JP2008052988A - Nonaqueous electrolytic solution for battery, and nonaqueous electrolytic solution battery equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution for a battery having high flame resistance and high reduction resistance. <P>SOLUTION: This nonaqueous electrolytic solution contains a nonaqueous solvent containing a cyclic phosphazene compound expressed by a general formula (I): (NPR<SP>1</SP><SB>2</SB>)n [in the formula, R<SP>1</SP>respectively and independently expresses a halogen element, an alkoxy group or an aryloxy group; n expresses 3 to 4], a difluoro phosphate compound expressed by a general formula (II): [in the formula, R<SP>2</SP>is an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy substituted alkyl group, or an aryl group], at least one kind of polycyclic compounds selected from a group consisting of 1,2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene, indene, fluorene, and 9,10-dihydroanthracene, and a supporting salt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte for a battery and a non-aqueous electrolyte battery including the same, and particularly a non-aqueous electrolyte for a battery having high flame retardancy and a non-aqueous electrolyte having excellent battery characteristics and high safety. It relates to batteries.

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 6). reference). However, in this case as well, there is a limit to the amount of addition, and the safety of the electrolyte is sufficiently ensured to the extent that the electrolyte is self-extinguishing due to a decrease in the flame retardancy of the phosphate ester itself. Can not do it.

  Japanese Patent Application Laid-Open No. 6-13108 (Patent Document 7) discloses a method of adding a phosphazene compound to a nonaqueous electrolytic solution in order to impart flame retardancy to the nonaqueous electrolytic solution. The phosphazene compound exhibits high nonflammability depending on the type, and the flame retardancy of the nonaqueous electrolyte tends to improve as the amount added to the nonaqueous electrolyte increases. However, phosphazene compounds exhibiting high incombustibility generally have low solubility and dielectric constant of the supporting salt, so increasing the amount added causes precipitation of the supporting salt and a decrease in conductivity, resulting in a decrease in battery discharge capacity. The charging / discharging characteristics may be hindered. Therefore, when adding the phosphazene compound which shows high nonflammability, there exists a problem that the addition amount is restrict | limited.

  Furthermore, Japanese Patent Application Laid-Open No. 2006-107910 (Patent Document 8) proposes a nonaqueous electrolytic solution in which a fluorinated phosphate ester and a phosphazene compound are combined as a technique that achieves both high flame retardancy and battery performance. . Although the non-aqueous electrolyte has high flame retardancy and excellent battery performance, the higher the battery operating voltage, the more the decomposition tends to occur.

  In recent years, battery devices have been required to have higher capacities, and one of effective means is to increase the operating voltage. Therefore, in recent years, improvement of decomposition resistance (reduction resistance) and ensuring safety (nonflammability) are becoming more important issues for electrolytes. However, in this respect, the prior art is sufficiently satisfactory. I can't say that.

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-6-13108 JP 2006-107910 A

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, comprising a non-aqueous electrolyte for a battery having high flame retardancy, that is, non-flammability and high reduction resistance, and the non-aqueous electrolyte for the battery, The object is to provide a non-aqueous electrolyte battery having stable battery performance and high safety even under high voltage conditions.

  As a result of intensive studies to achieve the above object, the present inventor has made nonaqueous electrolysis by further combining a specific polycyclic compound with a nonaqueous solvent comprising a specific cyclic phosphazene compound and a specific difluorophosphate ester compound. By configuring the liquid, it can be found that high flame retardancy can be imparted to the electrolyte, and that the nonaqueous electrolyte battery using the electrolyte can maintain excellent battery performance even under high voltage conditions, The present invention has been completed.

