JP2012212741A - Electric double-layer capacitor - Google Patents

Abstract

An electric double layer capacitor having excellent overcharge resistance is provided.
An electric double layer capacitor of the present invention has a structure in which a container includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. At least one of the positive electrode 21 and the negative electrode 22 is made of a mixture containing activated carbon and a carbon conductive agent. The nonaqueous electrolytic solution contains propylene carbonate as an organic solvent and a quaternary ammonium salt in a smaller volume ratio than propylene carbonate.
[Selection] Figure 1

Description

  The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor in which a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte are contained in a container.

  Conventionally, various electrochemical devices have been put into practical use. Among them, a coin-type electric double layer capacitor (EDLC) is widely used as a backup power source for small electric devices because it has a relatively high energy density, a small size and a light weight. Such a coin-type electric double layer capacitor is used, for example, in a state where it is surface-mounted on a printed wiring board by reflow soldering (see, for example, Patent Documents 1 and 2).

  In general, a coin-type electric double layer capacitor has a structure in which a positive electrode and a negative electrode are disposed in a container via a separator, and these are accommodated together with a non-aqueous electrolyte and hermetically sealed. In such a coin-type electric double layer capacitor, an organic solvent-based electrolyte is often used as a non-aqueous electrolyte. In recent years, a non-aqueous electrolyte that is a mixture of an organic solvent and an ionic liquid is used. It has also been proposed. Specifically, there is an example in which a mixture of a quaternary ammonium salt, which is a kind of ionic liquid, and an organic solvent is used as a nonaqueous electrolytic solution (see, for example, Patent Document 3).

JP-A-2005-64435 JP 2007-207942 A JP 2007-111281 A

  However, when a non-aqueous electrolyte that is a mixture of an organic solvent and an ionic liquid is used in the conventional coin-type electric double layer capacitor described above, and charging and discharging are continuously performed with a voltage difference exceeding 3 V, for example, The organic solvent in the electrolytic solution is decomposed, and gas is easily generated in the capacitor. Therefore, not only does the container swell and the appearance deteriorates, but also quality deterioration such as a rapid decrease in discharge capacity occurs. In addition, depending on the combination of the organic solvent and the ionic liquid, problems such as an increase in the viscosity of the mixture occur, and in many cases, the mixture is not suitable for use as a non-aqueous electrolyte. As described above, there has been a problem with the anti-overcharge characteristic in the prior art, and there is not much room for improvement.

  This invention is made | formed in view of said subject, The objective is to provide the electric double layer capacitor excellent in the overcharge-proof characteristic.

  In order to solve the above-mentioned problems, the inventors of the present application have conducted intensive research to find the appropriate conditions on the premise that a nonaqueous electrolytic solution containing an organic solvent and a quaternary ammonium salt that is a kind of ionic liquid is used. It was. As a result, when a specific organic solvent (PC: propylene carbonate) and a quaternary ammonium salt are combined and a small amount of the quaternary ammonium salt is used in a volume ratio than PC, the PC is unexpectedly decomposed during overcharge. Was found to be effectively suppressed. Based on this knowledge, the present inventors have been able to conceive the following problem solving means [1] to [4]. They are listed below.

  [1] In an electric double layer capacitor containing a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte in a container, at least one of the positive electrode and the negative electrode is made of a mixture containing activated carbon and a carbon conductive agent, An electric double layer capacitor, wherein the water electrolyte contains propylene carbonate as an organic solvent and a smaller amount of a quaternary ammonium salt in a volume ratio than the propylene carbonate.

  Therefore, according to the invention described in the means 1, since the decomposition of the PC is effectively suppressed as described above even during overcharge, the generation of gas in the capacitor is suppressed. Therefore, the container is prevented from being swollen and a rapid decrease in the discharge capacity is prevented, so that the overcharge resistance can be improved. In addition, a non-aqueous electrolyte solution containing PC and a quaternary ammonium salt in a smaller volume ratio than the PC has properties that are suitable for use as a non-aqueous electrolyte solution because the viscosity is not so high. be able to. In addition, at least one of the positive electrode and the negative electrode is made of a mixture containing activated carbon and a carbon conductive agent, and that these function under the non-aqueous electrolyte of the above composition also improves the overcharge resistance. It is thought that it contributed to plan.

