JP2010015720A - Nonaqueous electrolyte for battery, and nonaqueous electrolyte secondary battery equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte for a battery which gives a superior battery performance and a high safety to the battery even under a high-temperature environment. <P>SOLUTION: The nonaqueous electrolyte for the battery contains a cyclic phosphagen compound as expressed by a general formula (I): (NPR<SB>2</SB>)<SB>n</SB>[in the formula, R expresses each independently fluorine, alkoxy group, or aryl-oxy group, n expresses 3-4], a nonaqueous solvent, and at least one dicarboxylic anhydride compound selected from a group made of anhydrous 5-norbornene-2, 3-dicarboxylic acid, anhydrous 1, 2, 3, 6-tetrahydro-phthalic acid, and anhydrous bicyclo [2.2.2] octo-5-ene-2, 3-decarboxylic acid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a battery non-aqueous electrolyte and a non-aqueous electrolyte secondary battery including the same, and in particular, a non-flammable battery non-aqueous electrolyte and excellent battery characteristics and high safety even in a high temperature environment. The present invention relates to a non-aqueous electrolyte secondary battery having properties.

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, so they drive personal computers and mobile phones. 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. Such deterioration of battery characteristics is particularly noticeable under high temperature conditions.

  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 support salt solubility and dielectric constant, so increasing the amount added causes precipitation of the support salt and a decrease in conductivity, resulting in a decrease in battery discharge capacity. The charging / discharging characteristics may be hindered.

  In recent years, devices such as lithium batteries, lithium ion secondary batteries, and electric double layer capacitors have been actively developed as in-vehicle power supplies such as HEVs. And for this application, it is required that stable performance can be secured in a wider temperature range as well as high safety. In particular, the higher the operating environment temperature, the easier the battery electrode material and electrolyte components deteriorate, so an electrolyte solution for lithium secondary batteries with as little capacity reduction as possible due to repeated charge and discharge is desired even at high temperatures. ing. In this respect, the prior art is not necessarily satisfactory.

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

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a non-flammable battery non-aqueous electrolyte, and the battery non-aqueous electrolyte, which has excellent charge / discharge performance even in a high-temperature environment. The object is to provide a non-aqueous electrolyte secondary battery having safety.

  As a result of intensive studies to achieve the above object, the present inventor combined a specific cyclic phosphazene compound and a non-aqueous solvent with a dicarboxylic anhydride compound having a cyclic structure to constitute a non-aqueous electrolyte. It is found that high flame retardancy can be imparted to the electrolyte, and that the non-aqueous electrolyte secondary battery using the electrolyte can maintain excellent charge / discharge performance even in a high temperature environment, and the present invention is completed. It came to.

That is, the non-aqueous electrolyte for a battery of the present invention is
-The following general formula (I):
(NPR ₂ ) _n ... (I)
[Wherein, R independently represents a fluorine, an alkoxy group or an aryloxy group; n represents 3 to 4], and a cyclic phosphazene compound represented by:
A non-aqueous solvent,
-The group consisting of 5-norbornene-2,3-dicarboxylic anhydride, 1,2,3,6-tetrahydrophthalic anhydride and bicyclo [2.2.2] oct-5-ene-2,3-dicarboxylic anhydride And at least one dicarboxylic anhydride compound selected from the group consisting of:

  In the battery non-aqueous electrolyte of the present invention, the cyclic phosphazene compound is preferably a compound in which at least four of R in the general formula (I) are fluorine.

  In a preferred example of the battery non-aqueous electrolyte of the present invention, the content of the cyclic phosphazene compound represented by the general formula (I) is 10 to 60% by volume of the whole battery non-aqueous electrolyte, More preferably, it is 50% by volume.

  In another preferred embodiment of the battery non-aqueous electrolyte of the present invention, the content of the dicarboxylic anhydride compound is 0.5 to 2% 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 is an aprotic organic solvent, and the aprotic organic solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and More preferably, it contains at least one selected from the group consisting of methyl propionate.

  It is preferable that the nonaqueous electrolytic solution for a battery of the present invention further contains a supporting salt. The battery non-aqueous electrolyte consisting only of the cyclic phosphazene compound represented by formula (I), the non-aqueous solvent, the dicarboxylic anhydride compound and the supporting salt is a preferred embodiment of the battery non-aqueous electrolyte of the present invention. It is.

