JP2005276921A - Additive for nonaqueous electrolyte of electric double-layer capacitor, nonaqueous electrolyte for electric double-layer capacitor, and nonaqueous electrolyte electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an additive for nonaqueous electrolyte of electric double-layer capacitor having a sufficiently high boiling point, in which vaporizations do not take place during use under high temperature, safety of electrolyte can be ensured sufficiently, even at the time of emergency, e.g. short circuiting, and superior low-temperature characteristics can be imparted. <P>SOLUTION: The additive for nonaqueous electrolyte of electric double-layer capacitor is composed of a phosphagen compound containing at least two kinds of halogen element represented for formula (I): (NPX<SB>2</SB>)<SB>n</SB>(where, X is an independent halogen element, and n is an integer of 3-15). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an additive for a non-aqueous electrolyte of an electric double layer capacitor, a non-aqueous electrolyte for an electric double layer capacitor containing the additive, and a non-aqueous electrolyte electric double layer capacitor including the same. The present invention relates to a non-aqueous electrolyte electric double layer capacitor having excellent low temperature characteristics.

  An electric double layer capacitor is a capacitor that uses an electric double layer formed between an electrode and an electrolyte, and the mass transfer is the cycle in which ions are electrically adsorbed from the electrolyte on the electrode surface. This is different from a battery in which the cycle of the oxidation-reduction reaction involving is a charge / discharge cycle. For this reason, the electric double layer capacitor has superior instantaneous charge / discharge characteristics as compared with the battery, and does not involve a chemical reaction. Therefore, even if charge / discharge is repeated, the instantaneous charge / discharge characteristics hardly deteriorate. Further, in the electric double layer capacitor, since there is no charge / discharge overvoltage at the time of charge / discharge, a simple and inexpensive electric circuit is sufficient. In addition, the remaining capacity is easy to understand, has durability temperature characteristics over a wide range of temperatures from -30 to 90 ° C, and is non-polluting. It is in the limelight as an environmentally friendly new energy storage product. Furthermore, since the electric double layer capacitor has the above-described characteristics, it has been spotlighted as a power source for energy regeneration and engine start of electric vehicles, fuel cell vehicles, and hybrid electric vehicles.

The electric double layer capacitor is an energy storage device having positive and negative electrodes and an electrolyte, and at the contact interface between the electrode and the electrolyte, positive and negative charges are arranged to face each other at a very short distance. Forming an electric double layer. Therefore, since the electrolyte plays a role as an ion source for forming the electric double layer, it is an important substance that influences the basic characteristics of the electric double layer capacitor, like the electrode. Conventionally known aqueous electrolytes include non-aqueous electrolytes, non-aqueous electrolytes, and solid electrolytes. From the viewpoint of improving the energy density of electric double layer capacitors, non-aqueous electrolytes that can set a high operating voltage. However, it is particularly in the spotlight and is being put to practical use. Examples of the non-aqueous electrolyte include high-dielectric constant aprotic organic solvents such as carbonate carbonate (ethylene carbonate, propylene carbonate, etc.), γ-butyrolactone, (C ₂ H ₅ ) ₄ P · BF ₄ , ( A mixed solution in which a solute (supporting salt) such as C ₂ H ₅ ) ₄ N · BF ₄ is dissolved has been put into practical use.

  However, since the aprotic organic solvent has a low flash point, for example, when an electric double layer capacitor ignites due to heat generation or the like, there is a high risk of ignition. In addition, the aprotic organic solvent has a high risk of vaporizing and decomposing to generate gas as the electric double layer capacitor generates heat, or causing explosion and ignition of the electric double layer capacitor by the generated gas and heat. .

  In contrast, a phosphazene compound is added to a non-aqueous electrolyte for an electric double layer capacitor to give the non-aqueous electrolyte non-flammability, flame retardancy, or self-extinguishing properties. Non-aqueous electrolyte electric double layer capacitors have been developed that greatly reduce the risk of ignition and ignition. Among such phosphazene compounds, a phosphazene compound that is cyclic and has two fluorine atoms bonded to each phosphorus element in the molecule has a much lower viscosity than a phosphazene compound in which an organic group is bonded to a phosphorus element. By adding to the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte can be reduced, the internal resistance of the electric double layer capacitor at room temperature can be reduced, and further, the internal resistance of the electric double layer capacitor at low temperature can be reduced. It is known (see Patent Document 1).

International Publication No. 02/21631 Pamphlet

  However, a phosphazene compound that is cyclic and has two fluorine atoms bonded to each phosphorus element in the molecule has a low boiling point, so that the phosphazene compound may vaporize when used at high temperatures. In addition, when the temperature of the electric double layer capacitor rises during an emergency such as a short circuit, the phosphazene compound is vaporized before the aprotic organic solvent, so that the remaining aprotic organic solvent is vaporized and decomposed alone. Thus, there is a risk of generating gas, rupturing or igniting the electric double layer capacitor due to the generated gas and heat, and igniting the remaining aprotic organic solvent with sparks generated at the time of short circuit.

