JPS625328B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electric double layer capacitor using a solid electrolyte with high output energy density and low leakage current. Conventionally, examples of this type of solid-state device that applies an electric double layer formed at the interface between a polarizable electrode and a solid electrolyte include RbAg ₄ I ₅ , NR ₄ Ag ₄ I ₅ ,
Some use a silver ion conductive solid electrolyte such as Ag ₃ SI or Ag ₆ I ₄ WO ₄ , carbon or silver chalcogenide for the polarizable electrode, and Ag for the counter electrode.
Since these elements use Ag and silver salt, they are expensive and are often used as functional elements such as potential storage elements, but are rarely used as capacitors. The present inventors previously used a Cu ⁺ ion conductive solid electrolyte consisting of a reaction product of cuprous halide and an alkyl halide of a pseudoadmantane compound, carbon or Cu ₂ S for the polarizable electrode, and Cu for the counter electrode. ₂ proposed a capacitor element using S (Japanese Patent Application Laid-Open No. 133756
Publication No.). This proposal uses Cu ⁺ ion conductive solid electrolyte as the solid electrolyte, and solves the problems associated with this, such as the fact that simply replacing Ag on the counter electrode with Cu would cause premature short circuits _. This problem was solved and the cost of the capacitor was successfully reduced. However, when Cu ₂ S is used as a counter electrode, the polarization caused by current application is smaller than that of Cu, and it has excellent reversibility, but it exhibits a potential of about 310 mV with respect to the Cu electrode.
On the other hand, carbon has a voltage of 0 to about 600mV with respect to the Cu electrode.
(up to the electrolyte decomposition potential), RAM (Random Access
It is disadvantageous that it can be used as a capacitor for back-up of memory, etc., since it has about half the voltage of Cu counter electrode, which is about 600mV. In addition, the above-mentioned solid electrolyte had the disadvantage that, especially when heated to high temperatures, cuprous halide redeposited, resulting in a large leakage current, and as a result, its potential holding ability was worse than that of a capacitor made of silver salt. . The present invention uses a mixture of Cu ₂ S and Cu for the counter electrode, and makes the mixing ratio appropriate to create an electric double layer capacitor with a high storage energy density, high voltage retention, high withstand voltage, and long life. This is what we provide. That is, _the present invention provides a polarizable electrode made of a mixture of activated carbon and a solid electrolyte, a polarizable electrode made of a mixture of Cu ₂ S, Cu, and a solid electrolyte, and a polarizable electrode made of a mixture of activated carbon and a solid electrolyte.
An electric double layer capacitor is constituted by a counter electrode having a weight ratio of Cu ₂ S/Cu of 20/80 to 40/60 and a solid electrolyte interposed between both electrodes. Here, as a solid electrolyte, 1/5 of Cu ⁺ ions
When using CuCl in which 1/4 or more and less than 1/3 of the Cl ^- ions are replaced with I ^- ions with cations selected from K ⁺ , Rb ⁺ , NH ₄ ⁺ , and N(CH ₃ ) ₄ ⁺ , leakage The current is small and the potential holding ability is even better. Hereinafter, the present invention will be explained in detail with reference to Examples. Figures 1 to 3 show configuration examples of the electric double layer capacitor of the present invention. Figure 1 shows the configuration of the element, Figure 2 shows the stacked configuration, and Figure 3 shows the configuration of the electric double layer capacitor in series. Shows the connected configuration. In Figure ₁ , 1 is the counter electrode, which is press-molded by mixing a solid electrolyte with a Cu ₂ S/Cu mixture ratio of 40/60 to 20/80 by weight. be. The mixing ratio of solid electrolyte is 10 to 20
Weight%. Reference numeral 2 denotes a collector of counter electrodes, which is formed on the counter electrode 1 by vapor deposition or sputtering of gold, chromium, or an alloy of both. 3
is a press-molded solid electrolyte, and details of this manufacturing method will be described later. 4 is a polarizable electrode formed from a mixture of 10 parts by weight of activated carbon and 90 parts by weight of solid electrolyte. Reference numeral 5 denotes a current collector of the polarizable electrode, which is formed on the polarizable electrode 4 by vapor deposition or sputtering of gold, chromium, or an alloy of both. Here, the breakdown voltage of a single cell is 600 mV, and a predetermined breakdown voltage can be obtained by series connection. First, a configuration example of stacked connection will be explained with reference to FIG. 6 is the above-mentioned element, and a plurality of these are stacked. When the contact between the elements 6 and between the elements 6 and the metal case 7 is made through Ag paste rather than through pressure contact, there is less variation in characteristics. Leads 8 and 9 are respectively attached to the metal case 7 and the current collector 5 of the terminal element by welding, soldering, or the like. 10 is packing rubber, and 11 is an insulating resin plate. Curl the open end of the metal case 7 inward, and attach the packing rubber 10 and the resin plate 11.
