JP2005190869A - Electrolyte for polymer battery, and the polymer battery equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for a polymer battery, capable of reducing a risk of firing and flashing of an aprotic organic solvent remaining inside the battery and an aprotic organic solvent leaking to the outside of the battery, by evaporating or the like when the temperature of the polymer battery abnormally rises. <P>SOLUTION: This electrolyte for a polymer battery contains one or more kinds of aprotic organic solvents, a polymer and a support electrolyte. The electrolyte is characterized by containing, in each aprotic organic solvent, a compound for which the difference in the boiling point from that of the aprotic organic solvent is below 25°C and which has phosphorus and/or nitrogen in molecules. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrolyte for a polymer battery and a polymer battery including the same, and more particularly to an electrolyte for a polymer battery in which the risk of ignition in an emergency is greatly reduced.

  Conventionally, nickel-cadmium batteries have been mainly used as secondary batteries for memory backup of AV and information devices such as personal computers and VTRs, and driving power sources thereof. In recent years, it has the advantages of high voltage and high energy density and exhibits excellent self-discharge characteristics. Therefore, non-aqueous electrolyte secondary batteries have attracted much attention as alternatives to NiCd batteries, and various developments have been attempted. Has been commercialized in part. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries. In these non-aqueous electrolyte secondary batteries, a separator is used to prevent contact between the positive electrode and the negative electrode, and the separator is a porous thin film that does not hinder the movement of ions in the electrolyte. A layer film or the like is used. However, since the thin layer film does not have the ability to retain the electrolyte, the battery using the thin layer film as a separator has a risk of liquid leakage.

  On the other hand, in recent years, polymer batteries using polymers as electrolytes have been developed as batteries that do not have the risk of liquid leakage. In recent years, the polymer battery has been actively researched because it can be formed into a film, can be incorporated into an electronic device, and can effectively use a space, in addition to being free from the risk of liquid leakage. As the electrolyte used in the polymer battery, an intrinsic polymer electrolyte in which a lithium salt is held in a polymer and a gel electrolyte in which an organic solvent is swollen in the polymer are known. The intrinsic polymer electrolyte has an ionic conductivity. There is a problem that it is low in each stage as compared with the gel electrolyte. On the other hand, in a polymer battery using a gel electrolyte, a lithium metal or a lithium alloy is used as a negative electrode material as in the non-aqueous electrolyte secondary battery described above, and the negative electrode has a compound having active protons such as water and alcohol. The organic solvent used for the gel electrolyte is limited to aprotic organic solvents such as ester compounds and ether compounds.

  However, although the aprotic organic solvent has low reactivity with the negative electrode active material lithium, for example, when a polymer battery is short-circuited, a large current flows rapidly, and when the battery abnormally generates heat, There is a high risk of generating gas by decomposition, causing the battery to rupture or ignite due to the generated gas and heat, and sparks generated during a short circuit.

  In contrast, adding phosphazene compounds to polymer battery electrolytes gives the electrolyte nonflammability, flame retardancy, or self-extinguishing properties, greatly increasing the risk of polymer batteries igniting and igniting in the event of a short circuit or other emergency. A polymer battery having a reduced thickness has been developed (see Patent Document 1).

WO03 / 005478 pamphlet

  The electrolyte for polymer batteries to which the above phosphazene compound is added has greatly reduced the risk of ignition and ignition, but the phosphazene compound is aprotic organic when the temperature of the polymer battery rises in the event of an emergency such as a short circuit. When vaporized before the solvent, the remaining aprotic organic solvent vaporizes and decomposes alone to generate gas, or the generated gas and heat cause battery rupture / ignition, or sparks generated during a short circuit. However, it is impossible to eliminate the danger of igniting the aprotic organic solvent. Further, when the aprotic organic solvent is vaporized prior to the phosphazene compound, the vaporized aprotic organic solvent may leak out of the battery and ignite.

  Accordingly, an object of the present invention is to ignite / ignite the aprotic organic solvent remaining in the battery and the aprotic organic solvent that evaporates and leaks outside the battery when the temperature of the polymer battery rises abnormally. It is an object of the present invention to provide an electrolyte for a polymer battery with reduced risk of Another object of the present invention is to provide a polymer battery comprising such an electrolyte and having reduced risk of ignition and the like inside and outside the battery even when the temperature rises abnormally.

  As a result of intensive studies to achieve the above object, the inventors of the present invention, in a polymer battery electrolyte containing at least one aprotic organic solvent together with a polymer, further correspond to each aprotic organic solvent, Risk of ignition or ignition of aprotic organic solvent remaining in the battery and aprotic organic solvent leaking out of the battery due to vaporization, etc. by adding phosphorus and / or nitrogen-containing compounds having close boiling points Has been found to be significantly reduced, and the present invention has been completed.

  That is, the polymer battery electrolyte of the present invention is a polymer battery electrolyte containing at least one aprotic organic solvent, a polymer, and a supporting salt, and further, with respect to each of the aprotic organic solvents. A difference between the boiling points of the organic solvent and the organic solvent is 25 ° C. or less, and a compound having phosphorus and / or nitrogen in the molecule is contained.

  In a preferred example of the polymer battery electrolyte of the present invention, the compound having phosphorus and / or nitrogen in the molecule has a phosphorus-nitrogen double bond. Here, as the compound having phosphorus and / or nitrogen in the molecule and having a phosphorus-nitrogen double bond, a phosphazene compound is particularly preferable.

