JP2010245067A - Electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor having high withstand voltage characteristics. <P>SOLUTION: This electric double-layer capacitor has a positive electrode, consisting of carbonaceous material and polytetrafluoroethylene, a negative electrode consisting of carbonaceous material and a fluorinated polymer having a C/F ratio of ≤100%, and a nonaqueous electrolytic solution consisting of a quaternary ammonium salt. This allows a difference between the decomposition voltage of binder components of the negative electrode and the decomposition voltage of binder components of the positive electrode to be increased, so that an electric double-layer capacitor with proper withstand voltage characteristics can be provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor comprising a pair of polarizable electrodes and an electrolytic solution.

  Conventionally, an electric double layer capacitor composed of a pair of polarizable electrodes and an electrolytic solution is composed of a pair of polarizable electrodes, a separator existing therebetween, and a current collecting layer of each polarizable electrode, As a typical polarizable electrode, activated carbon powder, activated carbon fiber or the like is used.

  In this method for producing a polarizable electrode, a conductive material such as acetylene black and a resin such as polytetrafluoroethylene or tetrafluoroethylene resin are added to and mixed with activated carbon powder, which is a typical polarizable electrode. Thereafter, a method of pressure molding and a method of applying this mixture to a current collector can be mentioned.

  The withstand voltage of such an electric double layer capacitor has a problem that the withstand voltage of the electric double layer capacitor is 3.0 V or less even though the withstand voltage of the organic electrolyte is 3.5 V. In order to solve such a decrease in withstand voltage, there has been an attempt to improve the electrolyte (Patent Document 1), but the problem that the withstand voltage of the electrolyte does not become the withstand voltage of the electric double layer capacitor is solved. Not. Furthermore, there is a problem that a life characteristic of 3.0 V cannot be obtained, and it cannot be used as an electric double layer capacitor.

JP 2007-043105 A

  The present invention aims to improve the withstand voltage by focusing on the binder in the electrode, and an object thereof is to improve the withstand voltage of an electric double layer capacitor using a conventional electrolytic solution.

  In order to solve the above problems, the electric double layer capacitor of the present invention comprises a positive electrode made of a carbonaceous material and polytetrafluoroethylene, and a carbonaceous material and a fluorinated polymer having a C / F ratio of 100% or less. It has a negative electrode and a non-aqueous electrolyte.

  The solvent of the non-aqueous electrolyte is sulfolane or a derivative thereof, or an ionic liquid.

  Further, the electrolyte of the nonaqueous electrolytic solution is a quaternary ammonium salt or a quaternary phosphonium salt.

  The fluorinated polymer having a C / F ratio of 100% or less is polyvinylidene fluoride.

  The present invention comprises a positive electrode made of a carbonaceous material and polytetrafluoroethylene (PTFE), a negative electrode made of a carbonaceous material and a fluorinated polymer having a C / F ratio of 100% or less, and a non-aqueous electrolyte. This has the effect that the withstand voltage characteristic is high.

The figure which shows the charging / discharging characteristic of the internal resistance regarding the electrode of this invention The figure which shows the charge / discharge characteristic of the capacity | capacitance in connection with the electrode of this invention

  Hereinafter, embodiments of the present invention will be described in detail.

  The inventors of the present application have disclosed that the withstand voltage of the electric double layer capacitor is 3.0 V or less, even though the decomposition voltage of the electrolyte using sulfolane or a derivative thereof or an ionic liquid as a solvent is 3.0 V or more. For some reason, we focused on the decomposition potential of the binder component of the electrode. In particular, it is known that PTFE decomposes at −4 V in a lithium salt solution, and attention is paid to the decomposition potential in a quaternary ammonium salt solution. And it became clear that the decomposition potential in a quaternary ammonium salt solution was lower than the decomposition potential in a lithium salt solution.

  By contrast with the decomposition potential of the latex binder, PTFE is used as the positive electrode binder, and a fluorinated polymer having a C / F ratio of 100% or less is used as the negative electrode binder. A double layer capacitor can be obtained. The C / F ratio indicates the ratio of C and F in the molecule of the fluorinated polymer.

  Furthermore, the life characteristics at high temperature, that is, the durability is also good.

  Here, examples of the fluorinated polymer having a C / F ratio of 100% or less include polyvinylidene fluoride, polyvinyl fluoride, and a tetrafluoroethylene-ethylene copolymer.

  As the metal current collector foil used for the electrode, an aluminum foil or an aluminum etching foil is used. As the aluminum foil, high-purity aluminum having a purity of 99.9% or more is used. As the thickness, an aluminum foil having a thickness of about 10 to 50 μm is usually used.

  For example, a paste obtained by mixing activated carbon powder, a conductive additive, a binder, and a solvent such as an organic solvent or water is applied to the metal current collector foil. Alternatively, the paste is formed into a sheet shape, and this sheet is pressed against a current collector to form a polarizable electrode.

The raw material of the activated carbon is plant-based wood, sawdust, coconut husk, pulp waste liquid, fossil fuel-based coal, heavy petroleum oil, or coal and petroleum-based pitch, petroleum coke obtained by pyrolyzing them. Activated carbon is obtained by carbonizing these raw materials and then activating them.
As the conductive assistant, carbon black and graphite, which are carbon materials having conductivity, can be used. Examples of the carbon black include acetylene black, ketjen black, channel black, furnace black, and thermal black. Among these, ketjen black is preferable. Examples of graphite include natural graphite and artificial graphite.

