JP2010050020A - Nonaqueous electrolyte for battery and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte for a battery capable of giving excellent high-temperature storage characteristics and high safety to the battery. <P>SOLUTION: The nonaqueous electrolyte for a battery includes a ring phosphazen compound expressed by formula (I) of (NPR<SP>1</SP><SB>2</SB>)<SB>n</SB>, a nonaqueous solvent, an unsaturated ester compound expressed by formula (II), and supporting salt. Here, R<SP>1</SP>in formula (I) each independently shows fluorine, alkoxy, or aryloxy which; and n shows 3-4. R<SP>2</SP>in formula (II) is 1-2C alkyl; and R<SP>3</SP>is 2-4C alkenyl or propargyl. However, R<SP>2</SP>and R<SP>3</SP>may form a ring by combining each other. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte for a battery and a non-aqueous electrolyte secondary battery including the same, and in particular, a non-aqueous electrolyte for a non-flammable battery, and excellent storage characteristics at high temperatures, and high safety performance. The present invention relates to a non-aqueous electrolyte secondary battery having

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, since these phosphate esters have low reduction resistance, when a battery using a phosphate ester is stored in a charged state, the decomposition reaction of the phosphate ester proceeds due to a high battery voltage. There is a problem that the capacity after storage is greatly reduced.

  Japanese Patent Application Laid-Open No. 6-13108 (Patent Document 4) 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. The phosphazene compound generally has high stability to heat, but the solubility of the supporting salt is low. When the addition amount is increased, the content of other electrolyte components decreases, and the supporting salt dissolved in the component is reduced. The relative concentration of increases. For this reason, depending on the temperature environment and battery operating voltage conditions, decomposition and deterioration of the electrolyte component and the supporting salt are likely to occur, and as a result, the storage characteristics may be deteriorated.

Battery devices are required not only to have high safety but also to ensure stable performance over a wider temperature range, and as a storage characteristic, an electrolyte solution for lithium secondary batteries that has as little self-discharge as possible over a wide temperature range. It is desired. In these respects, it cannot be said that the prior art has reached a sufficiently satisfactory level.
JP-A-4-184870 JP-A-8-22839 JP 2000-182669 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 have excellent high-temperature storage characteristics and high safety. The object is to provide a non-aqueous electrolyte secondary battery.

  As a result of intensive studies to achieve the above object, the present inventor has constructed a non-aqueous electrolyte by combining a specific cyclic phosphazene compound and a non-aqueous solvent with a specific unsaturated ester compound, thereby forming an electrolyte solution. And found that a non-aqueous electrolyte secondary battery using the electrolyte can maintain a high battery capacity even when left in a high temperature environment for a long period of time. It came to complete.

［式中、Ｒ²は炭素数１〜２のアルキル基であり；Ｒ³は炭素数２〜４のアルケニル基又はプロパルギル基であり、但し、Ｒ²及びＲ³は互いに結合して環を形成してもよい］で表される不飽和エステル化合物と、
・支持塩と
を含むことを特徴とする。なお、式(I)で表される環状ホスファゼン化合物、非水溶媒、式(II)で表される不飽和エステル化合物及び支持塩のみからなる電池用非水電解液は、本発明の電池用非水電解液の好適一態様である。 That is, the non-aqueous electrolyte for a battery of the present invention is
-The following general formula (I):
(NPR ¹ ₂ ) _n ... (I)
[Wherein R ¹ 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 following general formula (II):

[Wherein R ² is an alkyl group having 1 to ² carbon atoms; R ³ is an alkenyl group or propargyl group having 2 to 4 carbon atoms, provided that R ² and R ³ are bonded to each other to form a ring. An unsaturated ester compound represented by:
-It is characterized by including supporting salt. Note that the nonaqueous electrolytic solution for a battery consisting only of the cyclic phosphazene compound represented by the formula (I), the nonaqueous solvent, the unsaturated ester compound represented by the formula (II) and the supporting salt is a non-aqueous electrolyte for a battery of the present invention. This is a preferred embodiment of the water electrolyte.

In the non-aqueous electrolyte for a battery of the present invention, the cyclic phosphazene compound is preferably a compound in which at least four 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 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.

  In another preferred embodiment of the battery non-aqueous electrolyte of the present invention, the content of the unsaturated ester compound is 0.2 to 1% 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.

  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, a specific unsaturated ester compound is used in combination. When used in a water electrolyte secondary battery, it is possible to provide a non-aqueous electrolyte capable of maintaining a high battery capacity with little self-discharge even in a high temperature environment. Moreover, the nonaqueous electrolyte secondary battery provided with this nonaqueous 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 unsaturated ester compound causes the catalytic decomposition of the electrolyte and the battery electrode material in a wide temperature range. In order to suppress it, it is considered that self-discharge due to decomposition is small even in a high temperature environment, and a high discharge capacity can be maintained even after long-term storage.

