EP1586100A1

EP1586100A1 - Electrode for an electrochemical cell, electrode coil, electrochemical cell, and production method

Info

Publication number: EP1586100A1
Application number: EP03815356A
Authority: EP
Inventors: Werner Erhardt; Andree Schwake
Original assignee: Epcos AG
Current assignee: TDK Electronics AG
Priority date: 2003-01-21
Filing date: 2003-12-23
Publication date: 2005-10-19
Also published as: CN1742350A; JP2006513574A; DE10302119A1; WO2004066325A1; US20060210874A1

Abstract

The invention relates to an electrode (1) for an electrochemical cell comprising a liquid electrolyte (3). Said electrode is provided with channels (2), within which an electrolyte liquid can flow. The inventive electrode has the advantage of allowing the impregnation time of the electrochemical cell to be reduced.

Description

description

Electrode for an electrochemical cell, electrode coil, electrochemical cell and method of manufacture

The invention relates to an electrode for an electrochemical cell which contains an electrolyte. The invention further relates to an electrode coil. In addition, the invention relates to an electrochemical cell with the coil.

Electrochemical cells are known, for example, in the form of electrical double-layer capacitors from the publication DE 100 60 653 AI. The electrochemical double-layer capacitors described there have the form of electrode layers formed from activated carbon, which are contacted with supply layers, for example an aluminum foil. To produce the electrochemical double-layer capacitor, a stack of electrodes one above the other with constantly changing polarity must be installed in a housing and impregnated there with a liquid electrolyte. To form the coil, either a large number of individual electrodes are stacked on top of one another or two electrodes of different polarity are wound along a longitudinal direction. In both cases, the electrodes of different polarity are electrically separated from one another by a separator.

The known electrodes have the disadvantage that the impregnation process takes a very long time, since it takes a very long time until the electrolyte liquid has penetrated into the separator arranged between the electrodes and displaced the air stored there. For example, with a winding for a capacitor with a capacity of 5000 F, which consists of approx.6.5 m anode foil and 6.5 m cathode foil and a corresponding amount of separator in between, a time of approx. 72 hours is required until the Wrap completely from the electrical saturated liquid and the entire gas from the pores of the activated carbon of the electrodes and the separator has exited the condenser through the impregnation opening.

In addition, there is the problem that in the event of an incomplete exchange of gas for electrolyte, outgassing may continue even after the capacitor has been closed, which in extreme cases leads to the capacitor bursting.

In order to shorten the impregnation time, it is also known from JP 11339770-A to impregnate an electrolyte into a wrap under reduced pressure. However, this method has the disadvantage that the problem of the impregnation time is only inadequately solved and that, in addition, an increased outlay on equipment is required for the impregnation of the winding.

It is therefore an object of the present invention to provide an electrode for an electrochemical cell which allows rapid impregnation.

This object is achieved by an electrode according to patent claim 1. Advantageous embodiments of the electrode, a coil from the electrode and an electrochemical cell can be found in the further patent claims.

The invention is based on the idea that the exchange of electrolyte for gas can take place more quickly by providing channels in the electrode, since such channels are suitable for quickly transporting small amounts of gas or gas bubbles from the inside of the winding to the outside or to provide the electrolyte in sufficient quantities through these channels also inside the capacitor, so that impregnation can take place more quickly than if only The electrolyte can be offered in sufficient quantities from the two ends of the winding.

Accordingly, an electrode for an electrochemical cell with an electrolyte is specified which contains channels in which an electrolyte liquid can flow.

The electrode has the advantage that the exchange of electrolyte liquid and gas in a winding can take place more quickly during the impregnation through the channels.

In one embodiment of the electrode, the channels can be designed in the form of grooves on the surface of the electrode. This has the advantage that the manufacture of the channels can be greatly simplified since the electrodes can be manufactured in a first process step and the grooves can be introduced into the electrode from the outside, for example by embossing, by subsequent machining of the electrodes ,

In one embodiment of the electrode, it has a coated film, the grooves being formed by uncoated partial areas of the film. Such an electrode has the advantage that the grooves can be formed simultaneously with the manufacture of the electrode, which can significantly reduce the duration for the manufacture of the electrode. Such an electrode also has the advantage that the depth of the grooves is automatically predetermined by the thickness of the coating.