The elements 6 are brought into contact with each other by pressure. Next, an example of a configuration in which the devices are connected in series laterally will be described. In FIGS. 3a and 3b, 6 is the above-mentioned element. An element group in which the current collectors 2 and 5 of the element 6 are connected with the metal foil lead 12 by an appropriate method such as soldering, spot welding, or ultrasonic bonding is inserted between the thermoplastic resin films 13, and the surroundings are heat welded. It is sealed by. 14 is a terminal in which a part of the film is cut out to expose a part of the lead 12 to the outside. The structure shown in FIG. 2 has the advantage of being strong and compact, and the structure shown in FIG. 3 allows it to be made thin. Next, an example of a method for producing a solid electrolyte will be explained. Cuprous halides, which had been heated in advance at 140°C for 2 hours to remove moisture and excess halogen, and alkali halides (alkali ions include Rb ⁺ , K ⁺ ,
NH ₄ ⁺ , N(CH ₃ ) ₄ ⁺ ) as raw material, 1/5 of Cu ⁺ ions are Rb ⁺ , K ⁺ , NH ₄ ⁺ , N
They are mixed at a predetermined ratio so that they are substituted with cations selected from (CH ₃ ) ₄ ⁺ , and this mixture is formed into a disk shape, then placed in a degassed container and heated at 200° C. for 17 hours. This heating produces a new material that exhibits an X-ray diffraction pattern different from that of the raw material. This diffraction image differs depending on the type of alkali ion.
In the case of (CH ₃ ) ₄ ⁺ , the interplanar spacing was slightly wider, and in the case of K ⁺ , it was slightly narrower, but the crystal shapes were exactly the same. This seems to be because the ionic radii of these alkali ions are almost equal. On the other hand, due to I ^-ion
When the Cl ^- ion replacement ratio is less than 1/3, no residual CuI is observed, but when the replacement ratio is higher than that, no CuI remains.
CuI remains. The situation is shown in Figure 4. Residual CuI is associated with an increase in the electron transport number of the electrolyte, leading to an increase in capacitor leakage current and a decrease in potential holding ability. In addition, the substitution ratio of I ^- is 1/4
If it is less than that, the electron transport number of the electrolyte will increase due to CuCl. By the way, the following conditions are necessary for a backup capacitor. (i) High storage energy density (ii) Capable of supplying and discharging large current (charging time can be shortened and large current can be supplied) (iii) Low leakage current (high charge acceptance, (iv) The polarization of the counter electrode is small, and the oxidation-reduction potential is Cu
(because the element has a high breakdown voltage and voltage loss can be reduced) (v) These conditions can be satisfied over a wide temperature range (because the operating temperature range can be wide) (vi) It can be constructed from inexpensive materials Next, the effect of the present invention was demonstrated using a mixture of 0.24 parts by weight of activated carbon and 90 parts by weight of solid electrolyte as a polarizable electrode.
g, 0.2 g of solid electrolyte, and Cu ₂ S/Cu as the counter electrode.
The explanation will focus on an element with a withstand voltage of 3 V and a capacity of 0.6 F, which is made by molding 0.48 g of a mixture of 80 parts by weight of 40/60 and 20 parts by weight of solid electrolyte into a cylindrical shape with a diameter of 10 mm. In addition, the electrolyte is manufactured by the above-mentioned method and has the formula
A compound represented by Rb ₂ Cu ₈ I ₃ Cl ₇ was used. First, regarding (i) and (iii) above, it has the features shown in the following table. The following table shows the stored energy density and leakage current (r _L value) at the same capacity and the same applied voltage in comparison with aluminum electrolytic capacitors.

[Table] As is clear from this table, the electric double layer capacitor of the present invention has an energy density of about 200 times that of an aluminum electrolytic capacitor, a unit capacity of about 1/3000, and a leakage current per unit voltage. In addition, when the solid electrolyte of the present invention is used, compared to the conventional one using a heated reaction product of pseudoadmantane alkyl halide and cuprous halide, the solid electrolyte is more effective than the above (ii), (iii), and (v). ) has the following characteristics.
