Fluorobenzonitrile compound, nonaqueous electrolyte solution for lithium ion secondary battery, and lithium ion secondary battery using same

Abstract

Provided are: a nonaqueous electrolyte solution for a lithium ion secondary battery, with which it is possible to achieve excellent charge / discharge cycle characteristics; and a lithium ion secondary battery which has excellent charge / discharge cycle characteristics.　The nonaqueous electrolyte solution for a lithium ion secondary battery according to the present invention is obtained by dissolving an electrolyte salt in a nonaqueous solvent, and contains at least one compound selected from among fluorobenzonitrile compounds having a specific structure (excluding 2-nitrile 4-fluorobenzoic acid). The lithium ion secondary battery according to the present invention is provided with a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte solution that is the above-described nonaqueous electrolyte solution for a lithium ion secondary battery.

Description

Nitrile fluorobenzoate compounds, non-aqueous electrolyte for lithium-ion secondary batteries, and lithium-ion secondary batteries using the same

[0001] The present invention relates to a fluorobenzoate nitrile compound useful as an intermediate raw material or battery material for pharmaceuticals, agrochemicals, electronic materials, polymer materials, etc., and to a non-aqueous electrolyte for lithium-ion secondary batteries using the fluorobenzoate nitrile compound, which is excellent in battery characteristics such as battery cycle life and also possesses safety features such as corrosion resistance, and to a lithium-ion secondary battery using the same.

[0002] Currently, lithium-ion batteries (LIBs) are the mainstream of secondary batteries and are widely used as power sources for mobile devices such as smartphones and laptops, as well as electric vehicles. The positive electrode active material of a lithium-ion battery is a lithium composite oxide containing Ni, the negative electrode is graphite, and the electrolyte is a non-aqueous solvent mixture of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), etc., with LiPF added. ６ Furthermore, lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) have come into use. In recent years, LIBs have become more high-capacity and high-voltage, and performance requirements (capacity, cycle characteristics, input / output characteristics, safety, etc.) have been increasing year by year. Current LIBs for electric vehicles are evolving in the direction of increasing nickel content for the positive electrode material, and further increasing the proportion of silicon-based materials in the negative electrode by mixing silicon-based materials with the graphite material that has been used for a long time. The purpose of this is to increase the overall energy density of the battery and extend the driving range of electric vehicles. For this reason, additives such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC), which have been used for many years as additives in the non-aqueous electrolyte of LIBs, are becoming less and less able to satisfy the increasingly high performance levels of the future.

[0003] In the prior art, Patent Document 1 discloses that when a fluorinated benzoic acid ester compound represented by the following general formula is added to a non-aqueous electrolyte, the reaction between the carbon material and the electrolyte is suppressed when a carbon material is used as an active material, thereby improving charge-discharge efficiency, and furthermore, an excellent solvent that could not be conventionally applied can be applied to the electrolyte. Therefore, it is disclosed that according to the present invention, a lithium secondary battery excellent in temperature characteristics and flame retardancy can be provided (see paragraph 0032 of the same document).

[0004] In the same document, R in the above general formula １ to R ５ are any one of H, F, CF ３ , and at least one of them is F or CF ３ , and R Ｈ is C ｎ H ２ｎ＋１ (1≦n≦3). Specific examples of the above specific fluorinated benzoic acid ester compounds include methyl 2-fluorobenzoate, methyl 3-fluorobenzoate, methyl 4-fluorobenzoate, methyl 2,6-difluorobenzoate, methyl 2,3,4,5,6-pentafluorobenzoate, ethyl 2,6-difluorobenzoate, propyl 2,6-difluorobenzoate, etc. (see paragraph 0021 of the same document). R of these fluorinated benzoic acid ester compounds Ｈ are all saturated hydrocarbons such as methyl groups, ethyl groups, and propyl groups, but the charge-discharge cycle characteristics of lithium ion secondary batteries using these compounds were not satisfactory. In addition, in the same document, a fluorinated benzoic acid ester compound having a nitrile group in R Ｈ is not disclosed.

[0005] Further, Patent Document 2 discloses that when an ester compound represented by the following general formula is added to a non-aqueous electrolyte, a non-aqueous electrolyte for a lithium secondary battery that is excellent in initial battery capacity and cycle characteristics and can maintain battery performance over a long period of time, and a lithium ion secondary battery using the same can be provided.

[0006] In the same document, in the ester compound, R１１ , R １３ , R １４ and R １５ Each of these independently represents either a hydrogen atom or a fluorine atom, R １２ R represents a hydrogen atom, a fluorine atom, a methoxy group, or an ethoxy group. １１ ~R １５ One or more of them are fluorine atoms, and L ２ It is stated that it is preferable that the group be a propynyl group (propargyl group) (see claims 3 and 4 of the same document).

[0007] As a specific combination, 2,4-difluorobenzoate 2-propynyl [R １１ = R １３ = Fluorine atom, R １２ = R １４ = R １５ = Hydrogen atom, L ２ = 2-propynyl group], 2,3,4,5,6-pentafluorobenzoate 2-propynyl [R １１ = R １２ = R １３ = R １４ = R １５ = Fluorine atom, L ２ Combinations such as [=2-propynyl group] are mentioned (see paragraph 0040 of the same document). These ester compounds L ２ These are hydrocarbons containing triple bonds, such as propynyl groups (propargyl groups), but the charge-discharge cycle characteristics of lithium-ion secondary batteries using these compounds were not satisfactory. Furthermore, in the same document, L ２ There is absolutely no mention of ester compounds containing nitrile compounds.

[0008] Furthermore, Patent Document 3 discloses that excellent battery characteristics can be obtained by adding ester derivatives represented by the following general formula to a non-aqueous electrolyte. Here, R3 is a saturated hydrocarbon group, an unsaturated hydrocarbon group, an oxygen-containing saturated hydrocarbon group, a halogenated group thereof, or a group to which two or more of these are bonded, and R4 is a cyano group-containing group, a halogenated group thereof, or a group to which two or more of these are bonded.

[0009] As a specific compound, 4-fluorobenzoic acid 2-nitrile is mentioned below (see paragraph 0091 of the same document, formula (2-19)). However, this compound is not mentioned in the examples, and there is absolutely no disclosure regarding what electrolyte composition is suitable when using this compound, or what electrode configuration of LIB it is effective in. Furthermore, there is no description whatsoever of the synergistic effects when combined with other additives such as VC and FEC.