In addition, it is advantageous if the channels have a width between 0.1 and 0.5 mm. This also ensures that the channels do not fall below a certain minimum width, which would make it more difficult to transport the electrolyte fluid. In addition, it is achieved at the same time that too much volume of the electrode is not lost through the formation of the channels, which would have negative effects on the capacitance of the electrochemical double-layer capacitor used, for example, as an electrochemical cell.

It is pointed out here that the term “electrochemical cell” is to be understood to mean all devices in which an electrical effect of some kind is to be achieved by an electrode and by the presence of a liquid electrolyte. For example, aluminum electrolytic capacitors, electrochemical double-layer capacitors or even batteries come into consideration here.

Furthermore, it is advantageous if the depth of the channels is between 50 and 100 μm. This measure has the advantage that it corresponds to the thickness usually chosen for the coating, which enables the channels to be easily formed as grooves in the coating.

In addition, it is advantageous if the electrode extends along a longitudinal direction, the channels running transversely to the longitudinal direction. Such an electrode has the advantage that it can be wound up in the longitudinal direction to form a rolled winding, it being possible for the channels to be arranged transversely to the longitudinal direction to achieve that of the

End faces of the winding forth the electrolyte liquid can penetrate into the interior of the winding along the channels.

In this case, the channels can advantageously be essentially along equidistant, parallel to one another

Straight lines. This simplifies the manufacture of the channels. For example, transverse grooves spaced equidistantly from one another could be produced by means of embossing, a roller being used which has a straight projection running parallel to the axis of rotation of the roller. In another embodiment of the electrode, it can be provided that the channels run obliquely to the longitudinal direction of the electrode. This embodiment in turn has advantages with regard to the manufacture of the channels. In contrast to the manufacture described above, it is no longer necessary here to provide a projection which runs parallel to the axis of rotation of the roller and which leads to discontinuous mechanical loads on the axis carrying the roller when it rolls on the electrode. This mechanical stress is due to the fact that every time the projection presses the electrode against an abutment to create an embossment in the electrode, a corresponding discontinuous force acts on the roller.

In another embodiment, the channels can run along curved lines that are offset parallel to one another.

Such an embodiment of the electrode has the advantage that, in turn, it can be produced by means of a roller provided with one or more features.

In another embodiment it is provided that the channels cross each other. This makes it possible to run the channels along two different ones, for example one

To integrate angles of 90 ° including preferred directions in the electrode.

It is also suitable for certain electrochemical cells such as EDLC or Li-ion batteries are particularly advantageous if the electrode contains a metal foil coated with carbon powder. For example, an aluminum foil can be used as the metal foil.

In addition, an electrode coil is specified in which several layers of one of the electrodes just described are arranged one above the other. Such an electrode coil has the advantage that it can be used as a capacitor winding in a double layer electrolytic capacitor.

At this point, it is pointed out that in order to achieve a high volume utilization in the manufacture of the winding, care is regularly taken to ensure that it is of a very compact design. This compactness of the winding additionally complicates the penetration of the electrolyte into the interior of the winding. This means that especially in the case of very compact windings in which there are either electrode layers lying one above the other in the form of a stack, the stack being pressed together or else the channels can advantageously be used in the case of a very tightly wound winding.

Accordingly, a winding is advantageous in which two electrodes of different polarity are wound.

In addition, an electrochemical cell is specified which contains a liquid electrolyte and which also contains one of the coils described above. Such an electrochemical cell has the advantage that the winding can be impregnated very quickly with the liquid electrolyte.

Accordingly, an electrode for an electrochemical double-layer capacitor with a liquid electrolyte is specified, which contains a metal foil coated with activated carbon powder. Channels are provided in the carbon coating in which an electrolyte liquid can flow and which serve to improve the exchange between the electrolyte liquid and the gas contained in the pores of the carbon coating.