  Moreover, the non-aqueous electrolyte secondary 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, a specific cyclic phosphazene compound is added to a non-aqueous solvent, and preferably has a high flame retardancy by adding 10% by volume or more, and further by using a specific dicarboxylic anhydride compound in combination. When used in a water electrolyte secondary battery, it is possible to provide a non-aqueous electrolyte capable of sufficiently maintaining battery characteristics even in a high temperature environment. In addition, a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte and having high safety and excellent battery characteristics can be provided.

  In the non-aqueous electrolyte for batteries of the present invention, it is considered that a highly incombustible gas component produced by reaction and thermal decomposition of a cyclic phosphazene 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 two compounds of the cyclic phosphazene compound and the dicarboxylic anhydride compound having a cyclic structure effectively suppresses the decomposition of the electrolytic solution. Therefore, stable charge / discharge characteristics can be realized, and since this film functions without being decomposed even at high temperatures, it is considered that charge / discharge performance can be maintained even in a high temperature environment.

<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 cyclic phosphazene compound represented by the above general formula (I), a non-aqueous solvent, and a specific dicarboxylic anhydride compound. It is preferable to contain an aprotic organic solvent as a 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 in the formula (I) independently represents fluorine, an alkoxy group or an aryloxy group, and n represents 3 to 4.

  Examples of the alkoxy group in R of the formula (I) 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. Etc. Furthermore, examples of the aryloxy group in R 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. In addition, R in the formula (I) may be linked to other R. In this case, two Rs are bonded to each other to form an alkylenedioxy group, an aryleneoxy group, or an oxyalkylenearyleneoxy group. Examples of such divalent groups formed include ethylenedioxy, propylenedioxy, and phenylenedioxy groups.

  R in the general formula (I) may be the same or different. In addition, R in the formula (I) is preferably such that four or more of R are fluorine in terms of both incombustibility 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.

  In the battery non-aqueous electrolyte of the present invention, the content of the cyclic phosphazene compound is preferably 5 to 70% by volume of the whole battery non-aqueous electrolyte, from the viewpoint of the balance between safety and battery characteristics, A range of 10 to 60% by volume is more preferable, and a range of 20 to 50% by volume is particularly preferable. When the content of the cyclic phosphazene compound exceeds 70% by volume, the load characteristics of the battery are deteriorated, which is not preferable. On the other hand, when the content is less than 5% by volume, when an organic solvent having a low flash point is used for the electrolyte, Incombustibility may not be manifested.

  The nonaqueous electrolytic solution for a battery according to the present invention further includes a specific dicarboxylic anhydride compound. Examples of the dicarboxylic anhydride compound include anhydrous 5-norbornene-2,3-dicarboxylic acid, anhydrous 1,2,3,6-tetrahydrophthalic acid, and anhydrous bicyclo [2.2.2] oct-5-ene-2. 1,3-dicarboxylic acid. These dicarboxylic anhydride compounds having a cyclic structure may be used alone or in combination of two or more.

  The content of the dicarboxylic anhydride compound is preferably in the range of 0.1 to 3% by mass of the whole battery non-aqueous electrolyte, and more preferably in the range of 0.5 to 2% by mass from the viewpoint of balance of battery performance.

  In the non-aqueous electrolyte for batteries of the present invention, various non-protonic organic solvents conventionally used in non-aqueous electrolytes for secondary batteries are used as the non-aqueous solvent as long as the object of the present invention is not impaired. can do. The content of the non-aqueous solvent is preferably 30 to 95% by volume of the entire non-aqueous electrolyte for batteries, and more preferably in the range of 40 to 90% by volume from the viewpoint of the balance between safety and battery characteristics. A range of 50 to 80% by volume is particularly preferable.

