JP2010015717A - 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 is superior in high-temperature durability and gives a high safety to the battery. <P>SOLUTION: The nonaqueous electrolyte for the battery contains a cyclic phosphagen compound as expressed by a general formula (I): (NPR<SP>1</SP><SB>2</SB>)<SB>n</SB>[in the formula, R<SP>1</SP>expresses each independently fluorine, alkoxy group, or aryl-oxy group, n expresses 3-4], a non-aqueous solvent, and an unsaturated carbonate compound as expressed by a general formula (II) [in the formula, R<SP>2</SP>is alkyl group of carbon number 1-2, R<SP>3</SP>is aryl group or vinyl group, and R<SP>2</SP>and R<SP>3</SP>may form a ring by mutually bonding, and hydrogen element of the substituent may be substituted with fluorine]. <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 storage stability even in a high temperature environment, and high The present invention relates to a non-aqueous electrolyte secondary battery having safety.

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. In addition, when a battery using a phosphate ester in a non-aqueous electrolyte is stored in a charged state, the decomposition reaction of the phosphate ester proceeds with a high battery voltage, so the charge / discharge capacity after storage is greatly reduced. There is also a problem of end.

  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 compounds generally exhibit high flame retardancy, but many of them have low solubility of the supporting salt. If the amount added is increased, the content of other electrolyte components decreases, and the phosphazene compounds dissolve in the electrolyte components. The relative concentration of the supporting salt is also high. As a result, depending on the temperature environment and battery operating voltage conditions, deterioration and decomposition of the electrolyte component and the supporting salt are likely to proceed, which may hinder battery characteristics such as cycle characteristics, electric capacity, and durability.

  Devices such as lithium batteries, lithium ion secondary batteries, and electric double layer capacitors are required to have high safety and durability that can ensure stable performance in a wider temperature range. In the prior art using the battery, the battery characteristics are not always satisfactory, and an electrolytic solution for a lithium secondary battery that does not cause deterioration in battery performance is desired.

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-described 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 durability and high safety. It is in providing the nonaqueous electrolyte secondary battery which has.

  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 carbonate compound, thereby forming an electrolyte solution. It was found that the present invention can maintain high battery performance even when a non-aqueous electrolyte secondary battery using the electrolytic solution is exposed to a high temperature for a long time. It came to complete.

［式中、Ｒ²は炭素数１〜２のアルキル基であり、Ｒ³はアリル基又はビニル基であり、Ｒ²及びＲ³は互いに結合して環を形成してもよく、また置換基中の水素元素は、フッ素で置換されていてもよい］で表される不飽和カーボネート化合物と
を含むことを特徴とする。 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 allyl group or a vinyl group, R ² and R ³ may be bonded to each other to form a ring, The hydrogen element therein may be substituted with fluorine], and an unsaturated carbonate compound represented by

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 carbonate compound is 0.5 to 3% 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, at least one selected from the group consisting of methyl propionate is included.

  It is preferable that the nonaqueous electrolytic solution for a battery of the present invention further contains a supporting salt. Note that the nonaqueous electrolyte for a battery consisting only of the cyclic phosphazene compound represented by the formula (I), the nonaqueous solvent, the unsaturated carbonate 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.

  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, preferably non-flammable by adding 10% by volume or more, and further using a specific unsaturated carbonate compound in combination. When used in a liquid secondary battery, it is possible to provide a non-aqueous electrolyte capable of suppressing deterioration of battery characteristics even when exposed to high temperature conditions for a long time. 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. Further, although the reason is not necessarily clear, a film having high heat resistance is formed on the electrode surface by the synergistic effect of the two compounds of the cyclic phosphazene compound and the unsaturated carbonate compound, and the film decomposes the electrolytic solution and the supporting salt. Therefore, it is considered that excellent charge / discharge performance can be maintained even when stored under high temperature conditions.