  In another preferred embodiment of the polymer battery electrolyte of the present invention, the aprotic organic solvent is at least selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate. It is a kind.

  Moreover, the polymer battery of this invention is equipped with the above-mentioned electrolyte, a positive electrode, and a negative electrode, It is characterized by the above-mentioned.

  According to the present invention, a polymer battery electrolyte containing at least one aprotic organic solvent together with a polymer, and further, phosphorus and / or nitrogen-containing compounds having close boiling points corresponding to the respective aprotic organic solvents, respectively. By adding, it is possible to provide a polymer battery electrolyte that greatly reduces the risk of ignition and ignition of an aprotic organic solvent remaining in the battery or leaking out of the battery. Moreover, even if the temperature rises abnormally with such an electrolyte, it is possible to provide a polymer battery in which the risk of ignition inside and outside the battery is greatly reduced.

<Electrolyte for polymer battery>
Hereinafter, the polymer battery electrolyte of the present invention will be described in detail. The electrolyte for a polymer battery of the present invention includes at least one aprotic organic solvent, a polymer, and a supporting salt, and further has a boiling point difference of 25 ° C. or less from each of the aprotic organic solvents, and phosphorus and And / or a compound having nitrogen.

  In the polymer battery electrolyte of the present invention, the compound having phosphorus and / or nitrogen in the molecule generates nitrogen gas and / or phosphate ester, etc., making the electrolyte incombustible, flame retardant or self-extinguishing, It has the effect of reducing the risk of ignition of the polymer battery. However, when the electrolyte containing an aprotic organic solvent does not contain phosphorus and / or a nitrogen-containing compound having a boiling point close to that of the aprotic organic solvent, the aprotic organic solvent either in the gas phase or in the electrolyte (gel) And the phosphorus and / or nitrogen-containing compounds are in a wide temperature range, so when the temperature of the polymer battery rises abnormally, the aprotic organic solvent vaporized or the aprotic organic solvent remaining in the electrolyte is ignited・ The risk of ignition cannot be reduced. In contrast, the polymer battery electrolyte of the present invention contains an aprotic organic solvent and a phosphorus and / or nitrogen-containing compound having a boiling point close to that of the aprotic organic solvent, and the temperature of the polymer battery is abnormally increased. Since the aprotic organic solvent and the phosphorus and / or nitrogen-containing compound are vaporized at a close temperature, the aprotic organic solvent is present in both cases where the aprotic organic solvent is present in the electrolyte and as a gas. And phosphorus and / or nitrogen-containing compounds coexist, and as a result, the risk of ignition and ignition of the electrolyte is greatly reduced.

  In addition, for example, when the polymer battery electrolyte of the present invention includes a low-boiling aprotic organic solvent and a high-boiling aprotic organic solvent, the electrolyte is near a temperature at which the low-boiling aprotic organic solvent is vaporized. Since the corresponding phosphorus and / or nitrogen-containing compound is vaporized, the risk of ignition and ignition of the vaporized aprotic organic solvent can be reduced. In addition, after the low boiling point aprotic organic solvent and the phosphorus and / or nitrogen-containing compound having a boiling point close to that of the low boiling point aprotic organic solvent are vaporized, together with the high boiling point aprotic organic solvent, the high boiling point Since phosphorus and / or nitrogen-containing compounds having a boiling point close to that of the aprotic organic solvent are present in the electrolyte, the risk of ignition and ignition of the high boiling aprotic organic solvent remaining in the electrolyte can also be reduced. .

  The electrolyte for polymer batteries of the present invention contains at least one aprotic organic solvent. The aprotic organic solvent can improve the ionic conductivity of the electrolyte more easily without reacting with the negative electrode. 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), γ-butyrolactone ( Preferred examples include esters such as GBL), γ-valerolactone, and methyl formate (MF), and ethers such as 1,2-dimethoxyethane (DME) and tetrahydrofuran (THF). Among these, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate are preferable. Cyclic esters are preferred in that they have a high relative dielectric constant and excellent solubility of the supporting salt. On the other hand, chain esters and chain ethers are low in viscosity and can be easily impregnated. It is suitable at that point. Here, the aprotic organic solvent preferably has a viscosity at 25 ° C. of 10 mPa · s (10 cP) or less, and more preferably 5 mPa · s (5 cP) or less. These aprotic organic solvents may be used alone or in combination of two or more.

The polymer battery electrolyte of the present invention contains a supporting salt. The supporting salt is preferably a supporting salt that serves as an ion source for lithium ions. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used alone or in combination of two or more.

  The polymer battery electrolyte of the present invention contains a polymer. As the polymer, all of the polymers usually used in polymer battery electrolytes can be used. Specific examples include polyethylene oxide, polyacrylate, polypropylene oxide, polyacrylonitrile, polyacrylate containing ethylene oxide units, and the like. . Among these polymers, polyethylene oxide, polypropylene oxide and the like are particularly preferable from the viewpoint of electrical stability. These polymers may be used alone or in combination of two or more. Further, the weight average molecular weight (Mw) of the polymer is preferably 100,000 or more, more preferably 5 million or more. When the weight average molecular weight of the polymer is less than 100,000, the strength is weak, and the polymer may be close to a sol rather than a gel.

  In the polymer battery electrolyte of the present invention, the amount of the polymer relative to the total amount of the polymer and the supporting salt is preferably 80 to 95% by mass, and particularly preferably about 90% by mass. When the amount of the polymer is less than 80% by mass, the strength of the electrolyte is decreased, and when it exceeds 95% by mass, the electrical conductivity may be decreased.

