JP2006286277A - Nonaqueous electrolyte for battery and nonaqueous electrolyte secondary battery having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte for a battery combining high fire retardancy and high battery performance and to provide a nonaqueous electrolyte secondary battery having the nonaqueous electrolyte. <P>SOLUTION: In the nonaqueous electrolyte for the battery containing a nonaqueous solvent and a supporting salt, the nonaqueous electrolyte for the battery contains a fluorophosphate compound represented by general formula (1), and the nonaqueous electrolyte secondary battery is equipped with the nonaqueous electrolyte, a positive electrode, and a negative electrode. [In the formula, R<SP>1</SP>independently represents fluorine, an alkoxy group, an aryloxy group, a fluorine atom-substituted alkoxy group, or a fluorine atom-substituted aryloxy group, and at least one of two R<SP>1</SP>s is the fluorine atom-substituted alkoxy group or the fluorine atom-substituted aryloxy group, and two R<SP>1</SP>s may form a ring by joining each other.]. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a battery non-aqueous electrolyte and a non-aqueous electrolyte secondary battery including the same, and particularly to a battery non-aqueous electrolyte having high flame retardancy and reduction resistance, and safety and cycle characteristics. The present invention relates to a non-aqueous electrolyte secondary battery excellent in.

Non-aqueous electrolytes are used as electrolytes for lithium batteries, lithium ion secondary batteries, electric double layer capacitors, etc., and these devices have high voltage and high energy density. Widely used as a power source. As these nonaqueous electrolytic solutions, generally used are solutions in which a supporting salt such as LiPF ₆ is dissolved in an aprotic organic solvent such as an ester compound and an ether compound. However, since the aprotic organic solvent is flammable, it may ignite and burn when it leaks from the device, and has a safety problem.

  To solve this problem, methods for making non-aqueous electrolytes flame-retardant have been studied. For example, phosphoric acid esters such as trimethyl phosphate are used for non-aqueous electrolytes, or phosphoric acid is used for aprotic organic solvents. Methods for adding esters have been proposed (see Patent Documents 1 to 3). However, these phosphate esters have a problem in that they are gradually reduced and decomposed at the negative electrode by repeating charge and discharge, and battery characteristics such as charge and discharge efficiency and cycle characteristics are greatly deteriorated.

  In order to solve this problem, methods such as further adding a compound that suppresses the decomposition of the phosphate ester to the nonaqueous electrolytic solution or devising the molecular structure of the phosphate ester itself have been tried (Patent Documents 4 to 7). reference). However, in this case, as the addition amount of the phosphate ester is increased, the decomposition suppressing effect is not sufficient, so that the addition amount of the phosphate ester is currently limited. In addition, these phosphate triesters have high viscosity and low electrical conductivity, so that even if the blending amount is low, the electrical conductivity is reduced, and charge / discharge efficiency is reduced under high load conditions and low temperature conditions. I will invite you. In particular, in charge and discharge at a high current density (high rate) which is a high load condition, the reductive decomposition of the phosphoric acid triester easily proceeds, and the cycle characteristics of the battery are greatly deteriorated even at a low blending amount.

  As described above, the technology using the phosphoric acid triesters so far is not necessarily sufficient in terms of ensuring the safety of the electrolytic solution and the battery performance, and fundamentally reexamines the structure of the phosphoric ester. There is a need.

JP-A-4-184870 JP-A-8-22839 JP 2000-182669 A Japanese Patent Laid-Open No. 11-67267 JP-A-10-189040 JP 2003-109659 A JP-A-11-260401

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a non-aqueous electrolyte for a battery that can achieve both high flame retardancy and excellent battery performance, and a non-aqueous electrolyte secondary comprising the non-aqueous electrolyte. To provide a battery.

  As a result of intensive studies to achieve the above object, the present inventor succeeded in finding a phosphate ester compound having a structure capable of solving the drawbacks of conventional phosphate esters, and completed the present invention. It was.