<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. The non-aqueous electrolyte for a battery according to the present invention contains a cyclic phosphazene compound represented by the general formula (I), a non-aqueous solvent, and an unsaturated carbonate 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. If the content of the cyclic phosphazene compound exceeds 70% by volume, although depending on the structure of the cyclic phosphazene compound, it is not preferable because the battery capacity and load characteristics tend to decrease. When an organic solvent having a low concentration is used for the electrolytic solution, incombustibility may not be exhibited. Moreover, from the viewpoint of the balance between battery safety and battery characteristics under overcharge conditions, the content of the cyclic phosphazene compound is more preferably in the range of 10 to 60% by volume of the whole non-aqueous electrolyte for batteries.

The nonaqueous electrolytic solution for a battery of the present invention is characterized by further containing an unsaturated carbonate 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 allyl group or a vinyl group, R ³ and R ⁴ may be bonded to each other to form a ring, The hydrogen element in the substituents R ³ and R ⁴ may be substituted with fluorine. Here, examples of the alkyl group in R ³ include a methyl group and an ethyl group, and examples of the group formed by combining R ² and R ³ include divalent unsaturated hydrocarbons such as vinylene group and vinylethylene group. Groups.

  Specific examples of the unsaturated carbonate compound of the formula (II) include methyl vinyl carbonate, ethyl vinyl carbonate, allyl methyl carbonate, allyl ethyl carbonate, vinylene carbonate, fluoro vinylene carbonate, vinyl ethylene carbonate and the like. Among these, methyl vinyl carbonate, allyl ethyl carbonate, vinylene carbonate, fluoro vinylene carbonate, and vinyl ethylene carbonate are preferable. These unsaturated carbonate 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 carbonate compound is preferably in the range of 0.2 to 5% by mass with respect to the entire battery non-aqueous electrolyte, and more preferably in the range of 0.5 to 3% 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. .

  Specific examples of the aprotic organic solvent include saturated carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Carboxylic acid esters such as methyl acetate, methyl propionate and methyl butyrate, ethers such as 1,2-dimethoxyethane (DME), tetrahydrofuran (THF) and diethyl ether (DEE), γ-butyrolactone (GBL), γ -Lactones such as 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 saturated carbonates and carboxylic acid esters from the viewpoint of the compatibility with the cyclic phosphazene compound and the balance of 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.

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), ^one of R ¹ is ethoxy group and 5 is fluorine, 13% by volume of ethylene carbonate, 37% by volume of diethyl carbonate Then, LiPF ₆ was dissolved in a mixed solvent consisting of 40% by volume of methyl propionate so as to be 1.2 mol / L, and 0.5% by mass of allyl ethyl carbonate 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 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 LiCo _0.2 Ni _0.8 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: 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) High-temperature durability evaluation 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 were performed in an environment of 40 ° 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 stored in an environment at 60 ° C. for 20 days. Then, after taking out to 40 degreeC environment, the discharge capacity when performing 20 cycles of discharge and charging / discharging on the same charging / discharging conditions was calculated | required, and the following formula:
Capacity retention = discharge capacity after high temperature storage / initial discharge capacity × 100 (%)
The capacity retention rate was calculated according to the above and used as an index for evaluating high temperature durability.