［式中、Ｒ²は、アルキル基、シクロアルキル基、アルケニル基、アルコキシ置換アルキル基又はアリール基である］で表されるジフルオロリン酸エステル化合物を含む非水溶媒と、１,２-ジヒドロナフタレン、１,２,３,４-テトラヒドロナフタレン、インデン、フルオレン、及び９,１０-ジヒドロアントラセンからなる群から選択される少なくとも１種の多環式化合物と、支持塩とを含むことを特徴とする。 That is, the nonaqueous electrolyte for a battery of the present invention has the following general formula (I):
(NPR ¹ ₂ ) _n ... (I)
[Wherein R ¹ independently represents a halogen element, an alkoxy group or an aryloxy group; n represents 3 to 4] and the following general formula (II):

[Wherein R ² represents an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group or an aryl group] and a 1,2-dihydronaphthalene containing a difluorophosphate compound represented by the formula: It includes at least one polycyclic compound selected from the group consisting of 1,2,3,4-tetrahydronaphthalene, indene, fluorene, and 9,10-dihydroanthracene, and a supporting salt. .

In the nonaqueous electrolytic solution for a battery of the present invention, the cyclic phosphazene compound is preferably a compound in which at least three of R ¹ in the general formula (I) are fluorine.

  In a preferred example of the battery non-aqueous electrolyte of the present invention, the volume ratio of the cyclic phosphazene compound represented by the general formula (I) and the difluorophosphate compound represented by the general formula (II) is 10 / 90 to 80/20.

  In another preferable example of the battery non-aqueous electrolyte of the present invention, the content of the polycyclic compound is 1 to 10% by mass of the whole battery non-aqueous electrolyte.

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

  The non-aqueous electrolyte for a battery of the present invention is a total content of the cyclic phosphazene compound represented by the general formula (I) and the difluorophosphate compound represented by the general formula (II) in the non-aqueous solvent. Is preferably 30% by volume or more.

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

  According to the present invention, by using a non-aqueous solvent containing a specific cyclic phosphazene compound and a specific difluorophosphate ester compound, it has high flame retardancy and reduction resistance, and further a specific polycyclic compound is combined. By using it, it is possible to provide a non-aqueous electrolyte capable of sufficiently maintaining battery characteristics even under high voltage conditions when used in a non-aqueous electrolyte battery. Moreover, the nonaqueous electrolyte battery provided with this nonaqueous electrolyte and having high safety and excellent battery characteristics can be provided.

  In the battery non-aqueous electrolyte of the present invention, it is considered that a highly incombustible gas component generated by the reaction and thermal decomposition of a cyclic phosphazene compound and a difluorophosphate compound exhibits high flame retardancy. Moreover, although the reason is not necessarily clear, the film on the electrode surface generated by the synergistic effect of the three compounds of the cyclic phosphazene compound, the difluorophosphate ester compound and the polycyclic compound effectively decomposes the electrolytic solution. Stable charge / discharge characteristics can be realized due to suppression, and this film functions without being decomposed even at a high voltage of 4.5 V or higher, so it is considered that charge / discharge performance can be maintained even under high voltage conditions. It is done.

<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. A non-aqueous electrolyte for a battery according to the present invention includes a non-aqueous solvent containing a cyclic phosphazene compound represented by the general formula (I) and a difluorophosphate ester compound represented by the general formula (II), Containing at least one polycyclic compound selected from the group consisting of 2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene, indene, fluorene, and 9,10-dihydroanthracene, and a supporting salt. Further, an aprotic organic solvent may be contained as a non-aqueous solvent.

The cyclic phosphazene compound contained in the nonaqueous electrolytic solution for batteries of the present invention is represented by the above general formula (I). R ¹ in formula (I), a halogen element independently, an alkoxy group or an aryloxy radical, n represents 3-4.

Examples of the halogen element in R ¹ of the formula (I) include fluorine, chlorine, bromine and the like. Examples of the alkoxy group in R ¹ include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an allyloxy group containing a double bond, or an alkoxy-substituted alkoxy group such as a methoxyethoxy group or a methoxyethoxyethoxy group. Can be mentioned. Furthermore, examples of the aryloxy group in R ¹ include a phenoxy group, a methylphenoxy group, a xylenoxy group (that is, a xylyloxy group), a methoxyphenoxy group, and the like. The hydrogen element in the alkoxy group and aryloxy group may be substituted with a halogen element, and is preferably substituted with fluorine. R ¹ in formula (I) may be linked to other R ^1, and in this case, two R ¹ are bonded to each other to form an alkylenedioxy group, an aryleneoxy group or an oxyalkylene arylene. Examples of the divalent group that forms an oxy group include an ethylenedioxy group, a propylenedioxy group, and a phenylenedioxy group.

