SE467602B - DEVICE FOR COOLING OR HEATING AN ELECTROCHEMICAL CELL - Google Patents

Description

4-67 602 and more recently also lead batteries. Closed cells are generally made with gelled or absorbed electrolyte and then have obvious advantages: you do not need to refill water and handling and handling becomes easier and safer.

Cooling of batteries can be performed in several different ways. The most common is of course to arrange the arrangement of the cells in the battery so that the air has the opportunity to circulate between the cells. However, this cooling is not always so efficient and one must resort to methods of cooling the cells from within. So e.g. cooling ducts have been drilled through pole bridges and pole studs and cooling water has been circulated through them. Another way is to insert a plastic hose into the upper part of the cell and let cooling water pass through the hose. Both methods involve cooling only the cells at the top and with a relatively small heat transfer area between the electrolyte and the cooling medium. Another way of cooling is to allow parts of the electrodes to protrude through the lid of the cell vessel and thereby dissipate excess heat.

Another method is described in Japanese patent 60-107274 (A) where flat "heat pipes" are mounted in the battery cell next to the electrodes.

There can of course be examples of applications where the battery cells need to be heated instead of cooled.

So e.g. it may be necessary to heat batteries which are discharged and charged with such low currents that they are not significantly heated thereby, but where the electrode reactions are advantageously conducted at such a high temperature that extra heat must be supplied. What has been stated here about cooling of battery cells and especially with regard to devices according to the invention also applies to heating.

Essential to the effect of the cooling in all these cases is that the electrolyte is free-flowing so that the heat can be transferred from the electrolyte in the cell to the cooling surface by convection. The best cooling would of course be obtained by forced circulation of the electrolyte, preferably through a special heat exchanger, but this f? 467 602 would be costly, increase maintenance through the need for pump supervision and also involve power leakage due to stray currents between the cells in the battery.

The object of the invention described here is to arrange the cooling of battery cells in an efficient manner with large heat-transferring cooling surfaces without thereby interfering with either capacity or current distribution. It is also the object of the invention that it should be able to effectively cool even closed battery cells with absorbed or gelled electrolyte. It should also be shown here that the proposed method of cooling also results in a better electrical conductivity of the electrodes.

In order to facilitate the description of the invention, the construction of a battery cell will first be described here. The description of the device according to the invention is shown in Figures 1 - 7 where: Figure 1 shows an electrode package from a battery cell Figure 2 shows the device of heat-dissipating bodies connected to a pole bridge and a pole pin with heat sink.

Figure 3 shows an example of a plane of symmetry in lead-acid battery electrodes a) tube electrode b) flat electrode Figure 4 shows an example of a heat-dissipating body at an electrode that is first divided into two equal halves.

Figure 5 shows an embodiment of a heat dissipating body for a pleated electrode.

Figure 6 shows a battery with cooling device according to the invention connected to a special pole pin with cooling flange.

Figure 7 shows the connection of the heat-dissipating bodies to one of the pole pins of the electrodes, which is provided with a cooling flange: 467 602 A battery cell consists essentially of vessels with electrolyte and a number of electrodes (1,2), at least one of each polarity, and separated by separators (3). Electrodes of the same polarity are connected to each other in parallel as Figure 1 shows. It is most common for the electrodes to be connected at the top of the cell and connected to a so-called pole bridge (5) which in turn is in metallic connection with a pole pin (6) which passes out through the cell via special penetrations in the lid. The number of pole pins can be one or more for each electrode stroke.

The electrodes usually consist of plane-parallel, porous disks, although in e.g. lead batteries occur that one electrode stroke may be composed of a number of rods or tubes (Figure 3a). However, these are arranged so that together they form a substantially plane-parallel disc. Each electrode is provided, usually at the top, with a current-dissipating tab (4), which is connected to the just-mentioned pole bridge (5) by soldering, casting or screwing. The electrodes are generally constructed so that an active material e.g. lead dioxide, nickel oxide or manganese dioxide in the positive electrodes are applied to or around an electrical conductor often specially designed to retain the active material. Such conductive (inactive) materials may be lead or lead alloys, nickel mesh, carbon or graphite sheets. The negative electrodes in the same way consist of active material but of a different composition and inactive material as current conductors. The separators (3) between the electrodes consist of porous, electrically conductive disks which are made as thin as possible in order to reduce the internal resistance while at the same time preventing short circuits between electrodes of opposite polarity.