  [2] The electric double layer capacitor according to the above means 1, wherein the non-aqueous electrolyte contains the propylene carbonate and the quaternary ammonium salt in a volume ratio of 70:30 to 90:10.

  Therefore, according to the invention described in the means 2, by setting the volume ratio of PC and quaternary ammonium salt within the above range, the overcharge resistance characteristics can be maintained while maintaining suitable properties as a non-aqueous electrolyte. It can certainly improve. If the PC is less than 70% by volume (the quaternary ammonium salt is more than 30% by volume), the viscosity becomes high and it may not be suitable for use as a non-aqueous electrolyte. On the other hand, if the PC is more than 90% by volume (the quaternary ammonium salt is less than 10% by volume), there is a possibility that the effect of suppressing the decomposition of PC due to the use of the quaternary ammonium salt cannot be obtained sufficiently. .

  [3] The electric double layer capacitor as described in the above means 1 or 2, wherein the carbon conductive agent is acetylene black (AB).

  Therefore, according to the invention described in the means 3, by specifically selecting AB as the carbon conductive agent, it is possible to improve the overcharge resistance more reliably and to improve the conductivity of the positive electrode and the negative electrode. Large current discharge can be expected.

  [4] The electric double layer capacitor according to any one of the above means 1 to 3, wherein the activated carbon is coconut shell activated carbon.

  Therefore, according to the invention described in the means 4, the overcharge resistance can be more reliably improved by specifically selecting the coconut shell activated carbon as the activated carbon.

  As described in detail above, according to the inventions described in means 1 to 4, it is possible to provide an electric double layer capacitor having excellent overcharge resistance.

1 is a schematic cross-sectional view showing a coin-type electric double layer capacitor according to an embodiment of the present invention. The graph which shows the result (relationship between discharge capacity maintenance rate and preservation days) of the evaluation test performed in the Example. The graph which shows the result (relationship between the relative value of internal resistance, and preservation days) of the evaluation test done in the Example.

  Hereinafter, an embodiment in which the present invention is embodied in a coin-type electric double layer capacitor will be described in detail with reference to FIG.

  As shown in FIG. 1, the electric double layer capacitor 11 of this embodiment is a type of non-aqueous electrolyte electrochemical element, and is a type of device that stores electric charges using a physical phenomenon called electric double layer. . The electric double layer capacitor 11 includes a bottomed cylindrical positive electrode can (first exterior metal) 12 that also serves as a positive electrode terminal, and a bottomed cylindrical negative electrode can (second exterior metal) 13 that also serves as a negative electrode terminal. Yes. Both the positive electrode can 12 and the negative electrode can 13 are made of stainless steel, and a single container 17 is constituted by these members. Between the outer edge part of the positive electrode can 12 and the outer edge part of the negative electrode can 13, a synthetic resin gasket 15 for sealing and sealing the gap is sandwiched and caulked. In this embodiment, a gasket 15 made of PEEK (polyether ether ketone) resin is used. In the accommodating space 14 formed by the positive electrode can 12 and the negative electrode can 13, a disk-shaped positive electrode 21 (that is, one polarizable electrode) and a disk-shaped negative electrode 22 (that is, the other polarizable electrode) are also formed. A separator 23 is arranged. The positive electrode 21 is supported on the positive electrode conductive paint 26 and is provided so as to contact the inner surface of the positive electrode can 12 through the positive electrode conductive paint 26. The negative electrode 22 is supported on a negative electrode conductive paint 27 and is provided so as to contact the inner surface of the negative electrode can 13 via the negative electrode conductive paint 27. The separator 23 is interposed between the positive electrode 21 and the negative electrode 22 to isolate them.

  The positive electrode 21 and the negative electrode 22 in the electric double layer capacitor 11 are a mixture containing activated carbon as an active material, a carbon conductive agent, and a binder. Here, as the activated carbon, for example, powdered activated carbon obtained by applying activation treatment to sawdust, coconut shell, pitch, or the like can be used. In addition, activated carbon obtained by applying infusibilization and carbonization activation treatment to a fiber such as phenol, rayon, acrylic, or pitch can be used. Among these, it is particularly preferable to select coconut shell activated carbon.