［式中、Ｒ¹は、それぞれ独立してフッ素、アルコキシ基、アリールオキシ基、フッ素原子置換アルコキシ基又はフッ素原子置換アリールオキシ基であって、２つのＲ¹のうち少なくとも一つはフッ素原子置換アルコキシ基又はフッ素原子置換アリールオキシ基であり、但し、２つのＲ¹は互いに結合して環を形成してもよい］で表されるフルオロリン酸エステル化合物を含むことを特徴とする。 That is, the battery non-aqueous electrolyte of the present invention is a battery non-aqueous electrolyte containing a non-aqueous solvent and a supporting salt, and the battery non-aqueous electrolyte is represented by the following general formula (I):

[Wherein R ¹ is independently fluorine, alkoxy group, aryloxy group, fluorine atom-substituted alkoxy group or fluorine atom-substituted aryloxy group, and at least one of the two R ¹ is fluorine atom-substituted. It is an alkoxy group or a fluorine atom-substituted aryloxy group, provided that two R ¹ may be bonded to each other to form a ring].

In a preferred example of the battery non-aqueous electrolyte of the present invention, in the general formula (I), one of two R ¹ is fluorine, and the other is a fluorine atom-substituted alkoxy group or a fluorine atom-substituted aryloxy. It is a group. In this case, the battery non-aqueous electrolyte is particularly low in viscosity and excellent in safety.

  In another preferred embodiment of the battery non-aqueous electrolyte of the present invention, the non-aqueous solvent further contains an aprotic organic solvent.

  In the nonaqueous electrolytic solution for a battery of the present invention, the content of the fluorophosphate compound represented by the general formula (I) is preferably 5% by volume or more of the whole nonaqueous electrolytic solution for a battery, 10 More preferably, it is at least volume%.

  Moreover, the non-aqueous electrolyte secondary battery of the present invention includes the above-described non-aqueous electrolyte for batteries, a positive electrode, and a negative electrode.

  According to the present invention, by using the fluorophosphate ester compound represented by the above formula (I) for the non-aqueous electrolyte for a battery, excellent electrical conductivity and reduction resistance, and high flame retardancy even at a low blending amount. Is obtained. Further, it is possible to provide a non-aqueous electrolyte secondary battery that has excellent cycle characteristics under high load conditions and has greatly reduced risk of rupture, ignition, and ignition, that is, significantly improved safety. it can.

  The reason for this is not necessarily clear, but the compound of formula (I) is a fluorophosphate ester containing a phosphorus-fluorine bond, and therefore has a smaller molecular size and lower viscosity than a normal phosphate triester. Decrease in the electrical conductivity of the liquid, and the specific structure containing a phosphorus-fluorine bond and a fluorine atom substituent of the compound of formula (I) enhances the reduction resistance of the non-aqueous electrolyte, or It is considered that a film which is stable and effective in suppressing reductive decomposition is formed on the electrode surface. Similarly, the high flame retardant effect is also considered to be due to a higher non-flammable gas component during pyrolysis due to the synergistic effect of the carbon-fluorine bond and phosphorus-fluorine bond contained in the compound of formula (I).

<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. The non-aqueous electrolyte for a battery of the present invention comprises a non-aqueous solvent containing a fluorophosphate ester compound represented by the above formula (I) and a supporting salt, and may further contain an aprotic organic solvent as a non-aqueous solvent. Good.

The fluorophosphate ester compound contained in the battery non-aqueous electrolyte of the present invention is represented by the above formula (I). In the formula (I), each R ¹ is independently a fluorine, an alkoxy group, an aryloxy group, a fluorine atom-substituted alkoxy group or a fluorine atom-substituted aryloxy group, and at least one of the two R ¹ is A fluorine atom-substituted alkoxy group or a fluorine atom-substituted aryloxy group. Examples of the alkoxy group in R ¹ of the formula (I) include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an allyloxy group containing a double bond, and the like, and an alkoxy substitution such as a methoxyethoxy group and a methoxyethoxyethoxy group Examples include an alkoxy group, and examples of the aryloxy group include a phenoxy group, a methylphenoxy group, and a methoxyphenoxy group.

The fluorine atom-substituted alkoxy group for R ¹ in formula (I) is a 2-fluoroethoxy group, a 2,2-difluoroethoxy group, a 2,2,2-trifluoroethoxy group, a 2,2,2-tri group. Fluoropropoxy group, 2,2,3,3-tetrafluoropropoxy group, 2,2,3,3,3-pentafluoropropoxy group, 2-fluoroisopropoxy group, 2,2-difluoroisopropoxy group, 2, 2,2-trifluoroisopropoxy group, tetrafluoroisopropoxy group, pentafluoroisopropoxy group, hexafluoroisopropoxy group, heptafluorobutoxy group, hexafluorobutoxy group, octafluorobutoxy group, perfluoro-t-butoxy group , Hexafluoroisobutoxy group, octafluoropentyloxy group and the like.

