JPH0282608A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To reduce the change rate of an electrostatic capacity and to improve reliability by applying a polarizable electrode and a collecting electrode with a silicate compound conductive inorganic bond layer containing conductive substance such as silicate alkali, graphite, carbon black, etc. CONSTITUTION:Silicate compound conductive inorganic bond layers 12, 12' for applying both polarizable electrodes 11, 11' and conductive collecting electrodes 13, 13' are provided therebetween. The layers 12, 12' contain silicate compound substance and conductive substance. The silicate compound includes as main ingredient silicate alkali represented by a formula X2.SiO2 (where X is alkali metal, n is 0.5-8). The conductive substance used includes graphite, furnace black, etc., by a furnace type incomplete combustion method. The conductive inorganic bond is applied to one or both of the polarizable electrode or electrode material before impregnating with electrolyte, the collecting electrodes, both are superposed as they are or under pressure in an undried state, then dried, and solidified to form the layers 12, 12'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric double layer capacitor, and more particularly to an improved binder layer between a polarizable electrode and a current collecting electrode.

rPrior art] Electric double layer capacitors have a capacitance per unit volume that is several thousand times greater than that of conventional capacitors, so they can function as both a capacitor and a battery, such as As an example of the latter application, it is used as a backup power source.

As shown in FIG. 6, this electric double layer capacitor is constructed by placing a structure consisting of polarizable electrodes 2 and 3 through a porous separator 1 in a metal case 4, and attaching a metal cap 6 through a gasket 5. They are stacked and crimped to seal.

Further, as shown in FIG. 7, a conductive adhesive 7 is placed between the polarizable electrode 1 and the metal case 4 having the structure shown in FIG.
An example in which a conductive adhesive 8 is provided between the metal cap 6 and the metal cap 6 is also known. For example, JP-A No. 59-3915 and JP-A No. 62-2O0715 disclose that the conductive adhesive is a conductive material such as graphite or carbon blank, a binder such as cellulose or polyvinyl alcohol, and an organic solvent such as ethanol. The product prepared by mixing with is described.

[Problem to be solved by the invention]

However, in the case of the electric double layer capacitor shown in FIG. If a voltage is applied and held for 1000 hours), a problem arises in that the internal impedance increases.

In addition, the electric double layer capacitor with the structure shown in Figure 7 uses a conductive adhesive to bond the polarizable electrode and the metal case, and the polarizable electrode and the metal camp. Although the characteristics such as internal impedance were good, there was a problem that the internal impedance increased after the above-mentioned high-temperature load test. This is thought to be because when kept at high temperatures for a long period of time, the binder of the conductive adhesive is made of organic matter, which dissolves and swells in the electrolyte, increasing contact resistance to polarizable electrodes, metal cases, and metal camps. .

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention has been provided on both sides of a structure of a non-electronically conductive and ion-permeable porous separator, a rake, and a polarizable electrode provided on at least one side of the porous separator. An electric double layer capacitor having a conductive current collecting electrode, characterized in that a silicate compound-based conductive inorganic binder layer is provided between the polarizable electrode and the conductive current collecting electrode to bind both. It provides a double layer capacitor. Examples of the silicate compound-based conductive inorganic binder layer include those using a binder containing an alkali silicate and a conductive substance such as graphite or carbon black.

Next, the present invention will be explained in detail.

In the present invention, the silicate compound-based conductive inorganic binder layer contains at least a silicate compound material and a conductive material.

Examples of the silicic acid compound include those whose main component is an alkali silicate represented by the general formula X2O.nSiO2 (where X is an alkali metal and n is 0.5 to 8). Specifically, Na2O・n 5i02 (n=0.5-4.0), K2
O-n 5i02 (n=1.8-3.8), Li2O
-n 5i02 (n=3.0-8.0).

These n (molar ratio to alkali metal oxide) products are industrially produced and can be used at low cost. These alkali silicates can be used alone, but two or more types can also be used in combination.