<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. The nonaqueous electrolytic solution for a battery according to the present invention contains a cyclic phosphazene compound represented by the general formula (I), a nonaqueous solvent, and an unsaturated ester compound represented by the general formula (II). Further, it is preferable to contain an aprotic organic solvent as the 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) each independently represent fluorine, an alkoxy group or an aryloxy radical, n represents 3-4.

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, or an alkoxy-substituted alkoxy such as a methoxyethoxy group and a methoxyethoxyethoxy group. Groups and the like. 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 4 or more of R ¹ in terms of both nonflammability 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. When the content of the cyclic phosphazene compound exceeds 70% by volume, the battery capacity and load characteristics are deteriorated, which is not preferable. In addition, incombustibility may not be exhibited.

The nonaqueous electrolytic solution for a battery of the present invention is characterized by further containing an unsaturated ester compound represented by the above general formula (II). In the formula (II), R ² is an alkyl group having 1 to ² carbon atoms, R ³ is an alkenyl group or propargyl group having 2 to 4 carbon atoms, provided that R ² and R ³ are bonded to each other to form a ring. May be formed. Here, as the alkyl group in R ^2, a methyl group, and ethyl group, the alkenyl group in R ^3, a vinyl group, an allyl group, isopropenyl group, etc., R ² and R ³ are bonded Examples of the group formed in this way include a divalent group such as a methylideneethylene group [—C (═CH ₂ ) CH ₂ —].

  Specific examples of unsaturated ester compounds of formula (II) include vinyl acetate, allyl acetate, methallyl acetate, isopropenyl acetate, propargyl acetate, vinyl propionate, allyl propionate, methallyl propionate, isopropenyl propionate, propionic acid Examples include propargyl and diketene. Among these, allyl acetate, vinyl propionate, propargyl acetate, and diketene are preferable. These unsaturated ester compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The content of the unsaturated ester compound is preferably in the range of 0.1 to 2% by mass, and more preferably in the range of 0.2 to 1% by mass, based on the 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. .

  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 carbonic acid esters and carboxylic acid esters from the viewpoint of compatibility with the cyclic phosphazene compound and battery performance. Among them, ethylene carbonate (EC), ethyl methyl carbonate (EMC), propion are preferable. More preferably, methyl acid 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.

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 (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
In the above general formula (I), n is 3, 10% by volume of cyclic phosphazene compound in which one of all R ¹ is a trifluoroethoxy group and 5 is fluorine, 18% by volume of ethylene carbonate, 52% of diethyl carbonate LiPF ₆ was dissolved in a mixed solvent consisting of 20% by volume and 20% by volume of methyl propionate so as to be 1.2 mol / L, and 0.2% by mass of allyl acetate 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.

(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 storage characteristics Using the laminate battery produced as described above, ² 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 in an environment of 20 ° 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. After further charging to 4.2 V, the battery was left in an environment at 60 ° C. for 40 days. Then, after taking out to 20 degreeC environment, the discharge capacity when discharging under the same discharge conditions is obtained, and the following formula:
Capacity remaining rate = discharge capacity after standing / initial discharge capacity × 100 (%)
The capacity remaining rate was calculated according to the above and used as an index of high temperature storage characteristics. The results are shown in Table 1.

(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. Place the cell on temperature control with battery holders (stainless steel), 20 by the current density of the battery temperature 5.0 mA / cm ² of ℃ was charged to 12.0 V, yet 0.25 mA / cm ² at the same voltage 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 above general formula (I), n is 3, and 5% by volume of the cyclic phosphazene compound in which one of all R ¹ is an allyloxy group and 5 is fluorine, and in the above general formula (I), n is 3. In addition, LiTFSI [Li (2) is added to a mixed solvent composed of 25% by volume of a cyclic phosphazene compound in which two of the total R ¹ are methoxy groups and four are fluorine, 14% by volume of ethylene carbonate, and 56% by volume of ethyl methyl carbonate. CF ₃ SO ₂ ) ₂ N] is dissolved to 0.5 mol / L, and 1% by mass of vinyl propionate is added thereto to prepare a non-aqueous electrolyte. The difficulty of the obtained non-aqueous electrolyte Flammability was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 3)
In the above general formula (I), n is 3, cyclic phosphazene compound 40% by volume of ethylene, 10% by volume of ethylene carbonate, 50% by volume of ethyl methyl carbonate, ^one of which is butoxy group and 5 is fluorine. % Of LiPF ₆ is dissolved in a mixed solvent consisting of 1% by weight of 1% by weight of propargyl acetate to prepare a non-aqueous electrolyte solution. Flame retardancy was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