R ¹ in the general formula (I) may be the same or different. Further, R ¹ in the formula (I) is preferably a halogen element from the viewpoint of improving safety, and more preferably fluorine from the viewpoint of low viscosity. Moreover, it is preferable that 3 or more of R < ¹ > is a fluorine from the point of coexistence of safety | security and low viscosity.

  Moreover, n of Formula (I) is 3-4, The said cyclic phosphazene compound may be used individually by 1 type, and may mix and use 2 or more types.

The difluorophosphate compound contained in the nonaqueous electrolytic solution for batteries of the present invention is represented by the above general formula (II). In the formula (II), R ² is an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group or an aryl group. Examples of the alkyl group in R ² of the formula (II) include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. Examples of the cycloalkyl group include a cyclopropyl group and a cyclohexyl group. Examples of the alkenyl group include an allyl group and a methallyl group. Examples of the alkoxy-substituted alkyl group include a methoxyethyl group and a methoxyethoxyethyl group. Examples of the aryl group include a phenyl group, a methylphenyl group, A methoxyphenyl group etc. are mentioned. The hydrogen element in the substituent may be substituted with a halogen element, and is preferably substituted with fluorine. Among these, a methyl group, an ethyl group, a propyl group, a trifluoroethyl group, a phenyl group, and a 3-fluorophenyl group are preferable in terms of excellent flame retardancy and low viscosity.

  Specific examples of the difluorophosphate compound of formula (II) include methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, propyl difluorophosphate, trifluoropropyl difluorophosphate, allyl difluorophosphate, Examples include butyl difluorophosphate, pentyl difluorophosphate, hexyl difluorophosphate, cyclohexyl difluorophosphate, methoxyethyl difluorophosphate, methoxyethoxyethyl difluorophosphate, phenyl difluorophosphate, fluorophenyl difluorophosphate, and the like. These difluorophosphate ester compounds may be used singly or in combination of two or more.

  In the nonaqueous electrolytic solution of the present invention, the volume ratio of the cyclic phosphazene compound to the difluorophosphate ester compound is preferably in the range of 5/95 to 95/5, and from the viewpoint of balance of battery performance, 10/90 to A range of 80/20 is more preferred. In addition, from the viewpoint of sufficiently ensuring the safety of the nonaqueous electrolyte battery in a fully charged state, the total content of the cyclic phosphazene compound and the difluorophosphate compound in the nonaqueous solvent is 30 volumes. % Or more is preferable.

  The non-aqueous electrolyte for a battery according to the present invention further includes a specific polycyclic compound. Such polycyclic compounds include 1,2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene (ie, tetralin), indene, fluorene, and 9,10-dihydroanthracene. These polycyclic compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The content of the polycyclic compound is preferably in the range of 1 to 10% by mass, and more preferably in the range of 2 to 7% by mass, based on the balance of battery performance.

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. For example, LiClO ₄ , LiBF ₄ , LiBC ₄ O ₈ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) Preferable examples include lithium salts such as ₂ N and Li (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 1.2 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. .

  In addition, various aprotic organic solvents conventionally used in battery non-aqueous electrolytes can be added to the non-aqueous solvent as long as the object of the present invention is not impaired. The addition amount of the aprotic organic solvent is preferably 70% by volume or less in the non-aqueous solvent in order to ensure high battery safety. 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), ethers such as diethyl ether (DEE), γ-butyrolactone (GBL), γ-valerolactone, methyl formate (MF), etc. Carboxylic acid esters, nitriles such as acetonitrile, amides such as dimethylformamide, sulfones such as dimethyl sulfoxide, sulfides such as ethylene sulfide, and the like. These aprotic organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  In forming a non-aqueous electrolyte battery, the non-aqueous electrolyte of the present invention can be used as it is. For example, an appropriate polymer, a porous support, or a gel material is impregnated. It can also be used in a holding method or the like.

