DE4007201C2 - - Google Patents

Description

The invention relates to a method for producing a polarizable electrode for an electrical double layer capacitor.

With such a capacitor two polarisable Electrodes via an electrically insulating separator connected with each other. The latter exists, for example from a polyolefin microporous film or from a non-woven structure, non-woven or paper. Such an arrangement can be achieved by an annular seal surrounded and above and below by a conductive plate be contacted, which form current collectors. Several Such capacitor cells can be stacked one on top of the other be.

Another type of construction of a double layer capacitor is that instead of the circular plates for contacting of the polarizable electrode layers metal networks used with the polarizable electrode material are coated.

With regard to the latter structure, is on DE 30 00 777 C2, from which document also the method according to the generic terms of Claims 1 and 2 is known. With the in the mentioned The process described in writing becomes a kneaded substance rolled onto an stretched metal net. The kneaded substance consists of activated carbon powder, polyvinyl pyrrolidone (PVP) and a polytetrafluoroethylene dispersoid. Preferably is still Acetylene black present. The dispersoid is an aqueous one Dispersion, the fine grains of polytetrafluoroethylene in one  Contains about 60 wt .-%. This dispersoid is in the kneaded substance with three of a total of 16.5 parts by weight present that predominantly little or no Contain water, so that the total proportion of liquid Lubricant is less than 10%.

Polarizable electrodes without a metal mesh are also used in the generally made of carbon powder, a fluorine-containing Polymer resin, e.g. B. Polytetrafluoroethylene (PTFE) resin and a liquid lubricant. The latter can e.g. B. consist of water, alcohol or glycol.

Conventionally, the mixtures mentioned are rolled out in order to Get slabs or layers. They were minimal Achieve layer thicknesses of 0.6 mm. Lower layer thicknesses are, however, achievable with a method as described in the Japanese Patent Laid-Open Publication JP-A-1 07 011 (1988) is described. This is where the liquid lubricant comes from a layered preform is removed, and then the preform is drawn uniaxially or multiaxially. Let it through layer thicknesses of less than 0.6 mm are produced, however, the procedure is because of the additional drawing step, which takes a relatively long time, very expensive.

The invention has for its object a method for Manufacture of a polarizable electrode for an electrical Double layer capacitor specify that on simple How to produce a polarizable electrode a layer thickness of less than 0.6 mm allowed.

Two solutions to this problem are due to the characteristics of the independent Claims 1 and 2 given. Advantageous further training and configurations are the subject of dependent claims.  

In both methods, a layered preform is between two rolls rolled out. In the first case, the Preform no longer has any lubricant and the rolling takes place between heated rollers to determine the phase transition properties of the To use fluorine-containing polymer resin. The second procedure works with a layered preform that still allows a certain amount of liquid lubricant that rolling is also possible without heated rollers. Of particular However, it is an advantage, both with a certain lubricant content how to work with heated rollers.

The invention is described below with reference to the Drawing described in more detail. Show it:

Fig. 1 shows the principle of rolling as it passes at a preform for application to,

Fig. 2 is a graphical representation of the relationship between the specific volume and temperature of polytetrafluoroethylene, and

Fig. 3 is a graph showing the relationship between the elongation and the temperature of drawn polytetrafluoroethylene.

As FIG. 1 shows a preform 21 is by means of two rollers 22 (pair of rollers) into a rolled layer 23. According to FIG. 1, a compression shear force acts within the shaded surface layers 24 as a result of the curling. The surface layers 24 must be quickly deformed and extended if the preform 21 passes through the two rollers 22 . It should be remembered that cracks or breaks occur when the proportion of surface layers 24 is increased for thin layers, based on the total rolled layer 23 , ie when the thickness of the rolled layer 23 decreases, since the preform 21 is not deformed can. The minimum thickness of the layer 23 , which is obtained by rolling, is thus limited to 0.6 mm.