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, the boiling point is sufficiently high, without being vaporized when used at high temperatures, it is possible to sufficiently ensure the safety of the electrolyte even in an emergency such as a short circuit, An object of the present invention is to provide an additive for a non-aqueous electrolyte of an electric double layer capacitor capable of imparting excellent low temperature characteristics. Another object of the present invention is to provide a non-aqueous electrolyte for an electric double layer capacitor containing such an additive, and a non-aqueous electrolyte electric double layer capacitor having the non-aqueous electrolyte and having excellent safety and low-temperature characteristics. It is to provide.

  As a result of intensive studies to achieve the above object, the present inventors have found that a cyclic phosphazene compound having a specific structure has a sufficiently high boiling point, a sufficiently low freezing point, and a very high oxygen index, By adding the phosphazene compound to the non-aqueous electrolyte, the phosphazene compound does not vaporize when the electric double layer capacitor is used at a high temperature, and the safety of the non-aqueous electrolyte can be sufficiently ensured even in an emergency such as a short circuit, Furthermore, the inventors have found that the low temperature characteristics of the electric double layer capacitor are improved, and have completed the present invention.

That is, the additive for non-aqueous electrolyte of the electric double layer capacitor of the present invention is represented by the following formula (I):
(NPX ₂ ) _n ... (I)
(Wherein X is independently a halogen element, and n is an integer of 3 to 15), and is characterized by comprising a phosphazene compound containing at least two kinds of halogen elements.

  In a preferred example of the additive for non-aqueous electrolyte of the electric double layer capacitor of the present invention, the phosphazene compound contains fluorine and chlorine. Here, in the phosphazene compound, it is more preferable that each X in the formula (I) is independently fluorine or chlorine.

  In another preferred embodiment of the additive for non-aqueous electrolyte of the electric double layer capacitor of the present invention, n in the formula (I) is 3-5. In this case, since the viscosity of the phosphazene compound is sufficiently low, the internal resistance of the electric double layer capacitor can be sufficiently reduced without increasing the viscosity of the non-aqueous electrolyte.

  The additive for non-aqueous electrolyte of the electric double layer capacitor of the present invention is a phosphazene compound in which n in the formula (I) is 3, 1-3 of 6 X are chlorine and the rest is fluorine, and / or More preferably, the compound is composed of a phosphazene compound in which n in the formula (I) is 4, 1 to 5 of 8 Xs are chlorine, and the remainder is fluorine. More preferably, the phosphazene compound contains two or more chlorine atoms in the molecule, and each chlorine atom is bonded to a different phosphorus atom. In this case, since the freezing point of the phosphazene compound is particularly low, the low temperature characteristics of the electric double layer capacitor can be greatly improved.

  In another preferred embodiment of the additive for non-aqueous electrolyte of the electric double layer capacitor of the present invention, the freezing point of the phosphazene compound is −5 ° C. or lower. Also in this case, since the freezing point of the phosphazene compound is sufficiently low, the low temperature characteristics of the electric double layer capacitor can be greatly improved.

  Moreover, the non-aqueous electrolyte for electric double layer capacitors of the present invention comprises the additive for non-aqueous electrolyte of the electric double layer capacitor, an aprotic organic solvent, and a supporting salt.

  In a preferred example of the non-aqueous electrolyte for electric double layer capacitors of the present invention, the difference in boiling point between the aprotic organic solvent and the additive for non-aqueous electrolyte of the electric double layer capacitor is 25 ° C. or less. In this case, the safety of the nonaqueous electrolytic solution in an emergency can be sufficiently improved.

  Furthermore, the non-aqueous electrolyte electric double layer capacitor of the present invention comprises the non-aqueous electrolyte for an electric double layer capacitor, a positive electrode, and a negative electrode, and is particularly excellent in safety and low temperature characteristics.

  According to the present invention, it consists of a cyclic phosphazene compound having a specific structure, does not vaporize when used at high temperatures, can sufficiently ensure the safety of a non-aqueous electrolyte even in an emergency such as a short circuit, and further, an electric double layer It is possible to provide an additive for a non-aqueous electrolyte of an electric double layer capacitor that can greatly improve the low temperature characteristics of the capacitor. In addition, it is possible to provide a non-aqueous electrolyte for an electric double layer capacitor that includes such an additive and has sufficiently high safety and can significantly improve the low temperature characteristics of the electric double layer capacitor. Furthermore, it is possible to provide a non-aqueous electrolyte electric double layer capacitor that is provided with the non-aqueous electrolyte for electric double layer capacitors and is excellent in safety and low-temperature characteristics.