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

As the positive electrode active material of the non-aqueous electrolyte 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 ₂ and Preferable examples include lithium-containing composite oxides such as 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, Al, and Ni. In this case, the composite oxide LiMn _x Co _y Ni _(1-xy) O ₂ [where 0 ≦ x <1, 0 ≦ y <1, 0 <x + y ≦ 1], LiMn _x Ni _(1-x) O ₂ [wherein , 0 ≦ x <1], LiMn _x Co _(1-x) O ₂ [where 0 ≦ x <1], LiCo _x Ni _(1-x) O ₂ [where 0 ≦ x <1], LiCo _x Ni _y Al [wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1] (1-xy) O 2, LiFe x Co y Ni (1-xy) O 2 [ wherein , 0 ≦ x <1, 0 ≦ y <1, 0 <x + y ≦ 1], or LiMn _x Fe _y O _{2 -xy} . Among these, composite oxides are preferable in terms of high capacity, high safety, and stability at high voltages. 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 nonaqueous electrolyte battery of the present invention, lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb or Zn, a metal oxide such as TiO ₂ doped with lithium ions, and Preferable examples include metal oxide composite materials such as TiO ₂ —P ₂ O ₄ and carbon materials such as graphite. 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. Examples of the binder include 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 battery of the present invention include a separator that is interposed between positive and negative electrodes in a role of preventing current short-circuit due to contact between both electrodes. 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. Among these, a polypropylene or polyethylene microporous film having a thickness of about 20 to 50 μm, a film made of cellulose, polybutylene terephthalate, polyethylene terephthalate, or the like is 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 battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button type, paper type, prismatic or spiral structure cylindrical battery are preferably mentioned. It is done. In the case of the button type, a non-aqueous electrolyte battery can be produced 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 the spiral structure, for example, a non-aqueous electrolyte battery can be 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. .

  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 mixture comprising 50% by volume of trifluoroethyl difluorophosphate and 50% by volume of a cyclic phosphazene compound in which n is 4 in the above general formula (I), ^one of all R ¹ is a propoxy group and seven is fluorine. LiPF ₆ was dissolved in a solvent so as to be 1 mol / L, and 5 mass% of 1,2-dihydronaphthalene was added thereto to prepare a nonaqueous electrolytic solution. Next, the flame retardancy of the obtained non-aqueous electrolyte was evaluated by the following method, and the results shown in Table 1 were obtained.

(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.

(2) Production of Battery Using LiMn _0.9 Co _0.1 O ₂ as a positive electrode active material, the oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are in a mass ratio of 94: 3: 3 The slurry was dispersed in N-methylpyrrolidone and applied to an aluminum foil as a positive electrode current collector, followed by drying and pressing to obtain a positive electrode sheet having a thickness of 70 μm. . This was cut into a rectangle (4 cm × 50 cm), and an aluminum foil current collecting tab was welded to produce a positive electrode. 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 mass of ethyl acetate and ethanol). % Mixed solvent) was applied to a copper foil as a negative electrode current collector, followed by drying and pressing to obtain a negative electrode sheet having a thickness of 50 μm. This was cut into a rectangle (4 cm × 50 cm), and a nickel foil current collecting tab was welded to produce a negative electrode. Next, the separator (microporous film: polyethylene) is cut into a rectangle (4 cm x 50 cm), sandwiched between the positive electrode and the negative electrode, flattened with a 4 cm x 3 cm spacer as the base, and heat-sealed It inserted in the exterior material which consists of an aluminum laminate film (polyethylene terephthalate / aluminum / polypropylene), inject | poured electrolyte solution, and vacuum-heated quickly and produced the flat laminated battery.