[0010] Japanese Patent Publication No. 2000-323169, International Publication No. 2008 / 093837, Japanese Patent Publication No. 2013-257958

[0011] The present invention aims to solve the aforementioned problems by providing a specific nitrile fluorobenzoate compound that is useful as an intermediate raw material or battery material for various materials, a non-aqueous electrolyte for lithium-ion secondary batteries using the nitrile fluorobenzoate compound that provides excellent charge-discharge cycle characteristics, which are important for secondary batteries used in vehicles such as electric vehicles, and a lithium-ion secondary battery using the same.

[0012] The inventors of the present invention conducted diligent research to solve the above problems and synthesized 11 types of fluorobenzoate nitrile compounds as shown below. They discovered that by adding these to a non-aqueous electrolyte, a lithium-ion secondary battery with excellent charge-discharge cycle characteristics can be obtained, thus completing the present invention.

[0013] In other words, the present invention comprises 11 types of fluorobenzoate nitrile compounds represented by the following formula.

[0014] Furthermore, the non-aqueous electrolyte for lithium-ion secondary batteries of the present invention is a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent, and is characterized by containing at least one fluorobenzoate nitrile compound selected from fluorobenzoate nitrile compounds represented by the following formulas (1) to (4) (excluding 4-fluorobenzoate 2-nitrile). In the formula, R １ ~R ５ Each of these atoms is independently either a hydrogen atom or a fluorine atom, and at least one of them is a fluorine atom.

[0015] In the non-aqueous electrolyte for lithium-ion secondary batteries of the present invention, it is preferable that the fluorobenzoate nitrile compound is contained in an amount of 0.01% to 5% by weight relative to the weight of the non-aqueous electrolyte, and that at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate is contained in an amount of 0.01% to 5% by weight relative to the weight of the non-aqueous electrolyte.

[0016] Furthermore, in the non-aqueous electrolyte for lithium-ion secondary batteries of the present invention, it is preferable that the fluorobenzoate nitrile compound is contained in an amount of 0.01% to 5% by weight relative to the weight of the non-aqueous electrolyte, and that 1,3-dioxane is contained in an amount of 0.01% to 5% by weight relative to the weight of the non-aqueous electrolyte.

[0017] The lithium-ion secondary battery of the present invention is a lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, characterized in that the non-aqueous electrolyte is the non-aqueous electrolyte for lithium-ion secondary batteries of the present invention.

[0018] By including a specific fluorobenzoic acid nitrile compound of the present invention, it is possible to provide a non-aqueous electrolyte for lithium-ion secondary batteries that provides excellent charge-discharge cycle characteristics, which are important for secondary batteries used in vehicles such as electric vehicles, and a lithium-ion secondary battery with excellent charge-discharge cycle characteristics.

[0019] The following are examples of embodiments and configurations of the present invention, but the present invention is not limited to these, and is included in the present invention as long as it is in line with the intent of the claims, means of solving the problem, effects of the invention, etc.

[0020] A non-aqueous electrolyte consists of an electrolyte salt and a non-aqueous solvent. The electrolyte salt in this invention is not particularly limited, but for example, LiPF2 containing phosphorus (P) ６、 LiPO ２ F ２ Equivalent to SO ２ LiN(SO) with a base ２ F) ２ (LiFSI), SO３ Lioso with a base ２ F, SO ４ LiOSO with a base ３ CH ３ , Lioso ３ C ２ H ５ Electrolyte salts such as lithium salts can be used. The electrolyte salt may be one type or two or more types. A preferred combination of these electrolyte salts is SO ２ Two types of combinations: an electrolyte salt with a group and an electrolyte salt with phosphorus (P), or SO ３ Electrolyte salts containing the group, SO ４ Three types of combinations are preferred: an electrolyte salt having a group, and an electrolyte salt having phosphorus (P). Specifically, LiFSI and LiPF ６ Or LiPO ２ F ２ Two types of combinations: LiFSI and LiOSO ３ CH ３ and LiPO ２ F ２ A combination of these three types is more preferable. The molar ratio of LiFSI to other Li salts is preferably 100 / 0 to 1 / 99, more preferably 100 / 0 to 60 / 40, and most preferably 100 / 0 to 80 / 20. Furthermore, the total concentration (mol / L) of the electrolyte salt is preferably in the range of 0.5 to 3, and more preferably in the range of 1 to 2. In addition, in the case of a non-aqueous electrolyte solution using an imide-based electrolyte salt such as LiFSI, there is a problem that operating under a high voltage exceeding 4.0V will corrode the aluminum used as the positive electrode current collector, but the fluorobenzoate nitrile compound of the present invention can improve the corrosion resistance of LIB.

[0021] As a non-aqueous solvent, a five-membered ring carbonate or a linear carbonate can be used as the main solvent. Suitable five-membered ring carbonates include, for example, ethylene carbonate (EC) and propylene carbonate (PC). When using a linear carbonate, suitable examples include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0022] In the non-aqueous electrolyte according to the present invention, a five-membered ring carbonate is used as the non-aqueous solvent, and the five-membered ring carbonate contains a chain-like ester (chain-like carbonate). From the viewpoint of improving electrochemical properties in high-temperature regions of 45°C or higher and low-temperature regions of -20°C or lower, the ratio of five-membered ring carbonate to chain-like carbonate (volume ratio) is preferably 10 / 90 to 50 / 50, and more preferably 20 / 80 to 40 / 60.

[0023] The content of the fluorobenzoic acid nitrile compound represented by the following formulas (1) to (4) (excluding 4-fluorobenzoic acid 2-nitrile) in the non-aqueous electrolyte for lithium-ion secondary batteries of the present invention is not particularly limited, but if it is too low, it may reduce the charge-discharge cycle characteristics. As a preferred range for the content of the fluorobenzoic acid nitrile compound relative to the total weight of the non-aqueous electrolyte for lithium-ion batteries of the present invention, if the content is too low, the effects of the present invention cannot be fully obtained, so the lower limit is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and most preferably 0.3% by weight or more relative to the non-aqueous electrolyte. Also, if the content is too high, the effects of the present invention cannot be fully obtained, so the upper limit is preferably 10% by weight or less, more preferably 5% by weight or less, and most preferably 3% by weight or less relative to the non-aqueous electrolyte.

[0024] In the formula, R １ ~R ５ Each of these atoms is independently either a hydrogen atom or a fluorine atom, and at least one of them is a fluorine atom.

