JP5277045B2 - Non-aqueous electrolyte and lithium ion secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte solution capable of more improving cell characteristics of a lithium ion secondary cell and to provide a lithium ion secondary cell having excellent cell characteristics using such a nonaqueous electrolyte solution. <P>SOLUTION: A nonaqueous electrolyte solution used for a lithium ion secondary cell further contains a compound of silicon fluoride such as 1,2-bis-(dimethylfluorosilyl)ethane together with a lithium salt having an oxalato complex as anion, or these two components and carbonate ester having halogen atoms. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a non-aqueous electrolyte and a lithium ion secondary battery using the same, and further relates to an electronic device, a transport device, and the like equipped with such a lithium ion secondary battery as a power source.

  In recent years, lithium-ion batteries as secondary batteries have attracted attention as batteries that can achieve high output and high energy density, and have already been used as power sources in the area of small consumer devices such as personal computers, mobile phones, and portable music players. The lithium ion secondary battery, which is small and light, is expected to be put into practical use as an in-vehicle energy source for electric vehicles and hybrid vehicles in the automobile industry.

  In addition, among these applications, batteries used in small consumer devices are often used near room temperature, and even in their lifetime, long-term reliability required for in-vehicle use is always necessary. However, batteries for electric vehicles or hybrid vehicles are required to operate normally in the region from extremely low temperatures close to −40 ° C. to high temperatures of 60 ° C. or more, compared to consumer use. Therefore, it is required that it can be used in a very wide temperature range, and further, its life is required to function much longer than that for consumer use. For example, the goal of the US Advanced Battery Consortium (USABC) is to function as an in-vehicle lithium-ion battery for 15 years, equivalent to 240,000 km travel.

  For this reason, active research has been conducted on such lithium ion secondary batteries, and the non-aqueous electrolyte used in the lithium-ion secondary battery, that is, an electrolytic solution obtained by dissolving an electrolyte salt containing lithium in a non-aqueous solvent. Various proposals have also been made for liquids. For example, in Patent Document 1, a lithium salt having an oxalato complex as an anion and a film forming agent such as vinylene carbonate are added at a high temperature. A method for improving the storage characteristics and improving the cycle characteristics has been proposed.

  However, in the non-aqueous electrolyte disclosed in Patent Document 1, a secondary salt is added by adding a lithium salt having an oxalato complex as an anion together with a film forming agent such as vinylene carbonate. Although the deterioration as a battery is small and improved as suggested, the effect is limited to use under mild conditions, and the problem is that it shows great deterioration when used under more severe conditions Therefore, a lithium-ion secondary battery that can sufficiently meet future advanced needs has not been obtained.

  In Patent Document 2, a non-aqueous electrolyte of a lithium ion secondary battery is used in combination with bis (trifluoromethanesulfonyl) imide lithium and a Si compound such as cyclic siloxane such as hexamethylcyclotrisiloxane. In addition, there has been proposed a technique for improving the high-temperature storage characteristics and the cycle characteristics while suppressing the excessive side reaction between the electrode and the non-aqueous electrolyte by improving the output characteristics. However, even if these methods are used, a certain effect is recognized, but a device that can exhibit higher battery characteristics is desired.

JP 2006-216378 A JP 2007-180015 A

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is to provide a non-aqueous electrolyte that can further improve the battery characteristics of the lithium ion secondary battery. In particular, by using such a non-aqueous electrolyte, a lithium ion secondary battery having excellent battery characteristics is realized, and further, an electronic device, a transportation device, etc. provided with such a lithium ion secondary battery Is to provide.

  The present invention can be suitably implemented in various modes as listed below in order to solve the problems described above or the problems grasped from the description of the entire specification. Each described aspect can be employed in any combination. It should be noted that aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the description of the entire specification or the inventive idea disclosed therein. Should be understood.

［但し、式中、Ｒ₁ は、アルキレン基、アルキレンジオキシ基、アルケニレン基、アルケニレンジオキシ基、アルキニレン基、アルキニレンジオキシ基、アリーレン基又はアリーレンジオキシ基を示す。Ｒ₂〜Ｒ₅は、各々独立して、アルキル基、アルケニル基、アルキニル基、シクロアルキル基、シクロアルケニル基、アリール基又はハロゲンを示す。］ (1) A lithium salt having an oxalato complex as an anion as a non-aqueous electrolyte solution used in a lithium ion secondary battery obtained by dissolving an electrolyte salt containing lithium in a non-aqueous solvent, and the following general formula (I) A non-aqueous electrolyte characterized by containing a silicon fluoride compound represented.