(3) High voltage cycle characteristic evaluation Using the laminated battery produced as described above, a charge / discharge cycle with an upper limit voltage of 4.5 V, a lower limit voltage of 2.5 V, and a current density of 0.1 mA / cm ² is performed in an environment of 20 ° C. The initial discharge capacity (mAh / g) was determined by repeating twice and dividing the discharge capacity at this time by the known positive electrode weight. Furthermore, charging / discharging was repeated up to 50 cycles under the same charging / discharging conditions, and the discharge capacity after 50 cycles was obtained, and the following formula:
Capacity remaining rate S = discharge capacity after 50 cycles / initial discharge capacity × 100 (%)
The capacity remaining rate was calculated according to the above and used as an index of the cycle characteristics of the battery under high voltage conditions.

(4) Nail penetration safety test The same laminated battery as described above was produced, and a safety test using a nail penetration was performed. The method of nail penetration test is to repeat the charge / discharge cycle at a current density of 0.1 mA / cm ² in a voltage range of 4.5 to 2.5 V in an environment of 20 ° C. twice, and further charge to 4.5 V. Place the battery on a battery holder (stainless steel) with a temperature control function, and use a stainless steel nail with a shaft diameter of 3 mm at a battery temperature of 30 ° C. The center was pierced at a right angle, and the presence or absence of ignition at the time of rupture was examined. The results are shown in Table 1.

(Example 2)
40% by volume of ethyl difluorophosphate, 10% by volume of the cyclic phosphazene compound in which n is 3 in the above general formula (I), ^one of the R ¹ groups is methoxyethoxyethoxy group, and 5 is fluorine, LiPF ₆ is 1.2 mol / L in a mixed solvent composed of 50% by volume of a cyclic phosphazene compound in which n is 3 in the general formula (I), and ^one of all R ¹ is a methoxy group and five are fluorine. Then, 7% by mass of anhydrous 1,2,3,4-tetrahydronaphthalene was added thereto to prepare a nonaqueous electrolytic solution, and the flame retardancy of the obtained nonaqueous electrolytic solution was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Example 3)
35% by volume of propyl difluorophosphate, 15% by volume of a cyclic phosphazene compound in which n is 3 in the above general formula (I), 3 of the total R ¹ are ethoxy groups and 3 are fluorine, propylene carbonate 5 LiPF ₆ was dissolved in a mixed solvent consisting of 45% by volume and 45% by volume of dimethyl carbonate so as to be 1 mol / L, and 5% by mass of indene was added thereto to prepare a nonaqueous electrolytic solution. The flame retardancy of the non-aqueous electrolyte was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

Example 4
15% by volume of phenyl difluorophosphate, 35% by volume of cyclic phosphazene compound in which n is 3 in the above general formula (I), ^one of R ¹ is cyclohexyloxy group and 5 is fluorine, propylene carbonate LiPF ₆ was dissolved in a mixed solvent consisting of 10% by volume and 40% by volume of diethyl carbonate so as to be 1 mol / L, and 5% by mass of fluorene was added thereto to prepare a non-aqueous electrolyte. The non-aqueous electrolyte was evaluated for flame retardancy. Next, in place of the LiMn _0.9 Co _0.1 O ₂ positive electrode used in Example 1, a nonaqueous electrolyte solution was used in the same manner as in Example 1 except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used. Secondary batteries were fabricated and evaluated for cycle characteristics and safety under high voltage conditions. The results are shown in Table 1.

(Example 5)
27% by volume of methyl difluorophosphate, 3% by volume of cyclic phosphazene compound in which n is 3 in the above general formula (I), 2 of the total R ¹ are chlorine and 4 are fluorine, and 23% of ethylene carbonate LiPF ₆ is dissolved in a mixed solvent consisting of 2% by weight and 47% by volume of dimethyl carbonate so as to be 1 mol / L, and 2% by mass of 9,10-dihydroanthracene is added thereto to prepare a non-aqueous electrolyte. The flame retardancy of the obtained non-aqueous electrolyte was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Example 6)
6% by volume of hexyl difluorophosphate, 24% by volume of cyclic phosphazene compound in which n is 4 in the above general formula (I) and all R ¹ is fluorine, 21% by volume of γ-butyrolactone, 49% of diethyl carbonate In a non-aqueous electrolyte solution, LiPF ₆ is dissolved to 1 mol / L in 1% by weight, and 1,2,3,4-tetrahydronaphthalene 1% by mass and fluorene 1% by mass are added thereto. Were prepared, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Comparative Example 1)
To a mixed solvent consisting of 50% by volume of triethyl phosphate and 50% by volume of a cyclic phosphazene compound in which n is 4 in the above general formula (I), ^one of the total R ¹ is a propoxy group and seven is fluorine, LiPF ₆ was dissolved at 1 mol / L, and 1,2-dihydronaphthalene 5 mass% was added thereto to prepare a non-aqueous electrolyte. Next, the flame retardancy of the obtained non-aqueous electrolyte was evaluated by the following method, and the results shown in Table 1 were obtained.