  As the carbon conductive agent, for example, natural graphite such as flaky graphite or earthy graphite, artificial graphite, carbon black, carbon fiber, or the like can be used. Among these, it is preferable to use conductive carbon blacks. Specific examples include channel black, oil furnace black, lamp black, thermal black, acetylene black, ketjen black, etc., but acetylene black (AB) is selected because it has less impurities to elute when voltage is applied. It is particularly preferable to do this. In addition, carbon materials such as carbon nanotubes can be used as the carbon conductive agent.

  As the binder (binder), known resin materials that are generally used in the electric double layer capacitor 11 and insoluble in the non-aqueous electrolyte can be widely used. Specifically, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinyl fluoride (PVF), a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), polyvinyl pyrrolidone, polyvinyl chloride. Polyethylene (PE), polypropylene (PP), polyimide (PI), polyamide (PA), polyfluoroethylenepropylene, styrene butadiene rubber (SBR), carboxymethylcellulose, fluororubber, and the like can be used.

  And the positive electrode 21 and the negative electrode 22 can be produced by pressure bonding by drying and pressing a mixture of activated carbon, a conductive agent and a binder.

  The separator 23 in the electric double layer capacitor 11 is not particularly limited as long as it satisfies the requirements that the non-aqueous electrolyte easily passes, is an insulator, and is chemically stable. You can choose. Preferred examples thereof include rayon papermaking, polyolefin porous film, polyethylene nonwoven fabric, polypropylene nonwoven fabric, glass fiber nonwoven fabric, and cellulose. Although the thickness of the separator 23 is not limited, For example, it is good that it is about 10 micrometers-250 micrometers.

  As the electrolytic solution in the electric double layer capacitor 11, it is necessary to use a non-aqueous electrolytic solution containing PC as an organic solvent and a quaternary ammonium salt in a smaller volume ratio than the PC.

  PC is a kind of cyclic carbonate, and is often used as a high voltage type organic solvent. As the organic solvent in the non-aqueous electrolyte, it is preferable to use only one type of PC, but this does not completely prevent the combined use with other organic solvents. That is, ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 2methyl-γ- if the volume ratio is considerably small (for example, a fraction or less) compared with PC. Butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, 1,2-ethoxyethane, diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, tri Ethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, ethyl pro Carbonate, butylpropyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester, tetrahydrofuran (THF), alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3 -Dioxolane, 1,4-dioxolane, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, methyl propionate, ethyl propionate, phosphate triester, anhydrous It is allowed to be used in combination with maleic acid, sulfolane, 3-methylsulfolane and the like.

  The quaternary ammonium salt is a kind of salt having properties as an ionic liquid. The “ionic liquid” generally refers to an organic salt that exists in a liquid state even at room temperature, and is also called a room temperature molten salt (or room temperature molten salt). In general, ionic liquids have excellent heat resistance, nonflammability, relatively low viscosity, can be energized without adding a supporting electrolyte, wide potential window, high ionic conductivity, etc. Furthermore, it has various characteristics preferable as an electrochemical element material.

  Examples of the quaternary ammonium salt include pyrazolium salt, pyridinium salt, triazolium salt, pyridazinium salt, tetraalkylammonium salt, imidazolium salt, and the like. In addition, the quaternary ammonium salt mentioned below may use only 1 type, and may be used in combination of 2 or more type.

  Examples of pyrazolium salts include 1,2-dimethylpyrazolium tetrafluoroborate, 1-methyl-2-ethylpyrazolium tetrafluoroborate, 1-propyl-2-methylpyrazolium tetrafluoroborate, 1-methyl-2- A butyl pyrazolium tetrafluoroborate etc. can be illustrated.

