JPH0744127B2 - Method for manufacturing polarizable electrode for electric double layer capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing a polarizable electrode for an electric double layer capacitor.

[Prior Art] An outline of an electric double layer capacitor will be described with reference to FIGS. 4 and 5.

As shown in FIG. 5, when the electric double layer capacitor 1 is made into a product, generally, a plurality of, for example, 6 capacitor cells 2 are concentrically stacked and housed in a cup-shaped case 3. It is considered to be the form.

Each of the capacitor cells 2 has a disk shape, and
As shown in the figure, a pair of polarizable electrodes 4a and 4b, a separator 5, an annular gasket 6, and a pair of current collectors 7a and 7b thermally bonded to the upper and lower surfaces of the gasket 6, respectively.
It has and.

More specifically, the polarizable electrodes 4a and 4b include a solid carbonaceous molded body and are separated from each other by an electrically insulating separator 5. The separator 5 is made of a polyolefin microporous film or non-woven fabric, or papermaking, and preferably has a rising portion formed at the peripheral edge thereof. Since the rising portion surrounds one polarizable electrode 4b, it is possible to prevent the polarizable electrodes 4a and 4b from being short-circuited at their peripheral portions. Also, polarizable electrodes
The separators 4a and 4b and the separator 5 are fixed to each other by an adhesive 8 partially applied on the interface between them.
The polarizable electrodes 4a and 4b and the separator 5 are impregnated with an electrolytic solution such as a 50 wt% sulfuric acid aqueous solution.

The gasket 6 is made of, for example, low density polyethylene layers 10a and 10b on both sides of an ethylene / propylene vulcanized rubber substrate 9.
Is integrally formed. Also, the current collector
7a and 7b are composed of, for example, a polyethylene film to which conductivity is imparted by a carbon material such as carbon black, and not only act as means for electrical conduction with the polarizable electrodes 4a and 4b, but also the polarizable electrode 4a. And 4b
In addition, it also has a function of hermetically sealing the separator 5 in the gasket 6.

As shown in FIG. 5, the required number of the capacitor cells 2 configured as described above (for example, 6).
They are stacked and integrated by surrounding them with an electrically insulating heat-shrinkable tube 11. The cell assembly 12 obtained by such integration is housed in the case 3 under pressure.

In the case 3, elastic conductive plates 13a and 13b made of highly conductive resin or rubber are arranged so as to contact the upper and lower surfaces of the cell assembly 12, respectively. The terminal assembly 14 is arranged on the upper elastic conductive plate 13a. The terminal assembly 14 includes two terminals 15 made of a metal plate.
a and 15b, which are combined via an insulating plate 16. The terminal 15a is electrically connected to the upper surface of the cell assembly 12 via the elastic conductive plate 13a. Also, terminal 15
b is in contact with the upper edge of the case 3, and therefore
Cell assembly 1 via case 3 and elastic conductive plate 13b
2 is electrically connected to the lower surface. As is apparent from such an electrical connection state, the elastic conductive plates 13a and 13b are
Have a function of lowering the contact resistance between the upper surface of the cell assembly 12 and the terminal 15a and between the lower surface of the cell assembly 12 and the bottom surface of the case 3 to stabilize the electrical connection.

Further, the sealing resin 17 is applied so as to cover the opening of the case 3. The sealing resin 17 is the electric double layer capacitor 1
On the other hand, for the purpose of imparting cleaning resistance, the inside of the case 3 is hermetically sealed. Further, since the outer peripheral surface of the case 3 is covered with an insulating material, a heat-shrinkable tube
18 is overlaid.

[Problems to be Solved by the Invention] When attempting to downsize the electric double layer capacitor 1 described above, particularly to reduce its height (to reduce the height dimension H in FIG. 5), the cell assembly 12 is configured. The thinning of each capacitor cell 2 must be achieved. To make the capacitor cell 2 thinner, the polarizable electrodes 4a and 4b are used.
The most effective method is to make the film into a thin film (sheet).

Conventionally, a sheet-shaped polarizable electrode is produced by rolling a rubber-like viscous mixture of carbon fine powder (activated carbon and / or carbon black), polytetrafluoroethylene (PTFE) resin and liquid lubricant by means of rolling rolls. It was manufactured by forming into a sheet. Water, alcohol, glycol or the like is used as the liquid lubricant.