The invention further relates to a method for producing the above-mentioned electrode. The grooves and channels according to the invention can be obtained, for example, using the following methods: a) calendering coated and not yet embossed electrodes at elevated temperature. This process can also be integrated into the winding process; b) coating an already embossed metal foil (for example an Al foil) with activated carbon; c) Scoring grooves and channels in the activated carbon coating of an untreated electrode, eg. B. with the help of a vibrating tip, with simultaneous suction of the scraped coating; d) covering the areas of a non-embossed metal foil provided for the formation of grooves or channels in the form of a regular pattern during the coating of the metal foil with the activated carbon, thereby producing uncoated areas of the electrodes which function as channels according to the invention.

The invention is explained in more detail below on the basis of exemplary embodiments and the associated figures:

Figure 1 shows an example of an electrode in a schematic longitudinal section.

FIGS. 2A, 2B show examples of further electrodes in a schematic longitudinal section.

Figure 3 shows an example of an electrode in a plan view.

FIGS. 3A, 3B, 3C show an example of a further electrode in a top view.

FIG. 4 shows a winding in a schematic cross section. FIG. 5 shows an electrochemical cell in a schematic cross section.

FIG. 5A shows a further electrochemical cell in a schematic cross section.

At this point, it is pointed out that in the figures, the same reference numerals are assigned to either the same elements or elements with the same or an equivalent function.

Figure 1 shows an electrode 1, which consists of a film 5, which is coated on the top and on the bottom with a coating 41, 42, respectively. The film 5 is an aluminum film, the thickness of the film dF being between 10 and 100 μm.

A dimension between 30 and 300 μm is usually selected for the thickness dB of the coating 41, 42. The coating is e.g. B. an activated carbon powder which has been applied to the electrode by powder coating. The average diameter of the activated carbon particles is z. B. in the range 0.2 - 5 microns. The density of the electrodes is approximately 0.6 to 0.8 g / cm ³ . The porosity of the electrodes is approx. 35 to 65%. The capacitance density is approx. 10 to 25 F / cm ³ .

Channels 2 are provided in both the upper and the lower coating 41, 42. The channels 2 are formed by interrupting the coating of the film 5. The channels 2 have the shape of grooves. They can also be viewed as depressions in the coatings 41, 42, ie it is not essential that the coatings 41, 42 are completely interrupted at the locations of the channels 2, rather it would also be sufficient if the coatings 41, 42 were on the locations of the channels 2 are only thinner than in the other areas. The width b of the channels 2 is between 0.1 and 1 mm. These dimensions are only to be regarded as advantageous dimensions. Other widths can therefore also be selected for channels 2. The distance a between two channels on the same side of the film 5 is advantageously chosen between 30 and 100 mm. In order to evenly distribute the channels 2 in the coil to be formed from the electrode 1, it is advantageous if the channels 2 on the top side are offset with respect to the channels 2 on the bottom side of the film 5.

In addition to creating the channels 2 by interrupting the coating 4, it is also possible to produce the channels 2 by removing material.

FIG. 2A shows an electrode 1 in which the channels 2 are produced by being stamped into the electrode 1. It can be seen here in particular that the depth t of the channels 2 can be set variably, so it is not as in the example according to FIG. 1, where in particular reference is made to channels 2 which are produced by interrupting the coating 4 the thickness of the coating is limited. Rather, the depth t can take many different dimensions. The depth t is advantageously between 10 and 200 μm.

The channels 2 produced by embossing according to FIG. 2 also have the advantage that on the side of the film opposite channel 2 there is an elevation of the film which is later used when the electrode is wound into a coil for additional distances between the electrode layers lying one above the other ensures and thus generate additional channels for the transport of the electrolyte liquid.

FIG. 2B shows the electrode 1, in which the channels 2 are again produced by stamping in accordance with FIG. 2A, but there is no longer any significant distance between the electrodes Channels 2 provided, rather they are directly adjacent to each other. As a result, the density of the channels can be increased to a maximum, whereby the duration of the impregnation can be reduced to a minimum time.

