JP2005135951A - Non-aqueous electrolyte electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte electric double-layer capacitor that is superior in charging and discharging characteristics and electrostatic capacitance holding performance, and is reduced in leakage current, when a high voltage is used. <P>SOLUTION: The nonaqueous electrolytic solution electric double layer capacitor is provided with a non-aqueous electrolytic solution, a positive pole, and a negative pole. The leakage current ratio of the capacitor, before and after heating tests at 60°C, is adjusted to ≤60%. It is preferable that the non-aqueous electrolytic solution contains a compound containing at least either phosphorus or nitrogen in its molecule. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte electric double layer capacitor provided with a non-aqueous electrolyte, and more particularly to a non-aqueous electrolyte electric double layer capacitor having excellent electrostatic capacity retention performance and reduced leakage current when using a high voltage. It is.

  A non-aqueous electrolyte electric double layer capacitor is a capacitor that uses electric energy stored in the electric double layer formed at the interface between a polarizable electrode made of activated carbon or the like and the electrolyte, and instantaneously achieves farad order capacitance. It is a large-capacity capacitor that can be charged and discharged. The structure of the non-aqueous electrolyte electric double layer capacitor is formed by winding a polarizable electrode and a separator spirally in a cylindrical case and laminating a flat polarizable electrode and a separator. There is a flat plate type. In particular, a flat type capacitor can be made into a bipolar structure by laminating a plurality of one cell composed of two polarizable electrodes and a current collector plate sandwiching one separator, and is suitable for high voltage applications. ing. That is, the withstand voltage per cell is determined by the electrolysis voltage of the electrolyte impregnated in the polarizable electrode. When an organic electrolyte is used, the withstand voltage is as low as about 2.2 to 2.5 V. By stacking a plurality of cells and connecting them in series, they can be used for applications requiring high voltage. Capacitor units with an output voltage of 100V in which 40 to 50 flat cells using an organic electrolyte are stacked have been developed as practical level capacitors. To achieve higher voltage in each cell. Therefore, it is required to reduce the number of stacked cells. The applications of the above-mentioned wound type and flat type capacitor are widely studied from small capacity type for memory backup, medium capacity type for electric vehicle power assist and large capacity type for power storage battery replacement. However, any type is required to have a high withstand voltage and a long life.

  Further, the conventional non-aqueous electrolyte electric double layer capacitor has inferior capacitance holding performance at a high voltage of 2.7 V or higher. Therefore, it has been difficult for conventional non-aqueous electrolyte electric double layer capacitors to maintain a capacitance for a long time. On the other hand, when using a capacitor at a low voltage, a large number of cells are stacked in a flat type electric double layer capacitor, and each capacitor is connected in series according to a required voltage in a wound type capacitor. A predetermined voltage was ensured by connection or the like.

  Furthermore, the conventional non-aqueous electrolyte electric double layer capacitor has a low reliability due to a reactive current (leakage current) flowing particularly in a high voltage state of charge, and cannot withstand long-term use.

  On the other hand, the following Non-Patent Document 1 describes various active material manufacturing methods for improving capacitor characteristics, and various active material materials are important factors for improving capacitor characteristics. Although the raw materials have been introduced, there is no description about efforts to improve the electrolytic solution and improve the capacitance retention performance of the capacitor.

Ikuo Okamura, “Electric Double Layer Capacitor and Storage System”, Nikkan Kogyo Shimbun

  On the other hand, in recent years, large electric double layer capacitors, which are required as a main power source or auxiliary power source for electric vehicles and fuel cell vehicles, have long-term stability in pulse discharge characteristics, large current discharges, and charging characteristics in various environments. In order to stabilize these characteristics over a long period of time, there is a strong demand for a technology for improving the capacitance holding performance of a capacitor and a technology for reducing leakage current when using a high voltage. .

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, in addition to being excellent in charge / discharge characteristics, in addition to being excellent in capacitance retention performance and having reduced leakage current when using a high voltage, It is to provide a double layer capacitor.

  As a result of intensive studies to achieve the above object, the present inventors have added a specific compound to a conventional non-aqueous electrolyte for electric double layer capacitors or mainly constitute a non-aqueous electrolyte from the compound. Thus, it was found that the leakage current when using a high voltage can be reduced while suppressing the reaction of the non-aqueous electrolyte with the electrode active material and improving the capacitance holding performance of the electric double layer capacitor. It came to complete.