Furthermore, the conductive substances used in the present invention include graphite,
Furnace blank made using the furnace incomplete combustion method,
Examples include lamp blanks, thermal blanks produced by endothermic decomposition methods, acetylene blacks produced by exothermic decomposition methods, channel blanks produced by contact incomplete combustion methods, disk blacks, and roll blacks. We also use spherical, amorphous, and fibrous materials made of carbonized polymer materials such as resol-type phenolic resin, resol-7 novolac-type phenolic resin, modified phenolic resin, rayon, polyacrylonitrile, and pitch-based resin. Furthermore, pure metals, alloy powders, and fibrous materials can also be used. These may be used not only alone but also in combination of two or more.

The solid composition ratio of the alkali silicate and the conductive substance is preferably 5 to 200% by weight, more preferably 10 to 150% by weight of the alkali silicate.

These silicic acid compounds and conductive substances are used as main components, and by adding at least a solvent as another component, a conductive inorganic binder is obtained. Water, an organic solvent that dissolves in water, and other organic solvents are used as the solvent, and the composition ratio in the binder is 4 parts by weight of alkali silicate, 1.2 M parts of the conductive material, and 11 M parts of water. is preferred.

The conductive inorganic binder produced in this way is applied to one or both of the polarizable electrode, the electrode material before it is impregnated with electrolyte, and the current collecting electrode, and both are left in an undried state either as is or by applying pressure. They are stacked together and then dried and solidified to form a silicate compound-based conductive inorganic binder layer. The drying temperature in this case is preferably from room temperature to 200°C, more preferably from 70 to 150°C.

The thickness of the conductive inorganic binder layer is preferably 5 to 50 μm.

Application methods for applying the conductive inorganic binder include a screen printing method, a roller transfer method, and a spray method. At this time, an organic solvent such as alcohol or cellosolve may be added to improve wetting of the coated surface.

In the present invention, the polarizable electrode contains at least activated carbon and an electrolytic solution, and optionally contains a conductive substance and a binder. Regarding these activated carbon, electrolytic solution, conductive substance, and binder, see Japanese Patent Application Laid-open No. 190318/1982 and Japanese Patent Application No. 2009216/1983! Examples include those described in Book III.

[Effect]

The conductive inorganic binder layer provided between the polarizable electrode and the current collecting electrode uses an inorganic binder, so it will not melt or swell even if it comes into contact with the electrolyte at high temperatures and for long periods of time. It can be held stably without any problems.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

Example 1 Activated carbon 100M parts, carbon blank 2O parts by weight, 4
15 parts by weight of fluoroethylene resin diversion and 10 M parts of ethanol were added and kneaded, and the kneaded product was formed into a sheet using a molding machine to form electrode materials 11a for two polarizable electrodes as shown in FIG. , ll'a was created. The following conductive inorganic binder was applied to one side of each of these electrode materials by screen printing to form conductive inorganic binder coating layers 12a and 12'a.

Sodium silicate No. 3 10 parts by weight (Sodium silicate (Na2O・nSiO2: n=3.12) min. 40
% and the rest is water) (manufactured by Nihon Kagaku Kogyo ■) 2 parts by weight of carbon black (trade name: Toka Blank Iru 5500) 5 parts by weight of water (/IJ's Co., Ltd.) Next, conductive inorganic binder was added to the metal case 13. The conductive inorganic binder coating layer 12'a is overlaid on the coating layer 12a and the metal cap 14, respectively, and is bonded by drying at 90° C. for 1 hour. In this way, a pair of capacitor members 15.
Make 15゛.

Electrode material 12a of these capacitor members 15.15"
, electrolyte solution (propylene carbonate containing 0.5 molar concentration of tetraethylammonium perchlorate) in 12゛a.
is impregnated in vacuum (under 10 torr for 1 hour), and as shown in FIG. 1(b), a porous separator 14 made of polypropylene of 0.1 and 1.0 mm, which has been previously impregnated with the same electrolytic solution as above, is sandwiched therebetween.

In this way, as shown in FIG. 1(b), the polarizable electrodes 11.11' on both sides of the porous separator 14 are connected to the metal case 13 by the conductive inorganic binder layer (20 μm thick) 12.12'. , and a metal cap 13°, and their peripheral sides are caulked and sealed via a gasket 16 to complete an electric double layer capacitor. In this case, the metal case and metal cap also serve as current collecting electrodes.

This electric double layer capacitor was subjected to a high temperature load test (7
A voltage of 2.4 V was applied for 1000 hours at 0° C.), and the internal impedance (Ω) and capacitance of the electric double layer capacitor before and after loading for 1000 hours were determined as follows.

