GB1576273A

GB1576273A - Circulating electrolyte batteries

Info

Publication number: GB1576273A
Application number: GB4684/77A
Authority: GB
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1976-02-05
Filing date: 1977-02-04
Publication date: 1980-10-08
Also published as: IT1080816B; JPS5296326A; FR2340624A1; FR2340624B1; DE2704314A1; CA1070376A

Description

(54) CIRCULATING ELECTROLYTE BATTERIES (71) We, WESTINGHOUSE ELECTRIC CORPORATION of Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania, United States of America, a company organised and existing under the laws of the Commonwealth of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to circulating electrolyte batteries.

Secondary electric storage cells, operating at high rates of charge and discharge, require some method of cooling to prevent overheating. This is especially true for electric vehicle applications, where a large number of interconnected cells and a tight packaging arrangement may be required. One solution is to circulate electrolyte as a heat exchange medium through a cell and into a cooling reservoir, and then to recirculate the electrolyte back into the cell.

This solution was recognized in U.S. Patent 400,215 where an electrolyte supply pipe was arranged at the bottom of a galvanic battery.

This forced fresh electrolyte up and around the electrodes in each cell stack-up. U.S. Patent 3,666,561 discloses a zinc-air battery with circulation of electrolyte through a series of electric battery cells. The circulation was accomplished by pumping electrolyte into the bottom of each cell. Electrolyte, from an electrolyte chamber, flows up through each cell and is removed from the top of each cell through outlet pipes. The electrode stack-up is not sealed against the container, so that electrolyte may flow around one of the three plates of each cell, and oxygen gas is introduced into the electrolyte circulation system to reduce internal battery current.

Necessarily, a circulating electrolyte cooling system for a battery is complicated, and to date not all of the problems associated with such systems have been solved. Nearly all secondary electric storage cell cases are composed of metal, glass, rubber, or plastics. Cell stack-ups are inserted into the boxes and then a cover is attached. When it is desired to circulate electrolyte through the cell stack-up for cooling purposes, standard case and electrode stack-up construction has not proved satisfactory.

Associated with circulating electrolyte systems are the problems of: cooling every cell on charge and/or discharge to permit high current rates to be used, hermetic joints between terminals, inlet and outlet tubes and case walls; encapsulation and sealing of cell stack-ups, so that electrolyte will be forced to go through them when going from an inlet to an outlet in the case; electrolyte level maintenance; electrolyte specific gravity control and uniformity; collection and elimination of explosive hydrogen and oxygen gases at one location, where proper safety precautions can be taken; and making the system simple, so that cell size changes can be readily and inexpensively accomplished.

To solve all of these problems, the battery has to have the following features: leakproof, since electrolyte is circulating under pressure, all the cell cases and plumbing connections must be of the highest order of hermeticity; low pressure drop, to keep the size of the circulation pump small and for leakage and safety reasons; high resistance in the electrolyte connections between cells, to minimize selfdischarge; uniform pressure drop among all cells, to allow the cells to be connected in parallel arrangement and still achieve uniform flow through each cell; and most importantly, uniform flow through the cell cross-section, so that all plates receive adequate electrolyte flow and assurance that electrolyte flows through the stack-up of a cell, rather than around, so that the most effective cooling during charging is achieved.

The invention consists in a battery which comprises a plurality of cells each containing a stack-up of electrode plates comprising porous metallic plaques containing active battery material; an electrolyte cooling means containing alkaline electrolyte spaced from said cell; electrolyte pumping means connected to said cooling means; and electrolyte circulation means connected from the pumping means to the cell and from the cell to the cooling means; face and edge sides of said electrode plates being sealed and at least one surface channel being provided on one side of at least one electrode plate in each stack-up, along which the alkaline electrolyte flows from the bottom to the top of the stackup, the channel being on the surface of but not through the electrode plate and constituting from 0.5% to 10% of the electrode plate surface area so the pumped electrolyte flows only along the at least one channel in the stack-up to cool the battery.