[0025] The aforementioned fluorobenzoate nitrile compounds consist of 75 types, each comprising a combination of the fluorobenzoic acid structure and the R structure shown in Table 1.

[0026]

[0027] The non-aqueous electrolyte for lithium-ion secondary batteries of the present invention preferably contains at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, along with the compounds shown in Table 1, from the viewpoint of further improving the charge-discharge cycle characteristics of lithium-ion secondary batteries. In this case, it is preferable that the compounds shown in Table 1 be combined in an amount of 0.01% to 5% by weight relative to the non-aqueous electrolyte, and vinylene carbonate and / or fluoroethylene carbonate in an amount of 0.01% to 5% by weight. The lower limit of the content of the compounds shown in Table 1 is preferably 0.1% or more by weight, more preferably 0.5% or more by weight, and even more preferably 1% or more by weight relative to the non-aqueous electrolyte. Similarly, the upper limit is preferably 3% or less by weight, and more preferably 2% or less by weight relative to the non-aqueous electrolyte. The lower limit of the content of vinylene carbonate and / or fluoroethylene carbonate is preferably 0.1% or more by weight, more preferably 0.5% or more by weight, and even more preferably 1% or more by weight relative to the non-aqueous electrolyte. Similarly, the upper limit is preferably 3% by weight or less, and more preferably 2% by weight or less, relative to the non-aqueous electrolyte.

[0028] To improve the cyclic properties and corrosion resistance of the fluorobenzoate nitrile compound used in the present invention, the electrolyte of the present invention may contain 1,3-dioxane (DOX), a six-membered ring ether, in an amount ranging from 0.01% to 5% by weight. This makes it possible to achieve a high level of both cyclic properties and corrosion resistance at high voltages exceeding 4.2 V and / or above room temperature.

[0029] The reason why the combined use of DOX is preferable is speculative, but it is thought that when the fluorobenzoate nitrile compound acts electrochemically within the battery, the six-membered ring ether DOX also undergoes ring-opening polymerization, forming a polymer adsorption layer with a strong synergistic effect at the interface of the positive electrode active material and the negative electrode active material, thereby preventing contact with the main solvent of the electrolyte. The range of DOX use is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and most preferably 0.5% by weight or more relative to the non-aqueous electrolyte. The upper limit is preferably 5% by weight or less, more preferably 4% by weight or less, and most preferably 3% by weight or less relative to the non-aqueous electrolyte.

[0030] The present invention enables the use of lithium-ion secondary batteries without compromising corrosion resistance, even in non-aqueous electrolytes containing 0.01% to 5% by weight of 2-propargyl methanesulfonic acid (CAS RN: 16156-58-4) and 2-cyanoethyl methanesulfonic acid (CAS RN: 65885-27-0), which are preferable to use from the viewpoint of improving cycle life but are usually avoided due to their high corrosiveness.

[0031] Furthermore, the present invention makes it possible to use non-aqueous electrolytes containing dinitriles with carbon chain lengths of 2 to 5, such as succinonitrile, glutaronitrile, adiponitrile, and pimeronitrile, and carbodiimides such as N,N'-dicyclohexylcarbodiimide (DCC), without impairing the LIB's cycle characteristics. These compounds are preferably added in an amount of 0.1 to 5% by weight relative to the entire non-aqueous electrolyte.

[0032] The lithium-ion secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and the electrolyte for the lithium-ion secondary battery of the present invention. The positive electrode, negative electrode, and separator in the present invention are not particularly limited as long as they can be used in a lithium-ion secondary battery.

[0033] The separator used in the lithium-ion secondary battery of the present invention is most preferably a separator made of a microporous membrane (porous sheet) formed from a polyolefin material such as polypropylene or polyethylene, but a separator made of a nonwoven fabric can also be used. The porous sheet or nonwoven fabric may be single-layer or multi-layer, and the separator surface may be coated with an oxide such as alumina. The thickness of the separator needs to be as thin as possible in order to increase the volumetric energy density of the battery. For this reason, it is preferably 20 μm or less, and particularly preferably 10 μm or less.

[0034] In order to improve the volumetric energy density, graphite materials such as natural graphite or artificial graphite that can reversibly intercept and release lithium ions are preferred as the negative electrode active material for the lithium-ion secondary battery of the present invention. Furthermore, in order to increase capacity, silicon (Si), SiO, and SiO are added to the negative electrode in addition to the negative electrode active material. ２ Such silicon oxides can be suitably added. When the negative electrode active material is graphite and the negative electrode contains silicon or silicon oxide, the weight of silicon or silicon oxide in the solid content (non-volatile components) of the negative electrode mixture is preferably 1 to 30%, and more preferably 5 to 20%. Generally, when silicon or silicon oxide is included in the negative electrode, there is a problem that the charge-discharge cycle characteristics become poor. However, when using the non-aqueous electrolyte for secondary batteries to which the fluorobenzoate nitrile compound of the present invention has been added, the charge-discharge cycle characteristics can be improved even with a silicon or silicon oxide-containing negative electrode, and it is possible to achieve this while also improving capacity.

[0035] The negative electrode is manufactured by kneading the negative electrode active material with a binder selected from ethylene propylene diene polymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethylcellulose (CMC) to form a slurry-like negative electrode mixture. This negative electrode mixture is then applied to the copper foil or aluminum foil of the current collector, dried, pressure-molded, and then heat-treated, for example, under vacuum at 80°C.

[0036] Examples of positive electrode active materials used in the lithium-ion secondary battery of the present invention include LiCoO ２ (LCO), LiCo １／３ Ni １／３ Mn １／３ O ２ (NCM111), LiNi ０．５ Co ０．２ Mn ０．３ O ２ (NCM523), LiNi ０．６ Co ０．２ Mn ０．２ O ２ (NCM622), LiNi ０．８ Co０．１ Mn ０．１ O ２ Examples include (NCM811). To increase the volumetric energy density, NCM811 is preferably used as a positive electrode active material containing a lithium composite oxide with an atomic ratio of 50% or more Ni. In addition, to improve rapid charging and discharging, LiMn with a spinel-type structure is used. ２ O ４ (LMO), LiFePO with an olivine-type structure ４ (LFP) is preferably used.