A capacitor cell is manufactured by making the electrodes face each other with a separator interposed therebetween, and the capacitor cell is impregnated with an electrolytic solution to obtain an electric double layer capacitor.

  In the present invention, as the electrolyte, sulfolane or a derivative thereof, or an ionic liquid is used as the main solvent, but carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate are used as the auxiliary solvent. Lactones such as γ-butyrolactone and δ-valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; Oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; methyl formate, methyl acetate, ethyl acetate, butyl acetate Organic acid esters such as chill, methyl propionate, and ethyl propionate; inorganic acid esters such as phosphoric acid triester and carbonic acid diesters such as dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; diglymes; triglymes; 3-methyl Oxazolidinones such as 2-oxazolidinone; sultones such as 1,3-propane sultone, 1,4-butane sultone, naphtha sultone, and the like can be used.

  Examples of the ionic liquid include N, N-dimethyl-N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate, 1-methyl-1-propyl-pyrrolidinium bis (trifluoromethanesulfonyl) imide, 1- Mention may be made of methyl-1-propyl-piperidinium bis (trifluoromethanesulfonyl) imide, N-methoxymethyl-N-methyl-pyrrolidinium tetrafluoroborate.

Examples of the electrolyte dissolved in the organic solvent include metal cations, quaternary ammonium cations, quaternary phosphonium cations, carbonium cations, and the like, BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , AsF ₆ ^{−, and the like.} SbF ₆ ⁻ , AlCl ₄ ⁻ , RfSO ₃ ⁻ , (RfSO ₂ ) ₂ N ⁻ , RfCO ₂ ⁻ (Rf is a fluoroalkyl group having 1 to 8 carbon atoms). Preferably, the electrolyte uses a quaternary ammonium cation or a quaternary phosphonium cation.

  The electric double layer capacitor of the present invention may have any shape such as a coin type, a wound type, and a laminated type. Such an electric double layer capacitor is obtained by, for example, cutting an electrode sheet into a desired size and shape, stacking or winding the separator sheet between both electrodes, inserting the electrolyte into the container, It can be produced by caulking the seal using a sealing plate or gasket.

The invention according to the embodiments of the present invention will be specifically described.
(Example)
(Production method of negative electrode)
Activated carbon, carbon black (CB), and polyvinylidene fluoride (PVDF) were weighed so as to have a weight ratio of 10: 1: 1, and mixed and dispersed in N-methylpyrrolidone to prepare a slurry. The obtained slurry was applied on an Al foil current collector and dried at 150 ^° C. to obtain an electrode body made of PVDF.
(Production method of positive electrode)
Activated carbon, CB, and polytetrafluoroethylene (PTFE) were mixed and kneaded at a weight ratio of 10: 1: 1, and then pressure-molded to obtain a sheet-like electrode body. The obtained sheet-like electrode body was stuck on an Al foil current collector using a conductive adhesive to obtain an electrode body made of PTFE. At this time, the thickness of the electrode body was adjusted so that the capacity per unit area of the electrode body was equal to the capacity per unit area of the electrode body formed from the latex.
(Capacitor cell fabrication method)
The electrode body made of PVDF is the negative electrode and the electrode body made of PTFE is the positive electrode, facing each other through a separator, dried in a vacuum at 150 ^° C., and then a mixed solvent of sulfolane and ethyl methyl carbonate containing 1M quaternary ammonium salt A capacitor cell was produced by impregnating as an electrolyte.
(Measurement method)
The obtained capacitor cell was sealed with a laminate film, and the capacity and internal resistance were calculated by charging and discharging in a voltage range of current density ² mAcm ⁻² and 0 to 3.0 V. Thereafter, a voltage of 3.0 V was applied in a constant temperature bath at 60 ° C., and a durability acceleration test was performed. In the acceleration test, the cells were taken out in 100, 300, 500, and 1000 hours, and the capacity and internal resistance were measured by the charge / discharge test described above.
(Comparative example)

An acceleration test was performed in the same manner as in Example 1 except that the negative electrode of Example 1 was changed to an electrode body made of PTFE.

The capacity charge / discharge test results are shown in FIG. 1 and the internal resistance charge / discharge test results are shown in FIG. As can be seen from the figure, both the capacitance and the internal resistance are better than the comparative example, and an electric double layer capacitor of 3.0 V is obtained.

Claims (4)

  An electric double layer capacitor having a positive electrode made of a carbonaceous material and polytetrafluoroethylene, a negative electrode made of a carbonaceous material and a fluorinated polymer having a C / F ratio of 100% or less, and a non-aqueous electrolyte.   The electric double layer capacitor according to claim 1, wherein the solvent of the non-aqueous electrolyte is sulfolane or a derivative thereof, or an ionic liquid.   The electric double layer capacitor according to claim 1 or 2, wherein the electrolyte of the non-aqueous electrolyte is a quaternary ammonium salt or a quaternary phosphonium salt. 4. The electric double layer capacitor according to claim 1, wherein the fluorinated polymer having a C / F ratio of 100% or less is polyvinylidene fluoride.