  Examples of the pyridinium salt include N-methylpyridinium tetrafluoroborate, N-ethylpyridinium tetrafluoroborate, N-propylpyridinium tetrafluoroborate, N-butylpyridinium tetrafluoroborate and the like. Examples of the triazolium salt include 1-methyltriazolium tetrafluoroborate, 1-ethyltriazolium tetrafluoroborate, 1-propyltriazolium tetrafluoroborate, 1-butyltriazolium tetrafluoroborate and the like. it can.

  Examples of pyridazinium salts include 1-methylpyridazinium tetrafluoroborate, 1-ethylpyridazinium tetrafluoroborate, 1-propylpyridazinium tetrafluoroborate, 1-butylpyridazinium tetrafluoroborate and the like. It can be illustrated.

  Tetraalkylammonium salts include tetraethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, trimethylethylammonium tetrafluoroborate, dimethyldiethyl Ammonium tetrafluoroborate, trimethylpropylammonium tetrafluoroborate, trimethylbutylammonium tetrafluoroborate, dimethylethylpropylammonium tetrafluoroborate, methylethylpropylbutylammonium tetrafluoroborate, N, N-dimethylpyrrolidinium tetrafluoroborate N-ethyl-N-methylpyrrolidinium tetrafluoroborate, N-methyl-N-propylpyrrolidinium tetrafluoroborate, N-ethyl-N-propylpyrrolidinium tetrafluoroborate, N, N-dimethylpiperidinium Tetrafluoroborate, N-methyl-N-ethylpiperidinium tetrafluoroborate, N-methyl-N-propylpiperidinium tetrafluoroborate, N-ethyl-N-propylpiperidinium tetrafluoroborate, N, N- Dimethylmorpholinium tetrafluoroborate, N-methyl-N-ethylmorpholinium tetrafluoroborate, N-methyl-N-propylmorpholinium tetrafluoroborate, N-ethyl-N-propylmorpholinium tetrafluoroborate, etc. The It can Shimesuru.

  Examples of the imidazolium salt include 1,3-dimethylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,3-diethylimidazolium tetrafluoroborate, 1,2-dimethyl-3-ethyl. Examples thereof include imidazolium tetrafluoroborate and 1,2-dimethyl-3-propylimidazolium tetrafluoroborate.

  The anion in the ionic liquid containing a quaternary ammonium ion as a cation is not particularly limited, and can be selected from those other than the above tetrafluoroborate ions. Specific examples of the anion include chloride ion, bromide ion, iodide ion, hexafluorophosphate ion, trifluoromethanesulfonate ion, trifluoroacetate ion, thiocyanate ion, and organic borate ion.

  The ratio (volume ratio) of PC and quaternary ammonium salt in the nonaqueous electrolytic solution is preferably 70:30 to 90:10, and more preferably 75:25 to 85:15. The reason is that if the PC is less than 70% by volume (the quaternary ammonium salt is more than 30% by volume), the viscosity becomes high and may not be suitable for use as a non-aqueous electrolyte. On the other hand, if the PC is more than 90% by volume (the quaternary ammonium salt is less than 10% by volume), there is a possibility that the effect of suppressing the decomposition of PC due to the use of the quaternary ammonium salt cannot be obtained sufficiently. Because.

  Hereinafter, examples embodying the present embodiment will be described.

  Here, as shown in Table 1, the following eight types of electric double layer capacitors 11 were actually fabricated.

  The electric double layer capacitor 11 of Example 1 basically has the structure shown in FIG. The positive electrode 21 and the negative electrode 22 were obtained by mixing coconut shell activated carbon, AB as a carbon conductive agent, and FEP as a binder in a volume ratio of 90: 5: 5. The mixture of these was dried and pressed to produce the positive electrode 21 and the negative electrode 22 by pressure bonding. This was arrange | positioned in the container 17 so that it might contact with the positive electrode conductive paint 26 and the negative electrode conductive paint 27 which were made into the paste form with the organic solvent. The cell outer dimensions of the electric double layer capacitor 11 were a diameter of 4.8 mmφ and an overall height of 1.4 mm. As the non-aqueous electrolyte, a mixture of PC as an organic solvent and a quaternary ammonium salt (anion: tetrafluoroborate ion, cation: imidazolium ion) which is an ionic liquid is used, and the volume ratio is 70: 30.