Further, the fluorine atom-substituted aryloxy group in R ¹ of the formula (I) includes 2-fluorophenoxy group, 3-fluorophenoxy group, 4-fluorophenoxy group, 2,4-difluorophenoxy group, 2-fluoro-4 -Methylphenoxy group, trifluorophenoxy group, tetrafluorophenoxy group, pentafluorophenoxy group, 2-fluoromethylphenoxy group, 4-fluoromethylphenoxy group, 2-difluoromethylphenoxy group, 3-difluoromethylphenoxy group, 4- A difluoromethylphenoxy group, a 2-trifluoromethylphenoxy group, a 3-trifluoromethylphenoxy group, a 4-trifluoromethylphenoxy group, a 2-fluoro-4-methoxyphenoxy group, and the like can be given.

The general formula fluorophosphate ester compound (I) may be any two of the at least one fluorine atom substituted alkoxy group or a fluorine atom-substituted aryl group of R ^1, the two R ¹ may be the same or different Good. In addition, two R ¹ may be linked, and in this case, the two R ¹ are bonded to each other to form a fluorine atom-substituted alkylenedioxy group, a fluorine atom-substituted arylenedioxy group, or a fluorine atom-substituted oxy An alkylenearyleneoxy group is formed, and examples of the divalent group include a fluoroethylenedioxy group, a difluoroethylenedioxy group, a fluoropropylenedioxy group, a difluoropropylenedioxy group, and a trifluoropropylenedioxy group. . In particular, among the fluorophosphate compounds of the above general formula (I), difluorophosphoric acid in which one of two R ¹ is fluorine and the other is a fluorine atom-substituted alkoxy group or a fluorine atom-substituted aryloxy group Esters are most preferred in terms of low viscosity and flame retardancy.

  Specific examples of the fluorophosphate ester compound of the formula (I) include methyl fluorophosphate (trifluoroethyl), ethyl fluorophosphate (trifluoroethyl), propyl fluorophosphate (trifluoroethyl), fluorophosphoric acid Allyl (trifluoroethyl), butyl fluorophosphate (trifluoroethyl), phenyl fluorophosphate (trifluoroethyl), bis (trifluoroethyl) fluorophosphate, methyl fluorophosphate (tetrafluoropropyl), fluorophosphoric acid Ethyl (tetrafluoropropyl), tetrafluoropropyl fluorophosphate (trifluoroethyl), phenyl fluorophosphate (tetrafluoropropyl), bis (tetrafluoropropyl) fluorophosphate, methyl fluorophosphate (fluorophenyl), fluorophosphate Ethyl acetate (fluorophenyl), Fluorophenyl fluorophosphate (trifluoroethyl), difluorophenyl fluorophosphate, fluorophenyl fluorophosphate (tetrafluoropropyl), methyl fluorophosphate (difluorophenyl), ethyl fluorophosphate (difluorophenyl), difluorophenyl fluorophosphate (Trifluoroethyl), bis (difluorophenyl) fluorophosphate, difluorophenyl fluorophosphate (tetrafluoropropyl), fluoroethylene fluorophosphate, difluoroethylene fluorophosphate, fluoropropylene fluorophosphate, difluoropropylene fluorophosphate, Trifluoropropylene fluorophosphate, fluoroethyl difluorophosphate, difluoroethyl difluorophosphate, fluoropropyl difluorophosphate, diphf difluorophosphate Oropropyl, trifluoropropyl difluorophosphate, tetrafluoropropyl difluorophosphate, pentafluoropropyl difluorophosphate, fluoroisopropyl difluorophosphate, difluoroisopropyl difluorophosphate, trifluoroisopropyl difluorophosphate, tetrafluoroisopropyl difluorophosphate, difluoro Pentafluoroisopropyl phosphate, hexafluoroisopropyl difluorophosphate, heptafluorobutyl difluorophosphate, hexafluorobutyl difluorophosphate, octafluorobutyl difluorophosphate, perfluoro-t-butyl difluorophosphate, hexafluorodifluorophosphate Isobutyl, fluorophenyl difluorophosphate, difluorophenyl difluorophosphate, difluorophosphoric acid -Fluoro-4-methylphenyl, trifluorophenyl difluorophosphate, tetrafluorophenyl difluorophosphate, pentafluorophenyl difluorophosphate, 2-fluoromethylphenyl difluorophosphate, 4-fluoromethylphenyl difluorophosphate, difluorophosphoric acid 2-difluoromethylphenyl, 3-difluoromethylphenyl difluorophosphate, 4-difluoromethylphenyl difluorophosphate, 2-trifluoromethylphenyl difluorophosphate, 3-trifluoromethylphenyl difluorophosphate, 4-trifluorophosphoric acid Examples thereof include fluoromethylphenyl and 2-fluoro-4-methoxyphenyl difluorophosphate. Among these, fluoroethylene fluorophosphate, bis (trifluoroethyl) fluorophosphate, fluoroethyl difluorophosphate, trifluoroethyl difluorophosphate, propyl difluorophosphate, and phenyl difluorophosphate are preferable, low viscosity, flame retardant From the viewpoint of properties, fluoroethyl difluorophosphate, tetrafluoropropyl difluorophosphate, and fluorophenyl difluorophosphate are more preferred. These fluorophosphate ester compounds may be used singly or in combination of two or more.

