WO1989010011A1

WO1989010011A1 - Means for heat battery management of batteries and lead acid battery with this means

Info

Publication number: WO1989010011A1
Application number: PCT/SE1989/000200
Authority: WO
Inventors: Ove Nilsson; Erik Sundberg
Original assignee: Ove Nilsson; Erik Sundberg
Priority date: 1988-04-11
Filing date: 1989-04-11
Publication date: 1989-10-19
Also published as: SE467602B; EP0403569A1; SE8801318L; SE8801318D0

Abstract

A means for cooling or heating electrochemical batteries or cells comprising heat conducting bodies (7) made in the form of sheets of same width and height as the electrodes and placed in the symmetry plane (12) of the electrodes not to influence the current distribution. The heat conducting bodies have higher heat transfer capability than the electric conductive material in the electrodes. The heat is transferred from the interior of the batteries or cells to the surroundings via the heat conducting bodies (7), a post strap (8) that joins the heat conducting bodies and one or more posts (10), which protrude through the battery lid or walls and are provided with devices (11) for enhanced heat dissipation. The means has efficient cooling capacity for all kinds of batteries and cells, but is of particular interest for batteries with immobilized - gelled or absorbed - electrolyte.

Description

MEANS FOR HEAT BATTERY MANAGEMENT OF BATTERIES AND LEAD ACID BATTERY WITH THIS MEANS

Electrochemical batteries or cells are usually warmed up by the currents passing through them during charging as well as during discharging. The heating is depending on the intensity of the currents. The reason for the heating is mainly due to the inner resistance that characterize the battery. Further, the irreversible electrode processes i.e. gas evolution that occurs especially at the end of the charging period, also warm up the battery. Batteries that are used for e.g. electrical trucks, electrical cars and submarines are often discharged and also charged by high currents and thus need to be cooled so that the maximum allowed temperature is not exceeded. For instance, cooling may be needed when a battery driven truck provided with only one exchange battery is used continuously during three shifts. In such cases the batteries have to be charged during 8 hours and thereafter immediately put on duty.

The inner resistance of a battery can certainly be decreased by e.g. giving the current conducting parts larger cross section areas. This, however, causes a higher weight and a larger volume and it also increases the cost. Another way to reduce the inner resistance might be a decreased distance between the electrodes. The result will be less electrolyte and, at least when lead acid batteries are considered, a decreased capacity. Alkaline Ni/Cd batteries on the other hand will not suffer in the same way, since their capacities do not depend on the amount of electrolyte.

A short electrode distance has the advantage that the so called oxygen recombination in the battery is enhanced. This phenomenon implies that oxygen, which is evolved at the positive electrodes, is transferred to the opposite negative electrodes, where it is electrochemically reduced to water. As a consequence, hydrogen can not be evolved on these electrodes surfaces. If this process is functioning well, there will be no gas evolution at all in the battery, which accordingly can be sealed. Since long there have been Ni/Cd batteries on the market working in sealed condition and lately also lead acid batteries. Sealed batteries are usually made with gelled or absorbed electrolyte and have thus following advantages: they need not to be topped up with water and the handling and management is easier and safer.

The cooling of the batteries can be made in several ways. The most usual is of course to arrange the battery so that the surrounding air will circulate around the cells. This solution to the problem of cooling is however not always efficient enough. In stead one has to cool the interior of the cells. To achieve this one then has to e.g. arrange channels within the posts and the post straps through which cooling water is circulated. Another way is to put a plastic tube inside the cells in the electrolyte and above the electrodes and circulate the cooling water through the tube. These methods however allow the cells to be cooled only in their upper part. Further, the surface for heat transfer is rather small.

Another way to enhance cooling is to allow parts of the electrodes to protrude through the lid of the cell jar and thus conduct the excess heat to the ambient air. Still another method is described in the Japanese patent 60-107274 (A), where a number of flat heat pipes are arranged in the battery cells at the side of the electrodes.