  The electrolyte for a polymer battery of the present invention includes a compound having a difference in boiling point from an aprotic organic solvent contained in the electrolyte of 25 ° C. or less and having phosphorus and / or nitrogen in the molecule. When the difference in boiling point between the aprotic organic solvent and the phosphorus and / or nitrogen-containing compound contained in the electrolyte exceeds 25 ° C, the aprotic organic solvent is vaporized first and the gaseous aprotic organic solvent ignites. There is a high risk that phosphorus and / or nitrogen-containing compounds will vaporize first and the aprotic organic solvent remaining in the electrolyte will ignite. Here, from the viewpoint of further reducing the risk of ignition of the aprotic organic solvent, the difference in boiling point between the aprotic organic solvent and the compound having phosphorus and / or nitrogen in the molecule is 20 ° C. or less. preferable. The electrolyte for a polymer battery of the present invention may contain at least a phosphorus and / or nitrogen-containing compound having a boiling point of 25 ° C. or less from that of each of the aprotic organic solvents, and the difference in boiling point of 25 ° C. More phosphorus and / or nitrogen containing compounds may also be included.

  Examples of the compound having phosphorus and / or nitrogen in the molecule include compounds having phosphorus in the molecule such as phosphate ester compounds, polyphosphate ester compounds, and condensed phosphate ester compounds; triazine compounds, guanidine compounds, pyrrolidine compounds, etc. Compound having nitrogen in molecule; and composite of phosphazene compound, isomer of phosphazene compound, phosphazane compound, compound exemplified as compound having phosphorus in molecule and compound exemplified as compound having nitrogen in molecule Examples thereof include compounds having phosphorus and nitrogen in the molecule such as compounds. Note that the compound having phosphorus and nitrogen in the molecule is also an example of a compound having phosphorus in the molecule and a compound having nitrogen in the molecule. The phosphorus and / or nitrogen-containing compound is appropriately selected according to the aprotic organic solvent used for the electrolyte.

  Among the compounds containing phosphorus and / or nitrogen in the molecule, compounds having phosphorus and nitrogen in the molecule are preferable from the viewpoint of the cycle characteristics of the polymer battery. Among the compounds having phosphorus and nitrogen in the molecule, compounds having a phosphorus-nitrogen double bond such as a phosphazene compound are particularly preferable from the viewpoint of improving the thermal stability and high-temperature storage characteristics of the polymer battery. .

（式中、Ｒ¹、Ｒ²及びＲ³は、夫々独立して一価の置換基又はハロゲン元素を表し；Ｘ¹は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、硫黄、セレン、テルル及びポロニウムからなる群から選ばれる元素の少なくとも１種を含む置換基を表し；Ｙ¹、Ｙ²及びＹ³は、夫々独立して２価の連結基、２価の元素又は単結合を表す。）

(ＮＰＲ⁴ ₂)_n ・・・ (II)
（式中、Ｒ⁴は夫々独立して一価の置換基又はハロゲン元素を表し；ｎは３〜１５を表す。） Specific examples of the phosphazene compound include a chain phosphazene compound represented by the following formula (I) and a cyclic phosphazene compound represented by the following formula (II).

(Wherein R ¹ , R ² and R ³ each independently represents a monovalent substituent or a halogen element; X ¹ represents carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth) And represents a substituent containing at least one element selected from the group consisting of oxygen, sulfur, selenium, tellurium and polonium; Y ¹ , Y ² and Y ³ are each independently a divalent linking group, divalent Represents an element or a single bond.)

(NPR ⁴ ₂ ) _n ... (II)
(In the formula, each R ⁴ independently represents a monovalent substituent or a halogen element; n represents 3 to 15)

  Among the phosphazene compounds represented by formula (I) or formula (II), those which are liquid at 25 ° C. (room temperature) are preferable. The viscosity at 25 ° C. of the liquid phosphazene compound is preferably 300 mPa · s (300 cP) or less, more preferably 20 mPa · s (20 cP) or less, and particularly preferably 5 mPa · s (5 cP) or less. In the present invention, the viscosity is measured at 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm and 50 rpm using a viscometer [R-type viscometer Model RE500-SL, manufactured by Toki Sangyo Co., Ltd.] The measurement was performed at a speed of 120 seconds, and the rotation speed when the indicated value reached 50 to 60% was set as an analysis condition, and the viscosity was measured at that time. When the viscosity of the phosphazene compound at 25 ° C. exceeds 300 mPa · s (300 cP), the supporting salt becomes difficult to dissolve, and the wettability of the polymer and the supporting salt to the dry gel, the positive electrode material, the negative electrode material, etc. decreases, and the electrolyte In particular, the ionic conductivity of the resin decreases significantly, and the performance becomes insufficient particularly when used under a low temperature condition such as below the freezing point. In addition, since these phosphazene compounds are in a liquid state, they have the same conductivity as that of a normal liquid electrolyte, and exhibit excellent cycle characteristics when used as an electrolyte for a polymer battery.