  The content of the fluorophosphate ester compound of the above formula (I) is preferably 5% by volume or more, more preferably 10% by volume or more of the whole battery non-aqueous electrolyte. When the content of the fluorophosphate ester compound of formula (I) is 5% by volume or more, the non-aqueous electrolyte tends to exhibit flame retardancy. When the content is 10% by volume or more, the non-aqueous electrolyte is non-flammable. There is a tendency to express.

  In addition, an aprotic organic solvent can be added to the nonaqueous electrolytic solution as long as the object of the present invention is not impaired. Since the fluorophosphate ester of the above formula (I) has high flame retardancy, the non-aqueous electrolyte exhibits flame retardancy when the amount of the aprotic organic solvent added is 95% by volume or less. However, in order for the nonaqueous electrolyte to obtain nonflammability, it is more preferable that the amount of the aprotic organic solvent added is 90% by volume or less. Specific examples of the aprotic organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC). Carbonates such as 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), diethyl ether (DEE), ethers such as phenyl methyl ether, γ-butyrolactone (GBL), γ-valerolactone, methyl formate Carboxylic acid esters such as (MF), nitriles such as acetonitrile, amides such as dimethylformamide, and sulfones such as dimethyl sulfoxide. These aprotic organic solvents may contain an unsaturated bond or a halogen element. Among these aprotic organic solvents, ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC) are preferable. Moreover, these aprotic organic solvents may be used individually by 1 type, and may use 2 or more types together.

  The nonaqueous electrolytic solution for a battery of the present invention can be used as it is, but it can also be used by, for example, impregnating it with a suitable polymer, a porous support, or a gel material.

As the supporting salt used in the non-aqueous electrolyte for a battery of the present invention, a supporting salt serving as a lithium ion source is preferable. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. Among these, LiPF ₆ is more preferable in terms of excellent nonflammability. These supporting salts may be used alone or in combination of two or more.

  The concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.2 to 1.5 mol / L (M), more preferably 0.5 to 1 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

<Nonaqueous electrolyte secondary battery>
Next, the nonaqueous electrolyte secondary battery of the present invention will be described in detail. The non-aqueous electrolyte secondary battery of the present invention includes the above-described non-aqueous electrolyte, a positive electrode, and a negative electrode, and is usually used in the technical field of non-aqueous electrolyte secondary batteries such as a separator as necessary. Other members are provided.

As the positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention, metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO Preferable examples include lithium-containing composite oxides such as ₂ and LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni [wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1] (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  As the negative electrode active material of the non-aqueous electrolyte secondary battery of the present invention, lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb, Zn or the like, a carbon material such as graphite doped with lithium, etc. Among these, carbon materials such as graphite are preferable, and graphite is particularly preferable in view of higher safety and excellent wettability of the electrolyte. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Other members that can be used in the non-aqueous electrolyte secondary battery of the present invention include a separator interposed in the non-aqueous electrolyte secondary battery between positive and negative electrodes to prevent current short-circuit due to contact between both electrodes. It is done. As the material of the separator, it is possible to reliably prevent contact between the two electrodes and to allow the electrolyte to pass through or to contain, for example, synthesis of polytetrafluoroethylene, polypropylene, polyethylene, cellulose, polybutylene terephthalate, polyethylene terephthalate, etc. Preferred examples include resin non-woven fabrics and thin layer films. These may be a single substance, a mixture or a copolymer. Of these, polypropylene or polyethylene microporous films having a thickness of about 20 to 50 μm, cellulose-based films, polybutylene terephthalate, polyethylene terephthalate, and the like are particularly suitable. In the present invention, in addition to the separators described above, known members that are normally used in batteries can be suitably used.