In one embodiment of the invention, electrolyte is circulated through the plurality of connected cells of the battery and a reservoir containing a cooling mechanism by means of the pumping means. Any heat exchanging means, such as cooling water circulated through coils in the reservoir, can be used to cool the electrolyte. Electrolyte is circulated at rate adequate to remove the heat generated by various charge, discharge rates. The reservoir and pump are attached to the cells of the battery with quick disconnect couplings so they may be discharged with or without them.

Electrolyte level and specific gravity are maintained by adding water to the reservoir to maintain a constant height level. The battery can be vented to the atmosphere at the reservoir through a barrier venting means, which allows explosive hydrogen and oxygen to escape.

The aforesaid features can be embodied in a battery of the present invention as follows: a) The cell electrodes of each stack-up are sealed and encapsulated in a molded case, preferably by means of an epoxy resin sealant filler, which adheres to the case walls, terminals, and electrolyte inlet and exhaust tubes, proviing an effective hermetic seal in all of these locations.

b) Low and uniform cell to cell pressure drops, and uniform flow of electrolyte through the cell stack-ups is accomplished by providing channels in the plates, as by cutting or pressing narrow slits in them. The channels are spaced apart for effective cooling and constitute from 0.5% to 10% of the plate surface area.

c) Electrolyte is forced to flow through these channels, and not around the periphery of the cell stack-ups, by the tight fit between the stack faces and the wide front case walls, and by filling the space between the stack-up edges and the narrow edge case walls with a suitable sealant filler. The filler can be any number of materials, such as a liquid, curable, plastic resin or rubber, foam in place materials, or already foamed material cut to fit.

d) High electrical resistance in the electrolyte plumbing network is accomplished by the use of long inlet and exhaust tubes. The inlet tube preferably extends from the top to the bottom of the cell, while the exhaust tube is preferably formed in a coil at the top of the cell. The manifolds connecting cells with each other are preferably above the cells, which allows electrolyte to drain back into the cells when circulation stops. This latter feature reduces the electrical path between cells to the conductivity of the electrolyte film which clings to the piping walls.

Flow of electrolyte through the system can be summarized as follows: Reservoir; Pump; Battery manifold; Cell inlet manifolds; Cell electrolyte inlet tubes; Cell reservoirs; Through channels in sealed cell stack-ups; Cell electrolyte outlet tubes; Cell exhaust manifold; Battery manifold; and then on to the Reservoir for cooling.

This improved, cell stack-up electrolyte flow system offers many advantages and benefits over the conventional systems, some of which are: a) Effective cooling of the stack-up enables higher charge rates to be employed, thus reducing charge time. A typical cycle of charging/discharging, at the C/2 rate (that is to say half the capacity C per hour), maintains the temperature at between 30"C and 35"C with circulation. Without circulation, temperatures would exceed 70"C, which severely hampers battery life.

b) The hermeticity of the system eliminates many safety hazards such as spills and mists which lead to short circuit grounding paths and potential failures.

c) The parallel flow arrangement, with associated plumbing, insures each cell of proper maintenance, and eliminates failures due to over or under filling and improper specific gravity.

d) The plumbing also provides for safe gas handling and lends itself well for elimination of hydrogen and oxygen formed during charging.

In order that the invention can be more clearly understood, convenient embodiments thereof will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a three dimensional view of a circulating electrolyte battery module containing five series connected battery cells; Figure 2 is a top view, partially in section, of the battery module of Figure 1; Figure 3 is a side view, partially in section, of the battery module of Figure 2, along the line III; Figure 4 is a cross-section of the battery module of Figure 2, along the line IV, showing an electrode plate, having spaced apart channels sealed into the container, cell inlet manifold, cell electrolyte inlet tube, cell reservoir, and the cell electrolyte outlet tube; Figure 5 is a cut-off cross-section of the plate stackup of a cell of one embodiment of the invention, showing the sealed electrode plate sides and edges, and the channels in the plate stack-up providing uniform flow of electrolyte through the stack-up rather than around the periphery of the stack-up; and Figure 6 is a schematic view of an assembly of battery modules fed by a circulating electrolyte system, with associated electrolyte cooling reservoir and pump.

Referring now to Figure 1 of the drawings, a battery module 10 is shown with associated dimensions, which may vary greatly depending on battery use. The battery module, containing five cells, can comprise case 11, which may be, for example, a metal, rubber or plastic box.