The present invention is described in detail below.
<Additive for non-aqueous electrolyte of electric double layer capacitor>
The additive for non-aqueous electrolyte solution of the electric double layer capacitor of the present invention is characterized by comprising a cyclic phosphazene compound represented by the above formula (I) and containing at least two halogen elements. Since the phosphazene compound has a sufficiently high boiling point, it does not vaporize at the time of high temperature use, and the electric double layer capacitor including the non-aqueous electrolyte containing the additive of the present invention swells even at the time of high temperature use. There is no concern. In addition, the phosphazene compound has a sufficiently low freezing point, so it exists as a liquid even at a low temperature. By adding the phosphazene to the non-aqueous electrolyte of the electric double layer capacitor, the low temperature characteristics of the electric double layer capacitor are improved. can do. Further, the phosphazene compound has a very high oxygen index and generates nitrogen gas and / or phosphate ester in the event of an electric double layer capacitor to make the non-aqueous electrolyte non-flammable, flame retardant or self-forming. Extinguishes fire and has the effect of significantly reducing the risk of ignition of the electric double layer capacitor.

  The phosphazene compound constituting the additive for the non-aqueous electrolyte of the electric double layer capacitor of the present invention is represented by the above formula (I) and contains at least two halogen elements. In the formula (I), X is independently a halogen element, and examples of the halogen element include fluorine, chlorine, bromine and the like. Among these, fluorine and chlorine are preferable. The phosphazene compound preferably contains at least fluorine and chlorine, and all X are preferably fluorine or chlorine. Note that when a compound containing a halogen element is used, the generation of a halogen radical may be a problem. However, since the phosphorus element in the molecule captures the halogen radical and forms phosphorus halide, Such a problem does not occur.

  Moreover, in Formula (I), n is an integer of 3-15, and it is preferable that it is 3-5. When n exceeds 5, the viscosity of the phosphazene compound increases, so the viscosity of the non-aqueous electrolyte increases, the conductivity of the electrolyte decreases, and the internal resistance of the electric double layer capacitor tends to increase. Here, the viscosity of the phosphazene compound at 25 ° C. is preferably 10 mPa · s or less, and more preferably 5 mPa · s or less, from the viewpoint of suppressing an increase in internal resistance of the electric double layer capacitor. In the present invention, the viscosity is 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.] It is a value measured at that time, measured at the rotational speed for 120 seconds, with the rotational speed when the indicated value is 50 to 60% as the analysis condition.

  The phosphazene compound preferably has a limiting oxygen index of 30% by volume or more, and more preferably 40% by volume or more. By adding a phosphazene compound having a limiting oxygen index of 40% by volume or more to the non-aqueous electrolyte, the risk of ignition and ignition of the electrolyte can be greatly reduced. Here, the limiting oxygen index means a value of the minimum oxygen concentration expressed by volume% necessary for the material to continue to burn under a predetermined test condition specified in JIS K 7201. A high value means a low risk of ignition or ignition.

  The phosphazene compound has a freezing point of preferably −5 ° C. or lower, more preferably −20 ° C. or lower, and even more preferably −30 ° C. or lower. By adding a phosphazene compound having a freezing point of −5 ° C. or lower to the non-aqueous electrolyte, the low temperature characteristics of the electric double layer capacitor can be reliably improved, and such a phosphazene compound can be added to the non-aqueous electrolyte. The non-aqueous electrolyte electric double layer capacitor thus obtained is particularly suitable as a moving (HEV) electric double layer capacitor because of its excellent low-temperature characteristics.

  Among the above phosphazene compounds, from the viewpoint of a low freezing point, n in the formula (I) is 3, 1 to 3 out of 6 Xs are chlorine and the rest are fluorines, and in the formula (I) It is particularly preferable that n is 4 and 1 to 5 of 8 Xs are chlorine and the rest is fluorine. The freezing points of phosphazene compounds in which X in the formula (I) is fluorine or chlorine are shown in Table 1 together with the boiling point and oxygen index.

  As is clear from Table 1, in the phosphazene compound in which X in the formula (I) is fluorine or chlorine, the boiling point rises as the chlorine number increases (increase in molecular weight), but the freezing point is in the specific chlorine number range. When n is 3, the range of 1 to 3 chlorine atoms is particularly preferable. When n is 4, the range of 1 to 5 chlorine atoms is preferable, and the range of 2 to 4 chlorine atoms is particularly preferable. Is preferred.

  The phosphazene compound is prepared by, for example, using commercially available phosphazene compounds in which X in the formula (I) is all chlorine as a starting material, fluorinating all chlorine with a fluorinating agent, and then at the target chlorine substitution site. After introducing an alkoxy group, an amine group, or the like, chlorinating again with a chlorinating agent such as HCl or phosgene, or a commercially available phosphazene compound in which X in the formula (I) is all chlorine After calculating the equivalent of fluorine to be introduced, it can be synthesized by a method of adding a necessary amount of a fluorinating agent. In addition, the said phosphazene compound may be used individually by 1 type, or may be used as a 2 or more types of mixture.