  In the electric double layer capacitor 11 of Example 2, the volume ratio of PC constituting the non-aqueous electrolyte and the quaternary ammonium salt was set to 80:20, and other matters were the same as in Example 1.

  In the electric double layer capacitor 11 of Example 3, the volume ratio of PC constituting the non-aqueous electrolyte and the quaternary ammonium salt was 90:10, and other matters were the same as in Example 1.

  In the electric double layer capacitor 11 of Comparative Example 1, the volume ratio of the PC constituting the non-aqueous electrolyte and the quaternary ammonium salt was 20:80, and other matters were the same as in Example 1.

  In the electric double layer capacitor 11 of Comparative Example 2, the volume ratio of PC constituting the non-aqueous electrolyte and the quaternary ammonium salt was 50:50, and the other matters were the same as in Example 1.

  In the electric double layer capacitor 11 of Comparative Example 3, the organic solvent constituting the non-aqueous electrolyte is changed to EC, the volume ratio of EC to the quaternary ammonium salt is 80:20, and other matters are described. Same as Example 1.

  In the electric double layer capacitor 11 of Comparative Example 4, the organic solvent constituting the non-aqueous electrolyte was changed to sulfolane, the volume ratio of sulfolane to the quaternary ammonium salt was 80:20, and other matters were Same as Example 1.

In the electric double layer capacitor 11 of Comparative Example 5, the current PC-based organic solvent (containing LiClO ₄ as a supporting electrolyte) is used as a non-aqueous electrolytic solution containing no quaternary ammonium salt. These items were the same as in Example 1.

And about 50 each of the electric double layer capacitors 11 of Examples 1 to 3 and Comparative Examples 1 to 5 having the above-described configuration were produced and put into a reflow furnace having a maximum temperature of 240 ° C. Next, after leaving at room temperature and normal humidity for 24 hours, the discharge capacity and internal resistance before the test were measured. Next, as a test for investigating the overcharge resistance characteristics during long-term storage, the battery was charged continuously at a voltage of 3.3 V in a high temperature environment (60 ° C.). At that time, the discharge capacity and the internal resistance were measured every 10 days, and the average value was obtained. The results are shown in Table 1. Moreover, the transition by storage of the discharge capacity about Example 2 and Comparative Example 5 is shown in the graph of FIG. 2, and the transition by storage of internal resistance is shown by the graph of FIG.

  As apparent from Table 1 and FIG. 2, in Examples 1 to 3, the decrease in discharge capacity was relatively small. In particular, in Example 2, the decrease in discharge capacity was extremely small, and the discharge capacity did not drop rapidly. Moreover, in these things, the swelling of the container 17 etc. were not recognized. That is, it turned out that the thing of Examples 1-3 is equipped with the outstanding overcharge characteristic. On the other hand, in Comparative Examples 1 and 2, the reduction in discharge capacity was relatively large. In Comparative Example 5, the discharge capacity decreased most, and a rapid decrease in discharge capacity was also observed. Therefore, it was clear that Comparative Examples 1, 2, and 5 did not have overcharge resistance characteristics as excellent as those of Examples 1 to 3. Incidentally, for some of Comparative Example 5, swelling of the container 17 was observed. In Comparative Example 4, the viscosity of the non-aqueous electrolyte becomes too high (the viscosity is 16.4 mPa · s when measured at 28 ° C. with a vibration viscometer) and can be used as a non-aqueous electrolyte. There wasn't. In Comparative Example 3, the viscosity was 4.41 mPa · s when measured at 28 ° C. with the viscometer. However, since sulfolane (and EC) crystallizes at room temperature (23 ° C.), the viscosity. Regardless, it was difficult to use as a non-aqueous electrolyte. In that respect, for example, those of Examples 1 to 3, the non-aqueous electrolyte does not have too high a viscosity (when measured at room temperature under the above conditions, 6.1 mPa · s to 12.4 mPa · s). ), Suitable for use as a non-aqueous electrolyte.

  Further, in Example 2, the increase in internal resistance was relatively moderate, whereas in Comparative Example 5, a rapid increase in internal resistance was observed from a relatively early stage (see FIG. 3).