  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 methyl acetate, methyl propionate and methyl butyrate, ethers such as 1,2-dimethoxyethane (DME), tetrahydrofuran (THF) and diethyl ether (DEE), and γ-butyrolactone (GBL), lactones such as γ-valerolactone, nitriles such as acetonitrile, amides such as dimethylformamide, sulfones such as dimethyl sulfoxide, sulfides such as ethylene sulfide, and the like. Among these, it is preferable to use carbonates and carboxylic acid esters from the viewpoint of compatibility with the cyclic phosphazene compound and the balance of battery performance, and among them, ethylene carbonate (EC), ethyl methyl carbonate (EMC), propionic acid. More preferably, methyl is used. These aprotic organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

The nonaqueous electrolytic solution for a battery of the present invention preferably contains a supporting salt, and the supporting salt is preferably a supporting salt that serves as an ion source of lithium ions. 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 (FSO ₂ ) ₂ N Suitable examples include lithium salts such as Li (CF ₃ SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N. Among these, LiPF ₆ , Li (FSO ₂ ) ₂ N, and Li (CF ₃ SO ₂ ) ₂ N are more preferable in terms of excellent nonflammability and battery performance. These supporting salts may be used alone or in combination of two or more.

  The total concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.3 to 2.5 mol / L (M), more preferably 0.8 to 2.0 mol / L (M). If the total concentration of the supporting salt is less than 0.3 mol / L, the conductivity of the electrolyte cannot be sufficiently secured, which may hinder battery discharge characteristics and charge characteristics. As the viscosity of the electrolyte increases and the mobility of lithium ions cannot be sufficiently secured, the conductivity of the electrolyte cannot be sufficiently secured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. is there.

  Further, when forming a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte for a battery 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 by a method of holding it.

<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 for a battery, a positive electrode, and a negative electrode, and is usually used in the technical field of a non-aqueous electrolyte secondary battery such as a separator as necessary. It includes other members that are used. In addition to the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery of the present invention includes a polarizable carbon electrode in the positive electrode and lithium ions in the negative electrode in advance and reversibly occludes lithium ions. An electric double layer capacitor (lithium ion capacitor or hybrid capacitor) using a nonpolarizable carbon electrode that can be detached is also included.

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 Preferred examples include lithium-containing composite oxides such as ₂ and LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , conductive polymers such as polyaniline, and carbon materials such as activated carbon. 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} . 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, metal oxide such as TiO ₂ doped with lithium ions And metal oxide composite materials such as TiO ₂ —P ₂ O ₄ , carbon materials such as graphite, and the like. 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 secondary 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, for example, preparing a sheet-like positive electrode, sandwiching a current collector, and superimposing 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
10% by volume of cyclic phosphazene compound in which n is 3 in the above general formula (I), 2 out of all R are methoxy groups and 4 are fluorine, 13% by volume of ethylene carbonate, 37% by volume of diethyl carbonate, LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved in a mixed solvent consisting of 40% by volume of methyl propionate to 1.0 mol / L, and anhydrous 1,2,3,6- A non-aqueous electrolyte was prepared by adding 0.5% by mass of tetrahydrophthalic acid. 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 127 mm × 12.7 mm SiO ₂ sheet was impregnated with 1.0 mL of the electrolytic solution, and a test piece was prepared and evaluated. The evaluation criteria for nonflammability, flame retardancy, self-extinguishing properties, and flammability are shown below.
<Evaluation of nonflammability> When the test flame was ignited, it was not ignited at all (burning length: 0 mm).
<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 on 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 flammability> The case where the ignited flame exceeded the 100 mm line was evaluated as flammability.

(2) Production of Battery Using LiMn _1/3 Co _1/3 Ni _1/3 O ₂ as a positive electrode active material, the oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder The mixture was mixed at a mass ratio of 94: 3: 3 and dispersed in N-methylpyrrolidone to form a slurry, which was applied to an aluminum foil as a positive electrode current collector, and then dried and pressed. A positive electrode sheet having a thickness of 70 μm was obtained. 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: made of polyethylene) is cut into a rectangle (4 cm x 50 cm), sandwiched between the positive electrode and the negative electrode, and flattened using a 4 cm x 3 cm spacer as a base Inserted into a heat-sealed aluminum laminate film (polyethylene terephthalate / aluminum / polypropylene) exterior material, injected the electrolyte, vacuumed and quickly heat-sealed to obtain a flat laminate battery (non-aqueous electrolyte 2 Secondary battery).

(3) Evaluation of high-temperature cycle characteristics Using the laminated battery produced as described above, ^two charge / discharge cycles with an upper limit voltage of 4.2 V, a lower limit voltage of 3.0 V, and a current density of 0.25 mA / cm ² are performed in an environment of 50 ° C. The initial discharge capacity (mAh / g) was determined by repeating this operation 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 determined.
Capacity remaining rate = 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 battery cycle characteristics under high temperature conditions.