[Wherein, R ₁ represents an alkylene group, an alkylenedioxy group, an alkenylene group, an alkenylene dioxy group, an alkynylene group, an alkynylene dioxy group, an arylene group or an arylene oxy group. R _{2 to} R ₅ each independently represents an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, a cycloalkenyl group, an aryl group or a halogen. ]

(2) The nonaqueous electrolytic solution according to the above aspect (1), further comprising a carbonic acid ester having a halogen atom.

(3) The nonaqueous electrolytic solution according to the above aspect (2), wherein the carbonic acid ester having a halogen atom is contained in the nonaqueous electrolytic solution in a proportion of 0.01% by weight or more.

(4) The above aspect (2), wherein the carbonic acid ester having a halogen atom is at least one fluorine atom-containing carbonic acid ester selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, fluoromethylethylene carbonate, and derivatives thereof. Or the nonaqueous electrolyte solution as described in (3).

(5) The nonaqueous electrolytic solution according to any one of the above aspects (1) to (4), wherein the lithium salt having the oxalato complex as an anion is lithium bis (oxalato) borate.

(6) In any one of the above embodiments (1) to (5), a lithium salt having the oxalato complex as an anion is contained in a non-aqueous electrolyte at a ratio of 0.01% by weight or more. The non-aqueous electrolyte described.

(7) The said aspect (1) thru | or (6) in which the silicon fluoride compound represented by the said general formula (I) is contained in the ratio of 0.01 weight% or more in the non-aqueous electrolyte. The nonaqueous electrolytic solution according to any one of the above.

(8) In a lithium ion secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolytic solution that is interposed between the positive electrode and the negative electrode and conducts lithium ions, A lithium ion secondary battery, wherein the non-aqueous electrolyte according to any one of the above aspects (1) to (7) is used as the electrolyte.

  Thus, in the non-aqueous electrolyte used for the lithium ion secondary battery according to the present invention, a lithium salt having an oxalato complex as an anion, and a silicon fluoride compound represented by the general formula (I) In this case, the cycle characteristics in the repeated charge / discharge of such a lithium ion secondary battery can be further improved, and the increase in internal resistance can be effectively suppressed. . Further, such an improvement in characteristics can be realized even more advantageously by containing a carbonic acid ester having a halogen atom.

  The reason why such an effect can be obtained in the present invention has not yet been fully elucidated, but has been estimated as follows so far. That is, the lithium salt having an oxalate complex as an anion and the specific silicon fluoride compound, or these two components and a carbonic acid ester having a halogen atom react appropriately at the negative electrode and the positive electrode, and the lithium ion permeability This composite coating suppresses excessive side reactions between the highly active electrode and the non-aqueous electrolyte, and reduces the reaction resistance related to lithium ion desorption. As a result, it is estimated that the high-temperature storage characteristics and the cycle characteristics are improved while suppressing the increase in resistance and improving the output characteristics.

By the way, the non-aqueous electrolyte used in the lithium ion secondary battery is generally one that can be prepared by dissolving an electrolyte salt containing lithium in a predetermined non-aqueous solvent. As is well known, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Inorganic salts and organic salts such as LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, and LiClO ₄ can be mentioned. In addition, two or more of these lithium salts can be used in combination. The electrolyte salt generally has a concentration in the non-aqueous electrolyte of about 0.1 mol / L to 3.0 mol / L, preferably about 0.5 mol / L to 2.0 mol / L, more preferably It is contained at about 0.8 mol / L to 1.6 mol / L. If the concentration of the electrolyte salt is too low, the ionic conductivity of the non-aqueous electrolyte is lowered, and if the concentration is too high, the viscosity increases and the battery performance is lowered. It will be.

  As the non-aqueous solvent for dissolving the electrolyte salt containing lithium, various known organic solvents can be used, for example, carbonates, lactones, ethers, sulfolanes, dioxolanes, ionic liquids, etc. I can do it. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-carbonate, Examples include chain carbonates such as -i-propyl carbonate and t-butyl-i-propyl carbonate, and examples of lactones include γ-butyl lactone and γ-valerolactone, and ethers. Can include cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran, and chain ethers such as dimethoxyethane and dimethoxymethane. Examples of tramethylsulfolane and the like, and examples of dioxolanes include 1,3-dioxolane.