  That is, the non-aqueous electrolyte electric double layer capacitor of the present invention is a non-aqueous electrolyte electric double layer capacitor comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode, a leakage current ratio before and after a heating test at 60 ° C., That is, the ratio of the leakage current after the heating test to the leakage current before the heating test is 60% or less. Here, in the present invention, the heating test is performed in a constant temperature bath at 60 ° C., after charging at a charging voltage of 2.7 to 3.5 V and a charging current of 2 mA, and after performing supplementary charging for 200 hours, then discharging at a constant current of 2 mA. And carried out.

  In a preferred example of the non-aqueous electrolyte electric double layer capacitor of the present invention, the non-aqueous electrolyte contains a compound having at least one of phosphorus and nitrogen in the molecule. Here, as the compound, a compound having phosphorus and nitrogen in the molecule is preferable, and a compound having a phosphorus-nitrogen double bond is more preferable.

  In another preferred embodiment of the non-aqueous electrolyte electric double layer capacitor of the present invention, the non-aqueous electrolyte further contains an aprotic organic solvent.

  In another preferred embodiment of the non-aqueous electrolyte electric double layer capacitor of the present invention, the active material of the positive electrode and the negative electrode is porous carbon. Here, activated carbon is preferable as the porous carbon.

  In the non-aqueous electrolyte electric double layer capacitor of the present invention, the rate of change in capacitance before and after the heating test at 60 ° C. is preferably 8% or less, and more preferably 5% or less.

  In another preferred embodiment of the non-aqueous electrolyte electric double layer capacitor of the present invention, the capacitor has a charging voltage of 2.7 V or more.

  According to the present invention, the reaction between the non-aqueous electrolyte and the electrode active material is suppressed by adding a specific compound to the non-aqueous electrolyte or mainly forming the non-aqueous electrolyte from the compound. In addition, it is possible to provide a non-aqueous electrolyte electric double layer capacitor having excellent capacitance retention performance and reduced leakage current when using a high voltage.

  The present invention is described in detail below. The non-aqueous electrolyte electric double layer capacitor of the present invention comprises a non-aqueous electrolyte, a positive electrode, and a negative electrode, characterized in that the leakage current ratio before and after the heating test at 60 ° C. is 60% or less, more specifically Specifically, at 60 ° C., (i) after charging at 2.7 to 3.5 V and charging current: 2 mA, (ii) after 200 hours supplementary charging, and (iii) after discharging at a constant current of 2 mA The leakage current value is 60% or less of the leakage current value before the heating test. The leakage current value was measured as a current value at the time of supplementary charging for 2 hours at 25 ° C. with a charging current of 2 mA after charging to a charging voltage of 2.7 to 3.5 V. Here, since the heating test is an acceleration test, the leakage current value after operating the capacitor at 60 ° C. for a certain time corresponds to the leakage current value after operating for a longer time at room temperature. Therefore, the non-aqueous electrolyte electric double layer capacitor of the present invention, whose leakage current value after the heating test is 60% or less compared to the leakage current value before the heating test, is operated for a long time at a high voltage of 2.7 V or more. The leakage current value is greatly reduced and the reliability is high. The reason why the leakage current of the non-aqueous electrolyte electric double layer capacitor of the present invention is greatly reduced after the heating test is that the active surface functional groups in the active material are inactivated during the heating test. It is done.

  Conventional non-aqueous electrolytes for electric double layer capacitors have high reactivity with surface functional groups contained in the electrode active material of the capacitor. For this reason, the conventional electric double layer capacitor provided with a non-aqueous electrolyte cannot retain the capacitor characteristics such as capacitance for a long period of time. When the 3.14 high-temperature storage test of EIAJ RC-2377 (electric double layer capacitor test method) was performed, the capacitance value changed by 10% or more before and after the test, and the reactive leakage current The value was also high. On the other hand, the non-aqueous electrolyte used in the electric double layer capacitor of the present invention has low reactivity with the electrode active material even at a high voltage of 2.7 V or higher, and can retain the capacitor characteristics for a long time. Therefore, the non-aqueous electrolyte electric double layer capacitor of the present invention has a small change in the capacitance value of the capacitor, is excellent in the long-term characteristics of the capacitor, and the value of the reactive leakage current is greatly reduced. Especially, it is suitable as a large electric double layer capacitor for electric vehicles and fuel cell vehicles.