  The form of the non-aqueous electrolyte secondary battery of the present invention described above is not particularly limited, and various known forms such as a coin type, a button type, a paper type, a square type or a spiral type cylindrical battery are available. Preferably mentioned. In the case of the button type, a non-aqueous electrolyte secondary battery can be manufactured by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of a spiral structure, for example, a non-aqueous electrolyte secondary battery is manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding up the sheet-like negative electrode on the current collector. Can do.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
A non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ in a mixed solvent of 10% by volume of fluorophenyl difluorophosphate, 45% by volume of ethylene carbonate, and 45% by volume of methyl ethyl carbonate so as to be 1 mol / L. The flame retardancy of the liquid was evaluated by the method (1) below. The results are shown in Table 1.

(1) Flame Retardancy Evaluation The combustion length and combustion time of a flame ignited in an atmospheric environment were measured and evaluated by a method in which the UL94HB method of UL (Underwriting Laboratory) standard was arranged. Specifically, based on the UL test standard, a test piece was prepared by impregnating a 127 mm × 12.7 mm SiO ₂ sheet with the above electrolytic solution 1.0 mL, and evaluated. The evaluation criteria for nonflammability, flame retardancy, self-extinguishing properties, and flammability are shown below.
<Evaluation of Nonflammability> A case where the test flame did not ignite at all (ignition length: 0 mm) was evaluated as nonflammable.
<Evaluation of Flame Retardancy> The case where the ignited flame did not reach the 25 mm line of the apparatus and the fallen object from the net was not ignited was evaluated as flame retardant.
<Evaluation of self-extinguishing property> When the ignited flame was extinguished in the 25 to 100 mm line and no ignition was observed on the falling object from the net, it was evaluated as having self-extinguishing property.
<Evaluation of combustibility> The case where the ignited flame exceeded the 100 mm line was evaluated as combustible.

Next, lithium cobalt composite oxide [LiCoO ₂ ] is used as a positive electrode active material, and the oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are in a weight ratio of 94: 3: After mixing in 3 and dispersing this in N-methylpyrrolidone and applying it to an aluminum foil as the positive electrode current collector and drying it, it was punched into a disk shape with a diameter of 12.5 mm to produce a positive electrode did. Further, artificial graphite is used as the negative electrode active material, and the artificial graphite and polyvinylidene fluoride as a binder are mixed at a mass ratio of 90:10, and this is mixed with an organic solvent (50/50 of ethyl acetate and ethanol). A slurry dispersed in (mass% mixed solvent) was applied to a copper foil as a negative electrode current collector and dried, and then punched into a disk shape having a diameter of 12.5 mm to produce a negative electrode. Next, the positive electrode and the negative electrode are stacked and accommodated in a stainless steel case that also serves as a positive electrode terminal via a separator (microporous film: made of polypropylene) impregnated with an electrolytic solution, and the negative electrode terminal is inserted through a polypropylene gasket. A coin-type battery (non-aqueous electrolyte secondary battery) having a diameter of 20 mm and a thickness of 1.6 mm was produced by sealing with a stainless sealing plate that also serves as a battery. Moreover, the charging / discharging test was done with the method of following (2) with respect to the obtained coin-type battery.

(2) Charging / discharging test using a coin-type battery Charging / discharging cycle with a current density of ² mA / cm ² in a voltage range of 4.2 to 3.0 V in a 20 ° C environment using the coin-type battery produced as described above. Was repeated twice and the initial discharge capacity (mAh / g) was determined by dividing the discharge capacity at this time by the known electrode mass. Furthermore, charging / discharging was repeated up to 50 cycles under the same charging / discharging conditions, and the discharge capacity after 50 cycles was determined.
Capacity remaining rate S = discharge capacity after 50 cycles / initial discharge capacity × 100 (%)
The capacity remaining rate S was calculated according to the above and used as an index of cycle characteristics under high load conditions. The results are shown in Table 1.

(Example 2)
In the same manner as in Example 1 except that 50% by volume of bis (trifluoroethyl) fluorophosphate, 25% by volume of ethylene carbonate, and 25% by volume of methyl ethyl carbonate in “Preparation of non-aqueous electrolyte” in Example 1 A non-aqueous electrolyte solution was prepared, and the flame retardancy of the obtained non-aqueous electrolyte solution was evaluated. Further, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity and the cycle characteristics of the battery in the charge / discharge test were measured and evaluated. The results are shown in Table 1.