All electrodes included in battery cells are mostly symmetrically built around a plane (12) in the middle of the electrode, parallel to the electrode's distribution in height and width and perpendicular to the current lines. This provides the best distribution of current within the cell and the best utilization of the active material. In the height of the electrodes, on the other hand, there may be varying amounts of active and inactive material.

In some cases the electrodes are folded or cupped, but this does not prevent one from finding planes of symmetry with the above-mentioned definition.

In some constructions known e.g. by the Swedish patent application 8300141-2, the plane of symmetry in its entirety is not parallel to a plane in the distribution of the electrode, but nevertheless the electrode is divided into two symmetrical halves in such a way that each half works separately against the opposite electrode.

The object of the present invention is to place in the electrodes of symmetry (12) of the kind described here heat-dissipating bodies (7) which by this placement do not affect the working methods of the electrodes with respect to current distribution or utilization of the active material. Such heat dissipating bodies of e.g. copper plate can furthermore be given an extension over the entire plane of symmetry of the electrode, i.e. the entire height and width of the electrode. Such a device is thus not limited only to the upper parts of the cell with its heat transfer surface. The heat dissipating bodies can even made larger than the surface of the electrode and also supported against the walls of the cell vessel. By placing the bodies in close contact with e.g. the negative electrodes in a lead-acid battery by soldering to the current-conducting grids, the heat dissipation is further improved and in addition the conductivity of the grids is increased, i.e. the internal resistance of the cell decreases.

As copper has a particularly good thermal conductivity, this material is protected in various geometric shapes as a thermal conductor. For example, the heat dissipating bodies can be provided with a surface enlarging structure, made in a folded form or provided with holes if this proves to be suitable. However, copper in contact with the positive electrode can corrode greatly, especially if the electrolyte is sulfuric acid. In such a case, it should be protected with some durable pore-free coating, e.g. polythene plastic or 467,602 the like which can be applied e.g. as a powder on the heated metal. If copper is used as a heat-dissipating body in contact with the negative electrode, it is generally cathodically protected and hardly even needs to be given any extra protection in sulfuric acid, although it must be considered advantageous to give it a protective layer of e.g. lead with an intermediate layer of tin.

However, the invention is not limited to copper as a heat-dissipating material in a manner known per se.

The object of the invention is further to provide these heat-dissipating bodies in the plane of symmetry of the electrodes with connections (9) and to connect them to a pole bridge (8) and a pole pin (10) in a corresponding manner which takes place with the electrodes. This pole pin can have a polarity depending on whether the heat-dissipating bodies are uninsulated and in contact with one of the electrodes or be electrically non-conductive if the bodies have been insulated by e.g. a thin coating of plastic. The connection can of course be made to more than one pole pin of the same polarity and heat-dissipating bodies can be placed in both negative and positive electrodes with corresponding poles in one and the same battery cell. To better dissipate the heat from the pole pins, these can be fitted with cooling fins (11). The heat can then be quickly dissipated from the pole pin (10) or the heat sink (II). The heat can then be quickly dissipated from the pole pin (10) or the heat sink (II) by blowing air or by allowing cooling water to flow through or around the heat sink. Cooling can also be done by immersing the battery cell in water, especially if the cell is of the closed type.

The pole pins from a battery are usually placed in the lid of the cell vessel. Figure 7. However, the bushing of the cooling device's pole pin or pin pins is not restricted to the lid of the cell but can be applied just as well to the walls or bottom of the cell. Such a device is advantageous if space cannot be provided for these pole pins with their heat sinks on the top of the cell.

It is particularly advantageous to supply battery cells which have absorbed or gelled acid with the device according to the invention when f? 467 602 in these cells cooling by convection i.e. transport of heated electrolyte can not easily take place to the upper parts of the cell. In the case of closed cells, the device is particularly advantageous when not only the electrolyte is absorbed but the separators and the pores of the electrodes are usually not completely filled with electrolyte ("starved electrolyte"), in order thereby to facilitate the oxygen recombination. In such cells not only is the heat convection further complicated but there is an addition of heat due to the exothermic reaction between the oxygen gas and the negative electrodes and particularly good cooling action is achieved then by the heat dissipating bodies being applied to the negative electrodes.