  Among these, a combination of at least one cyclic carbonate that is a high dielectric constant solvent and at least one chain carbonate or ether that is a low viscosity solvent is advantageously used. That is, when Li-containing electrolyte salt coexists in a non-aqueous electrolyte solution, unless ionization of the Li-containing electrolyte salt is promoted, its ionic conductivity changes greatly. This is because it is desirable to use a solvent having a high dielectric constant in order to further promote ionization. In addition, since the high dielectric constant solvent has a high viscosity and it is difficult to obtain sufficient ion mobility as it is, a low-viscosity solvent that does not decompose in the potential window of the lithium ion battery is further mixed with lithium ions. This is because it becomes easy to move.

  In the present invention, a non-aqueous electrolyte obtained by dissolving an electrolyte salt containing lithium as described above in a predetermined non-aqueous solvent, a lithium salt having an oxalato complex as an anion, and the general formula ( The battery characteristics in the lithium ion secondary battery could be further improved by containing the silicon fluoride compound represented by I) or by containing a carbonate ester having a halogen atom together with these two components. It is.

Here, as is well known, the lithium salt used in the present invention having the above oxalate complex as an anion is a lithium salt having an anion in which C ₂ O ₄ ²⁻ is coordinated to the central atom. Examples thereof include lithium bis (oxalato) borate, lithium difluorooxalatoborate, lithium difluorobis (oxalato) phosphate, lithium tris (oxalato) phosphate, etc. In particular, in the present invention, lithium bis ( Oxalato) borate (LiBOB) will be used advantageously. In addition, two or more of these lithium salts can be used in combination.

  Such a lithium salt having an oxalato complex as an anion is generally contained in a non-aqueous electrolyte at a ratio of 0.01% by weight or more, and more preferably 0.05% by weight or more and 10% by weight or less. In particular, it is more preferably 0.1% by weight or more and 5% by weight or less. If the content is 0.01% by weight or more, it is possible to sufficiently suppress the decrease in battery capacity when repeated charging and discharging, and further, as a content of 10% by weight or less, By suppressing the content of the lithium salt having an oxalato complex as an anion, an increase in resistance due to the coating film formed on the electrode can be advantageously suppressed. In particular, when the content is 0.1% by weight or more and 5% by weight or less, the above effect can be further enhanced.

Further, the silicon fluoride compound represented by the general formula (I), which is further added to the non-aqueous electrolyte according to the present invention, is not particularly limited, but as R ₁ , methylene, ethylene, Alkylene groups such as trimethylene, 2,2-dimethyltrimethylene, tetramethylene, pentamethylene, hexamethylene, or alkylenedioxy groups derived from these groups; alkenylene such as vinylene, propenylene, isopropenylene, butenylene, pentenylene, etc. Or alkenylene dioxy groups derived from these groups; alkynylene groups such as ethynylene, propynylene, butynylene, pentynylene, 1,1,4,4-tetramethylbutynylene, or alkynylenes derived from these groups Rangeoxy group; phenylene, methylphenylene, dimethyl Eniren, arylene groups such as t- butyl phenylene, or arylene dioxy group derived from these groups. R _{2 to} R ₅ are each independently an alkyl group such as methyl, ethyl, propyl, butyl, s-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, 2-ethyl-hexyl, nonyl, decyl, etc. Alkenyl groups such as vinyl, allyl, 1-propenyl, isopropenyl, 2-butenyl, 1,3-butadienyl, 2-pentenyl, 2-octenyl, nonenyl, decenyl; ethynyl, 2-propynyl, 1,1-dimethyl- Alkynyl groups such as 2-propynyl; cycloalkyl groups such as cyclopentyl, cyclohexyl and cycloheptyl; cycloalkenyl groups such as cyclopentenyl and cyclohexenyl; aryl groups such as phenyl, methylphenyl, dimethylphenyl and t-butylphenyl; or fluorine Atoms, chlorine atoms, bromine atoms, iodine atoms, etc. It can be mentioned androgenic atom.