[0037] The positive electrode is manufactured by kneading the positive electrode active material with a conductive additive and a binder to form a slurry-like positive electrode mixture, then coating this positive electrode mixture onto aluminum foil to be used as a current collector, drying and press-molding it, and finally heat-treating it, for example, under vacuum at 80°C. As the conductive additive, known or commercially available conductive additives such as acetylene black, Ketjen black or other carbon blacks, carbon nanotubes, carbon fibers, activated carbon, and graphite can be used. As the binder, binders selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethylcellulose (CMC) can be used.

[0038] In the lithium-ion secondary battery of the present invention, suitable combinations of positive electrode active material and negative electrode active material include LCO / graphite, NCM523 / graphite, and NCM811 / graphite in order to increase the volumetric energy density.

[0039] The current collector used in the present invention is not particularly limited, but aluminum foil or copper foil is preferred, and a porous current collector may be used to further improve the permeability of the electrolyte.

[0040] In the present invention, there are no particular restrictions on the solvent used as the binder, and various solvents can be selected depending on the active material or binder used. Specifically, when PVDF is used as the binder, N-methyl-2-pyrrolidone is preferably used as the solvent, while when rubber-based binders such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinyl alcohol, or carboxymethylcellulose (CMC) are used, water is preferably used as the solvent.

[0041] The structure of the lithium-ion secondary battery of the present invention is not particularly limited, but examples of secondary batteries having a positive electrode, a negative electrode, and a separator include coin-type batteries, cylindrical batteries, prismatic batteries, and pouch-type batteries. Among these, pouch-type batteries, which have excellent heat dissipation properties, are preferred.

[0042] The following describes examples of the synthesis of fluorobenzoate nitrile compounds of the present invention and examples using the non-aqueous electrolyte of the present invention. The present invention will be described in detail based on examples and comparative examples, but these are presented for illustrative purposes only. That is, the following examples are not intended to be exhaustive or to limit the present invention in the form described. Therefore, the present invention is not limited to the following examples unless it exceeds the spirit of the invention. Also, unless otherwise specified, all parts and percentages are by weight.

[0043] [Synthesis Example 1] Synthesis of 1,1-dimethyl-2-nitrile pentafluorobenzoate (compound C-1)

[0044] Under a nitrogen atmosphere, 2.31 g (0.0100 mol) of pentafluorobenzoate chloride was dissolved in 7.2 mL of tetrahydrofuran (hereinafter referred to as "THF"), and then a solution of 1.21 g (0.0120 mol) of triethylamine (hereinafter referred to as "TEA") dissolved in 2.4 mL of THF was added. Subsequently, a solution of 1.02 g (0.0120 mol) of acetone cyanohydrin dissolved in 2.4 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO４ After drying, concentration under reduced pressure using an evaporator gave 2.46 g of an off-white solid ester compound. For the obtained compound, １ 1H-NMR (manufactured by JEOL Ltd., model: JNM-ECS400 used), IR (manufactured by PerkinElmer LLC, model: SpectrumTwo used) and GC-MS (manufactured by Shimadzu Corporation, model: GCMS-QP2010 Ultra used) were measured to confirm the structure thereof (the same applies to all the following Synthesis Examples). The results are shown below. It was confirmed that the obtained compound was Compound C-1, and the yield was 88%. (1) １ 1H-NMR (400 MHz, CDCl ３ 3): δ = 1.9 (s, 6H) (2) IR (cm-1 －１ ): 1742, 1666, 1497, 1417, 1326, 1223, 1198, 1139, 1098, 991, 925, 785 (3) GC-MS (EI) m / z (%) = 279 (8), 212 (70), 195 (100), 167 (40), 117 (53), 68 (44), 41 (98)

[0045] [Synthesis Example 2] Synthesis of 1,1-dimethyl 2-nitrile 2,4,6-trifluorobenzoate (Compound C-2)

[0046] Under a nitrogen atmosphere, after dissolving 2.92 g (0.0150 mol) of 2,4,6-trifluorobenzoyl chloride in 10.8 mL of THF, a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Then, a solution of 1.53 g (0.0180 mol) of acetone cyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after completion of the dropwise addition, the mixture was stirred at 25°C for 3 hours. A solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine, and Na ２ 2SO ４ After drying, concentration under reduced pressure using an evaporator gave 3.27 g of a reddish-brown liquid ester compound. The results of confirming the structure of the obtained compound are shown below. It was confirmed that the obtained compound was Compound C-2, and the yield was 90%. (1) １ 1H-NMR (400 MHz, CDCl ３): δ = 6.7-6.8 (t, 2H), 1.9 (s, 6H) (2) IR (cm －１ ): 1744, 1641, 1618, 1444, 1271, 1127, 1094, 1049, 1002, 847, 622, 512 (3) GC-MS (EI) m / z (%) = 243 (5), 199 (24), 176 (39), 159 (100), 131 (43), 81 (47), 41 (40)

[0047] [Synthesis Example 3] Synthesis of 1,1-dimethyl 2-nitrile 2,6-difluorobenzoate (Compound C-3)

[0048] Under a nitrogen atmosphere, after 2.65 g (0.0150 mol) of 2,6-difluorobenzoyl chloride was dissolved in 10.8 mL of THF, a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Thereafter, a solution of 1.53 g (0.0180 mol) of acetone cyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after completion of the dropwise addition, the mixture was stirred at 25°C for 3 hours. A solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine, and Na ２ SO ４ After drying, the mixture was concentrated under reduced pressure using an evaporator. Then, the obtained mixture was purified by silica gel chromatography using a mixed solvent of hexane / ethyl acetate = 5 / 1. As a result, 2.39 g of an ester compound as a pale yellow liquid was obtained. The results of confirming the structure of the obtained compound are shown below. It was confirmed that the obtained compound was Compound C-3, and the yield was 71%. (1) １ H-NMR (400 MHz, CDCl ３ ): δ 7.5 (m, 1H), δ 7.0 (t, 2H), δ 1.9 (s, 1H) (2) IR (cm －１ ): 1743, 1624, 1470, 1289, 1265, 1151, 1099, 1013, 797, 691, 585 (3) GC-MS (EI) m / z (%) = 225 (18), 181 (17), 158 (73), 141 (100), 113 (58), 63 (54), 41 (47)

[0049] [Synthesis Example 4] Synthesis of 1,1-dimethyl 2-nitrile 2,4-difluorobenzoate (Compound C-4)