(Comparative Example 2)
3% by volume of trimethyl phosphate, 3% by volume of a cyclic phosphazene compound in which n is 3 in the above general formula (I), 2 of the total R ¹ is chlorine and 4 is fluorine, and 23% by volume of ethylene carbonate LiPF ₆ was dissolved in a mixed solvent consisting of 47% by volume of dimethyl carbonate so as to be 1 mol / L, and 2% by mass of 9,10-dihydroanthracene was added thereto to prepare a nonaqueous electrolytic solution. The non-aqueous electrolyte obtained was evaluated for flame retardancy. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Comparative Example 3)
A mixture comprising 50% by volume of trifluoroethyl difluorophosphate and 50% by volume of a cyclic phosphazene compound in which n is 4 in the above general formula (I), ^one of all R ¹ is a propoxy group and seven is fluorine. LiPF ₆ was dissolved in a solvent so as to be 1 mol / L to prepare a nonaqueous electrolytic solution, and the flame retardancy of the obtained nonaqueous electrolytic solution was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Comparative Example 4)
15% by volume of phenyl difluorophosphate, 35% by volume of cyclic phosphazene compound in which n is 3 in the above general formula (I), ^one of R ¹ is cyclohexyloxy group and 5 is fluorine, propylene carbonate A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at 1 mol / L in a mixed solvent consisting of 10% by volume and 40% by volume of diethyl carbonate, and the flame resistance of the obtained non-aqueous electrolyte was evaluated. did. Next, in place of the LiMn _0.9 Co _0.1 O ₂ positive electrode used in Example 1, a nonaqueous electrolyte solution was used in the same manner as in Example 1 except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used. Secondary batteries were fabricated and evaluated for cycle characteristics and safety under high voltage conditions. The results are shown in Table 1.

(Comparative Example 5)
In the above general formula (I), n is 3, cyclic phosphazene compound in which 3 out of all R ¹ are ethoxy groups and 3 are fluorine 15 volume%, propylene carbonate 9 volume%, dimethyl carbonate 76 volume% LiPF ₆ is dissolved in a mixed solvent consisting of 1 to 1 mol / L, and 5% by mass of indene is added thereto to prepare a non-aqueous electrolyte. The resulting non-aqueous electrolyte has flame retardancy. evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Comparative Example 6)
In a mixed solvent consisting of 50% by volume of propyl difluorophosphate, 5% by volume of propylene carbonate, and 45% by volume of dimethyl carbonate, LiPF ₆ is dissolved to 1 mol / L, and 5% by mass of indene is added thereto. A non-aqueous electrolyte solution was prepared, and the flame retardancy of the obtained non-aqueous electrolyte solution was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

(Example 7)
18% by volume of methyl difluorophosphate, 2% by volume of cyclic phosphazene compound in which n is 3 in the above general formula (I), 2 of the total R ¹ are chlorine and 4 are fluorine, and 27% of ethylene carbonate % And dimethyl carbonate 53% by volume LiPF ₆ was dissolved to 1 mol / L, and 9,10-dihydroanthracene 2% by mass was added thereto to prepare a non-aqueous electrolyte. The flame retardancy of the obtained non-aqueous electrolyte was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and the cycle characteristics and safety under high voltage conditions were evaluated. The results are shown in Table 1.

