Electrochemical energy storing device

Abstract

A very high capacity capacitor or energy storage comprising a two-layer electrode structure with a separator and an electrolytic fluid, where the electrodes are parallel and connected to one of two terminals. The electrodes are connected to the terminal along a large length so that the connection to the terminal has a low resistance and so that charging may take place faster and with less heat generation.

Claims

1. A high capacitance capacitor having: a housing, a first plurality of first electrodes, a second plurality of second electrodes, a separator between each pair of a first and a second electrode, and an electrolytic liquid between electrodes and in the separator, wherein: the first plurality of first electrodes are at least substantially parallel plate-shaped conductors each attached, along a furthermost edge thereof, directly to a first terminal, each first electrode extending a predetermined first distance, along a first predetermined direction, from the first terminal, the second plurality second electrodes are plate-shaped conductors at least substantially parallel to each other and to the first conductors and each attached, along a furthermost edge thereof, directly to a second terminal, one of the second plurality of conductors being positioned between a pair of neighbouring conductors of the first plurality, each second electrode extending a predetermined second distance, along a second, predetermined direction, from the second terminal, each of the first electrodes is connected to the first terminal over a distance exceeding the first distance, each of the second electrodes is connected to the second terminal over a distance exceeding the second distance, one side of the first terminal is exposed to the surroundings forming an outer surface of the housing, one side of the second terminal is exposed to the surroundings forming an outer surface of the housing, and the first and second electrodes are directly attached to the first and second terminal, respectively.

2. The capacitor of claim 1, wherein the first and second terminals form two opposite outer surfaces of the housing.

3. The capacitor of claim 1, wherein the first and second terminals each have an area that overlaps, when projected to a plane parallel to the terminal, with at least 50% of the edges of the electrodes at which the electrodes are connected to said terminal.

4. The capacitor according to claim 1, wherein the first and second terminals each have an area, which does not exceed, when projected to a plane parallel to the terminal, the area between the edges of the two outermost electrodes at which the electrodes are connected to the inner side of the terminal.

5. The capacitor according to claim 1, wherein the electrodes are planar.

6. The capacitor according to claim 1, wherein each of the first electrodes are connected to the first terminal over a distance exceeding 1.5 times the first distance and each of the second electrodes are connected to the second terminal over a distance exceeding 1.5 times the second distance.

7. The capacitor according to claim 6, wherein each of the first electrodes are connected to the first terminal over a distance exceeding 2 times the first distance and each of the second electrodes are connected to the second terminal over a distance exceeding 2 times the second distance.

8. The capacitor according to claim 1, wherein at least one electrode comprises a base layer and a coating on two opposite sides of the base layer.

9. A capacitor according to claim 8, wherein the coating comprises nanotubes.

10. A capacitor according to claim 8, wherein the base layer comprises an electrically conducting material.

11. A capacitor according to claim 8, wherein the coating comprises carbon.

12. A capacitor according to claim 8, wherein the base layer comprises aluminium.

13. A capacitor according to claim 1, wherein the electrolytic liquid comprises 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (C.sub.8H.sub.11F.sub.6N.sub.3O.sub.4S.sub.2).

14. The capacitor according to claim 1, wherein the separator comprises PTFE comprising pores allowing the electrolytic fluid pass there-into.

15. The capacitor of claim 1, wherein the first and second terminals each have an area that overlaps, when projected to a plane parallel to the terminal, with at least 90% of the edges of the electrodes at which the electrodes are connected to said terminal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments will be described with reference to the drawing,

(2) wherein:

(3) FIG. 1 illustrates a prior art high capacity capacitor,

(4) FIG. 2 illustrates a high capacity capacitor (the housing is only partly shown) according to the invention,

(5) FIG. 3 illustrates the dimensions of an electrode for use in the capacitor of FIG. 2,

(6) FIG. 4 illustrates the capacitor of FIG. 2 including housing seen from the side and

(7) FIG. 5 illustrates the capacitor of FIG. 4 from the top.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 illustrates a prior art high capacitance capacitor having a number of first and second electrodes of which a first electrode 12 and a second electrode 16 are illustrated. The electrodes are provided in a parallel fashion and all first electrodes are connected to a first terminal 14 and all second electrodes are connected to a second terminal 18. Usually, in order to obtain a higher capacity (surface area), a fluid electrolyte is provided between the electrodes, and a separator material (not illustrated) is provided between each pair of neighbouring electrodes.

(9) The connections are made via thin extensions of the electrode materials (at the top). A problem seen in this design is that the charge provided on an electrode must travel through the narrow extension of the electrode to be available at the terminal. This narrow extension creates a bottle neck increasing the internal resistance and thus the heat generation during fast charging/discharging. Also, the narrow extension limits the charging/discharging speed altogether.

(10) In FIG. 2, a capacitor 20 according to the invention is seen, where the elements of the circle have been expanded to illustrate the internal structure. For a better understanding of the construction details, parts of the capacitor housing are not shown. However, the first terminal 24 and the second terminal 28 that form the outer conducting surfaces of the housing are shown. The first and second terminals 24/28 form two opposite surfaces of the capacitor housing.