In the formula (I), R ¹ , R ² and R ³ are not particularly limited as long as they are monovalent substituents or halogen elements. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Among these, an alkoxy group is preferable in that the phosphazene compound has low viscosity. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like. R ^{1 to} R ³ may all be the same type of substituent, and some of them may be different types of substituents. Here, examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group. Among these, a methoxy group, An ethoxy group, a methoxyethoxy group, and a methoxyethoxyethoxy group are preferable, and a methoxy group or an ethoxy group is particularly preferable from the viewpoint of low viscosity and high dielectric constant. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element. As the halogen element, fluorine, chlorine and bromine are preferred, fluorine is most preferred, and chlorine is then preferred. When the hydrogen element in the monovalent substituent is substituted with fluorine, the effect of improving the cycle characteristics of the polymer battery tends to be greater than when the hydrogen element is substituted with chlorine.

In the formula (I), examples of the divalent linking group represented by Y ¹ , Y ² and Y ³ include CH ₂ group, oxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium, Yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten, iron, cobalt, And divalent linking groups containing at least one element selected from the group consisting of nickel. Among these, at least one element selected from the group consisting of CH ₂ groups and oxygen, sulfur, selenium, and nitrogen is included. A divalent linking group containing a seed is preferred, and a divalent linking group containing a sulfur and / or selenium element is particularly preferred. Y ¹ , Y ² and Y ³ may be a divalent element such as oxygen, sulfur or selenium, or a single bond. Y ^{1 to} Y ³ may all be the same type, or some of them may be different types.

［式(III)、式(IV)及び式(V)において、Ｒ⁵〜Ｒ⁹は、それぞれ独立に一価の置換基又はハロゲン元素を表し；Ｙ⁵〜Ｙ⁹は、それぞれ独立に２価の連結基、２価の元素又は単結合を表し；Ｚは２価の基又は２価の元素を表す。］ In the formula (I), X ¹ is a substituent containing at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur from the viewpoint of toxicity, environment, and the like. preferable. Of these substituents, substituents having a structure represented by the following formula (III), formula (IV) or formula (V) are more preferred.

[In Formula (III), Formula (IV) and Formula (V), R ^{5 to} R ⁹ each independently represents a monovalent substituent or a halogen element; Y ^{5 to} Y ⁹ each independently represents a divalent group. A linking group, a divalent element or a single bond; Z represents a divalent group or a divalent element. ]

In formula (III), formula (IV) and formula (V), R ^{5 to} R ⁹ are the same monovalent substituents or halogen elements as those described for R ^{1 to} R ³ in formula (I). Any of these is preferably mentioned. In addition, these may be the same type within the same substituent, or some of them may be different from each other. R ⁵ and R ^{6 in} formula (III) and R ⁸ and R ^{9 in} formula (V) may be bonded to each other to form a ring.

In the formula (III), formula (IV) and formula (V), the group represented by Y ^{5 to} Y ⁹ is a divalent linkage similar to that described for Y ^{1 to} Y ³ in the formula (I). In the same manner, a group containing a sulfur and / or selenium element is particularly preferable because the risk of ignition and ignition of the electrolyte is reduced. These may be the same type within the same substituent, or some of them may be different from each other.

In the formula (III), as Z, for example, CH ₂ group, CHR (R represents an alkyl group, an alkoxyl group, a phenyl group, etc .; the same shall apply hereinafter) group, NR group, oxygen, sulfur, selenium, Boron, aluminum, scandium, gallium, yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin, germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium, Examples include divalent groups containing at least one element selected from the group consisting of polonium, tungsten, iron, cobalt and nickel. Among these, in addition to CH ₂ groups, CHR groups, NR groups, oxygen, sulfur A divalent group containing at least one element selected from the group consisting of selenium is preferred. In particular, a divalent group containing an element of sulfur and / or selenium is preferable because the risk of ignition and ignition of the electrolyte is reduced. Z may be a divalent element such as oxygen, sulfur, or selenium.

  As these substituents, a substituent containing phosphorus as represented by the formula (III) is particularly preferable in that the risk of ignition / flammability can be particularly effectively reduced. In addition, when the substituent is a substituent containing sulfur as represented by the formula (IV), it is particularly preferable from the viewpoint of reducing the interface resistance of the electrolyte.

In the formula (II), R ⁴ is not particularly limited as long as it is a monovalent substituent or a halogen element. Examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group. Among these, an alkoxy group is preferable in that the phosphazene compound has low viscosity. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like. Here, examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group, and a phenoxy group, and among these, a methoxy group, an ethoxy group, a methoxyethoxy group, and a phenoxy group are particularly preferable. The hydrogen element in these monovalent substituents is preferably substituted with a halogen element. Preferred examples of the halogen element include fluorine, chlorine, bromine and the like. Examples of the substituent substituted with a fluorine atom include Examples thereof include a trifluoroethoxy group.

By appropriately selecting R ^{1 to} R ⁹ , Y ^{1 to} Y ³ , Y ^{5 to} Y ⁹ , and Z in the formulas (I) to (V), it has more suitable viscosity, solubility suitable for addition / mixing, and the like. A phosphazene compound is obtained. These phosphazene compounds may be used alone or in combination of two or more.

Among the phosphazene compounds of the above formula (II), the phosphazene compounds represented by the following formula (VI) are preferable from the viewpoint of improving the low temperature characteristics of the polymer battery and further improving the deterioration resistance and safety of the electrolyte.

(NPF ₂ ) _n ... (VI)
(In the formula, n represents 3 to 13.)

