JP2008010613A - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor that uses an electrolyte formed of ionic liquid, which is found out as a suitable electrolyte that enables the electric double layer capacitor to display a practical lifetime performance from an ionic fluid group where N, N-dialkyl pyrrolidinium serves as a cation. <P>SOLUTION: The electric double layer capacitor uses a non-aqueous electrolyte that is formed of only an ionic fluid where N-methyl-N-propyl pyrrolidinium serves as a cation and bis(trifluoromethane sulfonyl)imido serves as an anion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an electric double layer capacitor using a non-aqueous electrolyte.

  In recent years, various ionic liquids have been studied as non-aqueous electrolytes for electricity storage devices. Among these ionic liquids, an ionic liquid having N-methyl-N-propylpyrrolidinium as a cation has excellent reduction stability, so that it can be used as a solvent for an electrolytic solution of a secondary battery such as a lithium ion battery. It is known that it can be performed (see, for example, Patent Document 1).

  Furthermore, the ionic liquid group containing N-methyl-N-propylpyrrolidinium and having N, N-dialkylpyrrolidinium as a cation is known to exhibit high ionic conductivity and a wide potential window. (For example, refer to Patent Document 2).

  However, when an ionic liquid is used as an electrolytic solution of an electricity storage device, even if the electrolytic solution made of the ionic liquid has high ionic conductivity, even if the initial performance of the capacitor using the electrolytic solution is good, It is not clear if it is a capacitor with practical life performance alone. Depending on the composition of the electrolytic solution, such as the combination of the cation and anionic species of the ionic liquid constituting the electrolytic solution, the ion concentration, the viscosity, and the presence or absence of a solvent, it may not be a practical electricity storage device.

JP 2003-331918 A JP 2005-139100 A

  The present invention has been made in view of such circumstances, and an electrolytic solution in which an electric double layer capacitor can exhibit practical life performance is selected from an ionic liquid group having N, N-dialkylpyrrolidinium as a cation. An object of the present invention is to find an appropriate ionic liquid as a liquid and to provide an electric double layer capacitor using an electrolytic solution composed of the ionic liquid.

  That is, according to the present invention, in an electric double layer capacitor using a non-aqueous electrolyte, the non-aqueous electrolyte is an ion having N-methyl-N-propylpyrrolidinium as a cation and bis (trifluoromethanesulfonyl) imide as an anion. An electric double layer capacitor comprising only a liquid.

  The electric double layer capacitor of the present invention uses an electrolytic solution consisting only of an ionic liquid having N-methyl-N-propylpyrrolidinium as a cation and bis (trifluoromethanesulfonyl) imide as an anion. It has excellent lifetime performance as a capacitor and is very useful.

Hereinafter, the present invention will be described in more detail.
The electric double layer capacitor according to the present invention is an electric double layer capacitor using a non-aqueous electrolyte, wherein the non-aqueous electrolyte uses N-methyl-N-propylpyrrolidinium as a cation and bis (trifluoromethanesulfonyl) imide. It consists only of an ionic liquid as an anion.

In general, when the viscosity of the electrolytic solution is considered as one of the factors affecting the performance of the capacitor, an electrolytic solution whose viscosity is reduced by mixing a liquid organic solvent at room temperature is used. However, in the electric double layer capacitor of the present invention, the mixing of the organic solvent reduces the life performance of the capacitor.
Therefore, the non-aqueous electrolyte composition in the electric double layer capacitor of the present invention includes N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide as a main component and an organic solvent that is liquid at least at room temperature. Absent.

  The configuration of the electric double layer capacitor according to the present invention comprises a pair of polarizable electrodes and a separator interposed between the polarizable electrodes, using the non-aqueous electrolyte described above.

Here, as the polarizable electrode, an electrode obtained by applying a polarizable electrode composition containing a carbonaceous material and a binder polymer on a current collector can be used.
The carbonaceous material is not particularly limited, and plant-based wood, sawdust, coconut husk, pulp waste liquid, fossil fuel-based coal, heavy petroleum oil, coal obtained by pyrolyzing these, or Petroleum pitch, tar pitch fiber, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, polycarbodiimide resin, liquid crystal polymer, plastic waste, waste Examples thereof include tires and other raw materials that are carbonized, and activated carbon produced by further activating them.

In addition, there is no limitation in particular as the method of the said activation process, Although various methods, such as chemical activation and a steam activation method, can be used, The activated carbon obtained by the chemical activation using KOH is compared with a steam activation product. It is preferable because the capacity tends to be large. In addition, the carbonaceous material has various shapes such as crushing, granulation, granule, fiber, felt, woven fabric, and sheet shape, any of which can be used in the present invention.

  Furthermore, a conductive material can be added to the carbonaceous material. The conductive material is not particularly limited as long as it can impart conductivity to the carbonaceous material. For example, carbon black, ketjen black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, titanium oxide, Examples thereof include metal fibers such as ruthenium oxide, aluminum, and nickel, and these can be used alone or in combination of two or more. Among these, ketjen black and acetylene black which are a kind of carbon black are preferable.

Here, the average particle diameter of the conductive material is not particularly limited, but is 10 nm to 10 μm, preferably 10 to 100 nm, more preferably 20 to 40 nm, and in particular, 1 of the average particle diameter of the carbonaceous material. / 5000 to 1/2, and particularly preferably 1/1000 to 1/10.
Also, the amount of addition is not particularly limited, but in consideration of the capacitance, the effect of imparting conductivity, etc., 0.1 to 20 parts by weight, preferably 0. 5 to 10 parts by weight.

