 5.2 mm. The electrolyte 1 of the present invention was injected into the battery case, and finally the injection port was sealed. In this way, a non-aqueous electrolyte battery having a design capacity of 5 Ah was assembled.

(Low temperature performance test)
The discharge test was performed in each temperature environment of 25 degreeC, 0 degreeC, -10 degreeC, and -20 degreeC. Prior to each discharge test, charging was performed. In each case, charging was performed at a temperature of 25 ° C., a current of 1 CmA, a voltage between terminals of 4.2 V, and a constant current and constant voltage of 3 hours. As a result, assuming that the discharge capacity at 25 ° C. was 100%, a discharge capacity of 83% at 0 ° C., 47% at −10 ° C., and 17% at −20 ° C. was obtained.

The above results are summarized in Table 1.

Claims (3)

A non-aqueous electrolyte comprising a non-aqueous solvent containing an alkali metal salt, wherein the non-aqueous solvent includes a carbonate-based solvent, a fluorine-containing phosphate ester represented by Chemical Formula 1, and a fluorine-containing compound represented by Chemical Formula 2. It contains ether, and its flash point is not measured at a temperature of 80 ° C. or lower by the flash point measuring method with a setter hermetic flash point measuring instrument specified in JIS K2265-2, and is specified in JIS K2265-4. A nonaqueous electrolyte characterized in that the nonaqueous electrolyte boils before ignition by a flash point measurement method using a Cleveland open flash point tester.
(However, R ₁ , R ₂ , and R ₃ are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms, At least one of R _{1 to} R ₃ is a fluorine-containing alkyl group.)
(Wherein, R ₄ and R ₅ are each independently a linear or branched fluorinated alkyl group having 1 to 6 carbon linear or branched alkyl group or a C 1 to 6 carbon atoms, R ₄ and At least one of R ₅ is a fluorine-containing alkyl group.) In the non-aqueous solvent, the proportion of the carbonate-based solvent in the non-aqueous solvent is 65% by volume or less, and the proportion of the fluorine-containing phosphate ester and the fluorine-containing ether in the non-aqueous electrolyte is 35 volumes. 2. The nonaqueous electrolyte according to claim 1, wherein the volume ratio of the fluorine-containing phosphate ester to the fluorine-containing ether is 25:75 to 45:55. A nonaqueous electrolyte battery comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte according to claim 1.