  The phosphazene compound represented by the formula (VI) is a low-viscosity liquid at room temperature (25 ° C.) and has a freezing point lowering action. Therefore, by adding the phosphazene compound of the formula (VI) to the electrolyte, it is possible to impart excellent low temperature characteristics to the electrolyte, and to provide a polymer battery having low internal resistance and high conductivity. It becomes possible. For this reason, it is possible to provide a polymer battery that exhibits excellent discharge characteristics over a long period of time even when used under low temperature conditions, particularly in regions and periods where the temperature is low.

  In the formula (VI), n is preferably from 3 to 5, more preferably from 3 to 4, and particularly preferably 3 from the viewpoint of imparting excellent low temperature characteristics to the electrolyte. When the value of n is small, the boiling point is low, and the ignition prevention property at the time of flame contact can be improved. On the other hand, since the boiling point increases as the value of n increases, it can be used stably even at high temperatures. A plurality of phosphazenes can be selected and used in a timely manner in order to obtain the desired performance using the above properties.

  By appropriately selecting the n value in the formula (VI), a phosphazene compound having a more suitable viscosity, solubility suitable for mixing, low temperature characteristics and the like can be obtained. These phosphazene compounds may be used alone or in combination of two or more.

  The viscosity of the phosphazene compound represented by the formula (VI) is not particularly limited as long as it is 20 mPa · s or less, but is preferably 10 mPa · s or less from the viewpoint of improving conductivity and improving low-temperature characteristics, and 5 mPa · s. -S or less is more preferable.

Among the phosphazene compounds of the above formula (II), a phosphazene compound represented by the following formula (VII) is preferable from the viewpoint of improving the deterioration resistance and safety of the electrolyte.

(NPR ¹⁰ ₂ ) _n ... (VII)
(In the formula, each R ¹⁰ independently represents a monovalent substituent or fluorine, at least one of all R ¹⁰ is a monovalent substituent or fluorine containing fluorine, and n represents 3 to 8) (However, not all R ¹⁰ are fluorine.)

If the phosphazene compound of the above formula (II) is contained, the electrolyte can be given excellent self-extinguishing properties or flame retardancy, and the safety of the electrolyte can be improved. ^If at least one of ¹⁰ contains a phosphazene compound which is a monovalent substituent containing fluorine, it is possible to impart superior safety to the electrolyte. Furthermore, if a phosphazene compound represented by the formula (VII) and at least one of all R ¹⁰ is fluorine is contained, further excellent safety can be imparted. That is, as compared with a phosphazene compound not containing fluorine, a phosphazene compound represented by the formula (VII), in which at least one of all R ¹⁰ is a monovalent substituent containing fluorine or fluorine, has the effect of making the electrolyte more difficult to burn. And can provide further excellent safety to the electrolyte.

  Examples of the monovalent substituent in the formula (VII) include an alkoxy group, an alkyl group, an acyl group, an aryl group, and a carboxyl group, and an alkoxy group is preferable because it is particularly excellent in improving the safety of the electrolyte. . Here, examples of the alkoxy group include methoxy group, ethoxy group, n-propoxy group, i-propoxy group, butoxy group and the like, alkoxy group-substituted alkoxy groups such as methoxyethoxy group, and the like. A methoxy group, an ethoxy group, and an n-propoxy group are particularly preferable in terms of excellent improvement.

  In the formula (VII), n is preferably 3 to 5 and more preferably 3 to 4 in that it can impart excellent safety to the electrolyte.

The monovalent substituent is preferably substituted with fluorine, and when at least one R ^{10 in} formula (VII) is not fluorine, at least one monovalent substituent contains fluorine.

  The fluorine content in the phosphazene compound of the formula (VII) is preferably 3 to 70% by mass, more preferably 7 to 45% by mass. When the fluorine content is 3 to 70% by mass, “excellent safety” can be particularly suitably imparted to the electrolyte.

  The phosphazene compound of the formula (VII) may contain a halogen element such as chlorine and bromine in addition to the above-mentioned fluorine. However, fluorine is most preferred, followed by chlorine. Those containing fluorine tend to have a greater effect of improving the cycle characteristics of the polymer battery than those containing chlorine.

By appropriately selecting R ¹⁰ and n value in the formula (VII), a phosphazene compound having more suitable safety, viscosity, solubility suitable for mixing, and the like can be obtained. These phosphazene compounds may be used alone or in combination of two or more.

  The viscosity of the phosphazene compound of the formula (VII) is not particularly limited as long as it is 20 mPa · s or less, but is preferably 10 mPa · s or less, and 5 mPa · s or less from the viewpoint of improving conductivity and improving low-temperature characteristics. Is more preferable.

Among the phosphazene compounds of the above formula (II), from the viewpoint of improving the deterioration resistance and safety of the electrolyte, a phosphazene compound represented by the following formula (VIII) that is solid at 25 ° C. (room temperature) is also preferable. .

(NPR ¹¹ ₂ ) _n ... (VIII)
(In the formula, each R ¹¹ independently represents a monovalent substituent or a halogen element; n represents 3 to 6)

  Since the phosphazene compound represented by the formula (VIII) is not easily vaporized, it remains in the electrolyte even when the polymer battery becomes extremely hot, and can suppress the combustion of the polymer constituting the electrolyte. The safety of the polymer battery can be significantly improved. Further, the phosphazene compound of the formula (VIII) can improve the long-term stability of the electrolyte.

