JPS5953693B2 - Manufacturing method of electric double layer capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electrical device that is made small and thin by utilizing the electric double layer capacitance, which generates at the interface between an activated carbon electrode with a large specific surface area and a solid electrolyte, and has a small leakage current and a large capacity. Regarding the manufacturing method of double layer capacitors, by forming both the solid electrolyte layer and the bonded electrode layer by hot pressing, the ton δ can be improved to surpass that of currently used electrolytic capacitors.
It is an attempt to improve the

Conventionally, the capacitors used in general are:
Some applied space charges distributed on the surface of semiconductor materials such as Si, and others applied charges induced on both sides of oxide dielectrics such as AI, Ta, and Ti.

Among these, capacitances with small capacitances of nF or less are integrated on the same substrate of circuits or components, as seen in the example of integrated circuits, but capacitances with larger capacitances have larger dimensions. Therefore, it is difficult to integrate them into one piece, so they are used as a single component externally attached to these boards.

Recently, electronic devices are becoming smaller and thinner, as seen in the examples of radio receivers and desktop computers.
The large capacity capacitors used for this purpose are also required to be smaller and thinner.

On the other hand, recently, Ag5S■, Rb, A
Formed at the interface between silver salt electrolytes such as Ag6I4WO4 and copper salt electrolytes such as the reaction products of cupric halides and halogenated methyltriethylenediamine or hexamethylenetetramine and activated carbon electrodes. Elements that apply large electric double layer capacitance have been developed, but the operating voltage range is low at 0.67 V for silver salt and 0.72 V for copper salt, and single cells are difficult to use in electronic circuits. For reasons such as the fact that the required withstand voltage of several volts cannot be satisfied, or simply forming a thin solid electrolyte or carbon electrode layer would result in a large tan δ, capacitors that are smaller and thinner are needed. Its practical application was delayed.

Among the above-mentioned reasons, the breakdown voltage can be solved by directly connecting multiple single cells, but in exchange, the problem of further increase in tan δ arises, and basically there are no improvements regarding tan δ. progress was slow.

By the way, screen printing is usually used as a means to thinly apply a coatable material into a desired shape.
If the solid electrolyte layer and carbon electrode layer constituting the capacitor are formed by screen printing and then simply drying and curing according to a conventional method, tan δ remains large.

This is thought to be due to the fact that in each of the solid electrolyte layer and the carbon electrode layer, the binder made of resin gets into the spaces between the particles of the solid electrolyte powder or activated carbon powder, which are the main components thereof.

In the present invention, by forming each of the solid electrolyte layer and the carbon electrode layer by hot pressing, tan δ
This is based on the discovery that the series resistance, which is an element of

The present invention will be explained in detail below using the drawings.

Figure 1 shows 7CuBr-C6H1□N2(CH3Br)2
15wt% per 1g of copper ion conductive solid electrolyte powder
The binder and 0.4 cc of solvent were added and kneaded to make three types of ink with different types of binders as described below, and each was placed in a mold with a diameter of 1 cm to a thickness of about 2 mm. After evaporating the solvent at 80°C, hot pressing was performed at the maximum compression molding temperature of each binder and a pressure of 300 kg/cm2. This figure shows the relationship between the value of specific resistance measured under alternating current and pressing time.

Here, the types of binders and their respective maximum compression molding temperatures are shown together with the symbols in the figure.

(Binder) (,==BE" (symbol) Molding temperature) Xylene or resol 200°C 1-based resin Polyester resin 180°C 2 Epoxy-based resin 160°C 3. Next, Figure 2 shows a similar hot press. The relationship between pressing pressure and specific resistance when pressed for 30 minutes is shown.

Further, FIG. 3 shows the relationship between the specific resistance and the amount of binder obtained by preparing inks with different amounts of each binder and hot pressing them at a pressure of 300 kg/cm2 for 30 minutes.

The amount of binder here is based on the ink minus the solvent.

Note that the symbols in each of FIGS. 2 and 3 are common to those in FIG. 1.

As is clear from FIG. 1, if the pressing time is 10 minutes or more, the specific resistance of any type of binder reaches a sufficiently low value.

Next, regarding the relationship with press pressure, as shown in Figure 2, if the pressure is 200 kg/cm' or more,
Similarly, any type of binder has a sufficiently low specific resistance.