  Further, as the silicon fluoride compound represented by the general formula (I), more specifically, bis (dimethylfluorosilyl) methane, 1,2-bis (dimethylfluorosilyl) ethane, 1,3-bis (Dimethylfluorosilyl) propane, 1,4-bis (dimethylfluorosilyl) butane, 1,4-bis (dimethylfluorosilyl) methylbutane, 1,4-bis (dimethylfluorosilyl) benzene, 1,2-bis (dimethyl) Fluorosilyl) ethylene, 1,4-bis (dimethylfluorosilyl) -2-butene, 1,2-bis (dimethylfluorosilyl) acetylene, 1,4-bis (dimethylfluorosilyl) -2-butyne I can do it. Moreover, it is also possible to use them combining 2 or more types.

  The silicon fluoride compound represented by the general formula (I) is generally contained in a ratio of 0.01% by weight or more in the nonaqueous electrolytic solution, and more preferably 0.05% by weight or more and 5% by weight or less. In particular, it is more preferably 0.1% by weight or more and 2% by weight or less. If the content is 0.01% by weight or more, an increase in battery resistance when charging and discharging is repeated can be sufficiently suppressed, and the content is 5% by weight or less. By suppressing the increase in resistance, an increase in resistance due to the coating formed on the electrode can be advantageously suppressed. In addition, the said effect can be acquired much larger by making this content into 0.1 to 2 weight%.

  Further, according to the present invention, the halogenated carbonate ester further added to the non-aqueous electrolyte includes 4-fluoroethylene carbonate, 4-chloroethylene carbonate, 4-bromoethylene carbonate, 4,5-difluoroethylene carbonate. , 4-fluoromethylethylene carbonate, 4-trifluoromethylethylene carbonate, and the like can be mentioned. Particularly, in the present invention, 4-fluoroethylene carbonate (FEC) is advantageously used. Moreover, it is also possible to use in combination of two or more of these carbonates having halogen.

  The halogenated carbonate ester is generally contained in the non-aqueous electrolyte at a ratio of 0.01% by weight or more, and preferably 0.05% by weight or more and 10% by weight or less. More preferably, the content is 0.1% by weight or more and 5% by weight or less. If the content is 0.01% by weight or more, an increase in battery resistance when charging and discharging is repeated can be sufficiently suppressed, and the content is 10% by weight or less. By suppressing this, an increase in resistance due to the coating formed on the electrode can be advantageously suppressed. It should be noted that by making the content 0.1% by weight or more and 5% by weight or less, it is possible to obtain a greater effect as described above.

  As described above, in the present invention, the lithium salt having an oxalato complex as an anion, the silicon fluoride compound represented by the general formula (I), and the carbonic acid ester having a halogen are each in the proportions described above. In particular, these two or three components are preferably adjusted so that the total content thereof is 10% by weight or less in the non-aqueous electrolyte. It is more preferably 5% by weight or less, and further more preferably 3% by weight or less. And considering the relationship between the contents of these three components and the effect obtained and the cost, the total content of these two or three components is a ratio of 0.1 wt% or more and 2 wt% or less. It can be said that such adjustment is even more preferable.

The non-aqueous electrolyte of the lithium ion secondary battery according to the present invention may contain various known additive components in addition to the above-described essential additive components without impairing the effects of the present invention. It can be contained in any amount within the range. Specific examples of such other compounds that are optional components include, for example,
(1) Aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Overcharge inhibitors such as partially fluorinated compounds of the aromatic compounds such as benzene and p-cyclohexylfluorobenzene;
(2) Unsaturated bond-containing carbonates such as vinylene carbonate and vinyl ethylene carbonate; negative electrode film forming agents such as acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, and citraconic anhydride;
(3) Ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, propene sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl Sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, sulfate esters such as glycol sulfate and propylene glycol sulfate; Cathode protection of sulfonic acid esters such as methyl methanesulfonate Agent;
(4) Phosphate esters such as trimethyl phosphate and triethyl phosphate; Flame retardants such as polyphosphates such as melamine polyphosphate, ammonium polyphosphate, ethylenediamine diamine phosphate, hexamethylenediamine polyphosphate, piperazine polyphosphate Agent;
Etc.

  Of the various optional additives described above, biphenyl, terphenyl (or a partially hydrogenated product thereof), cyclohexylbenzene, and t-butylbenzene are preferably used as the overcharge inhibitor. They may be used in combination of two or more types.

  Of the above, vinylene carbonate, vinyl ethylene carbonate, succinic anhydride, and maleic anhydride are preferably used as the negative electrode film forming agent. Two or more of these may be used in combination. Furthermore, as the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, or methyl methanesulfonate is preferably used. Two or more of these may be used in combination. And combined use with a negative electrode film formation agent and a positive electrode protective agent, and combined use with an overcharge inhibitor, a negative electrode film formation agent, and a positive electrode protective agent are employ | adopted especially preferably.