There are certainly also occasions when the batteries need to be warmed up instead of cooled. For instance, it might be necessary to warm batteries that are discharged and charged by currents so small that no substantial heat is evolved by these currents. It could in some case be advantageous for the electrode reactions to take place at a higher temperature and thus addition of extra heat could be useful. What is here said about cooling of bat teries and expecially concerning the devices according to this invention is also applicable to heating.

Important for the cooling efficiency in the so far mentioned applications is that the electrolyte is free flowing so that the heat can be tranferred by convection from e electrolyte in the cell to the surface of the cooling equipment. Most efficient cooling is obtained by forced flow of electrolyte especially if through an efficient heat exchanger. This will however be costly, increase the need of maintenance of pumps and also cause current leakage due to stray currents between the cells in the battery.

The object of the invention described here is to arrange the cooling of the cells in a battery in an efficient way using larger surfaces for heat transfer without any change in neither the cell capacity nor the current distribution.

The object of the invention is further to provide means to efficiently cool also sealed battery cells with absorbed or gelled electrolyte.

It shall here also be shown that the proposed method for cooling means a better electric conductivity of the electrode.

In order to facilitate the description of the invention, the construction of a battery cell is first depicted. The design of the device and the arrangement according to the invention is given in figure 1-7 where:

Figure 1 shows a group of electrodes constituting a battery cell.

Figure 2 shows an arrangement of heat transferring bodies connected to a post strap and a post with a cooling flange.

Figure 3 shows an example of a plane of symmetry in a lead acid battery electrode A) a tubular electrode B) a flat electrode. Figure 4 shows an example of a heat transferring body according to the invention at an electrode parted in two symmetrical halves.

Figure 5 shows a design of a heat transferring body intended for a plaited electrode.

Figure 6 shows a battery with heat transferring bodies according to the invention and connected to a special post that is provided with a cooling flange.

Figure 7 shows a battery with heat transferring bodies according to the invention and connected to the negative post that is provided with a cooling flange.

An electrochemical cell of battery consists in principle of a container with the electrolyte and a number of electrodes (1,2) at least one of each polarity, parted by separators (3). Electrodes of equal polarity are connected with each other in parallel as is shown in figure 1. Usually the electrodes are connected in the upper part of the cell via a post strap (5) which is in its turn is connected to a post (6) protruding through the cell via special arrangements in the lid. The number of posts can be one or more for each kind of electrode.

The electrodes are generally flat, porous plates (figure 3 B) though it e.g. in lead acid batteries also occurs that one kind of electrode can be built of a number of round poles of tubes (figure 3 A). These are arranged side by side to make a plate with mainly parallel surfaces. Each electrode is provided with a current collecting lug (4), often placed in the upper part of the electrode which by soldering, casting or screwing then is connected to the post strap (5). The electrodes are generally constructed so that an active material e.g. lead dioxide, nickel oxide or manganese dioxide in the positive electrode is fixed on to or around an electric conductor often especially designed to keep the active material in place. Such conductive (in-active) material could be made from lead or lead alloys, nickel screens, carbon- or graphite plates. The negative electrodes consist in the same way of active material, but of another composition, and inactive material as the current conductor.

The separators (3) between the electrodes are made in e form of porous, electric non-conducting plates. They are made as thin as possible in order to reduce the inner resistance but at the same time being able to prevent short circuits between electrodes of opposite polarity.

All electrodes in a battery cell are in most cases built symmetrically with reference to a plane (12) parting the electrode parallel to its extension with regard to width and height and perpendicular to the current flow. This will give the best current distribution within the cell and also the best utilization of the active material. Considering the height of the electrode, there could however be variations in the amounts of active and inactive materials. In some cases the electrodes could be plaited or globular, but his should not prevent the location of a symmetry plane with said definition.

In some constructions known e.g. by the Swedish Patent Appl. 8300141-2 the plane of symmetry is not entirely parallel to a plane in the extension of the electrodes, but never the less the electrode is divided in two symmetric halves in a way that each of these half electrodes works against the opposite electrode.