<Nonaqueous electrolyte for electric double layer capacitor>
The non-aqueous electrolyte for electric double layer capacitors of the present invention is characterized by containing the above-described additive for non-aqueous electrolyte of electric double layer capacitors, an aprotic organic solvent, and a supporting salt.

  The aprotic organic solvent used in the non-aqueous electrolyte for electric double layer capacitors of the present invention can reduce the viscosity of the electrolyte and can easily achieve optimum ionic conductivity as an electric double layer capacitor. it can. Specific examples of the aprotic organic solvent include nitrile compounds such as acetonitrile (AN), propiononitrile, butyronitrile, isobutyronitrile, and benzonitrile; ether compounds such as 1,2-dimethoxyethane and tetrahydrofuran; dimethyl carbonate Preferred examples include ester compounds such as diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate (PC), diphenyl carbonate, γ-butyrolactone (GBL), and γ-valerolactone. Among these, propylene carbonate, γ-butyrolactone and acetonitrile are preferable. Note that the cyclic ester compound has a high relative dielectric constant and is excellent in the ability to dissolve the supporting salt, and the chain ester compound and the ether compound are suitable in terms of reducing the viscosity of the electrolyte because of low viscosity. It is. These may be used alone or in combination of two or more. The viscosity of the aprotic organic solvent at 25 ° C. is not particularly limited, but is preferably 10 mPa · s (10 cP) or less, and more preferably 5 mPa · s (5 cP) or less.

  In the non-aqueous electrolyte for electric double layer capacitors of the present invention, the difference in boiling point between the aprotic organic solvent and the additive for non-aqueous electrolyte of the electric double layer capacitor is preferably 25 ° C. or less. More specifically, the non-aqueous electrolyte for an electric double layer capacitor of the present invention contains one or more aprotic organic solvents and a supporting salt, and further, for each of the aprotic organic solvents, It is preferable that the difference between the boiling points of the aprotic organic solvent is 25 ° C. or less and each phosphazene compound containing at least two halogen elements represented by the above formula (I) is contained.

  As described above, the phosphazene compound has a function of reducing the risk of ignition of the electric double layer capacitor, but the non-aqueous electrolyte containing the aprotic organic solvent has a boiling point close to that of the aprotic organic solvent. When the phosphazene compound is not included, the aprotic organic solvent and the phosphazene compound do not coexist in either the gas phase or the liquid phase, and the temperature range of the electric double layer capacitor is abnormally increased. The risk of ignition and ignition of the aprotic organic solvent or the aprotic organic solvent remaining in the electric double layer capacitor cannot be reduced. On the other hand, when the non-aqueous electrolyte contains a phosphazene compound having a boiling point close to that of the aprotic organic solvent together with the aprotic organic solvent, when the temperature of the electric double layer capacitor is abnormally increased, the aprotic organic solvent Since the solvent and the phosphazene compound are vaporized at close temperatures, the aprotic organic solvent and the phosphazene compound coexist both in the case where the aprotic organic solvent exists as a liquid and in the case where it exists as a gas. The risk of ignition and ignition of water electrolyte is greatly reduced.

  In addition, for example, when the non-aqueous electrolyte contains a low-boiling aprotic organic solvent and a high-boiling aprotic organic solvent, it is possible to cope with it near the temperature at which the low-boiling aprotic organic solvent vaporizes. Since the phosphazene compound is vaporized, the risk of ignition and ignition of the vaporized aprotic organic solvent can be reduced. In addition, after the low-boiling aprotic organic solvent and the phosphazene compound having a boiling point close to that of the low-boiling aprotic organic solvent are vaporized, the high-boiling aprotic organic solvent and the high-boiling aprotic organic solvent are used. Since the phosphazene compound having a boiling point close to that of the electrolyte is present in the electrolytic solution, the risk of ignition and ignition of the remaining nonaqueous electrolytic solution can be reduced.

  In the non-aqueous electrolyte for an electric double layer capacitor of the present invention, it is preferable to appropriately select and use a phosphazene compound (additive) having a boiling point close to that of the aprotic organic solvent according to the aprotic organic solvent to be used. . Here, since the phosphazene compound represented by the above formula (I) and containing at least two kinds of halogen elements can take a wide range of boiling points depending on the number of chlorines in the molecule and the value of n, the molecular structure of the phosphazene compound is appropriately determined. By selecting, the danger in the event of an emergency such as a short circuit of the non-aqueous electrolyte can be greatly reduced.

  The supporting salt used in the non-aqueous electrolyte for an electric double layer capacitor of the present invention can be selected from conventionally known salts, but a quaternary ammonium salt is preferred from the viewpoint of good electrical conductivity in the electrolyte. The quaternary ammonium salt is a solute that plays a role as an ion source for forming an electric double layer in a nonaqueous electrolytic solution, and can effectively improve electrical characteristics such as electrical conductivity of the electrolytic solution. In view of the possibility, a quaternary ammonium salt capable of forming a multivalent ion is preferable.