(Example 3)
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that tetrafluoropropyl difluorophosphate was 100% by volume in “Preparation of nonaqueous electrolytic solution” in Example 1. The flame retardancy of was evaluated. Further, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the negative electrode was a lithium sheet, and the initial discharge capacity and the battery cycle characteristics in the charge / discharge test were measured and evaluated. The results are shown in Table 1.

(Comparative Example 1)
A nonaqueous electrolyte solution was prepared in the same manner as in Example 1 except that in the “preparation of nonaqueous electrolyte solution” in Example 1, trimethyl phosphate was 10 vol%, ethylene carbonate 45 vol%, and ethyl methyl carbonate 45 vol%. The flame retardant properties of the prepared and obtained nonaqueous electrolytic solutions were evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity and the cycle characteristics of the battery in the charge / discharge test were measured and evaluated. The results are shown in Table 1.

(Comparative Example 2)
In the “Preparation of non-aqueous electrolyte solution” in Example 1, the same procedure as in Example 1 was conducted except that 50% by volume of tris (trifluoroethyl) phosphate, 25% by volume of ethylene carbonate, and 25% by volume of ethyl methyl carbonate were used. A nonaqueous electrolytic solution was prepared, and the flame retardancy of the obtained nonaqueous electrolytic solution was evaluated. In addition, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the initial discharge capacity and the cycle characteristics of the battery in the charge / discharge test were measured and evaluated. The results are shown in Table 1.

  As shown in Examples 1 to 3 of Table 1, a nonaqueous electrolyte containing 10% by volume or more of the compound of the general formula (I) exhibits nonflammability, and a secondary battery using the nonaqueous electrolyte is used even under high load conditions. Since the excellent initial discharge capacity and cycle characteristics are exhibited, it is determined that the compound of the general formula (I) is effective in improving the conductivity and reduction resistance of the nonaqueous electrolytic solution. As described above, the non-aqueous electrolyte of the present invention has high flame retardancy and reduction resistance. By using the non-aqueous electrolyte for a secondary battery, the non-aqueous electrolyte is excellent in safety and cycle characteristics. It was confirmed that the secondary battery was obtained.

  On the other hand, as shown in Comparative Examples 1 and 2 in Table 1, the phosphoric acid triesters reduce the conductivity of the nonaqueous electrolytic solution even when the substituent contains a fluorine atom-substituted alkoxy group. It can be seen that the reducibility is not sufficient, and the discharge capacity and cycle characteristics of the secondary battery are significantly reduced.

From the above results, by using a non-aqueous electrolyte characterized by containing a fluorophosphate ester compound represented by the above general formula (I), a non-aqueous solution that achieves both high flame retardancy and battery performance. An electrolyte secondary battery can be provided.

Claims (6)

In a non-aqueous electrolyte for a battery comprising a non-aqueous solvent and a supporting salt, the non-aqueous electrolyte for a battery is represented by the following general formula (I):

[Wherein R ¹ is independently fluorine, alkoxy group, aryloxy group, fluorine atom-substituted alkoxy group or fluorine atom-substituted aryloxy group, and at least one of the two R ¹ is fluorine atom-substituted. An alkoxy group or a fluorine atom-substituted aryloxy group, wherein two R ¹ may be bonded to each other to form a ring]. Water electrolyte. 2. The battery according to claim 1, wherein in the general formula (I), one of two R ¹ is fluorine, and the other is a fluorine atom-substituted alkoxy group or a fluorine atom-substituted aryloxy group. Non-aqueous electrolyte for use.   The battery nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous solvent further contains an aprotic organic solvent.   The content of the fluorophosphate ester compound represented by the general formula (I) is 5% by volume or more of the whole battery non-aqueous electrolyte solution, according to any one of claims 1 to 3. Non-aqueous electrolyte for batteries.   The content of the fluorophosphate ester compound represented by the general formula (I) is 10% by volume or more of the whole non-aqueous electrolyte for a battery, according to any one of claims 1 to 4. Non-aqueous electrolyte for batteries. A nonaqueous electrolyte secondary battery comprising the battery nonaqueous electrolyte solution according to any one of claims 1 to 5, a positive electrode, and a negative electrode.