Each cell 12 is in its own case or container having flat front and edge walls. The battery module case 11 is optional, however, as the separate cells may be held together solely by the cell exhaust manifold 13 and cell inlet manifold 14, shown disposed in a parallel arrangement. The cells may also be held together by electrical connections between the terminal studs 15. Of course, any other holding or clamping means can be used to hold the separate cells together, such as a bottom U plate, shown as 17 in the drawing, which would be used without the battery module case.

Figure 2 shows a top view of the battery module with terminal studs 15. Also shown is the coiled cell electrolyte outlet tube 21, which attaches to the cell exhaust manifold 13 at opening 22. The cell electrolyte inlet tube is shown as 23. Figure 3 also shows the position of these tubes within a cell, where the bottom of the cell electrolyte inlet tube is shown as 30.

Referring to Figure 4, electrolyte exhaust and inlet manifolds 13, 14 of cell 12 and an electrolyte circulation means (not shown) are preferably arranged in parallel, the latter being preferably connected to manifolds 13, 14 above the cell to allow electrolyte to drain back into the cell when circulation stops.

This reduces the electrical path between cells when electrolyte is not circulating, to the conductivity of the electrolyte film which clings to the manifold tube walls.

The inlet and outlet manifold tubes will have a relatively large internal cross-section.

This provides low fluid flow resistance and minimum pressure drop across the cell, which is required to minimize the pressure necessary for adequate electrolyte flow. The cell inlet and outlet manifold tubes have a long length for high electrical resistance when filled with electrolyte, which is required to minimize current leakage from cell to cell.

Preferably, electrolyte is pumped up through the electrode stack-up, so that hydrogen and oxygen gases generated during charging are easily exhausted to the cooling reservoir without dangerous pressure build-up. In the cell of Figure 4, electrolyte, from the manifold 14, flows from the top of the cell case to the bottom of the cell stack-up, by means of the cell electrolyte inlet tube 23. Cell electrolyte inlet tube 23 extends from the top of the electrode stack-up down along one edge of the battery cell between the edge side of the stackup and the edge wall of the cell case. Then, the tube bends around the bottom of the stack-up and extends into the bottom cell reservoir 40.

The cell stack-up, comprising a series of altemate positive and negative electrode plates, one of which is shown as 41, may rest on plastic rubber or foam blocks 42 to form the bottom reservoir 40.

Thus, electrolyte flowing into the cell case will fill up the bottom electrolyte reservoir formed by the blocks or other suitable stack-up supporting means. The electrolyte will then be forced up the channels 43 in the electrode plates.

Referring now to Figure 5, a top crosssection view of electrode plate 41, and other alternating positive and negative plates making up one type of cell electrode stack-up 50 is shown. The channels 43 can be formed by cutting narrow slits in the electrode plates, by coining the plates to form narrow channels in the plates, or by any other suitable means.

The cross-section of the channel can be circular as shown, square, or any other configuration. The channels can be on both sides of each plate if desired. The channels need not be on both positive and negative plates as shown, but may, for example, be pressed only into the positive or negative plates, so that channels would appear on alternate plates.

The channel should not extend through the electrode plate because this would substantially reduce the conductivity of the plate. The channel area comprises from 0.5% to 10% of the plate face area. If the channels constitute over 10% of the plate area, excessive active material is lost with a reduction in battery performance. Usually 1 to 6 channels per plate are adequate for good electrolyte circulation and battery cooling.

Channels on one side of the plate, as shown in Figure 5, are preferred, since this provides a strong electrode structure requiring minimal machining or pressing. Not shown are plate separators, which may be made of a continuous or perforated film of cellulose, polypropylene, nylon or other suitable insulating material between or wrapped in serpentine fashion around each plate. The separators of course should be compatible with the electrolyte. For adequate cooling it is essential that electrolyte flows only along the channels between the electrode plates in the stack-up, and not around the sides and edges of the stack-up, although there may be minimal electrolyte seepage through the plates.