However, in the above method, when the thickness of the sheet is reduced, the sheets are folded and stick to each other due to the elongation due to the rubber elasticity of the mixture and the adhesive force of the liquid lubricant, and the handling is substantially impossible. Met. Therefore, the lower limit of the sheet thickness that can be manufactured was set to 0.6 mm.

As a means for solving the above problem, a sheet-shaped preform having a certain thickness is first obtained, and after removing the liquid lubricant from the preform, it is finally thinned by a rolling roll. Conceivable. However,
Even with this method, in the end, if an attempt was made to obtain a sheet having a thickness of 0.6 mm or less, rolling could cause cracking or fragmentation, making production impossible.

Therefore, a method has been proposed in which the liquid lubricant is removed from the sheet-shaped preform and then the formed body is stretched uniaxially or polyaxially (Japanese Patent Laid-Open No. 63-107011).

According to this method, a thin sheet having a thickness of 0.6 mm or less can be manufactured. However, this method is not an industrially suitable method from the viewpoints that the drawing step is added after the rolling step, the process is complicated, and the drawing process itself takes a long time.

Therefore, an object of the present invention is to provide a method for manufacturing a polarizable electrode for an electric double layer capacitor, which enables thinning of the polarizable electrode, which leads to reduction in height of the electric double layer capacitor, with higher productivity. That is.

[Means for Solving the Problems] The present invention has several aspects as described below in order to solve the above-mentioned technical problems. In any of the aspects, in the method for producing a polarizable electrode according to the present invention, first, a step (starting step) of preforming a kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant into a sheet shape is carried out. To be done.

In the first aspect (claim 1) of the present invention, after the starting step, 1-a. Removing the liquid lubricant, 1-b. And then rolling the preform by heating to 40 to 350 ° C. Each step of forming into a predetermined thickness with a roll is provided.

In a second aspect (claim 2) of the present invention, after the starting step, 2-a. Adjusting the amount of liquid lubricant in the preform to 10 to 47 wt%, 2-b. The body is formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C., 2-c. And thereafter, the liquid lubricant is removed.

In a third aspect (claim 3) of the present invention, after the starting step, 3-a. Preforms are overlapped with each other at the ends and rolled and joined to form a continuous long preform, 3-b. Liquid lubricant is removed, 3-c. Then, each step of forming the preform into a predetermined thickness with a rolling roll heated to 40 to 350 ° C is performed.

In a fourth aspect (claim 4) of the present invention, in place of the steps "3-b" to "3-c" in the third aspect, 4-b. The amount of the liquid lubricant in the preform is set. Adjust to 10 to 47 wt%, 4-c. Then, preform is formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C, and 4-d. After that, the liquid lubricant is removed. , Each step is carried out.

In a fifth aspect (claim 5) of the present invention, after the starting step, 5-a. The amount of the liquid lubricant in the preform is adjusted to 20 to 47 wt%, and 5-b. After overlapping and rolling joining at the end to form a continuous long preform, 5-c. Next, the preform is formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C., 5-d. Thereafter, the steps of removing the liquid lubricant are performed.

The steps are performed.

In the present invention having various aspects described above, at least one of activated carbon and carbon black is used as the carbon fine powder.

Further, as the fluoropolymer resin, polytetrafluoroethylene (PTFE), elene-tetrafluoroethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, vinylidene fluoride copolymer, tetrafluoroethylene- A perfluoroalkyl vinyl ether copolymer, etc. can be used.

As the liquid lubricant, water, alcohol, propylene glycol, ethylene glycol, glycerin, white oil, etc. can be used.

Further, the above-mentioned carbon fine powder constituting the kneaded product, the mixing ratio of the fluoropolymer resin and the liquid lubricant, for example, 100 parts by weight of the carbon fine powder, the fluoropolymer resin 0.5 ~.
It is selected to contain 30 parts by weight and 95 to 150 parts by weight of liquid lubricant.

[Operation] If the thin film of the preformed body from which the liquid lubricant is removed can be realized by roll rolling instead of stretching, the present invention can simplify the process and shorten the time required for thinning, which is industrially optimal. It was made paying attention to the point that it is a method.