In the formula (VIII), R ¹¹ is not particularly limited as long as it is a monovalent substituent or a halogen element. Here, preferred examples of the monovalent substituent include an alkoxy group, an alkyl group, a carboxyl group, an acyl group, and an aryl group, and preferred examples of the halogen element include fluorine, chlorine, bromine, and iodine. . Among these, an alkoxy group is particularly preferable because it can suppress an increase in the viscosity of the solution when dissolved in the aprotic organic solvent. As the viscosity of the mixed solution of the phosphazene compound of formula (VIII) and the aprotic organic solvent increases, the permeability of the mixed solution into the dry gel composed of the polymer and the supporting salt deteriorates, so the viscosity of the mixed solution is The lower the better. As said alkoxy group, a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group (i-propoxy group, n-propoxy group), a phenoxy group, a trifluoroethoxy group, etc. are preferable, and a methoxy group, an ethoxy group, a propoxy group ( i-propoxy group, n-propoxy group), phenoxy group, trifluoroethoxy group and the like are more preferable. The monovalent substituent preferably contains the aforementioned halogen element. In formula (VIII), n is particularly preferably 3 or 4.

The phosphazene compounds of the formula (VIII), the structure R ¹¹ in formula (VIII) is an n-a methoxy group 3, be at least one R ¹¹ is a methoxy group and phenoxy group in formula (VIII) a structure in which n is 4, a structure in which R ¹¹ is an ethoxy group and n is 4 in formula (VIII), and a structure in which R ¹¹ is an i-propoxy group and n is 3 or 4 in formula (VIII) A structure in which R ¹¹ is an n-propoxy group and n is 4 in formula (VIII), a structure in which R ¹¹ is a trifluoroethoxy group and n is 3 or 4 in formula (VIII), ), A structure in which R ¹¹ is a phenoxy group and n is 3 or 4 is particularly preferable in that an increase in viscosity of a mixed solution with an aprotic organic solvent can be suppressed.

  By appropriately selecting each substituent and n value in the formula (VIII), the viscosity of the mixed solution of the aprotic organic solvent and the phosphazene compound can be adjusted. These phosphazene compounds may be used alone or in combination of two or more.

［式(IX)及び(X)において、Ｒ¹²、Ｒ¹³及びＲ¹⁴は、夫々独立して一価の置換基又はハロゲン元素を表し；Ｘ²は、炭素、ケイ素、ゲルマニウム、スズ、窒素、リン、ヒ素、アンチモン、ビスマス、酸素、硫黄、セレン、テルル及びポロニウムからなる群より選ばれる元素の少なくとも１種を含む置換基を表し；Ｙ¹²及びＹ¹³は、夫々独立して２価の連結基、２価の元素又は単結合を表す。］ Specific examples of the isomers of the phosphazene compound include compounds represented by the following formula (IX). The compound of formula (IX) is an isomer of a phosphazene compound represented by the following formula (X).

[In the formulas (IX) and (X), R ¹² , R ¹³ and R ¹⁴ each independently represents a monovalent substituent or a halogen element; X ² represents carbon, silicon, germanium, tin, nitrogen, Represents a substituent containing at least one element selected from the group consisting of phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; Y ¹² and Y ¹³ each independently represent a divalent linkage Represents a divalent element or a single bond. ]

R ¹² , R ¹³ and R ¹⁴ in formula (IX) are not particularly limited as long as they are monovalent substituents or halogen elements, and are the same as those described for R ^{1 to} R ³ in formula (I) above. Suitable examples include monovalent substituents and halogen elements. In the formula (IX), the divalent linking group or divalent element represented by Y ¹² and Y ¹³ may be the same divalent as described for Y ^{1 to} Y ³ in the formula (I). Suitable examples include a linking group or a divalent element. Further, in the formula (IX), as the substituent represented by X ² , any of the same substituents as those described for X ¹ in the formula (I) can be preferably exemplified.

  The isomer of the phosphazene compound represented by the formula (IX) and represented by the formula (X), when added to the electrolyte, can exhibit extremely excellent low temperature characteristics in the electrolyte, and further, the deterioration resistance of the electrolyte. And safety can be improved.

  The isomer represented by the formula (IX) is an isomer of the phosphazene compound represented by the formula (X), for example, the degree of vacuum when producing the phosphazene compound represented by the formula (X) and / or It can be manufactured by adjusting the temperature. The content (volume%) of the isomer of the phosphazene compound can be measured by gel permeation chromatography (GPC) or high performance liquid chromatography (HPLC).

  Specific examples of the phosphate ester include alkyl phosphates such as triphenyl phosphate, tricresyl phosphate, tris (fluoroethyl) phosphate, tris (trifluoroneopentyl) phosphate, alkoxy phosphate, and derivatives thereof.

  In the polymer battery electrolyte of the present invention, the content of the compound containing phosphorus and / or nitrogen in the molecule is preferably 0.5% by mass or more, and 1% by mass from the viewpoint of improving the safety of the electrolyte. The above is more preferable, and 2.5% by mass or more is even more preferable.

  The method for producing the electrolyte for a polymer battery of the present invention is not particularly limited. For example, the polymer and the supporting salt are mixed at a mass ratio (polymer / supporting salt) of 9/1, and a volatile solvent is added. And uniformly mixed at about 80 ° C., heated to about 40 ° C. in vacuum, volatilized volatile solvent, dried, and then mixed with aprotic organic solvent and phosphorus and / or nitrogen-containing compound. Examples include a method of obtaining an electrolyte by impregnating and swelling a mixed solution. Examples of the volatile solvent include acetonitrile and alcohols, and acetonitrile and the like are preferable from the viewpoint of excellent solubility.