That is, to measure capacitance, a sample electric double layer capacitor is connected to sample terminals 17 and 18 of the measurement circuit shown in FIG. In this state, connect the switch to the terminal 19 side, and after reaching 2.4V, switch to constant voltage charging,
Charge for 30 minutes. After that, switch the switch to the terminal 2O side and discharge at a constant current of 5 mA as shown in Figure 4.
The time T1 when the voltmeter 21 reached 1.5V, and 1. The time T2 when the temperature becomes OV is measured. Calculate the capacitance from these measured values using the following formula.

i: Current (Amp) Tl, T2: Time (minutes) The rate of change (%) of the capacitance thus obtained after the high temperature load test with respect to before the test was determined and shown in Table 1.

In addition, when measuring the internal impedance, the electric double layer capacitor of the above sample was heated at 70℃ and 2.4℃.
v, test of applying voltage for 1000 hours (high temperature load test)
A commercially available LCR meter (YHP4274
A) was used for measurement at IKHz, 10 mA, and room temperature, and the results are shown in Table 1.

Example 2 In Example 1, Na2O.0.
An electric double layer capacitor was produced in the same manner except that 55i02 was used, and the results obtained by measuring in the same manner as in Example 1 are shown in Table 1.

Example 3 In Example 1, Na2O.4.
O5i02 is used, and phenolic carbon fiber (manufactured by Nippon Kynor) is used instead of carbon black as the conductive material.
An electric double layer capacitor was produced in the same manner except that 1 was used, and the results were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 In Example 1, potassium silicate (K
An electric double layer capacitor was prepared in the same manner as in Example 1, except that phenolic carbon fiber (manufactured by Nippon Kynor) was used instead of the carbon blank as the conductive material. The results obtained are shown in Table 1.

Example 5 An electric double layer capacitor was produced in the same manner as in Example 1 except that 0.2 parts by weight of carbon blank was used instead of 2 parts by weight, and the results were obtained by measuring in the same manner as in Example 1. Shown in Table 1.

Example 6 In Example 1, the conductive inorganic binder sodium silicate 3
An electric double layer capacitor was produced in the same manner as in Example 1, except that colloidal silica (product name Silica Doll II, manufactured by Nippon Chemical Industry @, whose main component is sodium silicate) was used instead of No. The measured results are shown in Table 1.

Example 7 In Example 1, the conductive inorganic binder sodium silicate 3
In place of the number, organosol (product name 03CAL: ethanol liquid whose main component is sodium silicate manufactured by Catalysts and Chemicals)
An electric double layer capacitor was prepared in the same manner except that ethanol was used instead of water, and the results were measured in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 1 An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the silicate compound-based conductive inorganic binder layer was not provided, and the results obtained by measuring in the same manner as in Example 1 are shown in Table 1. Shown below.

Comparative Example 2 Same as Example 1 except that a conductive organic adhesive (a mixture of 3 parts by weight of carbon black, 7 parts by weight of cellulose, and 5 parts by weight of ethanol) was used instead of the silicate compound-based conductive inorganic binder. Fabricate an electric double layer capacitor using
Table 1 shows the results obtained by measuring in the same manner as in Example 1.

Table 1 Example 8 Similarly to Example 1, electrode materials 22a and 22'a of polarizable electrodes are prepared as shown in FIG. Next, a cylindrical unvulcanized insulating butyl rubber Gaskent (outer diameter 15 cm, inner diameter 10 mm, thickness 0.5 tm 24.24') and an unvulcanized conductive butyl rubber sheet made by kneading carbon black and butyl rubber. (Diameter 150, thickness 0.2um) 2
5.25' and a porous separator 26 made of polypropylene (diameter 13n, thickness 0.1 mm) are prepared.

After making such preparations, the electrode materials 22a, 22
A conductive inorganic binder is applied to one side of each of the conductive inorganic binders 27a and 27a in the same manner as in Example 1.
These coating layers are concentrically stacked on each of the unvulcanized conductive butyl rubber sheets 25a and 25'a and dried at 70° C. for 1 hour.

As a result, the layered electrode and the unvulcanized conductive butyl rubber sheet are bonded together.