Note that the value obtained by extrapolating the curve for each type of binder to the position of press pressure 0 can be regarded as the specific resistance value when hot pressing is not performed but merely heat curing is performed.

Regarding the amount of binder, as is clear from FIG. 3, regardless of the type of binder, if the amount is 20 wt% or less, the individual resistance value will be at a level close to the respective minimum.

As explained above, the solid electrolyte layer is made by adding a binder to the solid electrolyte powder so that the ratio is 20 wt% or less regardless of the type of binder, and then adding a solvent to make the ink. Apply to the object to be coated, dry the solvent, and then apply 2
By hot pressing at a pressure of 00 kg/cm2 or more, the specific resistance value can be reduced.

The resistivity value obtained in this way is, of course, much smaller than that obtained by simply heating without applying pressure as described above.

The compression rate of the applied ink in the thickness direction in the hot press as described above was about 50%.

Next, in the case of a solid electrolyte layer, in an electric double layer capacitor, the carbon electrode layer, which faces each other with a solid electrolyte layer in between and is a cause of the tan δ sky like the solid electrolyte layer, is formed using hot pressing. A similar study was carried out, and the results were almost the same in the case of a solid electrolyte layer, and it was found that the specific resistance value could be sufficiently reduced even in the formation of a carbon electrode layer by using hot pressing.

The composition of the ink used to form the active carbon electrode layer here is the same as that in the ink for the solid electrolyte layer described above, in which a part of the solid electrolyte powder is replaced with activated carbon powder.

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 4 and 5 show an electric double layer capacitor manufactured according to the present invention, and 4 and 5 are substrates, one of which may also be used as a circuit board or a component board.

Moreover, by doing so, the capacitor can be integrated into a circuit board or a component board.

As the material, ceramics with excellent insulation and heat resistance, or thermosetting resins such as phenol, polyester, and polyimide are used.

Reference numerals 6 and 7 denote metal electrodes formed by independently depositing a plurality of metal electrodes on each of the support substrates 4 and 5 by vapor deposition, sputtering, or electroless plating, and are made of Ni, stainless steel,
Chemically and electrochemically stable metals such as Au and Pt are used.

The reason why such a stable metal is used is especially to prevent reactions caused by the solid electrolyte and to maintain stable performance of the capacitor.

Note that as long as the thickness of the metal electrode is 1 μ or more, its own resistance will not be a problem.

Reference numerals 8 and 9 designate carbon electrode layers formed by applying carbon electrode ink on metal electrodes 6.7 by screen printing, drying, and solidifying through hot pressing.

Drying after application was performed with hot air at 80°C, and hot pressing was performed at 200°C and a pressure of 300 kg/cm2 for 10 minutes.

The ink for the carbon electrode is a mixture of solid electrolyte powder of silver salt or copper salt and activated carbon powder at a ratio of 30 wt%.
A solution of 0.10 g of resol adhesive dissolved in 0.4 cc of butyl cellosolve was added to 90 g and kneaded.

The solvent used for preparing the ink is preferably one that is chemically stable and has a boiling point of 120 to 200° C., since the viscosity does not change during the operation.

In addition to the above-mentioned butyl cellosolve, there are cyclohexanol, benzyl alcohol, and diacetone alcohol that satisfy these conditions, and there is no difference in performance no matter which one is used.

Regarding the amount of adhesive added, a small resistivity value can be obtained if the binder is added to the mixture of solid electrolyte powder and activated carbon powder at a ratio of 20 wt% or less as explained in Figure 3. When looking at the state after the carbon electrode layer 8.9 is formed, if the amount of binder added is less than 5 wt %, the adhesive strength becomes poor and it becomes easy to fall off.

Therefore, it is recommended that the amount of the binder added be in the range of 5 to 20 wt%.

It is desirable that the solid electrolyte has a specific resistance of 30Ω・cm or less, and examples of such solid electrolytes include Ag3SI and MAg.
4I5 (M: K, Rb, NR4 where R is an alkyl group), Ag6I4WO4, Ag19■1. P2O7
, MCN.4AgI (M: to, Rb), and copper salt solid electrolytes which are the reaction products of CuBr and N-methylhexamethylenetetramine bromide or NN'methyltriethylenediamine bromide.

Note that the amounts of the solvent and binder added and the solid electrolyte described above are also common to the formation of the solid electrolyte layer described later.

Here, the area and thickness of the carbon electrode layer will be further explained.