  Furthermore, the content ratio of these other compounds in the non-aqueous electrolyte solution is not particularly limited, but is preferably 0.01% by weight or more and 10% by weight or less, respectively, with respect to the entire non-aqueous electrolyte solution. More preferably, they are 0.1 weight% or more and 5 weight% or less, Most preferably, they are 0.2 weight% or more and 2 weight% or less. By adding these compounds, it is possible to suppress rupture / ignition of the battery at the time of abnormality due to overcharge, and to improve the capacity retention rate and cycle characteristics after high temperature storage.

  By the way, as is well known, a lithium ion secondary battery using a non-aqueous electrolyte according to the present invention as described above includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and these positive and negative electrodes. In the structure containing the nonaqueous electrolyte solution according to the present invention interposed between the two, it is basically configured.

  In this regard, the positive electrode is generally configured to include a positive electrode active material, a conductive material, and a binder. Specifically, a positive electrode slurry obtained by mixing the positive electrode active material, the conductive material, and the binder with an appropriate solvent is used, and this is applied to a predetermined positive electrode current collector foil with an appropriate coating device. By coating on top, a positive electrode sheet is formed and used as a target positive electrode.

Examples of the positive electrode active material that is one of the components that provide such a positive electrode include lithium-containing transition metal composite oxides and lithium-containing transition metal phosphorous oxides that can occlude and release lithium ions. Examples of the lithium-containing transition metal oxide include lithium cobalt-based composite oxide (typically LiCoO ₂ ), lithium nickel-based composite oxide (typically LiNiO ₂ ), lithium manganese-based composite oxide (typical Include LiMn ₂ O ₄ ), lithium vanadium-based composite oxides (typically LiV ₂ O ₃ ), and composite oxides containing two or more transition metals. Examples of the lithium-containing transition metal phosphorous oxide include iron phosphorous oxide (typically LiFePO ₄ ), cobalt phosphorous oxide (typically LiCoPO ₄ ), and composite phosphorous oxide containing two or more transition metals. Etc.

  In addition, the conductive material is for ensuring the electrical conductivity of the positive electrode, and generally, various known carbon powder materials are used. For example, there is no reaction with a non-aqueous electrolyte and a good volume resistivity. Therefore, carbon black such as acetylene black or carbon fine powder such as carbon fiber is used. Furthermore, the binder serves to bind the active material particles and the conductive material particles, and is generally a polymer that has no decomposition reaction at the potential of the lithium ion secondary battery and is insoluble in the non-aqueous electrolyte. For example, polyvinylidene fluoride, polyethylene oxide, polypropylene oxide and the like are preferably used. Examples of the solvent in which the positive electrode active material, the conductive material, and the binder are dispersed include, for example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like are used, and aluminum, stainless steel, nickel-plated steel, and the like are employed as the material of the current collector foil that becomes the current collector.

  Furthermore, the negative electrode in the lithium ion secondary battery is generally configured to include a negative electrode active material and a binder, and a conductive material is appropriately mixed and used in order to reduce the electric resistance. . In addition, an appropriate solvent is added to the conductive material blended as necessary with the negative electrode active material and the binder, as in the case of the positive electrode described above, and a predetermined negative paste material is obtained as a paste-like negative electrode material. It is used as a negative electrode sheet by coating on the surface of the current collector.

  The negative electrode active material, which is one of the components constituting such a negative electrode, is not particularly limited as long as it can electrochemically occlude and release lithium ions. Natural graphite, artificial carbon materials, coke Examples thereof include carbonaceous materials such as tin oxide, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, and metals that can form alloys with lithium such as Sn and Si. These may be used alone or in combination of two or more in any combination and ratio. Among these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety. As the binder, polyvinylidene fluoride, polyethylene oxide, polypropylene oxide, and the like are preferably used as in the case of the positive electrode described above, and the conductive material has no reaction with the non-aqueous electrolyte and is good. Therefore, carbon black such as acetylene black and fine powder such as vapor grown carbon fiber are advantageously used because of having a large volume resistivity (less than 100 Ω · cm). Furthermore, foils of copper, nickel, stainless steel, nickel-plated steel, etc. can be used for the negative electrode current collector.