In a preferred embodiment of the cooling device according to the invention, lead-clad copper plates 0.5 mm thin have been soldered between the double negative electrodes in a (momopolar) lead battery, which are provided with connection tabs at the top. The connection to a lead-clad copper pole with a round cross-section takes place via a pole bridge, also of lead-clad copper which is placed above the electrodes and perpendicular to them. The pole pin of the heat-dissipating bodies is mounted centrally in the lid and provided with a cooling flange of known construction.

In a preferred embodiment intended for electrodes according to the Swedish patent application 8300141-2, plastic coated plates 0.5 mm thick have been placed between the halves of the positive electrodes and isolated from the active material. (Figure 5). The plates have been given a pleated shape which corresponds to the shape of the electrode halves and are connected to a pole pin with a heat sink as previously described.

The material in the heat dissipating bodies is preferably of copper, since the heat dissipation in this material by volume is e.g. about 10 times better than for lead. For corresponding cooling, a 5 mm thick lead plate would thus be needed between the electrode halves. When particularly light constructions are desired, it may be more advantageous to design the heat-dissipating 467 602 bodies in aluminum protected by a thin plastic. Aluminum conducts heat about twice as well as copper by weight.

Table 1. Heat dissipation capacity of different metals at 298K according to Handbook of Chemistry and Physics 1978-79 in W / cm'OK Aluminum 2.37 Tin 0.56 Lead 0.34 Titanium 0.22 Carbon, amorphous 0.06 Zinc 1.16 graphite 0.8-2.2 Lithium 0.85 pyrolytic 0.06 * Silver 4.29 graphite 19.6 ** Gold 3.18 Copper 4.01 Nickel 0.9 Iron 0.8 *) Perpendicular to the plane **) Parallel to the plane

Claims (9)

467 602 PATENT REQUIREMENTS Device for cooling or heating an electrochemical cell by heat transport from the inner parts of the cell to the surrounding outer space via thermally conductive bodies having a higher thermal conductivity than the electrode conductive electrode material, characterized in that the thermally conductive bodies (7) are located in several electrodes and in the plane of symmetry of the respective electrodes (12) without appreciably affecting the current distribution and that said bodies are connected to one or more pole pins (6) arranged in the walls or lids of the cell. Device according to claim 1, characterized in that the heat dissipating bodies consist of metal plates of substantially the same extent in width and height as the electrodes and placed in the plane of symmetry of the electrodes (12) perpendicular to the current direction between electrodes of opposite polarity. Device according to claim 1, characterized in that the heat-conducting bodies placed in the symmetry plane of one electrode stroke are connected to a pole pin and the heat-dissipating bodies placed in the plane of symmetry of the other electrode stroke are connected to another pole pin. 4. Device according to claims 1-3, characterized in that the heat-conducting bodies in contact with the positive electrodes are electrically insulated from them by a coating of plastic, paint or such electrically non-conductive material. 5. Device according to claims 1-3, characterized in that the heat-conducting bodies at the negative electrodes are brought into close contact with them by pressing, soldering or similar methods. 467 602 10 Device according to claims 1-5, characterized in that the thermally conductive bodies are located in the plane of symmetry of the negative electrodes, in metallic contact with said electrodes and in that said thermally conductive bodies are connected to one or more pole pins (10) arranged in the walls of the cell. or lid. 'J Device according to claims 1-5, characterized in that the thermally conductive bodies (7) are located in the plane of symmetry of the positive and negative electrodes, at the positive electrodes isolated from them and at the negative electrodes in metallic contact with them and that said heat-conducting bodies are leading to one or more pole pins (6) for each electrode stroke arranged in the walls or lids of the cell. Device according to claims 1-7, characterized in that the heat-conducting bodies consist of copper plates coated with lead and at the positive electrodes protected with plastic coatings. Device according to claims 1-7, characterized in that the heat-conducting bodies are connected to at least one of the positive or negative poles of the battery cell connected to corresponding electrodes.