  The polymer battery electrolyte of the present invention is a gel obtained by impregnating and swelling a dry gel containing a polymer and a supporting salt with a mixed solution of an aprotic organic solvent and a compound containing phosphorus and / or nitrogen in the molecule. For an electrolyte, more specifically, a dry gel containing a polymer and a supporting salt, the difference in boiling point between at least one aprotic organic solvent and each of the aprotic organic solvent is 25 ° C. or less and phosphorus in the molecule and / or A gel electrolyte obtained by impregnating and swelling a mixed solution with each of compounds having nitrogen is preferable. The shape of the polymer battery electrolyte of the present invention is not particularly limited, but a sheet shape or the like is preferable from the viewpoint of thinning the polymer battery.

<Polymer battery>
Next, the polymer battery of the present invention will be described in detail. The polymer battery of the present invention includes the above-described polymer battery electrolyte, a positive electrode, and a negative electrode, and includes other members that are usually used in the technical field of polymer batteries as necessary.

There is no restriction | limiting in particular as a positive electrode active material of the polymer battery of this invention, It can select from a well-known positive electrode active material suitably, and can use it. Specific examples of the positive electrode active material include metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ and MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ and LiFePO ₄ . Preferable examples include lithium-containing composite oxides, metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni (wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1) (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  Preferred examples of the negative electrode active material of the polymer battery of the present invention include lithium metal itself, an alloy of lithium and Al, In, Pb, Zn, or the like, a carbon material such as graphite doped with lithium, and among these, From the viewpoint of higher properties, a carbon material such as graphite is preferable, and graphite is particularly preferable. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples thereof include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used in the same mixing ratio as in the past, and specifically, the mass ratio of active material: binder: conductive agent is preferably 94: 3: 3.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

  As other members used in the polymer battery of the present invention, known members usually used in polymer batteries can be suitably used.

  There is no restriction | limiting in particular as a form of the polymer battery of this invention demonstrated above, Various well-known forms, such as a coin type, a button type, a paper type, a square type or a cylindrical battery of a spiral structure, are mentioned suitably. In the case of the spiral structure, for example, a polymer battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and superimposing and winding up a negative electrode (sheet-like) on the current collector.

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

(Example 1)
<Preparation of mixed solution>
Ethylene carbonate (EC, boiling point 238 ° C.) 50% by volume, diethyl carbonate (DEC, boiling point 127 ° C.) 40% by volume, additive A [in formula (II), n is 3 and 3 of 6 R ⁴ A cyclic phosphazene compound having one methoxy group (CH ₃ O—) and three fluorines, viscosity at 25 ° C .: 3.9 mPa · s, boiling point 230 ° C., 5% by volume and additive B [in the formula (II), n is 3 A cyclic phosphazene compound in which one of the six R ⁴ groups is an ethoxy group (CH ₃ CH ₂ O—) and five are fluorine, viscosity at 25 ° C .: 1.2 mPa · s, boiling point 125 ° C.] from 5% by volume A mixed solution was prepared.

<Preparation of polymer battery electrolyte>
Next, 3.6 g of polyethylene oxide [manufactured by Aldrich, Mw = 5 to ₆ million] and 0.4 g of LiPF ₆ (supporting salt) are mixed, and 10 mL of acetonitrile (volatile solvent) is added and mixed uniformly. To obtain a polyethylene oxide sol (including polyethylene oxide and LiPF ₆ ). The sol was heated to 40 ° C. in vacuo to evaporate acetonitrile and dry. Thereafter, 1 mL of the above mixed solution was impregnated and swollen to obtain a gel polymer battery electrolyte. Moreover, the safety | security of the obtained electrolyte for polymer batteries was evaluated by the following method. The results are shown in Table 1.

(1) Electrolyte Safety The safety of the polymer battery electrolyte was evaluated from the combustion behavior of flames ignited in an atmospheric environment by the method of arranging UL94HB method of UL (Underwriting Laboratory) standard. At that time, ignitability, combustibility, formation of carbides, and secondary ignition phenomena were also observed. Specifically, a 127 mm × 12.7 mm test piece made of the polymer battery electrolyte was prepared based on the UL test standard. Here, when the test flame does not ignite the test piece (combustion length: 0 mm), it is “non-flammable”, and when the ignited flame does not reach the 25 mm line and the fallen object is not ignited, “flame retardant” The case where the ignited flame was extinguished on the 25 to 100 mm line and the fallen object was not ignited was evaluated as “self-extinguishing”, and the case where the ignited flame exceeded the 100 mm line was evaluated as “combustible”.

<Production of polymer battery>
3 parts by mass of acetylene black (conductive agent) and 3 parts by mass of polyvinylidene fluoride (binder) are added to 94 parts by mass of LiMn ₂ O ₄ (positive electrode active material), and an organic solvent (ethyl acetate and ethanol) is added. 50/50 mass% mixed solvent) and the kneaded product was applied to a 25 μm thick aluminum foil (current collector) with a doctor blade, and further dried with hot air (100 to 120 ° C.), A positive electrode sheet having a thickness of 80 μm was produced. A graphite sheet having a thickness of 150 μm was used for the negative electrode.

  Next, a polyethylene oxide sol was prepared in the same manner as in the preparation of the polymer battery electrolyte, and the sol was applied on both sides of a polyethylene separator to a thickness of 150 μm using a doctor blade, and then acetonitrile was evaporated. Thus, a polyethylene oxide-lithium gel electrolyte (dry gel) was produced. This was sandwiched between the positive electrode sheet and the negative electrode (graphite sheet) and rolled up, and further impregnated and swollen with the mixed solution to produce an AA polymer battery. The battery has a positive electrode length of about 260 mm. The obtained polymer battery was subjected to a nail penetration test and an overcharge test by the following methods. The results are shown in Table 1.