[0050] Under a nitrogen atmosphere, 2.65 g (0.0150 mol) of 2,4-difluorobenzoate chloride was dissolved in 10.8 mL of THF, and then a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Subsequently, a solution of 1.53 g (0.0180 mol) of acetone cyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO ４ After drying, the mixture was concentrated under reduced pressure using an evaporator. The resulting mixture was then purified by silica gel chromatography using a hexane / ethyl acetate = 5 / 1 mixed solvent. As a result, 2.35 g of a yellow liquid ester compound was obtained. The purity of this ester compound was 80%, and it contained a by-product accounting for 20%. The structure of the main product of the obtained compound was confirmed to be compound C-4, with a yield of 56%. The yield is calculated by multiplying the amount obtained by the content. (1) １ H-NMR (400MHz, CDCl ３ ): δ8.0-7.8 (m, 1H), δ7.0-6.8 (dt, 2H), δ1.9 (s, 6H) (2) IR (cm －１ ): 1739, 1614, 1503, 1433, 1288, 1261, 1153, 1114, 1075, 975, 854, 768, 681 (3) GC-MS (EI) m / z (%) = 225 (25), 181 (13), 158 (99), 142 (96), 141 (100), 113 (88), 63 (53), 41 (72)

[0051] [Synthesis Example 5] Synthesis of 1,1-dimethyl-2-nitrile 2-fluorobenzoic acid (compound C-5)

[0052] Under a nitrogen atmosphere, 2.38 g (0.0150 mol) of 2-fluorobenzoate chloride was dissolved in 10.8 mL of THF, and then a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Subsequently, a solution of 1.53 g (0.0180 mol) of acetone cyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO ４ After drying, the ester compound was concentrated under reduced pressure using an evaporator to obtain 2.96 g of a reddish-brown liquid. The structure of the obtained compound was confirmed to be compound C-5, and the yield was 95%. (1) １ H-NMR (400MHz, CDCl ３ ): δ8.0 (t, 1H), δ7.6 (m, 1H), δ7.3 (m, 1H), 7.1 (m, 1H), δ1.9 (s, 6H) (2) IR (cm －１ ): 1726, 1613, 1489, 1456, 1391, 1301, 1221, 1152, 1072, 858, 753 (3) GC-MS (EI) m / z (%) = 41 (22), 75 (28), 95 (27), 123 (100), 140 (45), 207 (8)

[0053] [Synthesis Example 6] Synthesis of 3-nitrile pentafluorobenzoate (compound C-6)

[0054] Under a nitrogen atmosphere, 3.46 g (0.0150 mol) of pentafluorobenzoate chloride was dissolved in 10.8 mL of THF, and then a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Subsequently, a solution of 1.28 g (0.0180 mol) of ethylenecyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO ４After drying, 3.12 g of a yellowish-brown oily ester compound was obtained by concentrated under reduced pressure using an evaporator. The structure of the obtained compound was confirmed to be compound C-6, and the yield was 80%. (1) １ H-NMR (400MHz, CDCl ３ ): δ4.6 (t, 2H), δ2.8 (t, 2H) (2) IR (cm －１ ): 1739, 1652, 1497, 1421, 1327, 1216, 987, 751 (3) GC-MS (EI) m / z (%) = 117 (78), 167 (62), 195 (100), 212 (42), 265 (32)

[0055] [Synthesis Example 7] Synthesis of 2,4,6-trifluorobenzoic acid 3-nitrile (compound C-7)

[0056] Under a nitrogen atmosphere, 2.92 g (0.0150 mol) of 2,4,6-trifluorobenzoate chloride was dissolved in 10.8 mL of THF, and then a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Subsequently, a solution of 1.28 g (0.0180 mol) of ethylenecyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO ４ After drying, 2.98 g of a yellowish-white crystalline ester compound was obtained by concentrated under reduced pressure using an evaporator. The structure of the obtained compound was confirmed to be compound C-7, and the yield was 87%. (1) １ H-NMR (400MHz, CDCl ３ ): δ6.8 (t, 2H), δ4.5 (t, 2H), δ2.8 (t, 2H) (2) IR (cm －１ ): 3106, 2255, 1721, 1619, 1443, 1264, 1113, 1051, 998, 858, 792, 514 (3) GC-MS (EI) m / z (%) = 81 (26), 131 (24), 159 (100), 176 (24), 229 (8)

[0057] [Synthesis Example 8] Synthesis of 2,6-difluorobenzoic acid 3-nitrile (compound C-8)

[0058] Under a nitrogen atmosphere, 2.65 g (0.0150 mol) of 2,6-difluorobenzoate chloride was dissolved in 10.8 mL of THF, and then a solution of 1.82 g (0.0180 mol) of TEA dissolved in 3.6 mL of THF was added. Subsequently, a solution of 1.28 g (0.0180 mol) of ethylenecyanohydrin dissolved in 3.6 mL of THF was added dropwise, and after the addition was complete, the mixture was stirred at 25°C for 3 hours. The solution obtained by adding water to this reaction solution was extracted with ethyl acetate. The organic layer was washed once with brine and Na ２ SO ４ After drying, the ester compound was concentrated under reduced pressure using an evaporator to obtain 3.11 g (98% yield) of a pale yellow liquid. The structure of the obtained compound was confirmed to be compound C-8, with a yield of 98%. (1) １ H-NMR (400MHz, CDCl ３ ): δ7.5 (m, 1H), δ7.0 (m, 2H), δ4.6 (t, 2H), δ2.8 (t, 2H) (2) IR (cm －１ ): 1733, 1625, 1469, 1287, 1260, 1111, 1058, 1015, 797, 695, 594 (3) GC-MS (EI) m / z (%) = 63 (50), 113 (54), 141 (100), 158 (28), 211 (23)

[0059] [Synthesis Example 9] Synthesis of 2,4,6-trifluorobenzoic acid 2-nitrile (compound C-9)