As FIG. 2 shows, polytetrafluoroethylene (PTFE) has transition points at approximately 20 ° C. and approximately 30 ° C. at which its specific volume changes. This is explained by a reversible change in the crystal structure at this temperature. An elongation or elongation of PTFE increases abruptly, as shown in FIG. 3, when it is heated to a temperature which is above the transition points.

It can thus be considered to heat PTFE to a temperature above the transition points in order to facilitate its deformation, so that the surface layers 24 , which are subjected to the shear force during rolling of the compression, can expand or deform.

From this point of view, a preform was created with the help of heated rolls processed, the temperature of the Rol  len was above room temperature. It was therefore possible Lich a plate or a layer in a simple way and quickly manufacture with a thickness that was smaller than 0.6 mm. Platelets or layers with such a small With the help of the conventional method, thicknesses could not be generated.

Although the above considerations regarding tempe ratur transition points were made with a view to PTFE, they also apply to the other materia mentioned above lien, for example for polymer resin with contained therein Fluorine.

In accordance with another aspect of the invention it was found that a thin layer by rolling can also be obtained without heating the rollers, and by adjusting the proportion of liquid lubricant or lubricant in the preform at any stage the rolling step. Is the preform in a so-called semi-dried state transferred to the proportion of the rivers sigen lubricant in the preform so that it to be within a range of 10 to 47% by weight comes, there is no pro in further handling problem because the remaining liquid lubricant is soft effect. The layer can then be in its thickness can be reduced because the surface layers that the Are subjected to compression shear as a result of the plasticizer effect caused by the liquid lubricant can easily deform.

The preform to be rolled out, the liquid lubricant still contains up to a portion that still has a handling is not prevented in this case by semi-drying of a compact (compact), which is sufficient Has amount of the liquid lubricant. It is impossible Lich, such a layer of a kneaded substance  manufacture that was originally only a small part of contained liquid lubricant, due to the ver poorer rollability.

The preform is semi-dried in the manner previously mentioned net, so before going to the endbe with other preforms are put together and together with them is rolled to form a continuous, long preform hold the proportion of liquid lubricant in the preform preferably set so that it is within a loading is from 20 to 47 wt .-%.

In accordance with the invention it is possible to use a Layer or a plate for a polarizable electric de from 0.20 to 0.25 mm thickness in a simple manner len within a relatively short time. Plat Chen or layers with such a small thickness can be with the help of a conventional rolling process put. The vertical size of an electric double Layer capacitor can thus be used in the polarizable manufactured in the manner described above Electrodes are significantly reduced.

example 1

120 parts by weight of propylene glycol, which is used as a liquid lubricant 100 parts by weight of activated carbon are used added fabric powder, which is obtained by pulverizing acti fourth carbon fibers using a 200 mesh screen will hold. The carbon fibers are made of polyacrylonitrile produced. With the help of a spiral mixer, these Ma materials mixed together. Then 5 parts by weight aqueous PTFE dispersion ("Polyfluon D-1" from Daikin Indu stries, Ltd.) added, the mixture kneaded is a rubber-like, viscous mixture or Beimi maintenance.  

This viscous mixture or admixture is made using Rolls processed so that a layered preform with with a thickness of 1 mm.

Then the liquid lubricant is reduced in thickness by rollers that are heated to 90 ° C to 120 ° C to produce a layer with a thickness of 0.25 mm. The rolling process is effective in a temperature range of 40 ° C to 350 ° C, however, the optimal temperature range is between 90 ° C and 120 ° C, with regard to egg facilitated rolling / deformation process, on a special more workability and with a view to better Water repellency.

The layer was made at a rate of 2 m / min.

Reference example 1

The preform according to Example 1 was pulled reduced in thickness to a layer with a thickness of Obtain 0.25 mm. The rate at which the layer was made was limited to 0.5 m / min. That rate is very much smaller than that in example 1.

Example 2

In comparison to Example 1, a semi-dry Nete preform used to reduce thickness in space to allow temperature.

A layered preform with a thickness of 1 mm prepared in a manner similar to Example 1.