  As shown in Examples 1 to 6 in Table 1, a non-aqueous electrolyte solution containing 30% by volume or more of the compound of formula (I), the compound of formula (II), and a specific polycyclic compound exhibits nonflammability, It can be seen that the battery using the non-aqueous electrolyte exhibits excellent battery performance and high safety even under high voltage conditions. As described above, it was confirmed that the nonaqueous electrolyte solution of the present invention can provide a nonaqueous electrolyte battery excellent in cycle characteristics and safety under high voltage conditions while exhibiting nonflammability.

  On the other hand, as shown in Comparative Examples 1 and 2, the non-aqueous electrolyte containing a normal phosphoric acid triester in the non-aqueous electrolyte can be prepared even if the compound of formula (I) or the polycyclic compound is added. It can be seen that the capacity is small and the capacity reduction due to repeated cycles cannot be suppressed. Further, as shown in Comparative Examples 3 and 4, it can be seen that in the case where no polycyclic compound is added, the cycle characteristics are gradually lowered as compared with Examples 1 and 4.

  In addition, when the difluorophosphate ester of the formula (II) is not used as in the comparative example 5, when a large amount of the phosphazene compound of the formula (I) is used, two-layer separation occurs. The phosphazene compound could not be added in an amount of 16% by volume or more, and as a result, the safety of the battery could not be ensured.

  Further, even when a polycyclic compound was used as in Comparative Example 6, when the phosphazene compound of the formula (I) was not added, the initial discharge capacity and cycle characteristics were inferior compared with Example 3. You can see that

  As shown in Example 7, when the total content of the compound represented by the formula (I) and the compound represented by the formula (II) is about 20% by volume, incombustibility is exhibited, In the nail penetration safety test in such a high voltage full charge state, ignition could not be suppressed. Therefore, it can be seen that the total content of the cyclic phosphazene compound of the formula (I) and the difluorophosphate compound of the formula (II) is preferably 30% by volume or more.

From the above results, a non-aqueous electrolyte characterized by containing a cyclic phosphazene compound represented by formula (I), a difluorophosphate compound represented by formula (II) and a specific polycyclic compound. It can be seen that by using this, a non-aqueous electrolyte battery having both nonflammability and excellent battery performance can be provided.

Claims (7)

The following general formula (I):
(NPR ¹ ₂ ) _n ... (I)
[Wherein R ¹ independently represents a halogen element, an alkoxy group or an aryloxy group; n represents 3 to 4] and the following general formula (II):

[Wherein R ² represents an alkyl group, a cycloalkyl group, an alkenyl group, an alkoxy-substituted alkyl group or an aryl group] and a 1,2-dihydronaphthalene containing a difluorophosphate compound represented by the formula: It includes at least one polycyclic compound selected from the group consisting of 1,2,3,4-tetrahydronaphthalene, indene, fluorene, and 9,10-dihydroanthracene, and a supporting salt. Non-aqueous electrolyte for batteries. 2. The battery non-aqueous electrolyte according to claim 1, wherein in the general formula (I), at least three of R ¹ are fluorine.   The volume ratio of the cyclic phosphazene compound represented by the general formula (I) and the difluorophosphate compound represented by the general formula (II) is in the range of 10/90 to 80/20. The nonaqueous electrolyte for batteries according to claim 1.   The battery nonaqueous electrolyte solution according to claim 1, wherein the content of the polycyclic compound is 1 to 10% by mass of the whole battery nonaqueous electrolyte solution.   The non-aqueous electrolyte for a battery according to claim 1, wherein the non-aqueous solvent further contains an aprotic organic solvent.   The total content of the cyclic phosphazene compound represented by the general formula (I) and the difluorophosphate compound represented by the general formula (II) in the non-aqueous solvent is 30% by volume or more. The nonaqueous electrolytic solution for a battery according to any one of claims 1 to 5. A non-aqueous electrolyte battery comprising the battery non-aqueous electrolyte according to claim 1, a positive electrode, and a negative electrode.