Therefore, the following findings were obtained by earnestly studying the mechanism of thinning the preformed body by roll rolling.

As shown in FIG. 1, the preform 21 is passed through a pair of rolling rolls 22 to form a rolled sheet 23. In FIG. 1, the surface layer 24 to which compressive shear force is applied by rolling.
Are indicated by hatched areas. The surface layer 24 needs to be rapidly deformed and stretched when passing the rolling roll 22. When the ratio of the surface layer 24 is large relative to the whole rolled sheet 23, that is, the rolled sheet
It is considered that when the thickness of 23 becomes thin, it becomes impossible to follow the deformation, and cracks or small pieces are formed. Conventionally, for this reason, the thickness of the sheet 23 obtained by rolling is 0.6 m.
It was up to m.

As shown in FIG. 2, polytetrafluoroethylene (PTFE) has a room temperature transition point at which the specific volume changes at about 20 ° C. and about 30 ° C. This is believed to be due to the reversible change in crystal structure near room temperature. When heated above the room temperature transition point, the elongation of PTFE suddenly increases as shown in FIG.

In this way, the deformation of the surface layer 24 to which the compressive shearing force is applied,
In order to follow the rolling, it is considered that PTFE should be heated above the room temperature transition point so that the deformation becomes easy.

Then, when the preform was rolled with a rolling roll heated to room temperature or higher, a sheet having a thickness of 0.6 mm or less, which was impossible in the past, could be easily and quickly manufactured.

Although the above-mentioned consideration regarding the room temperature transition point was made for PTFE, the same can be said for the other fluoropolymer resins listed above.

Further, according to another aspect of the present invention, it was found that a thin sheet can be obtained by roll rolling by adjusting the amount of the liquid lubricant in the preform at any stage before the rolling step. . That is, the preform is put in a so-called semi-dried state, and the amount of liquid lubricant in the preform is adjusted.
If it is adjusted in the range of 10 to 47 wt%, there will be no problem in handling, and the plasticizing effect of the residual liquid lubricant will be recognized. Due to the plasticizing effect of such liquid lubricant, the surface layer to which compressive shearing force is applied is It is considered that thinning is possible because it can be easily deformed.

However, in this case, the preform to be subjected to roll rolling contains the liquid lubricant to the extent that it can be handled, but the preform containing the liquid lubricant should be semi-dried. However, even if the amount of the liquid lubricant in the kneaded product is reduced from the beginning and an equivalent product is to be formed by rolling, it cannot be formed into a sheet because the rolling property is poor.

In order to obtain a continuous long preform, when the preform is semi-dried as described above before the preforms are overlapped at their ends and joined by rolling, the liquid in the preform is It is preferable to adjust the amount of lubricant to 20-47 wt%.

[Effects of the Invention] According to the present invention, a sheet for a polarizable electrode having a thickness of 0.20 to 0.25 mm, which could not be produced by a conventional rolling roll, can be easily produced in a short time. Therefore, the use of the polarizable electrode thus obtained can advantageously reduce the height of the electric double layer capacitor.

[Example] Example 1 Activated carbon fibers made of polyacrylonitrile as a raw material were crushed, and 120 parts by weight of propylene glycol as a liquid lubricant was added to 100 parts by weight of activated carbon powder that passed through 200 mesh, and mixed with a spiral mixer. did. Next, 5 parts by weight of a solid content of PTFE aqueous dispersion ("Polyflon D-1" manufactured by Daikin Industries, Ltd.) was added to this mixture and kneaded to obtain a rubber-like viscous mixture.

This viscous mixture was rolled with a roll to obtain a sheet-shaped preform having a thickness of 1 mm.

Next, the liquid lubricant in the preform was removed by a hot air dryer at 200 ° C.

Then, the preform was thinned with a rolling roll heated to 90 to 120 ° C. to manufacture a sheet having a thickness of 0.25 mm. The effect of the roll temperature was 40 to 350 ° C, but 90 to 120 ° C from the viewpoint of ease of rolling deformation, workability, and water repellency.
Was the best.

The sheet production rate was 2 m / min.