According to a separate experiment, the amount of carbon electrode layer controls the capacitance of the capacitor.

FIG. 6 shows the relationship between the weight and capacity of the carbon electrode when the solid electrolyte mixed with activated carbon powder is a silver salt and a copper salt, respectively.

In the figure, 10 is RbAg4■, in the case of silver salt solid electrolyte, 11 is 7CuBr-C6H1□N2 (CH3Br)
This is the case of a copper salt solid electrolyte.

As is clear from the figure, the capacitance is linearly proportional to the electrode weight in either case of silver salt or copper salt.

From another perspective, this is considered to be based on the fact that the capacity depends on the area of the electric double layer formed at the interface between the activated carbon and the solid electrolyte in the carbon electrode.

From the above, the thickness of the electrode is determined in order to obtain the desired capacitance with a constant electrode area.

Here, in order to ensure the desired withstand voltage, as will be described later,
In a capacitor made up of 0 single cells connected in series, the area of each carbon electrode 8, 9 is 1 mIt.
The thickness of the electrode was determined with the goal of obtaining a capacitance of 10 μF.

According to this, a thickness of 4.55 μm is required for a silver salt electrolyte and 8.00 μm for a copper salt electrolyte.

On the other hand, taking into consideration the compression ratio of 50% by hot press as described above, in the screen printing, a screen of approximately 250 meshes was used in the former case, and a screen of approximately 120 meshes in the latter case.

The explanation will be continued by returning to FIGS. 4 and 5 again.

Reference numeral 12 denotes a solid electrolyte layer, which is a solid electrolyte ink prepared in the same manner as described in the case of the carbon electrode layers 8 and 9 (however, in this case, activated carbon powder was not mixed).

) and a 100-mesh screen, the carbon electrode layers 8 and 9 were screen-printed so that two pieces were lined up on each layer, and then after drying with hot air at 80°C, one of the carbon The substrate 5 is stacked on the substrate 4 so that the other carbon electrode layer 9 alternately faces the electrode layer 8, and then hot pressing is performed under the same conditions as for the carbon electrode layers 8 and 9.

The printing thickness should be 5 to 20μ, and if it exceeds 20μ, it will be tan.
δ tends to get worse.

Note that, before overlapping the substrate 5 on the substrate 4, the adhesive 13 is applied to the periphery of the substrate 4 in advance.

Epoxy adhesive is suitable for the adhesive 13.

The adhesive 13 is hardened by hot pressing as described above, and has the function of sealing the components of the capacitor between the substrates 4 and 5 except for the externally extending portions of the metal electrodes 6 and 7.

Furthermore, here, to explain the mutual positional relationship between one carbon electrode layer 8 and the other carbon electrode layer 9 that face each other with the solid electrolyte layer 12 interposed in between, the carbon electrode layer 9 is located in half of the carbon electrode layer 8. It is off by .

With such a configuration, a single cell made of each solid electrolyte layer 12 and carbon electrode layers 8 and 9 facing each other with the solid electrolyte layer 12 interposed therebetween has a metal electrode 6,
This means that 7 and 10 units are connected in series.

Table 1 shows the results of measuring the characteristics of the capacitor made as described above, and lists the characteristics of an aluminum electrolytic capacitor for timers selected as a conventional capacitor with a similar capacity for comparison. Shown below.

Note that the capacitor according to the present invention shown in Table 1 uses a copper salt as the solid electrolyte.

Here, a method for measuring the characteristics shown in Table 1 will be explained.

The withstand voltage is determined by increasing the applied voltage V at a constant rate and determining the voltage at which the current suddenly increases, and the capacitance C is determined by increasing the applied voltage V at a constant rate.
It was determined by the formula C-i/dV/dt from the relationship between the rate of increase when increasing the voltage and the steady current i at that time.

The K value was determined by applying a voltage V' corresponding to the withstand voltage, measuring the current i' 10 minutes later, and using the equation i' - KCV'.

As can be seen from the above equation, this value corresponds to the leakage current.

The equal series resistance was determined from the instantaneous current value immediately after voltage application.

As is clear from Table 1, the capacitor according to the present invention sufficiently exceeds the aluminum electrolytic capacitor in CR product, which is an element of tan δ.

This is due to the improvement in the series resistance of the solid electrolyte layer and the carbon electrode layer, as described above, according to the present invention.