Examples of the quaternary ammonium salt include (CH ₃ ) ₄ N · BF ₄ , (CH ₃ ) ₃ C ₂ H ₅ N · BF ₄ , (CH ₃ ) ₂ (C ₂ H ₅ ) ₂ N · BF _4. CH ₃ (C ₂ H ₅ ) ₃ N · BF ₄ , (C ₂ H ₅ ) ₄ N · BF ₄ , (C ₃ H ₇ ) ₄ N · BF ₄ , CH ₃ (C ₄ H ₉ ) ₃ N · BF ₄ , (C ₄ H ₉ ) ₄ N · BF ₄ , (C ₆ H ₁₃ ) ₄ N · BF ₄ , (C ₂ H ₅ ) ₄ N · ClO ₄ , (C ₂ H ₅ ) ₄ N · AsF ₆ , (C ₂ H ₅ ) ₄ N · SbF ₆ , (C ₂ H ₅ ) ₄ N · CF ₃ SO ₃ , (C ₂ H ₅ ) ₄ N · C ₄ F ₉ SO ₃ , (C ₂ H ₅ ) ₄ N · (CF ₃ SO ₂ ) ₂ N, (C ₂ H ₅ ) ₄ N · BCH ₃ (C ₂ H ₅ ) ₃ , (C ₂ H ₅ ) ₄ N · B (C ₂ H ₅ ) ₄ , (C ₂ H ₅ ) ₄ N · B (C ₄ H ₉ ) ₄ , (C ₂ H ₅ ) ₄ N · B (C ₆ H ₅ ) _{4 and the} like are preferable. Also preferred are hexafluorophosphates in which the anion portion (for example, • BF ₄ , • ClO ₄ , • AsF _6, etc.) of these quaternary ammonium salts is replaced with • PF ₆ . Among these, quaternary ammonium salts in which different alkyl groups are bonded to N atoms are preferable in that the solubility can be improved by increasing the polarizability. Furthermore, as the quaternary ammonium salt, for example, compounds represented by the following formulas (a) to (j) are also preferable. Here, in the formulas (a) to (j), Me represents a methyl group, and Et represents an ethyl group.

Among these quaternary ammonium salts, salts that can generate (CH ₃ ) ₄ N ⁺ , (C ₂ H ₅ ) ₄ N ^+, etc. as cations, in particular, from the viewpoint of ensuring high electrical conductivity. preferable. Further, a salt capable of generating an anion having a small formula weight is preferable. These quaternary ammonium salts may be used individually by 1 type, and may use 2 or more types together.

  The concentration of the supporting salt in the non-aqueous electrolyte for an electric double layer capacitor of the present invention is preferably 0.2 to 2.5 mol / L (M), more preferably 0.8 to 1.5 mol / L (M). If the concentration of the supporting salt is less than 0.2 mol / L (M), sufficient electrical properties such as the electrical conductivity of the electrolytic solution may not be ensured, and if it exceeds 2.5 mol / L (M), the viscosity of the electrolytic solution may be insufficient. The electrical characteristics such as electrical conductivity may be lowered.

  From the viewpoint of improving the safety of the electrolytic solution, the content of the phosphazene compound in the non-aqueous electrolytic solution for an electric double layer capacitor of the present invention (that is, the content of the additive) is preferably 1% by volume or more, and 5% by volume. % Or more is more preferable, and from the viewpoint of improving the low temperature characteristics of the electric double layer capacitor, 10% by volume or more is preferable, and 15% by volume or more is more preferable.

<Non-aqueous electrolyte electric double layer capacitor>
The non-aqueous electrolyte electric double layer capacitor of the present invention comprises the above-described non-aqueous electrolyte for electric double layer capacitor, a positive electrode, and a negative electrode, and in the technical field of an electric double layer capacitor such as a separator, if necessary. Other members that are normally used are provided.

  Although there is no restriction | limiting in particular as a positive electrode and a negative electrode of the nonaqueous electrolyte electric double layer capacitor of this invention, Usually, a porous carbon type polarizable electrode is preferable. The electrode is preferably one having characteristics such as a large specific surface area and bulk specific gravity, electrochemical inactivity, and low resistance. Here, activated carbon etc. are mentioned as said porous carbon.

  The electrode generally contains porous carbon such as activated carbon, and contains other components such as a conductive agent and a binder as necessary. There is no restriction | limiting in particular as a raw material of the activated carbon which can be used suitably for the said electrode, For example, various heat resistant resins, pitch, etc. other than a phenol resin are mentioned suitably. Preferable examples of the heat resistant resin include polyimide, polyamide, polyamideimide, polyetherimide, polyethersulfone, polyetherketone, bismaleimide triazine, aramid, fluororesin, polyphenylene, polyphenylene sulfide and the like. These may be used alone or in combination of two or more. The activated carbon is preferably in the form of powder, fiber cloth or the like from the viewpoint of increasing the specific surface area and increasing the charge capacity of the non-aqueous electrolyte electric double layer capacitor. Further, these activated carbons may be subjected to treatment such as heat treatment, stretch molding, vacuum high temperature treatment, and rolling for the purpose of increasing the charge capacity of the electric double layer capacitor.