Comparative Example 1 The thinning of Example 1 was performed by stretching, and the thickness was 0.25 mm.
Sheets were manufactured.

The sheet production speed is limited to 0.5 m / min.
It turns out that it is very slow compared to.

Example 2 (outside the scope of the invention) * (Outline) Compared to Example 1, a semi-dried preform was used to enable thinning at room temperature. * In the same manner as in Example 1, a sheet-shaped preform having a thickness of 1 mm was obtained.

Next, the amount of liquid lubricant in this preform was adjusted to 10 to 47 wt% by a hot air dryer at 90 ° C.

This preform was rolled into a thin film at room temperature to produce a sheet having a thickness of 0.25 mm. After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

As described above, the reason why the thin sheet can be manufactured without heating the roll is that the surface layer to which the compressive shearing force is applied can be easily deformed by the plastic action of the residual liquid lubricant.

Example 3 * (Outline) Compared with Example 2, thinning with a heating roll made it possible to improve the sheet strength and further reduce the thickness.
* In the same manner as in Example 2, a sheet-shaped preform containing a liquid lubricant in an amount of 10 to 47 wt% was obtained.

This preformed body was rolled into a thin film by rolling with a roll heated to 90 to 120 ° C. to manufacture a sheet having a thickness of 0.20 mm. After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

In Examples 1 and 2, the minute cracks that existed before the thinning were left after the rolling, and the cracks might be generated from that portion. However, in Example 3, the crack disappeared after rolling, and no crack was generated. The lower limit of thinning in Examples 1 and 2 is 0.25 mm in thickness.
However, in Example 3, a sheet having a thickness of 0.20 mm could be easily obtained.

*** As described above, according to Examples 1 to 3, compared to the method of stretching the sheet-shaped preform of Comparative Example 1, it becomes possible to easily and quickly produce a thin sheet by roll rolling. .

******** Example 4 * (Overview) Lengthening of Example 1 * In Examples 1 to 3, since the thickness of each preform is reduced, the length of the obtained sheet is at most 4 m. However, a continuous long product could not be obtained. Example 4 makes it possible to obtain a continuous long product.

That is, in the same manner as in Example 1, a sheet-shaped preform having a thickness of 1 mm was obtained.

A plurality of preforms obtained in this way were overlapped at their ends and joined with a rolling roll to obtain a continuous long preform. The joining was possible because the joining portion was easily deformed by the plastic action of the liquid lubricant.

The liquid lubricant in the long preform was removed by a hot air dryer at 200 ° C.

Next, when a long preform was thinned by rolling with a rolling roll heated to 90 to 120 ° C., a continuous sheet having a thickness of 0.25 mm could be manufactured.

Example 5 (outside the scope of the invention) * (Outline) Lengthening of Example 2 * In the same manner as in Example 4, a continuous long sheet-shaped preform was obtained.

Next, the liquid lubricant in this long preform was adjusted to 10 to 47 wt% by a hot air dryer at 90 ° C.

Next, when this preform was thinned by rolling at room temperature, a continuous sheet having a thickness of 0.25 mm could be manufactured.

After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

Example 6 * (Outline) Lengthening of Example 3 * In the same manner as in Example 5, a continuous long sheet-like preform containing 10 to 47 wt% of a liquid lubricant was obtained.

Next, this preform was made into a thin film by rolling with a roll heated to 90 to 120 ° C., and a sheet having a thickness of 0.20 mm could be manufactured. After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

In Examples 4 and 5, the minute cracks that existed before the thinning were left after the rolling, and the cracks might be generated from that portion. However, in Example 6, after the rolling, the crack disappeared and no crack was generated.

Example 7 (outside the scope of the invention) * (Outline) A semi-dried preform was lengthened to form a thin film at room temperature. * A sheet-shaped preform containing 20 to 47 wt% of a liquid lubricant was obtained.

Next, the plurality of preforms were overlapped with each other at their ends and joined by a rolling roll to obtain a continuous long preform.
Here, if the liquid lubricant was 20 to 47 wt%, joining was possible due to the plasticizing action of this liquid lubricant.

Next, when the above long preform was thinned by rolling at room temperature, a continuous sheet having a thickness of 0.25 mm could be manufactured.