Then the proportion of liquid lubricant in the Preform set to 10 to 47 wt .-%, with Hil Fe of a hot air dryer at a temperature of 90 ° C.  

This preform becomes thicker by rolling at room temperature temperature reduced to a layer with a thickness of 0.25 mm to obtain. Then the liquid lubricant completely removed from the layer so that the layer as polarizable electrode can be used. To this There is no further change in the thickness of the layer at this time.

It is thus possible to apply a thin layer without a heated roller len because the surfaces of the layer, the exposed to compression shear, easily as a result the softening properties of the remaining lubricant can deform material.

Example 3

In comparison to example 2, the thickness is with Help heated rollers reduce the layer strength to improve and further reduce the thickness.

A layered preform with 10 to 47 wt .-% of liquid The lubricant is used in a similar manner as in Example 2 produced.

This preform is made with the help of roles that are based on a tem temperature between 90 ° C and 120 ° C are heated, so out rolls that finally a layer with a thickness of 0.20 mm is obtained. Then the liquid Lubricant completely removed from the layer so it can be used as a polarizable electrode. To there is no further change in thickness at this time the layer.

In Examples 1 and 2, fine cracks remain before the Thickness reduction has been observed even after Obtain roles so that the appropriate areas easily can break. In contrast, in example 3 these disappear  Cracks so that no breaks after rolling there are more. The minimum thickness, on the other hand, became limited to 0.25 mm in Examples 1 and 2 while it was possible according to Example 3, a simple Obtain layer with a thickness of 0.20 mm.

In accordance with Examples 1 to 3, in contrast to reference example 1, in which one layer like a preform is drawn, thin layers through a Produce the rolling process quickly and easily.

Example 4 Modification of example 1

In accordance with Examples 1 to 3, each Preform reduced in thickness so that the length of a he holding layer can be at most about 4 m. It is therefore not possible to be continuous or subtle to get broken, long layer. Example 4 judges focusing on making a continuous, long Layer.

A layer-like preform with a thickness of 1 mm is in prepared in a similar manner as in Example 1.

A plurality of such preforms are made on each of them End areas plugged together and rolled together other connected to an uninterrupted or continuous to form a long preform. The stacked ones Parts or areas of the preforms can be easily deformed by the softening effect of a liquid lubricant or lubricant that is in the preforms. In this way it becomes a verb  of the preforms.

Then the liquid lubricant from the long pre removed by hot air drying at a Temperature of 200 ° C.

The long preform is then rolled into it Reduced thickness, with the help of rollers on egg ner temperature in the range between 90 ° C and 120 ° C, around a continuous layer with a thickness of 0.25 mm to build.

Example 5 Modification of example 2

A continuously long layered preform is used in prepared in a similar manner as in Example 4.

Then the proportion of liquid lubricant in the long preform set to 10 to 47 wt .-%, namely by hot air drying at a temperature of 90 ° C.

This preform is then rolled up in thickness Room temperature reduced to finally a continuous uninterrupted layer with a thickness of 0.25 mm to obtain.

After that, the liquid lubricant is completely removed from the Layer removed so this layer as polarizable Electrode can be used. Is done at this time no further change in thickness of the layer.  

Example 6 Modification of example 3

A continuously long layered preform with 10 to 47% by weight of liquid lubricant is used in a similar manner prepared as in Example 5.

Then the preform is reduced in thickness by rolling adorned, the rollers at a temperature in the loading between 90 ° C and 120 ° C. In this way a layer with a thickness of 0.20 mm is obtained. On finally the liquid lubricant is completely eliminated removed the layer so that this layer as polarizable re electrode can be used. Is done at this time no further change in the thickness of the layer.

In Examples 4 and 5, fine cracks remain before the Thickness reduction has been observed even after Get rolling so that the corresponding parts can easily break. In example 6, however, disappear the cracks so that even after rolling there is absolutely no breakage there is a risk.

Example 7

A semi-dried preform is extended and reduced in thickness at room temperature.