The object of the invention is to place heat conducting bodies (7) in said symmetry planes (12) of the electrodes, meaning that said heat conducting bodies do not influence the function of the electrode with respect to current distribution or active material utilization. Such heat conducting bodies made of e.g. copper sheets can be given dimensions equal to the symmetry plane of the whole electrode i.e. equal to the height and width of the electrode. An arrangement of this kind is thus not limited to the upper part of the cell with regard to its surface for heat transfer. The heat conducting bodies can even be larger than the surface of the electrodes and also be supported by the side walls of the container. If said bodies are attached to the negative electrodes of a lead acid battery by soldering against the current conducting grids, the heat conducting is further improved and besides, the current conduction of the grid will increase i.e. the inner resistance of the cell will decrease.

Copper is an excellent heat conductor and thus this material is preferred in different geometrical forms. For instance, the heat conducting bodies can be given different kinds of surfaces enlargements, be made in plaited form or be perforated if this should fit the purpose of heat transfer. However, copper in contact with the positive electrode may corrode heavily especially if the electrolyte is sulphuric acid. It must in such cases be covered by durable, pore free material e.g. polyethylene. If copper is used as the heat conducting body in contact with the negative electrode it is generally protected by the cathodic potential and need not even in sulphuric acid be given any extra cover though it must be considered advantageous to cover the heat conducting copper plates with e.g. lead with a layer of tin in between. The invention is however not limited to copper as heat conducting material.

The objective of the invention is further to provide these heat conducting bodies placed in the symmetry plane of the electrodes with lugs (9) and to connect these lugs to a post strap (8) and a post (10) in a way corresponding to the way the electrodes are connected. This post has a polarity if the heat conducting bodies are in electrical contact with any of the electrodes but is nonconducting if said bodies are isolated by e.g. a thin layer of plastics. The connection can of course be made to more than one post of same polarity. The heat conducting bodies can be placed in both the negative and the positive electrodes and being connected to the posts of corresponding polarity. To improve the heat conduction, the posts can be provided with cooling flages (11) and the heat can be quickly dissipated from said post and said cooling flange by e.g. air blowing or by cooling water that flows through or around the post. Cooling can also be enhanced by placing the battery in water, especially if it is of the saled type.

The posts of the battery are usually protruding the lid of the container (figure 7). The position of the post or posts connected to the heat conducting bodies is however not limited to the lid but can be as well in the walls as in the bottom of the container. This arrangement is advantageous if there should not be room for said post and cooling flage on the upper area of the cell.

An alternative design (figure 8) in accordance with the invention is to connect the heat conducting bodies to that post which is connected to one kind of electrode or the other and to apply a cooling flange to this post.

It is of particular advantage to apply the invention to batteries with absorbed or gelled acid since the heat transfer is restrained in such cells i.e. the transport of warmed up electrolyte to the upper part of the cell can not easily occur. If the cells are sealed in this invention of special advantage due to the fact that the electrolyte in such cells is not only absorbed but the separators and the pores of the active materials are not fully filled up with electrolyte ("starved electrolyte") which is known to facilitate the oxygen recombination. In such cells is not only the heat transfer further aggravated but there will also be additional heat ensued from the exothermal reaction between oxygen and the negative electrodes. Especially effecient cooling is then obtained by applying the heat transfer bodies according to the invention, in the negative electrodes.

In a preferred embodiment of the cooling arrangement according to the invention are lead copper sheets (7), 0,5 mm thick and provided with lugs (9), interleaved between double negative electrodes (13) and soldered to said electrodes. The connection to a lead coated copper post (10) with circular cross section is made via a post strap (8) also made form lead coated copper and which is located above the electrodes and perpendicular to said electrodes. The post of the heat conducting bodies is protruding in the middle of the lid and provided with a cooling flange of known construction.

In a preferred embodiment referring to electrodes in accordance with the Swedish Patent Appl. 6300141-2 are plastic covered sheets of copper, 0,5 mm thick, placed between the positive half electrodes. The copper sheets have been given a plaited form that coincide with the form of the electrode and are connected to a post with cooling flange as described above.