  The conductive agent used for the electrode is not particularly limited, and examples thereof include graphite and acetylene black. The binder used for the electrode is not particularly limited, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. .

  The non-aqueous electrolyte electric double layer capacitor of the present invention preferably includes a separator, a current collector, a container and the like in addition to the above-described electrodes (positive electrode and negative electrode) and non-aqueous electrolyte, and moreover, a normal electric double layer capacitor. Each known member used can be provided. Here, the separator is interposed between the positive and negative electrodes for the purpose of preventing a short circuit of the non-aqueous electrolyte electric double layer capacitor. There is no restriction | limiting in particular as this separator, Usually, the well-known separator used as a separator of a nonaqueous electrolyte electric double layer capacitor is used suitably. As a material for the separator, for example, a microporous film, a nonwoven fabric, paper, and the like are preferably exemplified. Specifically, a nonwoven fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene, and polyethylene, a thin layer film, and the like are preferable. Among these, a microporous film made of polypropylene or polyethylene having a thickness of about 20 to 50 μm is particularly suitable.

  There is no restriction | limiting in particular as said collector, The well-known thing normally used as a collector of a nonaqueous electrolyte electric double layer capacitor is used suitably. The current collector is preferably one having excellent electrochemical corrosion resistance, chemical corrosion resistance, workability, mechanical strength, and low cost, such as a current collector layer of aluminum, stainless steel, conductive resin, etc. Is preferred. Moreover, there is no restriction | limiting in particular as said container, The well-known thing normally used as a container of a nonaqueous electrolyte electric double layer capacitor is mentioned suitably. As the material of the container, for example, aluminum, stainless steel, conductive resin and the like are suitable.

  There is no restriction | limiting in particular as a form of the non-aqueous-electrolyte electric double layer capacitor of this invention, Well-known forms, such as a cylinder type (cylindrical type and a square type), a flat type (coin type), are mentioned suitably. These non-aqueous electrolyte electric double layer capacitors are, for example, main power supplies or auxiliary power supplies for electric vehicles and fuel cell vehicles, memory backup devices for various electronic devices, industrial devices, aircraft devices, toys, cordless devices, etc. It is suitably used as a power source for electromagnetic holding such as industrial equipment, gas equipment and instantaneous water heater equipment, and for watches such as watches, wall clocks, solar watches, AGS watches and the like.

  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.

<Synthesis of phosphazene compounds>
(Synthesis Example 1)
(NPCl ₂ ) ₃ and sodium fluoride are mixed in nitrobenzene as a solvent and gradually heated from room temperature to 140 ° C. under reduced pressure (15 kPa) over about 1 hour. Obtained as product.

  The obtained product was analyzed by GC-MS. As a result, n in the formula (I) was 3, and all six Xs were fluorine. A cyclic phosphazene compound having a boiling point of 52 ° C. and a freezing point of 28 ° C. A cyclic phosphazene compound having a viscosity of 0.8 mPa · s at 25 ° C. and n of 3 in formula (I), one of the six X being chlorine and five of fluorine (boiling point is 82 ° C., Cyclic phosphazene compound (boiling point) having a freezing point of -30 ° C and a viscosity of 1.1 mPa · s at 25 ° C, n in the formula (I) being 3, 2 of 6 X being chlorine and 4 being fluorine Is 115 ° C, freezing point is -46 ° C, viscosity at 25 ° C is 1.3mPa · s), n in formula (I) is 3, 3 out of 6 X are chlorine, 3 are fluorine It was confirmed to be a mixture with a cyclic phosphazene compound (boiling point: 150 ° C., freezing point: −35 ° C., viscosity at 25 ° C .: 1.8 mPa · s). In addition, the mixture was separated by distillation to obtain four kinds of pure cyclic phosphazene compounds.

(Synthesis Example 2)
(NPCl ₂ ) ₄ and potassium fluoride sulfite are mixed in nitrobenzene as a solvent, and the temperature is gradually increased from room temperature to 180 ° C. under reduced pressure (1 kPa) over about 1 hour, and the fraction that volatilizes. Was obtained as the product.