(2) Nail penetration test After fully charging the test battery, a nail with a diameter of 5 mm penetrates in the middle of the battery in the direction perpendicular to the electrode surface and is allowed to stand for 24 hours. Observed whether or not.

(3) Overcharge test
The test battery was overcharged to 250% of the rated capacity with a current value of 1C (current value that reached full charge in 1 hour), and whether or not the battery ignited was observed. However, a safety circuit is not included with the test battery.

(Examples 2-9 and Comparative Examples 1-6)
A mixed solution having the composition shown in Table 1 or 2 was prepared, and an electrolyte for a polymer battery was prepared in the same manner as in Example 1 using the mixed solution. The safety of the obtained polymer battery electrolyte was evaluated in the same manner as in Example 1. In addition, a polymer battery was prepared using the mixed solution in the same manner as in Example 1, and a nail penetration test and an overcharge test were performed on the battery. The results are shown in Tables 1 and 2.

  In Tables 1 and 2, PC is propylene carbonate (boiling point 242 ° C.), DMC is dimethyl carbonate (boiling point 90 ° C.), EMC is ethyl methyl carbonate (boiling point 108 ° C.), and MF is methyl formate (boiling point). 32 ° C).

Additive C is a cyclic phosphazene compound (viscosity at 25 ° C .: 0.8 mPa · s, boiling point 86 ° C.) in which n is 4 and all 8 R ⁴ are fluorine in formula (II). Yes; additive D is a cyclic phosphazene compound (viscosity at 25 ° C .: 0.8 mPa · s, boiling point 51 ° C.) in which n is 3 and all six R ⁴ are fluorine in formula (II) Yes; Additive E is a cyclic phosphazene compound (viscosity at 25 ° C.) in which n is 3 and one of six R ⁴ is methoxy group (CH ₃ O—) and five are fluorine in formula (II) The additive F is represented by formula (II) in which n is 3, and three of the six R ⁴ groups are ethoxy groups (CH ₃ CH ₂ O—), Three are cyclic phosphazene compounds (viscosity at 25 ° C .: 4.0 mPa · s, boiling point> 300 ° C.); additive G is represented by formula (II) Te, n is a 3, one isopropoxy group of the six _{^{R 4 [(CH 3) 2}} CHO -], 5 one the viscosity of the cyclic phosphazene compound (25 ° C. is fluorine: 1.1 mPa · s, a boiling point 137 ° C).

  The polymer battery electrolytes of the examples using the mixed solutions obtained by adding phosphazene compounds having close boiling points to each of the aprotic organic solvents are highly safe, and the examples of the examples using the electrolytes are as follows. The polymer battery did not ignite in both the nail penetration test and the overcharge test, and it was confirmed that the safety was high even in an emergency.

  On the other hand, the polymer batteries of Comparative Examples 1 and 2 using a mixed solution containing no phosphorus and / or nitrogen-containing compound ignited in the nail penetration test and the overcharge test. Further, a polymer battery of Comparative Example 3 using a mixed solution containing a phosphazene compound having a boiling point close to that of DEC but not containing a phosphorus and / or nitrogen-containing compound having a boiling point close to that of EC, phosphorus and / or nitrogen having a boiling point close to that of EC A polymer battery of Comparative Example 4 using a mixed solution containing a phosphazene compound which does not contain a containing compound, does not contain a phosphorus and / or nitrogen containing compound having a boiling point close to that of DEC, and does not have a boiling point of either EC or DEC, and MF The polymer of Comparative Example 6 using a mixed solution containing a phosphazene compound having a boiling point close to that of EC and a phosphazene compound having a boiling point close to EC and MF. The battery ignited in a nail penetration test and an overcharge test. Furthermore, the polymer battery of Comparative Example 5 using a mixed solution containing a phosphazene compound having a boiling point close to that of DEC but not including a phosphorus and / or nitrogen-containing compound having a boiling point close to that of EC did not ignite in the nail penetration test. Fired in the overcharge test.

  Based on the above results, a mixed solution containing at least one aprotic organic solvent and a compound having a boiling point close to each aprotic organic solvent and having phosphorus and / or nitrogen in the molecule is used for a polymer battery. It can be seen that the use of the electrolyte can improve the safety of the electrolyte, and the use of the electrolyte for the polymer battery can significantly improve the safety of the polymer battery in an emergency.

Claims (5)

In an electrolyte for a polymer battery comprising at least one aprotic organic solvent, a polymer and a supporting salt,
Furthermore, each of the aprotic organic solvents contains a compound having a difference in boiling point from the aprotic organic solvent of 25 ° C. or less and having phosphorus and / or nitrogen in the molecule. Electrolyte for polymer battery.   2. The polymer battery electrolyte according to claim 1, wherein the compound having phosphorus and / or nitrogen in the molecule has a phosphorus-nitrogen double bond.   3. The polymer battery electrolyte according to claim 2, wherein the compound having phosphorus and / or nitrogen in the molecule is a phosphazene compound.   2. The polymer according to claim 1, wherein the aprotic organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate. Battery electrolyte.   A polymer battery comprising the electrolyte according to claim 1, a positive electrode, and a negative electrode.