(11) Again, first and second electrodes are provided in an interleaved, parallel structure. Again, separators 27 are provided between each pair of neighbouring electrodes, and a liquid electrolyte is provided between the electrodes and within the separator.

(12) The first electrodes 22 are attached to a first terminal 24, and the second electrodes 26 are attached to a second terminal 28.

(13) However, the electrodes are now directly attached to the terminal along a side thereof so that the charge is fed directly from the terminal to the electrode.

(14) In fact, see FIG. 3, the electrodes 22/26 preferably are quadrangular and directly attached to the terminals (upper fat line) and have a width, W, along the edge attached to the terminal, which exceeds a length, L, thereof, where the length is in a direction away from the terminal, such as perpendicular thereto.

(15) With this structure, the charge fed to the electrode is fed thereto over a large area, whereby the resistance is kept low. In addition, the distance which the charge has to travel is kept as short as possible, whereby also the resistance is minimized and the heat generation kept to a minimum while the charging/discharging time is optimized.

(16) The dimensions are directly influencing the parameters of the capacitor. The length describes the distance which the charge has to travel and thus the charging/discharging time and the resistance and heat generation, whereas the width describes the overall capacitance of the capacitor.

(17) Preferably, the electrodes comprise an inner layer, a current collector, and a coating thereof, the electrode material.

(18) The preferred current collector is made of Aluminium, as it has a high conductivity and at the same time is cheap and light. Other conductors, however, may also be used, such as Copper, Gold and Silver. Basically any conductive element or composite thereof may be used.

(19) Preferred electrodes are based on Porous Carbon and especially Carbon based materials with large surface areas, such as materials comprising nanotubes. Other conducting materials, such as silicon-based materials or composites with metal may be used.

(20) The presently preferred electrolyte is 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (C.sub.8H.sub.11F.sub.6N.sub.3O.sub.4S.sub.2). In general, water-based electrolytes are faster but have low decomposition voltages, whereas organic electrolytes are slower but have a higher decomposition voltages. Naturally, a fast electrolyte with a high decomposition voltage is desired.

(21) Alternative electrolytes may be common organic electrolytes, such as tetraelthylammonium tetrafluoroborate (TEABF.sub.4) (C.sub.8H.sub.20BF.sub.4N)—(C.sub.2H.sub.5).sub.4N(BF.sub.4) in either propylene carbonate (PC) or acetonitrile (AN). Common aqueous electrolytes include KOH and H.sub.2SO.sub.4.

(22) The presently preferred separator is a PTFE Based membranous material. Preferably, the separator is chemically inert, and has a customizable pore size and pore distribution.

(23) Alternative separator materials may be paper, textile or tailored plastics. Basically, any material may be used, as long as it has pores big enough to let the electrolyte pass.

(24) The present capacitor is especially suited for use with very large charges and thus as a very large capacitance. Capacitances on the order of 0.5 to 1 MF are foreseen, whereby the capacitor itself will have the size or volume as 10,000 cm.sup.3 to 15,000 cm.sup.3 (10-15 l). Thus, the present capacitor may be used in a very different context than small capacitors attached to a PCB.

(25) The present capacitor is provided in a housing (see FIGS. 4 and 5) wherein, the terminals 24/28 form the outer conducting surfaces of the housing. Preferably, the terminals 24/28 are exposed on two opposite surfaces, so that the present capacitors may be simply stacked into a pile to be able to handle a higher voltage—or combined in parallel to achieve a higher capacitance.

(26) Thus, the two largest surfaces of the housing 30 may be formed by the outer surfaces of the terminals 24/28 or elements connected to the electrodes. The housing 30 is preferably a box shaped housing. Preferably, these surfaces are the outermost surfaces so that capacitors may simply be stacked so that electrodes of adjacent capacitors touch. The first and second terminals 24/28 do not stick out, when projected to a plane parallel to the first and second terminals 24/28, of the outer edges of the remaining part of the housing 30. When projected to a plane parallel to the terminals, the first and second terminals 24/28 each has an area that overlaps with at least 50%, more preferably with at least 75%, in particular with at least 90% of the edges of the electrodes at which the electrodes are connected to the inner side of said terminal and also with at least 50%, more preferably with at least 75%, in particular with at least 90% of the area of the electrodes.

(27) In FIG. 5, the capacitor of FIG. 4 is illustrated from the top. Thus, the terminal 28 that is exposed to the surroundings has an area, which does not exceed, when projected to a plane parallel to the terminal (≙top view), the area between the edges of the two outermost electrodes that are connected to the inner side of the terminal.

(28) Furthermore, protruding elements 32 can be arranged at the side of the housing 30 comprising the terminal 28 forming the outer conductive surface, as the present type of capacitor is usually polarized. Corresponding indentations may be provided at the opposite side of the housing 30 comprising the terminal 24 (not indicated) forming the further outer conductive surface. Thus, the protruding elements 32 may be provided at one polarization to prevent oppositely polarized surfaces of other capacitors being connected to the terminal 28 of the housing. This is a simple physical encoding ensuring correct attachment of capacitors when stacking.