  In the non-aqueous electrolyte electric double layer capacitor of the present invention, the rate of change in capacitance before and after the heating test at 60 ° C. is preferably 8% or less, and more preferably 5% or less. Since the reactivity between the electrode active material of the capacitor and the non-aqueous electrolyte is higher at 60 ° C than at normal temperature, the capacitance change rate when the capacitor is operated at 60 ° C for a certain period of time is longer than at normal temperature. This corresponds to the capacitance change rate when operated for a period of time. Therefore, when the capacitance change rate before and after the heating test of the non-aqueous electrolyte electric double layer capacitor is 8% or less, the capacitor has a very high long-term stability of the capacitance.

  The non-aqueous electrolyte electric double layer capacitor of the present invention may have a charging voltage of 2.7 V or higher. In a conventional electric double layer capacitor using a non-aqueous electrolyte, when a voltage of 2.7 V or more is applied between the electrodes, the electrode active material and the non-aqueous electrolyte react to maintain the capacitor characteristics for a long time. However, in the non-aqueous electrolyte electric double layer capacitor of the present invention, since the reaction between the non-aqueous electrolyte and the electrode active material is sufficiently suppressed, a voltage of 2.7 V or more is applied between the electrodes. Even so, changes in capacitor characteristics such as capacitance can be sufficiently suppressed, and the capacitor characteristics can be maintained over a long period of time.

  The non-aqueous electrolyte electric double layer capacitor of the present invention comprises a non-aqueous electrolyte, a positive electrode, and a negative electrode, and, if necessary, a member usually used in the technical field of electric double layer capacitors such as a separator. Prepare.

  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. Suitable examples of the porous carbon include activated 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. Preferred examples of the heat resistant resin include resins such as polyimide, polyamide, polyamideimide, polyetherimide, polyethersulfone, polyetherketone, bismaleimidetriazine, aramid, fluororesin, polyphenylene, polyphenylene sulfide. 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 of the non-aqueous electrolyte electric double layer capacitor of the present invention is not particularly limited as long as the leakage current ratio before and after the heating test at 60 ° C. of the capacitor can be 60% or less, but at least the supporting salt It is preferable to contain a compound containing at least one of phosphorus and nitrogen in the molecule. Further, the non-aqueous electrolyte may contain an aprotic organic solvent such as a carbonate ester or a nitrile compound, if necessary.

  Examples of the compound having phosphorus in the molecule that can be suitably used in the non-aqueous electrolyte of the electric double layer capacitor of the present invention include a phosphate ester compound, a polyphosphate ester compound, and a condensed phosphate ester compound.

  Moreover, as a compound which has nitrogen in the molecule | numerator which can be used suitably for the non-aqueous electrolyte of the electric double layer capacitor of this invention, cyclic | annular nitrogen-containing compounds, such as a triazine compound, a guanidine compound, and a pyrrolidine compound, etc. are mentioned.

  Further, the compounds having phosphorus and nitrogen in the molecule that can be suitably used for the non-aqueous electrolyte of the electric double layer capacitor of the present invention include phosphazene compounds, isomers of phosphazene compounds, phosphazane compounds, and the above molecules. Examples thereof include composite compounds of a compound exemplified as a compound having phosphorus and a compound exemplified as a compound having nitrogen in the molecule. The compound having phosphorus and nitrogen in the molecule is also an example of the compound having phosphorus in the molecule and the compound having nitrogen in the molecule.

  Among the compounds containing at least one of phosphorus and nitrogen in the molecule, compounds having phosphorus and nitrogen in the molecule are preferable from the viewpoint of cycle characteristics. Of the compounds having phosphorus and nitrogen in the molecule, compounds having a phosphorus-nitrogen double bond such as a phosphazene compound are particularly preferred from the viewpoint of improving thermal stability and improving high-temperature storage characteristics.

（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、一価の置換基又はハロゲン元素を表す。ｎは３〜１５を表す。） Specific examples of the phosphazene 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, R ⁴ 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 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 carried out at a rotation speed for 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 at 25 ° C exceeds 300 mPa · s (300 cP), the supporting salt becomes difficult to dissolve, the wettability to electrodes, separators, etc. decreases, and the ionic conductivity decreases significantly due to the increase in the viscous resistance of the electrolyte. In particular, the performance becomes insufficient when used under low temperature conditions such as below the freezing point. Further, 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 in an electrolytic solution of a capacitor.