  Also in the lithium ion secondary battery constructed according to the present invention, an appropriate separator can be disposed between the negative electrode and the positive electrode, as in the prior art. As this separator, what is conventionally used with the lithium ion battery for small consumer devices may be used, and it is not specifically limited. However, it is desirable that the positive electrode and the negative electrode can be separated and the electrolyte solution can be held. For that purpose, a non-woven fabric, a polyolefin microporous film (film) such as polyethylene, polypropylene, etc. It will be used suitably.

  In addition, the shape of the lithium ion secondary battery to which the present invention is applied is not particularly limited, and the present invention can be applied to various conventionally known shapes or structures, For example, a coin shape, a button shape, a sheet shape, a stacked shape, a cylindrical shape, a flat shape, a square shape, or the like can be employed. In addition, the present invention can be advantageously applied to large-sized ones used for transportation equipment such as electric vehicles.

  The embodiment of the present invention has been described in detail above, but it is merely an example, and the present invention is interpreted in a limited manner by a specific description according to such an embodiment. It should be understood that it is not. The present invention can be implemented in variously modified, modified, improved, and other forms based on the knowledge of those skilled in the art, and such embodiments do not depart from the spirit of the present invention. It goes without saying that both belong to the category of the present invention.

  Hereinafter, representative examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited by the description of such examples. That should also be understood.

-Preparation of non-aqueous electrolyte-
LiPF ₆ has a concentration of 1 mol / L with respect to a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and dimethyl carbonate in a volume ratio of 1: 1: 1: 1. Furthermore, lithium bis (oxalato) borate (LiBOB) is blended in a proportion of 0.2% by weight as a lithium salt having an oxalato complex as an anion, and is represented by the general formula (I) As a silicon fluoride compound, 1,2-bis (dimethylfluorosilyl) ethane was blended at a ratio of 0.35% by weight, dissolved and contained, respectively, to prepare a non-aqueous electrolyte according to Experimental Example 1 did.

  In addition, Experimental Example 1 described above except that the blending amount of 1,2-bis (dimethylfluorosilyl) ethane in Experimental Example 1 is 0.1% by weight, 1.0% by weight, or 2.0% by weight. In the same manner as in the above, a nonaqueous electrolytic solution according to Experimental Example 2, 3 or 4 was prepared.

  Furthermore, a nonaqueous electrolytic solution according to Experimental Example 5 was prepared in the same manner as in Experimental Example 1 except that the blending amount of LiBOB in Experimental Example 1 was 1.0% by weight.

  Furthermore, instead of 1,2-bis (dimethylfluorosilyl) ethane in Experimental Example 1, 1,4-bis (dimethylfluorosilyl) methylbutane, 1,2-bis (dimethylfluorosilyl) ethylene, or 1,4- A nonaqueous electrolytic solution according to Experimental Example 6, 7 or 8 was prepared in the same manner as in Experimental Example 1 except that bis (dimethylfluorosilyl) benzene was used.

  On the other hand, for comparison, a nonaqueous electrolytic solution was prepared in the same manner as in Experimental Example 1 except that LiBOB and 1,2-bis (dimethylfluorosilyl) ethane in Experimental Example 1 were not added. The nonaqueous electrolytic solution according to Comparative Example 1 was obtained.

  Further, in Experimental Example 1, non-aqueous electrolysis was carried out in the same manner as in Experimental Example 1, except that only 1,2-bis (dimethylfluorosilyl) ethane was not added or only LiBOB was not added. A liquid was prepared and used as a non-aqueous electrolyte according to Comparative Example 2 or Comparative Example 3, respectively.

  Further, the content concentration of LiBOB in the electrolytic solution in Experimental Example 1 was set to 0.4% by weight, and 1,2-bis (dimethylfluorosilyl) ethane was not blended. Thus, a nonaqueous electrolytic solution according to Comparative Example 4 was prepared.

-Fabrication of lithium ion secondary battery-
[Production of positive electrode]
90% by mass of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the positive electrode active material, 5% by mass of acetylene black as the conductive agent, and 5% of polyvinylidene fluoride (PVdF) as the binder % By mass was mixed in N-methylpyrrolidone solvent to make a slurry. Next, the obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, and rolled into a thickness of 64 μm by a press machine, and the active material layer had a width of 80 mm and a length of 120 mm. And was cut out into a shape having an uncoated part with a width of 15 mm.