FIG. 3 shows an electrode 1 which runs along a longitudinal direction (indicated by the arrow). The electrode comprises an aluminum foil 5, which is partially provided with a coating 4. On the left edge, the film 5 has a free edge 7, which makes it possible to connect the winding to an external connection of the electrochemical cell by contacting the free edge. It can be seen from FIG. 3 that the channels 2 run along curved lines which, for example, can be offset parallel to one another. It can also be seen from FIG. 3 that the channels 2 cross each other and thus form crossing points 6.

The electrode shown in FIG. 3 has the advantage, on the one hand, that the channels 2 are very well homogeneously distributed over the surface of the electrode and, accordingly, later in the finished winding, accordingly homogeneously over the volume of the winding. In addition, the production can be carried out by means of a roller by stamping, wherein a discontinuity in the rolling of the roller can be largely avoided by means of projections running along the circumference of the roller.

FIGS. 3A, 3B and 3C show further possibilities for arranging the channels 2. The electrode 1 again runs in a longitudinal direction (indicated by the arrow) and is therefore particularly suitable for producing a coil according to FIG. In FIG. 3A, the channels 2 are arranged along equidistant straight pieces running parallel to one another. Such channels 2 can be produced, for example, by scratching the coating 4.

According to FIG. 3B, the channels 2 are arranged along straight lines running parallel to one another. Each channel goes 2 from an edge boundary of the electrode 1 and runs from there to the inside, but without reaching the opposite edge. The channels 2 alternately start from the upper and from the lower boundary edge of the electrode 1. Such a design of the channels 2 can have the effect that the inflow of the electrolyte from the top and from the bottom of the electrode can be promoted spatially offset from one another.

According to FIG. 3C, the channels 2 are arranged as straight lines which form an approximately right angle along a center line of the electrode 1. This makes it possible to achieve an equalization of the impregnation over the winding formed by stacking or winding electrodes 1. In particular, the distance between the channels 2 can be reduced so that there is no longitudinal section of the electrode 1 without a channel 2.

FIG. 4 shows a winding 8 which is formed from two electrodes 11, 12 and two separators 91, 92. The separators 91, 92 have the task of taking up the liquid electrolyte, which is essential for the functioning of the electrochemical cell. In addition, the separators 91, 92 have the task of avoiding a short circuit between directly opposite electrodes 11, 12 of different polarity. Paper or a porous plastic, for example, is used as the separator 91, 92. In the case of the use of paper, the separator 91, 92 is preferably formed in two layers in order to prevent the risk of pores running through the entire thickness of the separator 91, 92 in one go, which could cause a short circuit. The thickness dS of the separator 91, 92 is typically between 10 and 100 μm. The package of electrodes 11, 12 and the separators 91, 92 is wound around the winding axis 10 to form a winding 8. The channels 2 of the electrodes 1 are then evenly distributed in the finished winding 8. The layer thickness ratios in FIG. 4 also show why it is advantageous to incorporate the channels into the coating of the film. The coating of the film has the greatest thickness in the layer package, which is why the largest channels can also be produced here.

The larger the channels, the better the exchange between liquid electrolyte and gas in the coil.

Furthermore, it is advantageous if, in addition to the electrode, the separator 9 is also provided with channels for improving the impregnation.

FIG. 5 shows the impregnation process, with a winding 8 according to FIG. 4 being installed in a cylindrical housing 11. The axis of symmetry of the housing 11 and the winding axis 10 coincide. A filling opening 12 is provided on the top of the housing 11, where liquid electrolyte 3 can be filled into the housing by means of a funnel 13. The curved arrows show the direction of flow of the electrolyte 3 within the channels in the winding 8. In a comparative test, where a winding according to FIG. 4 without channels and a winding according to FIG. 4 in connection with FIG. 3A, where channels with approx. 5 cm from each other were provided, were impregnated with the same electrolyte, a reduction in the impregnation time by at least a factor of 60 could be determined. The channels can also be spaced from one another by approximately 4 to 6 cm or by approximately 1 to 10 cm. So that the electrical and mechanical properties of the electrode are not impaired, the distance between the channels is preferably greater than 0.1 cm. In order to improve the impregnation properties, the distance between the channels is preferably less than 30 cm. The distance between the channels is preferably between 0.5 and 25 cm. FIG. 5A shows an impregnation device similar to that in FIG. 5, but with the filling opening 12 being arranged directly above the core tube 14 of the winding 8 and accordingly the impregnation taking place from the underside of the winding 8, as indicated by the curved arrows.