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 because the viscosity of the electrolytic solution can be reduced. 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 methoxy group, ethoxy group, propoxy group, butoxy group, and alkoxy-substituted alkoxy groups such as methoxyethoxy group and methoxyethoxyethoxy group. Among these, as R ^{1 to} R ³ , all are preferably methoxy groups, ethoxy groups, methoxyethoxy groups, or methoxyethoxyethoxy groups, and all are methoxy groups from the viewpoint of low viscosity and high dielectric constant. Or an ethoxy group is particularly preferred. 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 formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group and the like. 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, and as the halogen element, fluorine, chlorine and bromine are preferred, among which fluorine is particularly preferred, and then chlorine is preferred. preferable. When the hydrogen element in the monovalent substituent is substituted with fluorine, the effect of improving the cycle characteristics of the capacitor 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, in addition to the 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 may be different types.

但し、式(III)、(IV)、(V)において、Ｒ⁵〜Ｒ⁹は、独立に一価の置換基又はハロゲン元素を表す。Ｙ⁵〜Ｙ⁹は、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 includes at least one element selected from the group consisting of carbon, silicon, nitrogen, phosphorus, oxygen, and sulfur from the viewpoint of consideration of toxicity, environment, and the like. Substituents are preferred. Of these substituents, substituents having a structure represented by the following formula (III), (IV) or (V) are more preferable.

However, in the formulas (III), (IV), and (V), R ^{5 to} R ⁹ independently represent a monovalent substituent or a halogen element. Y ^{5 to} Y ⁹ independently represent a divalent linking group, a divalent element, or a single bond, and Z represents a divalent group or a divalent element.

In formulas (III), (IV) and (V), R ^{5 to} R ⁹ are all monovalent substituents or halogen elements similar to those described for R ^{1 to} R ³ in formula (I). Preferably mentioned. Moreover, these may be the same kind in the same substituent, and some may be different kinds. 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 formulas (III), (IV) and (V), the groups represented by Y ^{5 to} Y ⁹ are the same divalent linking groups as those described for Y ^{1 to} Y ³ in the formula (I) or Similarly, a divalent element or the like can be used. Similarly, 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 in 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, and 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. Further, when the substituent is a substituent containing sulfur as represented by the formula (IV), it is particularly preferable in terms of reducing the interface resistance of the electrolytic solution.

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 because the viscosity of the electrolytic solution can be reduced. On the other hand, preferred examples of the halogen element include fluorine, chlorine, bromine and the like. Examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group, and a phenoxy group. 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 include 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. The electrolytic solution can be prepared. These phosphazene compounds may be used alone or in combination of two or more.

Among the phosphazene compounds of the formula (II), from the viewpoint of lowering the viscosity of the electrolytic solution to improve the low temperature characteristics of the capacitor, and further improving the deterioration resistance and safety of the electrolytic solution, it is represented by the following formula (VI). Preferred are phosphazene compounds.

(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. For this reason, by adding the phosphazene compound to the electrolytic solution, it is possible to impart excellent low-temperature characteristics to the electrolytic solution, and it is possible to reduce the viscosity of the electrolytic solution, to achieve low internal resistance and high conductivity. It becomes possible to provide the non-aqueous electrolyte electric double layer capacitor which has. For this reason, it is possible to provide a non-aqueous electrolyte electric double layer capacitor 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 3 to 5, more preferably 3 to 4, and particularly preferably 3 in that it can impart excellent low-temperature characteristics to the electrolyte and can reduce the viscosity of the electrolyte. preferable. 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), it is possible to prepare an electrolytic solution having a more suitable viscosity, solubility suitable for mixing, low temperature characteristics, and the like. 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 (20 cP) or less, but from the viewpoint of improving conductivity and improving low-temperature characteristics, 10 mPa · s (10 cP ) Or less, preferably 5 mPa · s (5 cP) or less.

Among the phosphazene compounds represented by the formula (II), the phosphazene compounds represented by the following formula (VII) are preferable from the viewpoint of improving the deterioration resistance and safety of the electrolytic solution.