To provide a hermetic seal and to assure that no electrolyte flows around the stack-up, the spaces 44 between the edge side of the stack-up 45 and the edge wall of the cell case 46, shown in Figures 4 and 5, are filled with a suitable sealant. The sealant can be a curable, liquid, epoxy resin or any other plastic resin, rubber or other material, such as polypropylene foam or polyethylene foam, effective to hermetically seal the space 44 yet not be chemically degraded by the electrolyte.

This sealant filler will seal and encapsulate the side edge of the stack-up and the middle portion of the electrolyte inlet tube. Preferably the sealant will be curable at about 25"C. Prevention of electrolyte flow between the wide face side of the cell stack-up and the flat, front cell case walls can be accomplished by a tight fit and intimate contact between the two, as shown in Figure 5 at 51. This arrangement seals the sides of the electrode stack-ups, i.e. the edge sides and the wide face sides but not the top and bottom of the stack-up.

The electrode plates making up the stack-ups in the cells are, preferably, flexible, porous plaques of 75% to 95% porosity, made from diffusion bonded metal fibers, such as nickel fibers, but preferably steel wool or nickel coated steel wool, as described in U.S. Patent 3,895,960. Other type plates, such as porous sintered nickel powder or cast porous nickel can be used, but have not been found as effective as the expansible fiber metal plates. The fiber metal plates can expand and contract during "formation", to provide superior active material loading.

These plaques contain active battery material distributed upon the flat surface and disposed within the pore volume of the plaque. When, for example, an iron-nickel cell is to be made, the active material of the positive electrode plates may comprise Ni(OH)2, with small effective amounts of Co(OH)2 activating additive. The negative electrode plates may comprise an iron oxide, such as FeO, Fe2 03.

Fe3O4, Fe203-H2O or their mixtures, with small effective amounts of sulfur containing activating additives fused thereon or mixed therewith, as described in U.S. Patent 3,853,624.

Of course other types of positive and negative active materials and other additives can be used.

Each electrode plaque has an electrical lead tab spot welded or otherwise attached, generally to a coined top area. These lead tabs 47 provide means for making electrical connections to the plates. Terminal connection lugs 48 are attached to the lead tabs to electrically connect the positive and negative plates to the terminal studs 15.

Once the electrolyte flows up through the channels 43 of the stack up, in the preferred embodiment of this invention, it exits from the cell through the cell electrolyte outlet tube 21 and cell exhaust manifold 13. The length of the cell electrolyte outlet tube 21 can preferably be increased, to provide high electrical resistance in the electrolyte plumbing network, by making it in a coiled or similar configuration to that shown in Figures 2 and 4.

In all cases, the plumbing in the cell and battery module, such as inlet and outlet tubes and manifolds should be made of a non-conducting tubular material such as polypropylene, polyethylene, polyvinyl chloride, acrylonitrile butadiene styrene, nylon or other type plastic or rubber materials not degradable by the electrolyte. These non-conducting tubes and manifolds can be attached by a suitable adhesive such as epoxy or polyvinyl chloride adhesive.

To insure electrolyte exit through the electrolyte exhaust tube 21, the space 49 between the top of the cell case and the top of the exhaust tube entrance may be filled with a suitable sealant similar to that described hereinabove. This would also provide a top for the cell case. In order to provide such a top, a barrier can be placed over the top of the bottom opening of the cell electrolyte outlet tube, and sealant injected or poured on top of the barrier to encapsulate the top of the outlet tube, the top of the inlet tube and the terminals.

Referring now to Figure 6, a battery is built by connecting cell inlet manifolds 14 and outlet manifolds 13 preferably in parallel. To facilitate constructing a high power battery, several sets of cells, i.e. sets of battery modules 10, are fastened in place with all the fluid flow in parallel to minimize the pressure required for the system and to provide uniform cell to cell cooling. The battery modules can then be positioned to build a complete high power battery system for the voltage and space requirements of each individual application.

Figure 6 shows a high power battery consisting of three banks of three battery modules. Each battery module contains five cells.

The modules are connected by common battery manifold electrolyte circulation means 60, the length and position of which are dependent on the battery layout. The battery manifolds can be detached from the heat exchanger means 61 and the electrolyte pumping means 62 by quick disconnect couplings 63, so that the high power battery can be discharged without the heat exchanger and pump.