(4) Overcharge safety test The same laminated battery as the above was produced, and the battery safety test by overcharge conditions was conducted. In the overcharge test method, a charge / discharge cycle with a current density of 0.25 mA / cm ² was repeated twice in a voltage range of 4.2 to 3.0 V in an environment of 20 ° C., and further charged to 4.2 V. The battery is placed on a battery holder (made of stainless steel) with temperature control function, charged to 12.0V with a current density of 5.0 mA / cm ² at a battery temperature of 20 ° C, and further 0.25 mA / cm ² at 12.0V. Charging was continued until the current density reached, and the presence or absence of rupture or ignition was examined. The results are shown in Table 1.

(Example 2)
In the general formula (I), n is 3, and 5% by volume of a cyclic phosphazene compound in which one of all R is a methoxyethoxy group and five is fluorine, and in the general formula (I), n is 3. Then, LiPF ₆ is added to a mixed solvent consisting of 25% by volume of a cyclic phosphazene compound, one of which is trifluoroethoxy group and five of which is fluorine, 14% by volume of ethylene carbonate, and 56% by volume of ethyl methyl carbonate. Dissolve to 1.0 mol / L and add 0.5% by weight of anhydrous 1,2,3,6-tetrahydrophthalic acid and 0.5% by weight of anhydrous 5-norbornene-2,3-dicarboxylic acid to the mixture. An electrolyte solution was prepared, and the flame retardancy of the obtained nonaqueous electrolyte solution was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Example 3)
In a mixed solvent composed of 40% by volume of a cyclic phosphazene compound in which n is 4 in the general formula (I) and all R is fluorine, 10% by volume of ethylene carbonate, and 50% by volume of ethyl methyl carbonate, LiPF ₆ Is dissolved to 1.0 mol / L, and 1% by mass of anhydrous 5-norbornene-2,3-dicarboxylic acid is added to the solution to prepare a non-aqueous electrolyte solution. Flammability was evaluated. In addition, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, and a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

Example 4
In the above general formula (I), n is 3 and one of all R is a propoxy group and 5 is fluorine 60% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 35% by volume of methyl propionate LiPF ₆ is dissolved at 1.0 mol / L and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved at 1.0 mol / L in a mixed solvent consisting of the following: anhydrous bicyclo [2.2.2]. ] 2% by mass of oct-5-ene-2,3-dicarboxylic acid was added to prepare a non-aqueous electrolyte, 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Comparative Example 1)
LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved at 1.0 mol / L in a mixed solvent consisting of 20% by volume of ethylene carbonate, 40% by volume of diethyl carbonate and 40% by volume of methyl propionate. Then, 0.5% by mass of 1,2,3,6-tetrahydrophthalic anhydride 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Comparative Example 2)
In the above general formula (I), n is 3 and one of all R is a propoxy group and 5 is fluorine 60% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 35% by volume of methyl propionate A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at 1.0 mol / L and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] at 1.0 mol / L in a mixed solvent consisting of 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Example 5)
4% by volume of cyclic phosphazene compound in which n is 3 in the general formula (I), 2 out of all R are methoxy groups and 4 are fluorine, 20% by volume of ethylene carbonate, 36% by volume of diethyl carbonate, LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved in a mixed solvent consisting of 40% by volume of methyl propionate to 1.0 mol / L, and anhydrous 1,2,3,6- A nonaqueous electrolytic solution was prepared by adding 0.5% by mass of tetrahydrophthalic acid, 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Example 6)
In the above general formula (I), n is 3 and one of all R is a propoxy group and 5 is fluorine. 73% by volume of cyclic phosphazene compound 2% by volume of ethylene carbonate 25% by volume of ethyl methyl carbonate LiPF ₆ was dissolved in a mixed solvent consisting of: 0.8 mol / L, and 2% by mass of anhydrous 5-norbornene-2,3-dicarboxylic acid 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Example 7)
In the above general formula (I), n is 3 and one of all R is a propoxy group and 5 is fluorine 60% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 35% by volume of methyl propionate LiPF ₆ is dissolved at 1.0 mol / L and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved at 1.0 mol / L in a mixed solvent consisting of the following: anhydrous bicyclo [2.2.2]. ] 0.05% by mass of oct-5-ene-2,3-dicarboxylic acid was added 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