Example 4
In the above general formula (I), n is 4, cyclic phosphazene compound in which one of all R ¹ is ethoxy group and seven is fluorine 60 volume%, ethylene carbonate 5 volume%, ethyl methyl carbonate 25 volume LiPF ₆ [1.0 mol / L] and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] at 1.0 mol / L in a mixed solvent consisting of 10% by volume and 10% by volume of methyl propionate. Diketene 0.5% by mass was added to prepare a nonaqueous electrolytic solution, and the flame retardancy of the obtained nonaqueous electrolytic solution was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Comparative Example 1)
A non-aqueous electrolyte was prepared by dissolving LiPF _{6 in a} mixed solvent consisting of 20% by volume of ethylene carbonate, 60% by volume of diethyl carbonate, and 20% by volume of methyl propionate so as to be 1.2 mol / L. The non-aqueous electrolyte obtained was evaluated for flame retardancy. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Comparative Example 2)
In the above general formula (I), n is 4, cyclic phosphazene compound in which one of all R ¹ is ethoxy group and seven is fluorine 60 volume%, ethylene carbonate 5 volume%, ethyl methyl carbonate 25 volume % and, in a mixed solvent consisting of 10 vol% methyl propionate, a LiPF ₆ 1.0 mol / L and _{LiTFSI [Li (CF 3 sO 2} ) 2 N] dissolved so that 1.0 mol / L in a non-aqueous An electrolyte solution was prepared, and the flame retardancy of the obtained nonaqueous electrolyte solution was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 5)
In the above general formula (I), n is 3, cyclic phosphazene compound in which one of all R ¹ is a trifluoroethoxy group and five is fluorine, 4 volume%, ethylene carbonate 18 volume%, diethyl carbonate 58 LiPF ₆ was dissolved in a mixed solvent consisting of 20% by volume and 20% by volume of methyl propionate so as to be 1.2 mol / L, and 0.5% by mass of allyl acetate was added thereto to prepare a non-aqueous electrolyte. The flame retardancy of the obtained non-aqueous electrolyte was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 6)
In the above general formula (I), n is 3 and ^one of all R ¹ is butoxy 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 in% consisting of mixed solvent by dissolving LiPF ₆ to be 0.8 mol / L, which in the non-aqueous electrolyte solution was prepared by adding 1 wt% acetic acid propargyl, resulting nonaqueous electrolytic solution of Flame retardancy was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 7)
In the above general formula (I), n is 4, cyclic phosphazene compound in which one of all R ¹ is ethoxy group and seven is fluorine 60 volume%, ethylene carbonate 5 volume%, ethyl methyl carbonate 25 volume LiPF ₆ [1.0 mol / L] and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] at 1.0 mol / L in a mixed solvent consisting of 10% by volume and 10% by volume of methyl propionate. A non-aqueous electrolyte was prepared by adding 0.05% by mass of diketene, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 8)
In the above general formula (I), n is 4, cyclic phosphazene compound in which one of all R ¹ is ethoxy group and seven is fluorine 60 volume%, ethylene carbonate 5 volume%, ethyl methyl carbonate 25 volume LiPF ₆ [1.0 mol / L] and LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] at 1.0 mol / L in a mixed solvent consisting of 10% by volume and 10% by volume of methyl propionate. Diketene (3.0% by mass) was added to the mixture to prepare a non-aqueous electrolyte, and the flame retardancy of the obtained non-aqueous electrolyte was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and the high temperature storage characteristic evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

  As shown in Examples 1 to 4 in Table 1, the non-aqueous electrolyte containing the compound of the formula (I) and the unsaturated ester compound represented by the formula (II) exhibits nonflammability, and the non-aqueous electrolyte is used. It can be seen that the stored battery maintains a high discharge capacity even after being stored at high temperature under full charge conditions, and has high safety in overcharging. 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 storage characteristics and safety.

  In addition, as shown in Comparative Example 2, it can be seen that when the unsaturated carbonate compound of the formula (II) is not added, the capacity remaining rate after high-temperature storage is inferior compared with Example 4.

  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 amount of the unsaturated ester compound represented by the formula (II) is less than 0.1% by mass, the improvement effect in high-temperature storage property evaluation is small, and as shown in Example 8. Thus, when it exceeded 2 mass%, the tendency for the initial capacity to decrease was recognized. Therefore, it can be seen that the amount of the unsaturated ester compound represented by the formula (II) is preferably about 0.2 to 1% by mass.

  From the above results, by using a non-aqueous electrolyte characterized by containing a cyclic phosphazene compound represented by the formula (I) and an unsaturated ester compound represented by the formula (II), high-temperature storage characteristics and It can be seen that a non-aqueous electrolyte secondary battery having both safety performance can be provided.

Claims (7)

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

[Wherein R ² is an alkyl group having 1 to ² carbon atoms; R ³ is an alkenyl group or propargyl group having 2 to 4 carbon atoms, provided that R ² and R ³ are bonded to each other to form a ring. A non-aqueous electrolyte for a battery, comprising: an unsaturated ester compound represented by the formula: 2. The battery non-aqueous electrolyte according to claim 1, wherein in the general formula (I), at least four of R ¹ 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 electrolysis for battery according to claim 1, wherein the content of the unsaturated ester compound represented by the general formula (II) is 0.2 to 1% by mass of the entire nonaqueous electrolyte for battery. liquid.   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.   A nonaqueous electrolyte secondary battery comprising the battery nonaqueous electrolyte solution according to claim 1, a positive electrode, and a negative electrode.