(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 solution can be given excellent self-extinguishing properties or flame retardancy to improve the safety of the electrolyte solution, but represented by the formula (VII), If at least one of all R ¹⁰ contains a phosphazene compound which is a monovalent substituent containing fluorine, it is possible to impart superior safety to the electrolytic solution. 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, makes the electrolyte more difficult to burn. There is an effect, and it is possible to give further excellent safety to the electrolytic solution.

In the formula (VII), the cyclic phosphazene compound itself in which all R ¹⁰ is fluorine and n is 3 is nonflammable and has a great effect of preventing ignition when the flame approaches, but the boiling point is low. Since it is very low, if all of them are volatilized, the remaining aprotic organic solvent will burn.

  Examples of the monovalent substituent in the formula (VII) include an alkoxy group, an alkyl group, an acyl group, an aryl group, a carboxyl group, and the like, and the alkoxy group is particularly excellent in improving the safety of the electrolytic solution. Is preferred. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, a butoxy group, and an alkoxy group-substituted alkoxy group such as a methoxyethoxy group. From the viewpoint of superiority, a methoxy group, an ethoxy group, and an n-propoxy group are particularly preferable. Moreover, a methoxy group is preferable in terms of reducing the viscosity of the electrolytic solution.

  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 electrolytic solution.

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

  The content of fluorine in the phosphazene compound is preferably 3 to 70% by weight, more preferably 7 to 45% by weight. If content is in the said numerical range, the safety | security excellent in electrolyte solution can be provided especially suitably.

  The molecular structure of the phosphazene compound represented by the formula (VII) may contain halogen elements such as chlorine and bromine in addition to the aforementioned 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 capacitor than those containing chlorine.

By appropriately selecting R ¹⁰ and n value in the formula (VII), it is possible to prepare an electrolytic solution having more suitable safety, viscosity, solubility suitable for mixing, and the like. These phosphazene compounds may be used alone or in combination of two or more.

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

Among the phosphazene compounds of the formula (II), from the viewpoint of improving the deterioration resistance and safety of the electrolytic solution while suppressing the increase in the viscosity of the electrolytic solution, it is solid at 25 ° C. (room temperature) and has the following formula: A phosphazene compound represented by (VIII) is also preferred.

(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 solid at room temperature (25 ° C.), when added to the electrolytic solution, it dissolves in the electrolytic solution and the viscosity of the electrolytic solution increases. However, if the addition amount is a predetermined amount, the rate of increase in the viscosity of the electrolyte is low, and a non-aqueous electrolyte electric double layer capacitor having low internal resistance and high conductivity is obtained. In addition, since the phosphazene compound represented by the formula (VIII) is dissolved in the electrolytic solution, the long-term stability of the electrolytic solution is excellent.

In the formula (VIII), R ¹¹ 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. Is mentioned. Moreover, as a halogen element, halogen elements, such as a fluorine, chlorine, a bromine, an iodine, are mentioned suitably, for example. Among these, an alkoxy group is preferable in that an increase in the viscosity of the electrolytic solution can be suppressed. The alkoxy group is preferably a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group (isopropoxy group, n-propoxy group), a phenoxy group, a trifluoroethoxy group, or the like, and can suppress an increase in the viscosity of the electrolytic solution. And more preferably a methoxy group, an ethoxy group, a propoxy group (isopropoxy group, n-propoxy group), a phenoxy group, a trifluoroethoxy group, or the like. The monovalent substituent preferably contains the aforementioned halogen element.

  In the formula (VIII), n is particularly preferably 3 or 4 from the viewpoint of suppressing an increase in the viscosity of the electrolytic solution.

The phosphazene compound represented by the formula (VIII), for example, the formula R ¹¹ in (VIII) is structured n a methoxy group is 3, the formula in (VIII) R ¹¹ is a methoxy group and phenoxy group A structure in which at least one of n is 4, a structure in which R ¹¹ is an ethoxy group and n is 4 in formula (VIII), and R ¹¹ is an isopropoxy group in formula (VIII) and n is 3 Or a structure in which R ¹¹ is an n-propoxy group and n is 4 in the formula (VIII), or a structure in which R ¹¹ is a trifluoroethoxy group and n is 3 or 4 in the formula (VIII) A structure in which R ¹¹ is a phenoxy group and n is 3 or 4 in the structure (VIII) is particularly preferable in that an increase in the viscosity of the electrolytic solution can be suppressed.