Next, as can be compared from the value of stored energy density, which is a measure of size, the capacitor according to the present invention has a large density and is therefore small.

Further, as shown in the dimensions, the capacitor according to the present invention has a thickness of 0.7 mm.

Regarding this thickness of 0.7 mm, as mentioned above, the thickness of the connection electrode, carbon electrode layer, and solid electrolyte layer sandwiched between two substrates is at most 2 mm.
0μ, and therefore most of the thickness is occupied by the two substrates.

From this point of view, the thickness can be further reduced by making the substrate itself thinner or by making one of the two substrates shared by another substrate.

Furthermore, as is clear from the comparison of the values, which are a measure of leakage current, the capacitor according to the present invention has a small leakage current.

Note that the breakdown voltage has a value that is sufficient for practical use as a result of the plurality of single cells being connected in series as described above.

To summarize the above, the capacitor manufactured according to the present invention has the advantages of small leakage current, small size and thin profile compared to the capacitively corresponding conventional capacitor, and also has the following advantages: The tan δ has been improved to a point where it sufficiently exceeds that of the conventional capacitor.

Furthermore, the capacitor according to the present invention has a wide operating temperature range as shown in Table 1.

Further, since a large number of main parts of the capacitor components can be simultaneously formed on the same substrate by a printing method, the capacitor can be manufactured at low cost.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the relationship between pressing time and specific resistance of pellets formed by hot pressing when solid electrolyte ink is hot pressed, and Figure 2 is a curve diagram showing the relationship between pressing pressure and specific resistance. FIG. 3 is a curve diagram showing the relationship between the amount of binder contained in the ink and the specific resistance. FIG. 4 is a cross-sectional view of the electric double layer capacitor manufactured according to the present invention. The figure is an exploded top view of the capacitor, and FIG. 6 is a curve diagram showing the relationship between the weight and capacity of the carbon electrode. 4.5...Substrate, 6,7...Metal electrode, 8,9...Carbon electrode, 12...
Solid electrolyte layer.

Claims (1)

[Claims] 1. A metal electrode is deposited on a substrate, activated carbon powder and a solid electrolyte are deposited on the metal electrode, and a content of 5 to 20 wt% based on the activated carbon powder and the solid electrolyte is applied. A first step of forming a carbon electrode layer by applying an ink containing a binder and a solvent such that Based on the solid electrolyte powder and the solid electrolyte mentioned above on the electrode layer,
A second step of applying and drying an ink containing a binder and a solvent with a content of 20 wt%; 200-500 kg/c after comparing the products made in the 1st process and the products made in the 2nd process above.
A method for producing an electric double layer capacitor, comprising a third step of forming a solid electrolyte layer by hot pressing at a pressure of m2 for 10 minutes or more. 2. The method for producing an electric double layer capacitor according to claim 1, wherein the metal electrode is made of at least one selected from the group of metals consisting of nickel, stainless steel, gold, and metal. 3. The method for producing an electric double layer capacitor according to claim 1, wherein the binder is at least one selected from the group of thermosetting resins consisting of xylene, resol, polyester, and epoxy resins. 4 The solid electrolyte is Ag5S■, MAg4I5 (however, M
, Rb or NR4゜where R is an alkyl group), A
g6■4W04, Ag19■15P207 and MCN
- The method for producing an electric double layer capacitor according to claim 1, wherein the electric double layer capacitor is at least one selected from the group of silver salt solid electrolytes consisting of 4AgI (where M is K or Rb). 5 Claims in which the solid electrolyte is at least one selected from the group of copper salt solid electrolytes consisting of a reaction product of CuBr and N-methylhexamethylenetetramine bromide and a reaction product of CuBr and NN-methyltoluethylenediamine bromide. 2. A method for producing an electric double layer capacitor according to item 1. 6. The method for producing an electric double layer capacitor according to claim 1, wherein the solvent is at least one selected from the group of alcohols consisting of butyl cellosolve, cyclohexanol, pencil alcohol, and diacetone alcohol. 7. The method for manufacturing an electric double layer capacitor according to claim 1, wherein the carbon electrode ink is applied by screen printing. 8. The method for manufacturing an electric double layer capacitor according to claim 1, wherein the solid electrolyte ink is applied by screen printing. 9. The method for producing an electric double layer capacitor according to claim 1, wherein a plurality of solid electrolyte layers are connected in series by metal electrodes via carbon electrode layers.