  When the obtained product was analyzed by GC-MS, n in the formula (I) was 4, and all of the eight Xs were fluorine-containing cyclic phosphazene compounds (boiling point was 80 ° C., freezing point was 30 ° C. A cyclic phosphazene compound having a viscosity of 0.8 mPa · s at 25 ° C. and n of 4 in formula (I), one of eight X being chlorine and seven being fluorine (boiling point is 117 ° C., A cyclic phosphazene compound (boiling point) having a freezing point of −6 ° C. and a viscosity of 1.2 mPa · s at 25 ° C., n in the formula (I) being 4, 2 of 8 X being chlorine and 6 being fluorine. Is 147 ° C, freezing point is -22 ° C, viscosity at 25 ° C is 1.5mPa · s), n in formula (I) is 4, 3 out of 8 X are chlorine, 5 are fluorine Cyclic phosphazene compound (boiling point is 178 ° C, freezing point is -29 ° C, viscosity at 25 ° C is 1.9mPa · s), n in formula (I) is 4, 4 out of 8 X are chlorine , Four are cyclic phosphazene compounds of fluorine (boiling point is 205 ° C, freezing point is -23 ° C, viscosity at 25 ° C is 2.3 mPa · s), n in formula (I) is 4, It was confirmed that the mixture was a cyclic phosphazene compound (boiling point is 232 ° C., freezing point is −11 ° C., viscosity at 25 ° C. is 2.8 mPa · s), 5 of which are chlorine and 3 are fluorine. In addition, the mixture was separated by distillation to obtain five pure cyclic phosphazene compounds.

<Preparation of non-aqueous electrolyte for electric double layer capacitor>
Next, a mixed solution (comprising an aprotic organic solvent and a phosphazene compound) having the composition shown in Table 2 was prepared, and tetraethylammonium tetrafluoroborate [TEATFB, (C ₂ H ₅ ) ₄ N · BF was added to the mixed solution. ₄ ] (supporting salt) was dissolved at a concentration of 1 mol / L (M) to prepare a non-aqueous electrolyte. The safety and critical oxygen index of the obtained nonaqueous electrolytic solution were measured and evaluated by the following methods. The results are shown in Table 2.

(1) Safety of electrolyte solution The safety of the non-aqueous electrolyte solution was evaluated from the combustion behavior of flames ignited in an atmospheric environment by the method of arranging the UL94HB method of UL (Underwriting Laboratory) standard. At that time, ignitability, combustibility, formation of carbides, and secondary ignition phenomena were also observed. Specifically, based on the UL test standard, a non-combustible quartz fiber was impregnated with 1.0 mL of the electrolytic solution, and a test piece of 127 mm × 12.7 mm was produced. 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”.

(2) Limiting oxygen index of electrolyte The limiting oxygen index of the electrolyte was measured according to JIS K7201. Specifically, a test piece was prepared in the same manner as the safety test of the electrolyte solution, and the test piece was perpendicular to the test piece support, and a combustion cylinder (inner diameter 75 mm, height 450 mm, diameter 4 mm glass particles). Is attached so that the thickness of the metal net is 100 ± 5mm evenly from the bottom and the metal mesh is placed on it at a distance of 100mm or more from the top, and then oxygen (JIS K) is attached to the combustion cylinder. 1101 or higher) and nitrogen (JIS K 1107 grade 2 or higher), and the test piece was ignited in air (the heat source is JIS K 2240 type 1) The combustion state was investigated. However, the total flow rate in the combustion cylinder is 11.4 L / min. This test was performed three times, and the average value is shown in Table 2. The oxygen index refers to the value of the minimum oxygen concentration expressed by the volume percent necessary for the material to continue burning. In this application, the test piece burns continuously for 3 minutes or longer, From the minimum oxygen flow rate required for burning 50 mm or more and the nitrogen flow rate at that time, the following formula:
Critical oxygen index = (oxygen flow rate) / [(oxygen flow rate) + (nitrogen flow rate)] × 100 (volume%)
The limiting oxygen index was calculated according to

<Preparation of non-aqueous electrolyte electric double layer capacitor>
Next, activated carbon [AC, trade name: Kuractive-1500, manufactured by Kuraray Chemical Co., Ltd.], acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are each in a mass ratio (activated carbon: acetylene black: PVDF) was mixed to 8: 1: 1 to obtain a mixture. 100 mg of the obtained mixture was sampled, put into a 20 mmφ pressure-resistant carbon container, and compacted under conditions of a pressure of 150 kgf / cm ² and a normal temperature to prepare a positive electrode and a negative electrode (electrode). A cell was assembled using the obtained electrodes (positive electrode and negative electrode), an aluminum metal plate (current collector) (thickness: 0.5 mm), and a polypropylene / polyethylene plate (separator) (thickness: 25 μm), and vacuum dried. Dry thoroughly. The cell was impregnated with the above non-aqueous electrolyte to produce a non-aqueous electrolyte electric double layer capacitor. The cycle characteristics and low temperature characteristics of the obtained electric double layer capacitor were tested by the following methods. The results are shown in Table 2.

(3) Cycle characteristics of electric double layer capacitor For the obtained non-aqueous electrolyte electric double layer capacitor, the capacitance after initial and 1000 cycle charge / discharge was measured, and the capacity retention rate after 1000 cycle was calculated. The cycle characteristics were evaluated.