  By appropriately selecting each substituent and n value in the formula (VIII), it is possible to prepare an electrolytic solution having a more suitable viscosity, solubility suitable for mixing, and the like. 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 group, 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) can exhibit extremely low temperature characteristics in the electrolyte when added to the electrolyte. Deterioration resistance 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 manufacture by adjusting temperature and content (volume%) of this isomer can be measured with the following measuring method.
<Measurement method>
Obtain the peak area of the sample by gel permeation chromatography (GPC) or high performance liquid chromatography, and obtain the molar ratio by comparing the peak area with the area per mole of the isomer determined in advance. It can be measured by converting the volume in consideration of the specific gravity.

  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. it can.

  The supporting salt to be contained in the non-aqueous electrolyte of the 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 the electrolytic solution, and can effectively improve electric characteristics such as electric conductivity of the electrolytic solution. In particular, quaternary ammonium salts capable of forming multivalent ions are preferred.

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, preferred examples of the quaternary ammonium salt include compounds represented by the following formulas (a) to (j). 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 non-aqueous electrolytic solution of the electric double layer capacitor of the present invention can reduce the viscosity of the electrolytic solution in addition to the compound containing at least one of phosphorus and nitrogen in the molecule and the supporting salt. It is preferable to contain an aprotic organic solvent in that optimum ionic conductivity as the multilayer capacitor can be achieved. The aprotic organic solvent is not particularly limited, and examples thereof include nitrile compounds, ether compounds, and ester compounds. Specifically, nitrile compounds such as acetonitrile, propiononitrile, butyronitrile, isobutyronitrile, benzonitrile; ether compounds such as 1,2-dimethoxyethane, tetrahydrofuran; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate Suitable examples include carbonate compounds such as propylene carbonate, diphenyl carbonate, γ-butyrolactone, and γ-valerolactone. Among these, cyclic carbonate compounds such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, chain carbonate compounds such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and chain ethers such as 1,2-dimethoxyethane Compounds and the like are preferred. The cyclic carbonate compound has a high relative dielectric constant and is excellent in the ability to dissolve the supporting salt, and the chain carbonate compound and the ether compound are suitable for 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 concentration of the supporting salt in the electrolytic solution is preferably 0.2 to 2.5 mol / L (M), and 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. The viscosity of the liquid increases, and electrical properties such as electrical conductivity may decrease.

  The content of the compound containing at least one of phosphorus and nitrogen in the molecule in the non-aqueous electrolyte used in the electric double layer capacitor of the present invention improves the capacitance retention performance of the capacitor, while using a high voltage. From the viewpoint of reducing leakage current, 3% by volume or more is preferable, and 5% by volume or more is more preferable. Further, from the viewpoint of improving the safety of the electrolytic solution, it is preferably 3% by volume or more, more preferably 5% by volume or more.

  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 positive electrode, the negative electrode, and the electrolyte described above, and is generally known as used in electric double layer capacitors. These members 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.

  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. Used as a power source for electromagnetic holding such as industrial equipment, gas equipment, instantaneous water heater equipment, and watches such as watches, wall clocks, solar watches, AGS watches, etc. Especially, the main power supply or auxiliary power supply for electric vehicles and fuel cell vehicles It is suitable as.

  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)
Petroleum coke-based activated carbon powder [average particle size: 50 μm, surface functional group content: 2.6 meq / g], acetylene black (conductive agent) and polytetrafluoroethylene (PTFE) (binder), respectively, in mass ratio (activated carbon : Acetylene black: PTFE) and mixed to 8: 1: 1 to obtain a mixture. 100 mg of the resulting mixture was sampled and placed in a 11 mmφ pressure-resistant carbon container and compacted under conditions of 150 kgf / cm ² and normal temperature to produce a positive electrode and a negative electrode (electrode), and vacuum dried And dried thoroughly.

In addition, 90% by volume of propylene carbonate (PC) (aprotic organic solvent) and cyclic phosphazene A (in the formula (II), n is 3, and one of six R ⁴ is a phenoxy group (PhO—)). Cyclic phosphazene compound in which 5 is fluorine, viscosity at 25 ° C .: 1.7 mPa · s (1.7 cP)) 10% by volume, tetraethylammonium tetrafluoroborate (TEATFB, (C ₂ H ₅ ) ₄ N · BF ₄ ) (Supporting salt) was dissolved at a concentration of 1 mol / L (M) to prepare an electrolytic solution.