[0060] Under air at 25°C, 0.97 g (0.0055 mol) of 2,4,6-trifluorobenzoic acid was dissolved in 24 mL of THF. To this solution, 1.66 g (0.0220 mol) of chloroacetonitrile and 1.11 g (0.0110 mol) of triethylamine were added sequentially. After these additions, the solution was heated under reflux at 75°C for 8 hours to complete the reaction, and then allowed to cool to 25°C. After cooling, 96 mL of hydrochloric acid prepared to 3 mol / L was added to the reaction solution, and the resulting solution was extracted with methylene chloride. The organic layer was washed once with brine and then Na ２SO ４ After drying, 1.18 g of a yellow liquid ester compound was obtained by concentrated under reduced pressure using an evaporator. The structure of the obtained compound was confirmed to be compound C-9, and the yield was 100%. (1) １ H-NMR (400MHz, CDCl ３ ): δ6.8 (m, 2H), δ5.0 (s, 2H) (2) IR (cm －１ ): 1744, 1604, 1445, 1256, 1129, 1096, 1051, 847, 512 (3) GC-MS (EI) m / z (%) = 44 (38), 81 (41), 132 (18), 159 (100), 207 (48), 215 (17)

[0061] [Synthesis Example 10] Synthesis of 2,6-difluorobenzoic acid 2-nitrile (compound C-10)

[0062] Under air at 25°C, 1.26 g (0.0080 mol) of 2,6-difluorobenzoic acid was dissolved in 35 mL of THF to which 2.42 g (0.0320 mol) of chloroacetonitrile and 1.62 g (0.0160 mol) of triethylamine were added in sequence. After these additions, the solution was heated under reflux at 75°C for 8 hours to complete the reaction, and then allowed to cool to 25°C. After cooling, 139 mL of hydrochloric acid prepared to 3 mol / L was added to the reaction solution, and the solution was extracted with methylene chloride. The organic layer was washed once with brine and Na ２ SO ４ After drying, the ester compound was concentrated under reduced pressure using an evaporator to obtain 1.54 g of an orange liquid. The structure of the obtained compound was confirmed to be compound C-10, and the yield was 98%. (1) １ H-NMR (400MHz, CDCl ３ ): δ7.5 (m, 1H), δ7.0 (m, 2H), δ5.0 (s, 2H) (2) IR (cm －１ ): 1742, 1524, 1470, 1257, 1101, 1015, 798 (3) GC-MS (EI) m / z (%) = 40 (18), 63 (92), 113 (81), 141 (100), 153 (27), 197 (39)

[0063] [Synthesis Example 11] Synthesis of 2,4-difluorobenzoic acid 2-nitrile (compound C-11)

[0064] Under air at 25°C, 1.26 g (0.0080 mol) of 2,4-difluorobenzoic acid was dissolved in 35 mL of THF to which 2.42 g (0.0320 mol) of chloroacetonitrile and 1.62 g (0.0160 mol) of triethylamine were added in sequence. After these additions, the solution was heated under reflux at 75°C for 8 hours to complete the reaction, and then allowed to cool to 25°C. After cooling, 139 mL of hydrochloric acid prepared to 3 mol / L was added to the reaction solution, and the solution was extracted with methylene chloride. The organic layer was washed once with brine and Na ２ SO ４ After drying, the mixture was concentrated under reduced pressure using an evaporator to obtain 1.58 g of an orange liquid ester compound. The structure of the obtained compound was confirmed to be compound C-11, and the yield was 100%. (1) １ H-NMR (400MHz, CDCl ３ ): δ8.0 (m, 1H), δ7.2-6.9 (m, 2H), δ5.0 (s, 2H) (2) IR (cm －１ ): 1732, 1613, 1504, 1429, 1255, 1115, 1083,957, 856,766 (3) GC-MS (EI) m / z (%) = 40 (13), 63 (59), 113 (62), 141 (100), 153 (12), 197 (25)

[0065] [Compounds C-12 to C-20] The following compounds were synthesized in accordance with the synthesis examples described above.

[0066] [Example 1] (Preparation of non-aqueous electrolyte) A mixed non-aqueous solvent was obtained by mixing propylene carbonate (PC) and dimethyl carbonate (DMC) in a volume ratio of PC / DMC = 1 / 2, and LiPF was added as the electrolyte salt. ６ The solution was adjusted to a concentration of 1.0 mol / L, and compound C-1 was added to the total weight of the solution consisting of the mixed non-aqueous solvent and the electrolyte salt to prepare a non-aqueous electrolyte.

[0067] (Fabrication of Lithium-ion Secondary Battery) A slurry was prepared by mixing 94% by weight of NCM523, 3% by weight of carbon black, and 3% by weight of polyvinylidene fluoride, and coated onto aluminum foil. The positive electrode was then fabricated by drying and pressure molding. Similarly, a slurry was prepared by mixing 96.5% by weight of artificial graphite, 0.5% by weight of carbon black, 1% by weight of carboxymethylcellulose, and 2% by weight of styrene-butadiene rubber, and coated onto copper foil. The negative electrode was then fabricated by drying and pressure molding. A polypropylene separator was used as the separator. The positive electrode, the separator impregnated with a non-aqueous electrolyte, and the negative electrode were stacked in that order to fabricate a CR2032 coin-type battery, which was designated as Example 1.

[0068] (Charge / Discharge Test) The fabricated coin-type battery was subjected to 300 charge / discharge cycles at 25°C using a Hokuto Denko charge / discharge test device (HJ1001SD8), with a charge rate of 1.0C, a discharge rate of 1.0C, a charge termination voltage of 4.2V, and a discharge termination voltage of 2.7V. The discharge capacity at the 5th cycle was calculated as a relative ratio compared to the discharge capacity at the 5th cycle of Comparative Example 2. The cycle characteristic (%) was calculated as: discharge capacity obtained at the 300th cycle / discharge capacity at the 5th cycle × 100.

[0069] [Examples 2-16, 19, 22-24] Coin batteries were prepared in the same manner as in Example 1, except that the compound added to the non-aqueous electrolyte was changed from compound C-1 to compounds C-2 to C-20, and charge-discharge tests were performed.

[0070] [Example 17] A coin cell was prepared in the same manner as in Example 1, except that compound C-1 was replaced with compound C-17 in the non-aqueous electrolyte, and compound C-17 was added to the total weight of the solution consisting of the mixed non-aqueous solvent and the electrolyte salt to a concentration of 0.1% by weight. A charge-discharge test was then performed.

[0071] [Example 18] A coin cell was prepared in the same manner as in Example 17, except that compound C-17 was added to a non-aqueous electrolyte at a concentration of 0.5% by weight, and a charge-discharge test was performed.

[0072] [Example 20] A coin cell was prepared in the same manner as in Example 17, except that compound C-17 was added to a non-aqueous electrolyte at a concentration of 2.0% by weight, and a charge-discharge test was performed.