At this point it is pointed out that the electrolyte for the electrochemical double-layer capacitor described in these examples is preferably 0.5 M to 1.6 M tetraethylammonium tetrafluoroborate in aeetonitrile.

The greater the viscosity of the electrolyte, the more channels or the wider channels are required.

The invention is not limited to electrochemical double-layer capacitors and electrodes with aluminum foil and carbon coating, but can be applied to all electrodes for all conceivable electrochemical cells that contain a liquid electrolyte.

LIST OF REFERENCE NUMBERS

1, 11, 12 electrode

2 channel 3 electrolyte

41, 42 coating

5 slide

6 crossing point

7 free edge 8 wraps

91, 92 separator

10 winding axis

11 housing

12 filling opening 13 funnel

14 Core hole dB Thickness of the coating dF Thickness of the foil dS Thickness of the separator b Width of the channel t Depth of the channel a Distance between two channels

Claims

claims

1. Electrode for an electrochemical cell with a liquid electrolyte (3) containing channels (2) in which an electrolyte liquid can flow.

2. Electrode according to claim 1, which contains a coated film (5), wherein the coating contains channels (2).

3. Electrode according to one of claims 1 or 2, wherein the channels (2) are in the form of grooves on the surface of the electrode (1).

4. Electrode according to one of claims 1 to 3, wherein the channels (2) in the electrode (1) are embossed.

5. Electrode according to one of claims 1 to 3, - which contains a coated film (5) and - in which the channels (2) are formed by uncoated partial areas of the film (5).

6. Electrode according to one of claims 1 to 5, wherein the channels (2) have a width (b) between 0.1 and 1 mm.

7. Electrode according to one of claims 1 to 6, wherein the channels (2) have a depth (t) between 10 and 200 microns.

8. Electrode according to one of claims 1 to 7, which extends along a longitudinal direction and in which the channels (2) extend transversely to the longitudinal direction.

9. Electrode according to one of claims 1 to 8, in which the channels (2) run essentially along equidistant, mutually parallel straight lines.

10. Electrode according to one of claims 1 to 7, which extends along a longitudinal direction and in which the channels (2) run obliquely to the longitudinal direction.

11. Electrode according to one of claims 1 to 8, in which the channels (2) run along curved lines which are offset parallel to one another.

12. Electrode according to one of claims 1 to 7 or 10, in which the channels (2) cross each other.

13. Electrode according to one of claims 1 to 12, which contains a metal foil coated with carbon powder.

14. Electrode coil, in which several layers of electrodes (11, 12) according to one of claims 1 to 13 are arranged one above the other.

15. Electrode coil according to claim 14, in which two electrodes (11, 12) are wound according to one of claims 1 to 13.

16. Electrochemical cell with a liquid electrolyte (3) containing a winding (8) according to one of claims 14 or 15.

17. A method for producing an electrode according to any one of claims 1 to 13, in which the coated and not yet embossed electrode is calendered at a high temperature.

18. The method according to claim 17, wherein the calendering of the electrode is integrated into the winding process for producing an electrode coil.

19. A method for producing an electrode according to any one of claims 1 to 13, in which an already embossed metal foil is coated with activated carbon.

20. A method for producing an electrode according to any one of claims 1 to 13, in which an electrode is provided by uniformly coating an embossed metal foil with an activated carbon, in which channels (2) are incised in the activated carbon layer of the electrode with simultaneous suction removal of the scraped-off coating ,

21. The method according to claim 20, b, wherein the carving of channels (2) is carried out with the aid of a vibrating tip.

22. A method for producing an electrode according to any one of claims 1 to 13, in which areas of a non-embossed metal foil provided for the formation of channels (2) are covered in a clock-shaped manner during the coating of the metal foil with activated carbon, as a result of which uncoated regions of the electrodes are formed and the Form channels (2).