(Example 8)
In the above general formula (I), n is 3 and one of all R is a propoxy group and 5 is fluorine 60% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 35% by volume of methyl propionate LiPF ₆ is dissolved at 1.0 mol / L and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] is dissolved at 1.0 mol / L in a mixed solvent consisting of the following: anhydrous bicyclo [2.2.2]. ] Non-aqueous electrolyte was prepared by adding 4% by mass of oct-5-ene-2,3-dicarboxylic acid, 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 a high-temperature cycle characteristic evaluation and an overcharge safety test were performed, respectively. The results are shown in Table 1.

  As shown in Examples 1 to 4 of Table 1, a non-aqueous electrolyte containing a compound of formula (I) and a specific dicarboxylic anhydride compound exhibits nonflammability, and a battery using the non-aqueous electrolyte is subjected to high temperature conditions. It can be seen that the excellent charge / discharge performance is maintained even under. As described above, it was confirmed that the nonaqueous electrolyte solution of the present invention can provide a nonaqueous electrolyte secondary battery exhibiting nonflammability and excellent in high-temperature cycle characteristics and safety.

  In addition, as shown in the comparative example 2, when not adding a dicarboxylic anhydride compound, compared with Example 4, it turns out that a high temperature cycling characteristic is inferior.

  Furthermore, as shown in Example 5, when the content of the compound represented by the formula (I) is less than 5% by volume, nonflammability was not exhibited, and bursting could not be suppressed even in the overcharge safety test.

  On the other hand, as shown in Example 6, when the content of the compound represented by the formula (I) exceeds 70% by volume, there is no problem in nonflammability and battery safety, but the initial capacity tends to be small. Was recognized. Therefore, it can be seen that the content of the cyclic phosphazene compound of the formula (I) is preferably about 10 to 60% by volume.

  Further, as shown in Example 7, when the addition amount of the dicarboxylic anhydride compound is less than 0.1% by mass, the improvement in charge / discharge performance under a high temperature condition is small, and as shown in Example 8, 3% by mass. In the case of exceeding the value, the initial capacity tended to decrease. Therefore, it can be seen that the addition amount of the dicarboxylic anhydride compound is preferably about 0.5 to 2% by mass.

  From the above results, by using a non-aqueous electrolyte characterized by containing a cyclic phosphazene compound represented by the formula (I), a non-aqueous solvent and a specific dicarboxylic anhydride compound, high safety and excellent It can be seen that a non-aqueous electrolyte secondary battery having both battery performances can be provided.

Claims (8)

The following general formula (I):
(NPR ₂ ) _n ... (I)
[Wherein R independently represents a fluorine, alkoxy group or aryloxy group; n represents 3 to 4], a non-aqueous solvent, and anhydrous 5-norbornene-2 , 3-dicarboxylic acid, 1,2,3,6-tetrahydrophthalic anhydride and at least one selected from the group consisting of bicyclo [2.2.2] oct-5-ene-2,3-dicarboxylic acid A non-aqueous electrolyte for a battery comprising the dicarboxylic anhydride compound.   2. The battery non-aqueous electrolyte according to claim 1, wherein in the general formula (I), at least four of R are fluorine.   2. The nonaqueous electrolytic solution for a battery according to claim 1, wherein the content of the cyclic phosphazene compound represented by the general formula (I) is 10 to 60% by volume of the entire nonaqueous electrolytic solution for the battery. .   2. The nonaqueous electrolytic solution for a battery according to claim 1, wherein the content of the dicarboxylic anhydride compound is 0.5 to 2 mass% of the entire nonaqueous electrolytic solution for a battery.   The battery nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous solvent is an aprotic organic solvent.   The battery for non-battery according to claim 5, wherein the aprotic organic solvent contains at least one selected from the group consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and methyl propionate. Water electrolyte.   The nonaqueous electrolytic solution for a battery according to claim 1, further comprising a supporting salt.   A nonaqueous electrolyte secondary battery comprising the battery nonaqueous electrolyte solution according to claim 1, a positive electrode, and a negative electrode.