[0073] [Example 21] A coin cell was prepared in the same manner as in Example 17, except that compound C-17 was added to a non-aqueous electrolyte at a concentration of 5.0% by weight, and a charge-discharge test was performed.

[0074] [Comparative Example 1] A coin cell was prepared in the same manner as in Example 1, except that the non-aqueous electrolyte did not contain compound C-1, and a charge-discharge test was performed.

[0075] [Comparative Examples 2-6] Coin batteries were prepared in the same manner as in Example 1, except that the compound added to the non-aqueous electrolyte was changed from compound C-1 to comparative compounds CC-1 to CC-5 listed below, and charge-discharge tests were performed.

[0076]

[0077] Table 2 shows the charge-discharge cycle characteristics of Examples 1-24 and Comparative Examples 1-6. From the results in Table 2, in the non-aqueous electrolyte using PC / DMC as the non-aqueous solvent, Comparative Example 1, which did not contain any additives, did not obtain sufficient discharge capacity. This phenomenon is thought to be due to the destruction of the artificial graphite anode. Comparative Example 6 showed the same result. Furthermore, while charge-discharge cycles were possible for Comparative Examples 2-5, the cycle characteristics when each additive (comparative compounds CC-1 to CC-4) was added at 1.0 wt% were below 90%, and the cycle characteristics cannot be said to be sufficient. On the other hand, the inclusion of the fluorobenzoate nitrile compound of the present invention (Examples 1-24) resulted in high charge-discharge cycle characteristics. From these results, it was found that using a non-aqueous electrolyte for lithium-ion secondary batteries containing the fluorobenzoate nitrile compound of the present invention improves the charge-discharge cycle characteristics of lithium-ion secondary batteries.

[0078]

[0079] [Example 25] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 0.6% by weight of compound C-17 and 1.4% by weight of vinylene carbonate (VC), and a charge-discharge test was performed.

[0080] [Example 26] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were compound C-17 at 1.0% by weight and VC at 1.0% by weight, and a charge-discharge test was performed.

[0081] [Example 27] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 1.4% by weight of compound C-17 and 0.6% by weight of VC, and a charge-discharge test was performed.

[0082] [Example 28] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 0.6% by weight of compound C-17 and 1.4% by weight of fluoroethylene carbonate (FEC), and a charge-discharge test was performed.

[0083] [Example 29] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were compound C-17 at 1.0% by weight and FEC at 1.0% by weight, and a charge-discharge test was performed.

[0084] [Example 30] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 1.4% by weight of compound C-17 and 0.6% by weight of FEC, and a charge-discharge test was performed.

[0085] [Example 31] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 0.6% by weight of compound C-17, 0.7% by weight of VC, and 0.7% by weight of FEC, and a charge-discharge test was performed.

[0086] [Example 32] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 0.6% by weight of compound C-17, 1.0% by weight of VC, and 0.4% by weight of FEC, and a charge-discharge test was performed.

[0087] [Example 33] A coin cell was prepared in the same manner as in Example 1, except that the compounds added to the non-aqueous electrolyte were 0.6% by weight of compound C-17, 0.4% by weight of VC, and 1.0% by weight of FEC, and a charge-discharge test was performed.

[0088] [Comparative Example 7] A coin cell was prepared in the same manner as in Example 1, except that the compound added to the non-aqueous electrolyte was VC in an amount of 2.0% by weight, and a charge-discharge test was performed.

[0089] [Comparative Example 8] A coin cell was prepared in the same manner as in Example 1, except that the compound added to the non-aqueous electrolyte was added so that the FEC was 2.0% by weight, and a charge-discharge test was performed.

[0090] Table 3 shows the results for Example 20 (reprinted), Examples 25-33, and Comparative Examples 7-8. As shown in Table 3, in the non-aqueous electrolyte, Examples 25-33, which contained compound C-17 and vinylene carbonate and / or fluoroethylene carbonate, showed higher charge-discharge cycle characteristics compared to the non-aqueous electrolyte with only compound C-17 added (Example 20), the non-aqueous electrolyte with only vinylene carbonate added (Comparative Example 7), and the non-aqueous electrolyte with only fluoroethylene carbonate added (Comparative Example 8). Thus, it was found that higher charge-discharge cycle characteristics can be obtained by adding vinylene carbonate and / or fluoroethylene carbonate to the non-aqueous electrolyte for lithium-ion secondary batteries in addition to the fluorobenzoic acid nitrile compound of the present invention.

[0091]

[0092] [Example 34] In a non-aqueous electrolyte, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC / EMC / DMC = 1 / 1 / 1 to form a mixed non-aqueous solvent. LiFSI was adjusted to a concentration of 1.0 mol / L as the electrolyte salt. Compound C-17 was added to the total weight of the solution consisting of the mixed non-aqueous solvent and the electrolyte salt to a concentration of 1.0% by weight to prepare a non-aqueous electrolyte. A coin cell was prepared in the same manner as in Example 1, except that the above non-aqueous electrolyte was used, and a charge-discharge test was performed.

[0093] [Example 35] In a non-aqueous electrolyte, LiFSI was used as the electrolyte salt at a concentration of 0.8 mol / L, and LiPF ６ A coin cell was prepared in the same manner as in Example 34, except that the concentration was adjusted to 0.2 mol / L, and a charge-discharge test was performed.

[0094] [Example 36] In a non-aqueous electrolyte, LiFSI is used as the electrolyte salt at a concentration of 0.5 mol / L, and LiPF ６ A coin cell was prepared in the same manner as in Example 34, except that the concentration was adjusted to 0.5 mol / L, and a charge-discharge test was performed.

[0095] [Example 37] In a non-aqueous electrolyte, LiFSI was used as the electrolyte salt at a concentration of 0.2 mol / L, and LiPF ６ A coin cell was prepared in the same manner as in Example 34, except that the concentration was adjusted to 0.8 mol / L, and a charge-discharge test was performed.

[0096] [Example 38] In a non-aqueous electrolyte, LiPF is used as the electrolyte salt. ６ A coin cell was prepared in the same manner as in Example 34, except that the concentration was adjusted to 1.0 mol / L, and a charge-discharge test was performed.

[0097] [Example 39] In a non-aqueous electrolyte, LiPO4 is used relative to the weight of the non-aqueous electrolyte. ２ F ２ A coin cell was prepared in the same manner as in Example 34, except that 1.0% by weight of was added, and a charge-discharge test was performed.