  The safety of the electrolyte was evaluated from the combustion behavior of flames ignited in an atmospheric environment by a method of arranging UL94HB method of UL (Underlighting 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, “difficult” `` Flammability '', `` Self-extinguishing '' when the ignited flame is extinguished on the 25-100 mm line and no ignition is observed even on falling objects, `` Flammability '' when the ignited flame exceeds the 100 mm line It was evaluated. The results are shown in Table 1.

  Next, the electrode (positive electrode and negative electrode) is impregnated with the electrolytic solution, and a polypropylene / polyethylene plate (separator) (thickness: 25 μm) is used. Assembled.

Using the manufactured capacitor, after reaching a charging voltage of 2.7 V at 25 ° C. and a charging current of 2 mA, supplementary charging was performed for 2 hours at the charging voltage. Here, the current value at the time of 2 hours of supplementary charging is i1. Next, discharging was performed at a constant current of I1 = 2 mA. This cycle is repeated, and in the sixth cycle, values of time t1 (seconds) from the start of discharge to voltage v1 = 2.0 V and time T1 (seconds) from the start of discharge to voltage V1 = 1.0 V are used. The following formula 1:
C1 = I1 × (T1-t1) / (v1-V1) Equation 1
From this, the capacitance C1 was obtained.

Moreover, the capacitor after charging / discharging was charged at a charging voltage of 2.7 V and a charging current of 2 mA in a constant temperature bath of 60 ° C., further supplemented for 200 hours, and then discharged at a constant current of 2 mA. Next, the capacitor was taken out of the thermostat and cooled to 25 ° C. Further, after reaching a charging voltage of 2.7 V at 25 ° C. and a charging current of 2 mA, supplementary charging was performed at the charging voltage for 2 hours. Here, the current value at the time of 2 hours of auxiliary charge is i2. Next, discharging was performed at a constant current of I2 = 2 mA. This cycle is repeated, and in the sixth cycle, the time t2 (seconds) from the start of discharge to the voltage v2 = 2.0 V and the time T2 (seconds) from the start of discharge to the voltage V2 = 1.0 V are used. The following formula 2:
C2 = I2 × (T2−t2) / (v2−V2) Equation 2
From this, the capacitance C2 was obtained.

Furthermore, the following formula 3:
Capacitance change rate (%) = | (C2-C1) / C1 | × 100 Formula 3
From the above, the capacitance change rate before and after the heating test was calculated.

Furthermore, the following formula 4:
Leakage current ratio (%) = i2 / i1 × 100 Equation 4
From the above, the leakage current ratio before and after the heating test was calculated. The results are shown in Table 1.

(Examples 2 to 15)
An electrolytic solution having a formulation shown in Table 1 was prepared, and the safety of the electrolytic solution was evaluated in the same manner as in Example 1. The results are shown in Table 1. In Table 1, GBL represents γ-butyrolactone, and AN represents acetonitrile.

Further, in Table 1, cyclic phosphazene B is a compound having a formula (II) in which n is 3, one of six R ⁴ is an ethoxy group, and five are fluorine (viscosity at 25 ° C .: 1.2 mPa · s). cyclic phosphazene C is a compound (viscosity at 25 ° C .: n in formula (II), n is 4 and one of eight R ⁴ is ethoxy group and seven is fluorine). 1.1 mPa · s (1.1 cP)); cyclic phosphazene D in formula (II), n is 3, and one of the six R ⁴ groups is a methoxyethoxyethoxyethoxy group (CH ₃ OC ₂ H ₄ OC) ₂ H ₄ OC ₂ H ₄ O—), and five are fluorine compounds (viscosity at 25 ° C .: 4.5 mPa · s (4.5 cP)).

鎖状ホスファゼンＧは、下記式(XII)で表される化合物（25℃における粘度：2.8mPa・s(2.8cP)）であり；

鎖状ホスファゼンＨは、下記式(XIII)で表される化合物（25℃における粘度：3.9mPa・s(3.9cP)）である。

Further, chain phosphazene E, in formula (I), with substituents X ¹ is represented by formula ^{(III), Y 1 R 1} , Y 2 R 2, Y 3 R 3, Y 5 R 5 and Y ⁶ R ⁶ is a compound wherein 3 are ethoxy groups, 2 are fluorine, and Z is O (oxygen) (viscosity at 25 ° C .: 4.7 mPa · s (4.7 cP));
Chain phosphazene F is a compound represented by the following formula (XI) (viscosity at 25 ° C .: 4.9 mPa · s (4.9 cP));

Chain phosphazene G is a compound represented by the following formula (XII) (viscosity at 25 ° C .: 2.8 mPa · s (2.8 cP));

The chain phosphazene H is a compound represented by the following formula (XIII) (viscosity at 25 ° C .: 3.9 mPa · s (3.9 cP)).