First, a layer-like preform with 20 to 47 % By weight of liquid lubricant.

A plurality of such preforms are made at their end parts or end areas placed on top of each other and by rolling with connected to one another in a continuous or uneven manner to get broken long preform. The put together  or superimposed preforms can be softening effect of the liquid lubricant connect, the proportion of which is 20 to 47 wt .-%.

The long preform mentioned above is at room temperature reduced in thickness by curling, so that finally receive a continuous or uninterrupted shift whose thickness is 0.25 mm.

Then the liquid lubricant is completely out removed from the layer so that this layer is polarized bare electrode can be used. At that time he there is no further change in thickness of the layer.

Example 8

A semi-dried preform is extended and reduced in thickness by heated rollers.

A continuously long layered preform with 20 to 47% by weight of liquid lubricant is used in a similar manner prepared as in Example 7.

This preform is then made with the help of rolls in its thickness reduced, with the rollers at a temperature in the range between 90 and 120 ° C. The layer will look so far rolled until it has a thickness of 0.20 mm.

Then the liquid lubricant is completely out the layer removed so that the layer as polarizable Electrode can be used. Is done at this time no further change in thickness of the layer.

In example 7 there are fine cracks that precede the thickness reduction tion have been observed, even after rolling hold so that the corresponding areas break easily  can. In Example 8, however, these disappear ge cracks completely, so that after the rolling process none There is a risk of breakage due to cracks.

Table 1 below shows results of the previous ones mentioned Examples 1 to 8 and Reference Example 1.

Table 1

As can be seen in Table 1, layers with a Thickness from 0.20 to 0.25 mm for a polarizable electrical de manufactured in a simple manner and in a short time those who would otherwise not be in the usual rolling process let form.

Circular plates are punched out of the layers obtained according to Examples 1 to 8 and Reference 1 in order to obtain polarizable electrodes. These polarizable electrodes are used to form the capacitor cells, which are integrated into electrical double-layer capacitors. The following Ta table 2 shows measurement results with regard to the product heights and the capacities of such electrical double-layer capacitors. To determine the capacitances given in Table 2, the samples were charged with constant currents of 2 mA. The times were measured between an increase in the voltage at the terminals of the capacitors from 2 V to 4 V.

Table 2

Claims (5)

1. A process for producing a polarizable electrode for an electrical double-layer capacitor, the electrode containing fine carbon powder and a fluorine-containing polymer resin, characterized by the following steps:

• a) preforming a kneaded substance from the fine carbon powder, the fluorine-containing polymer resin and a liquid lubricant to form a layer-like preform ( 21 ),
• b) removing the liquid lubricant from the preform and
• c) deforming this layer-like preform ( 21 ) into a layer ( 23 ) with a predetermined thickness by rolling between rollers ( 22, 22 ) which are heated.

2. A process for producing a polarizable electrode for an electrical double-layer capacitor, the electrode containing fine carbon powder and a fluorine-containing polymer resin, characterized by the following steps:

• a) preforming a kneaded substance from the fine carbon powder, the fluorine-containing polymer resin and a liquid lubricant to form a layer-like preform ( 21 ),
• b) adjusting the proportion of liquid lubricant in the layer-like preform ( 21 ) to 10 to 47% by weight,
• c) deforming the layer-like preform ( 21 ) into a layer ( 23 ) with a predetermined thickness by rolling between rollers ( 22 , 22 ) and
• d) removing the remaining liquid lubricant from the layer ( 23 ) obtained.

3. The method according to claim 1 or 2, characterized in that in step c) rollers ( 22 , 22 ) are used which are heated to a temperature above a phase transition point associated with a change in length of the fluorine-containing polymer resin. 4. The method according to claim 3, characterized in that the temperature of the rollers ( 22, 22 ) is in the range from 90 ° C to 120 ° C. 5. The method according to any one of the preceding claims, characterized in that a plurality of layer-like preforms ( 21 ) are placed one on top of the other in the respective end regions and connected by rolling or rolling to form a long, continuous layer-like preform.