The material chosen for the heat conducting bodies is preferential copper since the hat conducting of this material per volume is about ten times higher compared to lead. To obtain a heat transfer effect corresponding to said prefered embodiment one should need a 5 mm thick sheet of lead between the double negative electrodes. In battery constructions where weight saving is important it could be more advantageous to make the heat conducting bodies from aluminium covered by e.g. a thin layer of plastic. Aluminium has about twice the heat conducting capability per weight compared to copper. Table 1. Heat conduction in W/cm, K for some materials at 298 K according to Handbook of Chemistry and Physics 1978-79.

Aluminium 2.37 Carbon amorph 0.06

Lead 0.34 graphite 0.8-2.2

Copper 4.01 pyrolytic 0.06 *)

Iron 0.8 graphite 19.6 **)

Tin 0.56 Silver 0.29

Zinc 1.16 Gold 3.18

Nickel 0.9

*) perpendicular to the carbon layer **) parallel to the carbon layer

Claims

1. A means for cooling or heating a battery or an electrochemical cell having at least one positive and one negative electrode, by heat transfer from the interior of the cell or battery to the surroundings via heat conducting bodies having higher heat transfer capability than the electrical conducting material in the electrodes characterized in that said heat conducting bodies (7) are placed in the plane of symmetry (12) of one or several electrodes in such a way that the current distribution is not influenced and connected to one or several posts protruding through the lid or the walls of the battery or cell container.

2. A means according to claim 1 characterized in that said heat conducting bodies are sheets of metal of mainly the same width and height as said electrodes and placed in the symmetry plane of said electrodes perpendicular to the current flow.

3. A means according to claim 1 and 2 characterized in that said heat conducting bodies placed in the symmetry plane of one kind of electrodes are connected to one post and the heat conducting bodies placed in the symmetry plane of the other kind of electrodes are connected to another post.

4. A means according to claim 1-3 characterized in that said heat conducting bodies in contact with the positive electrodes are isolated from said positive electrodes by a coating of plastic, paint or similar non-conducting material.

5. A means according to claim 1-3 characterized in that said heat conducting bodies are in close metallic contact with the negative electrodes by pressure or solder or similar methods.

SUBSTITUTE SHEET

6. A means according to claim 1-5 characteized in that said heat conducting bodies are placed in the symmertry plane of the negative electrodes and in close contact with said electrodes and said electrodes being joined to one or several posts protruding through the lid or the walls of the container and said posts being provided with means for cooling by air or water.

7. A means according to claim 1-5 characterized in that said heat conducting bodies are placed in the symmetry plane of the positive and the negative electrodes, in the positive electrodes isolated from said positive electrodes and in the negative electrodes in close contact with said negative electrodes and said electrodes being joined to one or several posts for each kind of electrode protruding through the lid or the walls of the container and said posts being provided with means for cooling by air or water.

8. A means according to claim 1-7 characterized in that the heat conducting bodies are made from copper covered by a layer of lead and at the positive electrodes further covered by a plastic coating.

9. A means according to claim 1-8 characterized in that the heat conducting bud ies are connected to at least one of the pos iti ve or negative posts of the battery and said posts being provided with means for cooloing by air or water.

10. A lead acid battery comprising at least one positive and one negative electrode and interleaved separator, sulfuric acid in an amount sufficient for discharging the battery and a mean for cooling or heating said battery by transferring heat from the interior of said battery to the surroundings via heat conducting bodies having higher heat transfer capability than the electrical conducting material in the electrodes characterized in that said heat conducting bodies (7) are placed in the plane of symmetry (12) of one or several electrodes in such a way that the current distribution is not influenced and connected to one or several posts protruding through the lid or the walls of the battery or cell container.

11. A lead acid battery comprising at least one positive and one negative electrode and interleaved separator, sulfuric acid in an amount sufficient for discharging the battery and a mean for cooling or heating said battery by transferring heat from the interior of said battery to the surroundings via heat conducting bodies having higher heat transfer capability than the electrical conducting material in the electrodes characterized in that said heat conducting bodies (7) are placed in the plane of symmetry (12) of the negative electrodes, said negative electrodes being constructed of two identical parts (14) having said heat conducting body (9) interleaved and placed in the symmetry plane in such a way that the current distribution is not influenced and said negative electrode being connected to one or several posts protruding through the lid or the walls of the battery or cell container and said posts being provided with means for cooling by air or water.