[Production of negative electrode]
Also, 90% by mass of hard carbon as the negative electrode active material, 5% by mass of carbon nanofiber (VGCF manufactured by Showa Denko KK) as the conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as the binder. % In an N-methylpyrrolidone solvent and slurried. Subsequently, the obtained slurry was applied to both sides of a copper foil having a thickness of 14 μm, dried, and rolled to a thickness of 108 μm with a press machine, and the active material layer had a width of 83 mm and a length of 124 mm. A negative electrode was cut into a shape having an uncoated part with a size of 13 mm and a width of 13 mm.

[Battery assembly]
The 20 positive electrodes and 21 negative electrodes thus obtained were alternately arranged, and a porous polypropylene sheet separator (thickness 25 μm) was sandwiched between the electrodes, and the layers were laminated. . At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. A current collector tab is prepared by welding uncoated portions of each of the positive electrode and the negative electrode to a metal current collector, and an electrode group is formed as a laminated outer package (outside dimension: 160 × 90 × 6 mm). ). Thereafter, 18 mL of each of the non-aqueous electrolytes according to Experimental Examples 1 to 8 and Comparative Examples 1 to 4 prepared above was injected into the battery loaded with such an electrode group, and the electrodes were sufficiently infiltrated and sealed. As a result, lithium ion secondary batteries according to Experimental Examples 1 to 8 and Comparative Examples 1 to 4 were produced. The electric capacity of the battery element housed in one battery exterior of the secondary battery, that is, the rated discharge capacity of the battery is about 2 ampere hours (Ah), and the DC resistance measured by the 10 kHz AC method. The component was about 1 milliohm (mΩ).

<Battery evaluation>
-Capacity measurement-
Using the lithium ion secondary batteries of Experimental Examples 1 to 8 and Comparative Examples 1 to 4 prepared above, at 25 ° C., voltage range: 4.2 V to 2.7 V, current value: 0.2 C (1 hour rate 6 cycles initial charge / discharge was performed at a current value of 1 C for the rated capacity due to the discharge capacity of 1 C, and so on. And the 1C discharge capacity of the 6th cycle at this time was made into the initial stage capacity.

-Cycle test-
Using the lithium ion secondary batteries of Experimental Examples 1 to 8 and Comparative Examples 1 to 4 obtained above, a cycle test in a high temperature environment of 65 ° C. that is regarded as an actual use upper limit temperature of the lithium secondary battery Was done. In this cycle test, after charging the battery SOC (state of charge) to 60% at a constant current and constant voltage, the following charge / discharge mode was repeated for 3 cycles, and then the SOC was constant current and constant voltage to 70%. After charging the battery, the following charge / discharge mode is repeated for 3 cycles, and then the SOC is charged at a constant current / constant voltage up to 80%. Then, the following charge / discharge mode is repeated for 3 cycles, followed by a constant current until the SOC reaches 60%. It was decided to repeat the charge / discharge mode for a total of 9 cycles of discharging at a constant voltage and adjusting to SOC 60% at the start as one set. In one cycle of the charge / discharge mode, the discharge is 6.7 seconds at 100C, the regeneration is 6 times continuously at 1-2 seconds at 50C, and the rest time between the discharge and regeneration is 5 seconds. To make up. Moreover, the charge upper limit voltage was set to 4.2 V, the discharge lower limit voltage was set to 2.7 V, and in the event that the upper limit voltage was reached, current adjustment was performed so as to maintain the voltage. The above set was repeated up to 4000 sets.

-Initial resistance measurement and resistance measurement after cycle test-
Under the environment of 25 ° C, the state of charge is adjusted every 10% from SOC 20% to 80%, and discharged under 10C, 15C, 20C, 25C for 12 seconds under each state of charge. The voltage was measured. The area of the triangle surrounded by the current-voltage straight line and the lower limit voltage (2.4V) is the discharge output (W), and the area of the triangle surrounded by the current-voltage straight line and the upper limit voltage (4.2V) is Regenerative output (W). In addition, the discharge output in SOC50% is used for the comparison regarding resistance.

-Measurement of capacity retention rate-
The value obtained by dividing the 1C discharge capacity after the end of the cycle test consisting of the above 4000 sets by the initial 1C discharge capacity was defined as the capacity retention rate.