[0098] [Example 40] In a non-aqueous electrolyte, LiPO4 is used relative to the weight of the non-aqueous electrolyte. ２ F ２ 1.0% by weight, and LiOSO ３ CH ３ A coin cell was prepared in the same manner as in Example 34, except that 0.5% by weight of was added, and a charge-discharge test was performed.

[0099] [Example 41] A coin cell was prepared in the same manner as in Example 34, except that 1.0% by weight of 1,3-dioxane (DOX) was added to the non-aqueous electrolyte, and a charge-discharge test was performed.

[0100] [Example 42] A coin cell was prepared in the same manner as in Example 34, except that 1.0% by weight of 2-propargyl methanesulfonic acid was added to the non-aqueous electrolyte, and a charge-discharge test was performed.

[0101] [Example 43] A coin cell was prepared in the same manner as in Example 34, except that 1.0% by weight of DOX and 1.0% by weight of 2-propargyl methanesulfonic acid were added to the non-aqueous electrolyte, and a charge-discharge test was performed.

[0102] [Example 44] A coin cell was prepared in the same manner as in Example 34, except that 1.0% by weight of adiponitrile was added to the non-aqueous electrolyte, and a charge-discharge test was performed.

[0103] [Comparative Example 9] A coin cell was prepared in the same manner as in Example 34, except that the non-aqueous electrolyte did not contain compound C-17, and a charge-discharge test was performed.

[0104] The results for Examples 34-44 and Comparative Example 9 are shown in Table 4. As shown in Table 4, even in lithium-ion secondary batteries having a non-aqueous electrolyte containing highly corrosive LiFSI, Examples 34-37 and Examples 39-44, which contain the fluorobenzoate nitrile compound of the present invention, showed high charge-discharge cycles. Visual observation of the condition of the aluminum foil used in the positive electrode current collector after 300 cycles for Examples 34, 39, 40, and Comparative Example 9 revealed that aluminum corrosion was suppressed in Examples 34, 39, and 40. Furthermore, compared to Example 34, LiPO ２ F ２ Examples 39 and 40, which included [the specified ingredient], showed a remarkable effect in inhibiting aluminum corrosion. Furthermore, LiOSO ３ CH ３Example 40, which included [component name], showed lower resistance at the graphite negative electrode. Compared to Example 34, Example 41, which included DOX, showed greater suppression of aluminum corrosion. Compared to Example 34, it was found that aluminum corrosion was also suppressed in a lithium-ion secondary battery having a non-aqueous electrolyte containing the highly corrosive methanesulfonic acid 2-propargyl (Example 42). Furthermore, in a non-aqueous electrolyte containing the highly corrosive methanesulfonic acid 2-propargyl, Example 43, which included both compound C-17 and DOX, showed greater suppression of aluminum corrosion. Example 44, which included adiponitrile, which has a corrosion-inhibiting effect but whose use has been hesitated due to the deterioration of cycle characteristics as the amount added increases, also showed an aluminum corrosion-inhibiting effect and high cycle characteristics.

[0105]

[0106] [Example 45] Artificial graphite at 91.5% by weight, SiO ２ A slurry was prepared by mixing 5.0% by weight of [unclear material], 0.5% by weight of carbon black, 1.0% by weight of carboxymethylcellulose, and 2.0% by weight of styrene-butadiene rubber, and this slurry was coated onto copper foil. Subsequently, it was dried and pressure molded to produce SiO [unclear material]. ２ A negative electrode containing [LiPF] was prepared. In a non-aqueous electrolyte, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of EC / EMC / DMC = 1 / 1 / 1 to form a mixed non-aqueous solvent, and LiPF was used as the electrolyte salt. ６ The solution was adjusted to a concentration of 1.0 mol / L, and compound C-17 was added to the total weight of the solution consisting of the mixed non-aqueous solvent and the electrolyte salt to prepare a non-aqueous electrolyte. ２ A coin cell was prepared in the same manner as in Example 1, except that the negative electrode and the non-aqueous electrolyte were used, and a charge-discharge test was performed.

[0107] [Example 46] A coin cell was prepared in the same manner as in Example 45, except that compound C-17 was added to a non-aqueous electrolyte at a concentration of 5.0% by weight, and a charge-discharge test was performed.

[0108] [Comparative Example 10] A coin cell was prepared in the same manner as in Example 45, except that the non-aqueous electrolyte did not contain compound C-17, and a charge-discharge test was performed.

[0109] The results of Examples 45-46 and Comparative Example 10 are shown in Table 5. As shown in Table 5, by using the non-aqueous electrolyte to which compound C-17 was added (Examples 45 and 46), SiO ２ The negative electrode also exhibited high charge-discharge cycle characteristics.

[0110]

[0111] By using the non-aqueous electrolyte of the present invention, it is possible to improve the charge-discharge cycle characteristics of lithium-ion secondary batteries and achieve superior battery performance. This invention enables high-performance lithium-ion secondary batteries, and its contribution to a wide range of applications is immeasurable.

Claims

1. The following 11 types of nitrile fluorobenzoate compounds.

2. A non-aqueous electrolyte for lithium-ion secondary batteries, comprising an electrolyte salt dissolved in a non-aqueous solvent, characterized by containing at least one fluorobenzoate nitrile compound selected from fluorobenzoate nitrile compounds represented by the following formulas (1) to (4) (excluding 4-fluorobenzoate 2-nitrile). In the formula, R １ ~R ５ Each of these atoms is independently either a hydrogen atom or a fluorine atom, and at least one of them is a fluorine atom.

3. The non-aqueous electrolyte for a lithium-ion secondary battery according to claim 2, characterized in that the fluorobenzoate nitrile compound is contained in an amount of 0.01% by weight or more and 5% by weight or less relative to the weight of the non-aqueous electrolyte, and at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate is contained in an amount of 0.01% by weight or more and 5% by weight or less relative to the weight of the non-aqueous electrolyte.

4. The non-aqueous electrolyte for lithium-ion secondary batteries according to claim 2, characterized in that the fluorobenzoate nitrile compound is contained in an amount of 0.01% by weight or more and 5% by weight or less relative to the weight of the non-aqueous electrolyte, and 1,3-dioxane is contained in an amount of 0.01% by weight or more and 5% by weight or less relative to the weight of the non-aqueous electrolyte.

5. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for lithium-ion secondary batteries described in any one of claims 2 to 4.

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