(4) Low temperature characteristics of electric double layer capacitor The obtained non-aqueous electrolyte electric double layer capacitor was measured for internal resistance at 20 ° C and -10 ° C, and the low temperature characteristics of the capacitor were evaluated. Here, the internal resistance (Ω) is a well-known internal resistance measurement method, for example, a charge / discharge curve is measured. At that time, the fluctuation width of the potential accompanying charge stop or discharge stop (Discharge Rest) is calculated. Obtained by the measuring method.

  In Table 1, PC represents propylene carbonate (boiling point 242 ° C.), GBL represents γ-butyrolactone (boiling point 204 ° C.), and AN represents acetonitrile (boiling point 82 ° C.). Phosphazene A is a cyclic phosphazene compound (viscosity at 25 ° C .: 0.8 mPa · s, boiling point 82 ° C.) wherein n is 3 and one of the six Xs is chlorine and five are fluorines in formula (I). Phosphazene B is a cyclic phosphazene compound (viscosity at 25 ° C .: 1.1 mPa · s, boiling point) in which n is 3 and 2 out of 6 X are chlorine and 4 are fluorine in formula (I) Phosphazene C is a cyclic phosphazene compound (viscosity at 25 ° C .: 1.3 mPa · s) in which n is 3 and 3 out of 6 Xs are chlorine and 3 are fluorines in formula (I) Phosphazene D is a cyclic phosphazene compound (viscosity at 25 ° C .: 1.2 mPas) in which n is 4 and one of eight Xs is chlorine and seven are fluorines in formula (I) S, boiling point 117 ° C.), and phosphazene E has the formula (I ), A cyclic phosphazene compound (viscosity at 25 ° C .: 1.5 mPa · s, boiling point 147 ° C.) in which n is 4 and 2 out of 8 X are chlorine and 6 are fluorine, and phosphazene F has the formula In (I), a cyclic phosphazene compound (viscosity at 25 ° C .: 1.9 mPa · s, boiling point 178 ° C.) in which n is 4 and 3 out of 8 Xs are chlorine and 5 are fluorines. A cyclic phosphazene compound (viscosity at 25 ° C .: 2.3 mPa · s, boiling point 205 ° C.) in which n is 4 and 4 out of 8 X are chlorine and 4 are fluorine in formula (I), H is a cyclic phosphazene compound (viscosity at 25 ° C .: 2.8 mPa · s, boiling point 232 ° C.) in which n is 4 and 5 out of 8 X are chlorine and 3 are fluorine in the formula (I) .

  As is clear from Table 2, the non-aqueous electrolyte of the example has a high critical oxygen index and excellent safety, and the non-aqueous electrolyte electric double layer capacitor of the example has sufficient cycle characteristics, It can be seen that it has excellent low temperature properties.

Claims (11)

Formula (I) below:
(NPX ₂ ) _n ... (I)
(Wherein X is independently a halogen element and n is an integer of 3 to 15), and non-aqueous electrolysis of an electric double layer capacitor comprising a phosphazene compound containing at least two halogen elements Liquid additive.   The additive for a non-aqueous electrolyte of an electric double layer capacitor according to claim 1, wherein the phosphazene compound contains fluorine and chlorine.   The additive for a non-aqueous electrolyte for an electric double layer capacitor according to claim 2, wherein X in the formula (I) is independently fluorine or chlorine.   N in said Formula (I) is 3-5, The additive for nonaqueous electrolytes of the electric double layer capacitor of Claim 1 characterized by the above-mentioned.   5. The non-aqueous electrolyte for an electric double layer capacitor according to claim 3, wherein n in the formula (I) is 3, 1 to 3 out of 6 Xs are chlorine, and the rest is fluorine. Additives.   5. The non-aqueous electrolyte for an electric double layer capacitor according to claim 3, wherein n in the formula (I) is 4, 1 to 5 of 8 Xs are chlorine, and the remainder is fluorine. Additives.   The non-aqueous electrolysis of an electric double layer capacitor according to claim 5 or 6, wherein the phosphazene compound contains two or more chlorine atoms in the molecule, and each chlorine atom is bonded to a different phosphorus atom. Liquid additive.   The additive for a non-aqueous electrolyte of an electric double layer capacitor according to claim 1, wherein the freezing point of the phosphazene compound is -5 ° C or lower.   The non-aqueous electrolysis for electric double layer capacitor characterized by including the additive for non-aqueous electrolytes of the electric double layer capacitor in any one of Claims 1-8, an aprotic organic solvent, and a supporting salt. liquid.   The non-aqueous electrolysis for electric double layer capacitor according to claim 9, wherein the difference in boiling point between the aprotic organic solvent and the additive for non-aqueous electrolyte of the electric double layer capacitor is 25 ° C or less. liquid.   A non-aqueous electrolyte electric double layer capacitor comprising the non-aqueous electrolyte for an electric double layer capacitor according to claim 9 or 10, a positive electrode, and a negative electrode.