-Measurement of resistance increase rate-
The value obtained by dividing the discharge output at 50% SOC after the end of the cycle test consisting of the above 4000 sets by the discharge output at 50% of the initial SOC was defined as the resistance increase rate.

  The results of measurement relating to the discharge capacity maintenance rate, initial resistance characteristics, and battery resistance increase rate for the lithium ion secondary batteries according to Experimental Examples 1 to 8 and Comparative Examples 1 to 4 thus obtained are shown in Table 1 below. .

  As is clear from the results in Table 1, in accordance with the present invention, a lithium salt having an oxalato complex as an anion and a non-aqueous electrolyte obtained by dissolving an electrolyte salt containing lithium in a non-aqueous solvent, In the lithium ion secondary battery (Experimental Examples 1 to 8) using the non-aqueous electrolyte obtained by adding and blending the silicon fluoride compound represented by the formula (I), at least one of them is contained. Compared to the lithium ion batteries according to Comparative Examples 1 to 4, the initial resistance, the capacity retention rate after the cycle test, and the resistance increase rate are advantageous even when used under severe conditions such as those implemented this time. It has been confirmed that this has been improved.

  In Experimental Example 1, 4-fluoroethylene carbonate (FEC) was further added and contained at a ratio of 0.1% by weight, 1.0% by weight or 2.0% by weight, and Experimental Example 9, 10 or 11 was added. A non-aqueous electrolyte was prepared. In Experimental Example 10, 1,4-bis (dimethylfluorosilyl) methylbutane was used in place of 1,2-bis (dimethylfluorosilyl) ethane to prepare a nonaqueous electrolytic solution according to Experimental Example 12. Further, in Experimental Example 10, a nonaqueous electrolytic solution according to Experimental Example 13 was prepared using 4-fluoromethylethylene carbonate instead of FEC. Using these non-aqueous electrolytes, lithium ion secondary batteries were produced in the same manner as in Experimental Example 1.

  About the lithium ion secondary battery which concerns on Experimental Examples 9-13 obtained in this way, the test similar to previous Experimental Examples 1-8 was done, and the initial stage resistance, the capacity | capacitance maintenance factor, and the resistance increase rate were calculated | required. The obtained results are shown in Table 2.

  As can be seen from the results of Table 2, according to Experimental Examples 9 to 13, the capacity retention rate is improved and the effect of suppressing the resistance increase rate is seen as compared with Experimental Example 1 that does not contain a carbonate containing halogen. It was. That is, according to the present invention, a non-aqueous electrolyte obtained by dissolving an electrolyte salt containing lithium in a non-aqueous solvent is further mixed with a lithium salt having an oxalato complex as an anion and a fluorine represented by the general formula (I). It has been found that a higher effect can be obtained by adding and compounding a silicon fluoride compound and a carbonate containing halogen.

Claims (6)

Lithium bis (oxalato) borate and a fluoride represented by the following general formula (I) are prepared as a nonaqueous electrolyte solution for use in a lithium ion secondary battery by dissolving an electrolyte salt containing lithium in a nonaqueous solvent. A non-aqueous electrolyte characterized by containing a silicon compound.

[Wherein, R ₁ represents an alkylene group, an alkylenedioxy group, an alkenylene group, an alkenylene dioxy group, an alkynylene group, an alkynylene dioxy group, an arylene group or an arylene oxy group. R _{2 to} R ₅ each independently represents an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, a cycloalkenyl group, an aryl group or a halogen. ] The non-condensed product according to claim 1, further comprising at least one fluorine atom-containing carbonate selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, fluoromethylethylene carbonate, and derivatives thereof. Water electrolyte. The nonaqueous electrolytic solution according to claim 2, wherein the fluorine atom-containing carbonate is contained in the nonaqueous electrolytic solution in a proportion of 0.01% by weight or more. The nonaqueous electrolytic solution according to any one of claims 1 to 3 , wherein the lithium bis (oxalato) borate is contained in the nonaqueous electrolytic solution in a proportion of 0.01% by weight or more. Fluorinated silicon compound represented by the general formula (I), in the nonaqueous electrolyte solution, to any one of claims 1 to 4 are allowed to contain in the ratio of more than 0.01 wt% The non-aqueous electrolyte described. In a lithium ion secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte solution that is interposed between the positive electrode and the negative electrode and conducts lithium ions, A lithium ion secondary battery using the nonaqueous electrolytic solution according to any one of claims 1 to 5 .