Therefore, according to the present embodiment, the following effects can be obtained.
(1) In the electric double layer capacitor 11 of the present embodiment, as a result of using the non-aqueous electrolyte solution having the above composition, the decomposition of PC is effectively suppressed even during overcharge, so that gas generation in the capacitor is suppressed. Is done. Therefore, the container 17 is prevented from being swollen and a rapid decrease in discharge capacity and a rapid increase in internal resistance are prevented. Accordingly, the overcharge resistance can be improved. In addition, a non-aqueous electrolyte solution containing PC and a quaternary ammonium salt in a smaller volume ratio than the PC has properties that are suitable for use as a non-aqueous electrolyte solution because the viscosity is not so high. be able to. Moreover, in this embodiment, both the positive electrode 21 and the negative electrode 22 shall consist of a mixture containing activated carbon and a carbon electrically conductive agent. And, it is considered that the fact that they function under the non-aqueous electrolyte having the above composition also contributes to improving the overcharge resistance.

  (2) Moreover, in the electric double layer capacitor 11 of the present embodiment, the volume ratio of PC and quaternary ammonium salt is set within the preferred range. Accordingly, it is possible to reliably improve the overcharge resistance while maintaining suitable properties as a non-aqueous electrolyte.

  (3) In the electric double layer capacitor 11 of this embodiment, since AB is used as the carbon conductive agent, the overcharge resistance can be more reliably improved. In addition, since the conductivity of the positive electrode 21 and the negative electrode 22 is improved, a large current discharge can be expected accordingly. In addition, since coconut shell activated carbon is used as the activated carbon, the overcharge resistance can be improved more reliably. Moreover, according to the electric double layer capacitor 11 of the present embodiment, the individual constituent materials are selected from those that can withstand the temperature during reflow (230 ° C. to 270 ° C.), so that they have excellent heat resistance. be able to. In other words, according to the present embodiment, it is possible to realize a high-quality reflow electric double layer capacitor 11 having excellent overcharge characteristics.

  In addition, you may change each embodiment of this invention as follows.

  In the above embodiment, the present invention is embodied as a coin-type electric double layer capacitor. Instead, as a cylindrical electric double layer capacitor, a square electric double layer capacitor, a laminate type electric double layer capacitor. It may be embodied.

  In the above embodiment, both the positive electrode 21 and the negative electrode 22 are made of a mixture containing coconut shell activated carbon and the carbon conductive agent AB, but only the positive electrode 21 or only the negative electrode 22 may be made of the above mixture. Good.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the respective embodiments described above are listed below.
(1) In any one of the above means 1 to 4, the electric double layer capacitor is an electric double layer capacitor for reflow.
(2) In any one of the above means 1 to 4, the electric double layer capacitor is a coin-type electric double layer capacitor for reflow.
(3) In an electric double layer capacitor containing a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte in a container, both the positive electrode and the negative electrode are from a mixture containing coconut shell activated carbon and acetylene black which is a carbon conductive agent. And the non-aqueous electrolyte contains propylene carbonate as an organic solvent and a quaternary ammonium salt in a volume ratio of 70:30 to 90:10.

DESCRIPTION OF SYMBOLS 11 ... Electric double layer capacitor 17 ... Container 21 ... Positive electrode 22 ... Negative electrode 23 ... Separator

Claims (4)

In an electric double layer capacitor containing a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte in a container,
At least one of the positive electrode and the negative electrode is made of a mixture containing activated carbon and a carbon conductive agent, and the non-aqueous electrolyte is composed of propylene carbonate as an organic solvent and a small amount of fourth in volume ratio than the propylene carbonate. An electric double layer capacitor comprising a quaternary ammonium salt.   2. The electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte contains the propylene carbonate and the quaternary ammonium salt in a volume ratio of 70:30 to 90:10.   The electric double layer capacitor according to claim 1, wherein the carbon conductive agent is acetylene black.   The electric double layer capacitor according to any one of claims 1 to 3, wherein the activated carbon is coconut shell activated carbon.

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