That is, the solid electrolyte of the present invention has an ionic conductivity two to three times higher than that of conventional electrolytes, and the electron transport number does not increase even at high temperatures. Therefore, as shown in FIG. 5, there is little deterioration in the potential holding ability even when a large current is applied, and as shown in FIG. 6, leakage current is small even at particularly high temperatures. Figure 5 shows the electrolyte at room temperature of ¹ mA,
The figure shows the voltage drop after the terminal voltage is 600 mV at each constant current of mA, 10 mA, 15 mA, and 20 mA, and the current is stopped. As is clear from Fig. 5, in the case of using a conventional electrolyte with poor ionic conductivity, the potential decreases significantly when a current of 10 mA is applied, whereas in the case of the device of the present invention, there is no significant drop in potential even when a current of 20 mA is applied. unacceptable. In addition, Figure 6 shows the leakage current of various electrolytes using a constant voltage of 600 mV and the value at which the current attenuates and becomes constant, where A is room temperature and B is 70 mV. The values are shown in °C. As is clear from FIG. 6, the leakage current using the conventional electrolyte is large and increases significantly at high temperatures, whereas the leakage current is small and increases little with temperature in the case of the present invention. A small leakage current also leads to good potential holding ability. Next, the relationship between the mixing ratio of Cu ₂ S and Cu in the counter electrode and characteristics such as breakdown voltage will be explained. In addition, Cu ₂ S−Cu
The mixing ratio of the mixture and the solid electrolyte is 80 parts by weight of the former and 20 parts by weight of the latter. Figure 7 shows the mixture ratio Cu ₂ S/Cu and capacitor breakdown voltage.
(A) and the number of cycles (B) until a short circuit occurs when repeated charging and discharging between a terminal voltage of 0 and a voltage corresponding to the withstand voltage (see figure) with a current of 10 mA are shown. Also, Figure 8 also shows the mixing ratio.
The graph shows the relationship between the terminal voltages reaching 560 mV (A) and 360 mV (B) when discharging at 30 μA after charging at a constant voltage of 600 mV. From Figures 7 and 8, at the opposite pole
It can be seen that by setting Cu ₂ S/Cu in the range of 20/80 to 40/60, not only can the withstand voltage be increased, but also the polarization of the opposite electrode is small, so the emitted energy is large and the life is long. As described above, the present invention enables charging and discharging of larger currents than conventional copper salt electrolytes using materials mainly made of inexpensive copper salts, and also has low leakage current, making it possible to supply large amounts of energy. It is possible to provide an electric double layer capacitor that can withstand repeated use over a long period of time, such as for backup and operation of actuators.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views showing an electric double layer capacitor according to the present invention, FIG. 3 a is a longitudinal sectional view also showing an electric double layer capacitor according to the present invention, and FIG. Figure 4 is an X-ray diffraction diagram showing the difference in the residual state of CuI depending on the electrolyte composition, and Figure 5 is a diagram showing the influence of the applied current on the potential holding ability of the electrolyte of the present invention in comparison with a conventional copper salt electrolyte. , Figure 6 shows the relationship between the type of electrolyte and leakage current, Figure 7 shows the relationship between the composition of the counter electrode, withstand voltage and cycle life, and Figure 8 shows the relationship between the composition of the counter electrode and the 30μA discharge duration. It is a figure showing a relationship. 1...Counter electrode, 3...Solid electrolyte, 4...Polarizable electrode, 6...Element.

Claims (1)

[Claims] 1. A polarizable electrode made of a mixture of activated carbon and a solid electrolyte, made of a mixture of Cu ₂ S, Cu, and a solid electrolyte, where the mixing ratio of Cu ₂ S and Cu is Cu ₂ S/Cu by weight. An electric double layer capacitor comprising a counter electrode having a ratio of 20/80 to 40/60 and a solid electrolyte interposed between both electrodes. 2 The solid electrolyte converts 1/5 of Cu ⁺ ions into K ⁺ ,
Claim 1 which is CuCl in which 1/4 or more and less than 1/3 of the Cl ^- ions are replaced with I ^- ions using cations selected from Rb ⁺ , NH ₄ ⁺ and N(CH ₃ ) ₄ ⁺ .
The electric double layer capacitor described in .