As the binder, various known binders can be used. For example, polytetrafluoroethylene, polyvinylidene fluoride, polyamideimide, carboxymethylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, and the like. These can be used alone or in combination of two or more. Among these, polyvinylidene fluoride and polyamideimide are particularly preferable from the viewpoints of the applicability of the polarizable electrode, the binding force to the current collector, and the electrode resistance at the end of durability.
The addition amount of these binders is preferably 0.5 to 20 parts by mass, particularly 1 to 10 parts by mass with respect to 100 parts by mass of the carbonaceous material.

As the current collector, those usually used for electric double layer capacitors can be arbitrarily selected and used, but it is preferable to use an aluminum foil, particularly an aluminum foil whose surface is subjected to etching treatment. Further, regarding the negative current collector, in addition to the above, a copper foil, a nickel foil, or a metal foil whose surface is formed of a copper plating film or a nickel plating film may be used.
As the shape of the foil constituting the current collector, various shapes such as a general foil shape, a mesh shape in which holes are formed, and a three-dimensional mesh shape can be appropriately employed. The thickness of the current collector is usually about 10 to 200 μm, but considering the conductivity and strength of the current collector, it is preferably 15 to 100 μm and more preferably 20 to 70 μm.

  A polarizable electrode is formed by forming a coating film by applying a slurry obtained by adding a solvent to the polarizable electrode composition described above on both or one side of a current collector, and then removing the solvent by heating and drying. . The thickness of the single-sided polarizable electrode formed on the current collector is preferably 20 to 200 μm, more preferably 30 to 150 μm, still more preferably 40 to 120 μm.

  Examples of the separator for the electric double layer capacitor of the present invention include those generally used as a separator for an electric double layer capacitor. Examples of the separator include glass fiber, polyolefin, polyamideimide, polyester, fluororesin, and cellulose. Can be mentioned. Specifically, a porous film made of polyolefin such as polyethylene and polypropylene, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, etc .; polyolefin, polyester nonwoven fabric; glass fiber sheet, cellulose; cellulose paper, etc. may be used. it can. You may use the thing containing an insulating inorganic fine particle and an inorganic filler.

  The thickness of the separator is usually 5 to 200 μm, preferably 10 to 100 μm, and more preferably 20 to 60 μm. When the thickness is less than 5 μm, the leakage current may increase, and when the thickness is more than 200 μm, the energy density may decrease and the internal resistance may increase.

The structure and configuration of the electric double layer capacitor of the present invention includes the above-described pair of current collectors, positive and negative polarizable electrodes, a separator interposed between these electrodes, and at least the positive and negative polarizable electrodes and the separator described above. There is no particular limitation as long as it is configured to include an electrolytic solution. For example, various known structures such as a multilayer capacitor and a coin capacitor can be employed.
In addition, the electrolyte solution should just impregnate at least an electrode group, for example, electrolyte solution may be filled in the exterior container to such an extent that an electrode group is immersed in this.

  The electric double layer capacitor of the present invention is a memory backup power source for mobile phones, notebook computers and portable terminals, power sources for mobile phones and portable audio equipment, power supplies for instantaneous power failures such as personal computers, solar power generation, It can be suitably used for various low current power storage devices such as a load leveling power source by combining with wind power generation. An electric double layer capacitor that can be charged and discharged with a large current can be suitably used as a large current storage device that requires a large current, such as an electric vehicle or a power tool.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
Activated carbon powder (average particle size 7 μm, specific surface area 1800 to 2000 m ³ / g), conductive carbon, polyvinylidene fluoride resin (hereinafter referred to as PVdF), N-methyl-2-pyrrolidone (hereinafter referred to as NMP), activated carbon powder : Conductive carbon: PVdF: NMP = 85: 8: 7: 230 The mixture was made into a paste to prepare a polarizable electrode composition for an electric double layer capacitor. The obtained paste-like polarizable electrode composition was applied to an aluminum substrate with a doctor blade and dried at 80 ° C. for 4 hours. Thereafter, this was rolled and further dried under reduced pressure at 150 ° C. for 16 hours to obtain a polarizable electrode original plate. This polarizable electrode original plate was cut into an electrode area of 800 mm ² to form a polarizable electrode, and a cell was assembled with a polyethylene separator interposed between the pair of polarizable electrodes. Without using an organic solvent, N-methyl-N-propylpyrrolidinium bistrifluorosulfonylimide (manufactured by Kanto Chemical Co., Inc.) (hereinafter referred to as P13TFSI) was directly poured into the cell as an electrolytic solution. An electric double layer capacitor was obtained.

[Comparative Example 1]
In Example 1, an electric double layer capacitor was obtained in the same manner as in Example except that a propylene carbonate solution containing P13TFSI having a concentration of 1.0 mol / L as an electrolyte (hereinafter referred to as P13TFSI / PC) was used.

The following durability tests were conducted on the capacitors obtained in the above examples and comparative examples. The results are shown in Table 1.
[Durability test]
In a high temperature bath at a temperature of 70 ° C., constant voltage charging was performed with a set voltage of 3.0 V and a holding time of 1000 hours, and the subsequent capacitance was compared with the initial value.

As shown in Table 1, the electric double layer capacitor using the electrolyte solution of the propylene carbonate solution obtained in Comparative Example 1 had no problem in the initial performance, but the decrease in the capacity maintenance rate by the durability test was very large. It is not a capacitor with practical life performance. On the other hand, it can be seen that the electric double layer capacitor using the electrolytic solution made only of P13TFSI without the propylene carbonate obtained in Example 1 has a capacity retention rate of 82% and has an excellent life performance. .

Claims (1)

In an electric double layer capacitor using a non-aqueous electrolyte, the non-aqueous electrolyte consists only of an ionic liquid having N-methyl-N-propylpyrrolidinium as a cation and bis (trifluoromethanesulfonyl) imide as an anion. An electric double layer capacitor characterized.