  Moreover, the non-aqueous electrolyte electric double layer capacitor was produced like the Example 1 using the said electrolyte solution, and the electrostatic capacitance change rate before and behind a heating test and the leakage current ratio were measured. The results are shown in Table 1.

(Example 16)
The capacitance change rate and the leakage current ratio were measured in the same manner as in Example 1 except that the charging voltage in the heating test was 3.0 V, v1 and v2 were 2.4 V, and V1 and V2 were 1.2 V. The results are shown in Table 1.

(Example 17)
The capacitance change rate and the leakage current ratio were measured in the same manner as in Example 1 except that the charging voltage in the heating test was 3.3 V, v1 and v2 were 2.6 V, and V1 and V2 were 1.3 V. The results are shown in Table 1.

(Example 18)
The capacitance change rate and the leakage current ratio were measured in the same manner as in Example 1 except that the charging voltage in the heating test was 3.5 V, v1 and v2 were 2.8 V, and V1 and V2 were 1.4 V. The results are shown in Table 1.

(Comparative Examples 1-4)
An electrolytic solution having a formulation shown in Table 1 was prepared, and the safety of the electrolytic solution was evaluated. In addition, a non-aqueous electrolyte electric double layer capacitor was produced using the electrolytic solution in the same manner as in Example 1, and the capacitance change rate and the leakage current ratio before and after the heating test were measured. In Comparative Example 1, the heating test is performed under the same conditions as in Example 1. In Comparative Example 2, the heating test is performed under the same conditions as in Example 16. In Comparative Example 3, the heating test is performed under the same conditions as in Example 17. In Comparative Example 4, a heating test was performed under the same conditions as in Example 18. The results are shown in Table 1.

  As is clear from Table 1, the electric double layer capacitor of the example provided with the nonaqueous electrolytic solution to which a compound containing at least one of phosphorus and nitrogen in the molecule was added had a small capacitance change rate after the heating test. It can be seen that the leakage current ratio before and after the heating test is small. From the viewpoint of safety, it is understood that the content of the compound containing at least one of phosphorus and nitrogen in the molecule in the electrolytic solution is preferably 3% by volume or more. On the other hand, the electric double layer capacitor of the comparative example using the conventional non-aqueous electrolyte has a high capacity change rate after the heating test and a large leakage current ratio in addition to the high flammability of the electrolyte. I understand.

Claims (11)

  A non-aqueous electrolyte electric double-layer capacitor comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode, wherein a leakage current ratio before and after a heating test at 60 ° C. is 60% or less. Double layer capacitor.   The non-aqueous electrolyte electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte contains a compound having phosphorus in a molecule.   The non-aqueous electrolyte electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte contains a compound having nitrogen in the molecule.   The non-aqueous electrolyte electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte contains a compound having phosphorus and nitrogen in the molecule.   The non-aqueous electrolyte electric double layer capacitor according to claim 4, wherein the compound having phosphorus and nitrogen in the molecule has a phosphorus-nitrogen double bond.   The non-aqueous electrolyte electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte further contains an aprotic organic solvent.   The non-aqueous electrolyte electric double layer capacitor according to claim 1, wherein the active material of the positive electrode and the negative electrode is porous carbon.   The non-aqueous electrolyte electric double layer capacitor according to claim 7, wherein the porous carbon is activated carbon.   The non-aqueous electrolyte electric according to any one of claims 1 to 8, wherein the non-aqueous electrolyte electric double layer capacitor has a capacitance change rate of 8% or less before and after a heating test at 60 ° C. Double layer capacitor.   The non-aqueous electrolyte electric double layer capacitor according to claim 9, wherein the non-aqueous electrolyte electric double layer capacitor has a capacitance change rate of 5% or less before and after a heating test at 60 ° C.   The nonaqueous electrolyte electric double layer capacitor according to any one of claims 1 to 10, wherein the nonaqueous electrolyte electric double layer capacitor has a charging voltage of 2.7 V or more.