After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

Example 8 * (Outline) A semi-dried preform was elongated and thinned with a heated roll. * In the same manner as in Example 7, a continuous long sheet-like preform containing 20 to 47 wt% of the liquid lubricant was obtained.

When this preformed body was made into a thin film by rolling with a roll heated to 90 to 120 ° C., a sheet having a thickness of 0.20 mm could be manufactured.

After that, the liquid lubricant in the sheet was completely removed to obtain a polarizable electrode sheet. At this time, the thickness of the sheet did not change.

In Example 7, the minute cracks that existed before the thinning were left after the rolling, and the cracks might be generated from that portion. However, in Example 8, the crack disappeared after rolling, and no crack was generated.

*** A summary of Examples 1 to 8 and Comparative Example 1 described above is as shown in Table 1 below.

From Table 1, the thickness that could not be conventionally manufactured with rolling rolls
It can be seen that a 0.20 to 0.25 mm polarizable electrode sheet can be easily manufactured in a short time.

Further, the sheet obtained by each of Examples 1 to 8 and Comparative Example 1 was punched into a disc shape and used as the polarizable electrodes 4a and 4b shown in FIG. Then, install these capacitor cells 2,
An electric double layer capacitor 1 as shown in FIG. 5 was manufactured. The product height H and the capacitance of the electric double layer capacitor 1 thus obtained were measured, and the measurement results are shown in Table 2 below. In Table 2, the capacitance is 2mA
It was calculated by using the value obtained by measuring the time it takes for the voltage between terminals to reach from 2V to 4V after constant current charging.

[Brief description of drawings]

FIG. 1 is a diagram showing a roll rolling process applied to a preformed body. FIG. 2 is a graph showing the relationship between the specific volume of polytetrafluoroethylene and temperature. Figure 3 shows
It is a graph which shows the elongation in tension of polytetrafluoroethylene, and the relationship of temperature. FIG. 4 is a sectional view showing a capacitor cell included in the electric double layer capacitor. FIG. 5 is a sectional view showing an electric double layer capacitor constructed using the capacitor cell shown in FIG. In the figure, 1 is an electric double layer capacitor, 4a and 4b are polarizable electrodes, 21 is a preform, 22 is a rolling roll, and 23 is a rolled sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Mukaiyama 26-20 Tenjin, Nagaokakyo City, Kyoto Prefecture Murata Manufacturing Co., Ltd. (56) Reference JP-A-63-107011 (JP, A)

Claims (5)

[Claims] 1. A kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant is preformed into a sheet, the liquid lubricant is removed, and then the preform is heated to 40 to 350 ° C. Forming into a predetermined thickness with the above-mentioned rolling roll. A method for producing a polarizable electrode for an electric double layer capacitor, comprising: 2. A kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant is preformed into a sheet, and then the amount of the liquid lubricant in the preform is adjusted to 10 to 47 wt%. A method for producing a polarizable electrode for an electric double layer capacitor, comprising forming a preformed body into a predetermined thickness with a rolling roll heated to 40 to 350 ° C., and then removing the liquid lubricant. . 3. A continuous long preform in which a kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant is preformed into a sheet, and the preforms are overlapped at end portions and roll-bonded. After forming into a body, the liquid lubricant is removed, and then the preform is formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C. Electrode manufacturing method. 4. A continuous long preform in which a kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant is preformed into a sheet, and the preforms are overlapped at end portions and roll-bonded. After forming into a body, the amount of liquid lubricant in the preform is adjusted to 10 to 47 wt%, and then the preform is formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C, and then The method for producing a polarizable electrode for an electric double layer capacitor, comprising removing the liquid lubricant. 5. A kneaded product of carbon fine powder, a fluoropolymer resin and a liquid lubricant is preformed into a sheet, and the amount of the liquid lubricant in the preform is adjusted to 20 to 47 wt%, and the preform is preformed. After the bodies are overlapped with each other at the end by rolling to form a continuous long preform, the preform is then formed into a predetermined thickness with a rolling roll heated to 40 to 350 ° C., and thereafter. The method for producing a polarizable electrode for an electric double layer capacitor, characterized in that the liquid lubricant is removed.