(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 the cyclic phosphazene compound 10% by volume in which all R ¹ is fluorine, and in the above general formula (I), n is 3, and two of all R ¹ are LiTFSI [Li (CF ₃ SO ₂ ) ₂ N] was added to a mixed solvent consisting of 20% by volume of a cyclic phosphazene compound having four methoxy groups and four fluorines, 14% by volume of ethylene carbonate, and 56% by volume of ethyl methyl carbonate. It dissolved so that it might become 1.0 mol / L, methyl vinyl carbonate 1 mass% was added to this, the nonaqueous electrolyte solution was prepared, and the flame retardance of the obtained nonaqueous electrolyte solution was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and high temperature durability 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 and ^one of all R ¹ is a propoxy group and 5 is fluorine. 40% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 55% by volume of ethyl methyl carbonate % Of LiPF ₆ is dissolved at 1.0 mol / L in a mixed solvent consisting of 2% by weight, and a non-aqueous electrolyte is prepared by adding 2% by mass of fluorovinylene carbonate to the resulting solution. The flame retardancy of was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and high temperature durability 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 a trifluoroethoxy group and seven is fluorine, 60% by volume, 5% by volume of ethylene carbonate, methyl propionate, In a mixed solvent of 35% by volume, 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. % And vinylene carbonate 2% by mass were added 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 high temperature durability evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Comparative Example 1)
LiPF ₆ was dissolved 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 so as to be 1.2 mol / L, and 0.5% by mass of allyl ethyl carbonate was dissolved therein. Was added to prepare a non-aqueous electrolyte and 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 high temperature durability 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 a trifluoroethoxy group and seven is fluorine, 60% by volume, 5% by volume of ethylene carbonate, methyl propionate, In a mixed solvent consisting of 35% by volume, 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 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 high temperature durability 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 an ethoxy group and five is fluorine, 4 volume%, ethylene carbonate 14 volume%, diethyl carbonate 42 volume% LiPF ₆ is dissolved in a mixed solvent consisting of 40% by volume of methyl propionate so as to be 1.2 mol / L, and 0.5% by mass of allyl ethyl carbonate is 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 high temperature durability evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

(Example 6)
In the above general formula (I), a mixed solvent comprising 75% by volume of a cyclic phosphazene compound in which n is 3 and ^one of all R ¹ is a propoxy group and 5 is fluorine, and 25% by volume of ethyl methyl carbonate. , LiPF ₆ was dissolved to 0.8 mol / L, and 2% by mass of fluorovinylene carbonate was added thereto 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 high temperature durability 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 3 and ^one of all R ¹ is a propoxy group and 5 is fluorine. 40% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 55% by volume of ethyl methyl carbonate % Of LiPF ₆ is dissolved at 1.0 mol / L in a mixed solvent containing 0.1% by weight of fluorovinylene carbonate to prepare a non-aqueous electrolyte, and the resulting non-aqueous electrolyte is obtained. The flame retardancy of was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and high temperature durability 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 3 and ^one of all R ¹ is a propoxy group and 5 is fluorine. 40% by volume of cyclic phosphazene compound, 5% by volume of ethylene carbonate, 55% by volume of ethyl methyl carbonate % Of LiPF ₆ is dissolved at 1.0 mol / L in a mixed solvent consisting of 5% by weight, and 6% by mass of fluorovinylene carbonate is added to prepare a non-aqueous electrolyte, and the resulting non-aqueous electrolyte is obtained. The flame retardancy of was evaluated. Moreover, the nonaqueous electrolyte secondary battery was produced like Example 1, and high temperature durability evaluation and the overcharge safety test were implemented, respectively. The results are shown in Table 1.

  As shown in Examples 1 to 4 of Table 1, the non-aqueous electrolyte containing the compound of formula (I) and the unsaturated carbonate compound represented by formula (II) is non-flammable, and the non-aqueous electrolyte is It can be seen that the used battery maintains excellent battery performance even after high-temperature storage under full charge conditions and charge / discharge cycles at high temperatures. Thus, it was confirmed that the nonaqueous electrolyte solution of the present invention can provide a nonaqueous electrolyte secondary battery that exhibits nonflammability and is excellent in high temperature durability 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 retention 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.

  In addition, as shown in Example 7, when the amount of the unsaturated carbonate compound represented by the formula (II) is less than 0.2% by mass, the improvement effect in high temperature durability evaluation under high temperature conditions is small. As shown in Example 8, when the amount exceeds 5% by mass, the initial capacity tends to decrease. Therefore, it can be seen that the amount of the unsaturated carbonate compound represented by the formula (II) is preferably about 0.5 to 3% by mass.

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

Claims (8)

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 allyl group or a vinyl group, R ² and R ³ may be bonded to each other to form a ring, A non-aqueous electrolyte for a battery comprising: an unsaturated carbonate compound represented by: wherein the hydrogen element may be substituted with fluorine. 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 battery non-aqueous electrolysis according to claim 1, wherein the content of the unsaturated carbonate compound represented by the general formula (II) is 0.5 to 3 mass% of the whole battery non-aqueous electrolyte. 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.   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.