Next, the gaskets 24 and 24' are placed on each of the unvulcanized conductive butyl rubber sheets 25a and 25'a to which the polarizable electrodes are bound, so that their circumferential surfaces coincide with each other, and the respective electrode materials 22a are placed. , 22”a was vacuum impregnated with electrolyte (30% sulfuric acid solution) (10-2
Incubate under rr for 1 hour). Next, these were placed facing each other with the unvulcanized conductive butyl rubber sheet outside through the porous separator 26, and were further vulcanized by being left at 120°C for 5 hours under a pressure of 5 kg/ctA. be done. As a result, as shown in FIG. 2(b), a basic cell is completed in which the current collecting electrode 25, 25' and the polarizable electrode 22, 22' are bound together by the conductive inorganic binder layer 27, 27'.

Although not shown, six of the basic cells described above are stacked on a sealing container consisting of two upper and lower members made of stainless steel, and the ends of these upper and lower members are caulked via a polypropylene gasket to produce an electric double layer capacitor.

This electric double layer capacitor was subjected to a high temperature load test (7
The internal impedance (Ω) and capacitance were measured before and after applying a voltage of 5.5 V at 0° C. for 1000 hours, and the rate of change in capacitance was determined in the same manner as in Example 1. The results are shown in Table 2.

The internal impedance was determined in the same manner as in Example 1, and the capacitance was determined by using the circuit shown in Figure 3 and charging the sample electric double layer capacitor with a constant voltage of 5.5V for 30 minutes as shown in Figure 5. After that, discharge at a constant current of 5 mA, and 3. O
The time T when the voltage became V and the time T2 when the voltage became 2.5 V were measured and calculated from the formula used in Example 1.

Comparative Example 3 An electric double layer capacitor was produced in the same manner as in Example 8 except that the conductive inorganic binder layer was not provided, and the results obtained in the same manner as in Example 8 are shown in Table 2.

From the above results, it can be seen that all of the examples have not only a small rate of change in capacitance, but also a small rate of increase in internal impedance after the high-temperature load test.

〔Effect of the invention〕

According to the present invention, since the polarizable electrode and the current collecting electrode are bound together by the silicate compound-based conductive inorganic binder layer, the silicate compound-based conductive inorganic binder layer is stable to heat, and Since it does not dissolve or swell in the electrolytic solution, it is possible to reduce the increase in internal impedance even when used at high temperatures for a long period of time, thereby reducing the rate of change in capacitance and ensuring high reliability.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view showing the manufacturing process in the method for manufacturing an electric double layer capacitor according to an embodiment of the present invention, FIG. 1(b) is a completed view, and FIG. A sectional view showing the manufacturing process in the method for manufacturing an electric double layer capacitor according to the second embodiment, Figure (b) is a completed diagram, Figure 3 is a capacitance measurement circuit diagram of the capacitor, and Figure 4 is one operation thereof. FIG. 5 is an explanatory diagram of another operation, FIG. 6 is a sectional view of a conventional electric double layer capacitor, and FIG. 7 is a sectional view of another conventional electric double layer capacitor. In the figure, II, 11', 22.22' are polarizable electrodes, 1
2.12' and 27.27' are silicate compound-based conductive inorganic binder layers, 13 is a metal case that also serves as a current collecting electrode, and 13'
25.25゛ is the current collecting electrode. September 20, 1988

Claims (4)

[Claims] (1) An electric double layer capacitor having conductive current collecting electrodes on both sides of a structure consisting of a non-electronically conductive and ion permeable porous separator and a polarizable electrode provided on at least one side of the porous separator. An electric double layer capacitor characterized in that a silicate compound-based conductive inorganic binder layer is provided between the polarizable electrode and the conductive current collecting electrode to bind them together. (2) The electric double layer capacitor according to claim 1, wherein the silicate compound-based conductive inorganic binder layer is formed using a binder containing an alkali silicate and a conductive substance. (3) Alkali silicate has the general formula X_2O・nSiO_2(
3. The electric double layer capacitor according to claim 2, wherein X is an alkali metal and n is 0.5 to 8. (4) The electric double layer capacitor according to claim 2 or 3, wherein the conductive substance is made of one or more of graphite, carbon black, carbonaceous material obtained by carbonizing a synthetic polymer, or metal.