The heat exchanger or cooling means can comprise an electrolyte cooling reservoir 64 containing cold water cooling coils 65. A radiator or other cooling apparatus could be added to the system for air cooling to replace or supplement the cooling coils. Electrolyte will be circulated by the pump at rates effective to remove the heat generated by the various charge.

discharge rates.

Electrolyte level and specific gravity are con trolled by adding water to the electrolyte cooling reservoir 64 through inlet 66, to maintain a constant height level in the cells. The battery system is vented to the atmosphere, preferably at the reservoir, by any suitable means, such as, for example, a barrier venting means 67, which can be a sintered ceramic barrier, which allows hydrogen and oxygen to escape while acting as a flame and explosion barrier. A bubble tube extending from the opening in the reservoir into the bottom of an open container of water can also be used to allow gas to escape. The alkaline electrolyte generally used will be a 10 wt. % to 35 wt. % KOH or NaOH aqueous solution with preferably about 2 to 20 grams/liter of Li(OH)2. No gases are added to the electrolyte.

EXAMPLE Iron-nickel high power batteries similar to those shown in Figures 1 to 6 were constructed.

The battery plates were made from nickel plated steel fibers formed into plaques. Fibers approximately 0.001 x 0.002 x 0.25 inch long were used in the flexible, expansible, fiber metal plaques. They were then heated, in a protective environment, causing metal to metal diffusion bonds to form at fiber contact points. There was no melting of fibers so as to assure maximum pore volume.

The "nickel" plaques were then coined to about 8 percent of theoretical density, 92 percent porous, and the "iron" plaque bodies were coined to 17 percent of theoretical density, 83 percient porous. Each nickel plaque had two vertical /8 t wide pressed channels. The plaque was about 6.5" wide and about 0.09" thick. The channels were about 0.08" deep. The channels comprised about 4% of the plaque surface area. A steel sheet was then spot welded onto the top coined portion of the plaques to form electrical lead tab connections, shown as 47 in Figure 4.

The iron active material comprised sulfurized magnetic iron oxide particles. The magnetic iron oxide had a composition of about 79 percent Fe2O3, 22 percent FeO and 1 percent impurities. Enough sulfur was used to provide a ratio of sulfur to iron oxide of 0.1 to 10 percent of the sulfurized iron oxide. This additive helped keep the iron active material surface in the active state.

The "iron" plaques were loaded with the sulfurized magnetic iron oxide by a wet pasting technique. These iron electrode plates were then sized and dried. They contained 1.5 to 1.9 grams/cm3 plaque volume of sulfurized iron active material.

The nickel active material comprised nickel hydroxide doped with a small amount of cobalt hydroxide. The nickel plaques were loaded by an impregnation "formation" impregnation technique. They contained 0.9 to 1.3 grams/ cm3 of active material. The "iron" and "nickel" plates were then ready for the cell stack-up operation.

A battery module having dimensions about 7" wide x 10" high, as shown in Figure 1 was used and consisted of five cells. The cell cases, made of high density polyethylene and having an open top, were about 7 wide x 2 deep x 10" high. They would contain the electrode stack-ups.

In the stack-up operation, iron and nickel plates were alternately stacked, insulated from each other with a serpentine wound polypropylene separator, and then the terminal connection lugs, shown as 48 in Figure 4, were inert gas welded to the tabs to provide means for making electrical connections to the plates.

The cell stack-up, along with a 3/16tut inside diameter polypropylene cell electrolyte inlet tube, was then inserted into the cell case on top of two polyethylene foam blocks, about 1' wide x 2'' deep x 5/8 " high, shown as 42 in Figure 4.

The inlet tube ran down the edge side of the stack-up and next to the narrow edge wall of the cell container, curving at the bottom to run underneath the cell stack-up. The inlet tube stopped at about the middle of the bottom reservoir, shown as 40 in Figure 4, formed by the cell stack-up and foam blocks 42. A groove had been formed in the foam block which the inlet tube ran- through so that the inlet tube would fit around the bottom of the stack-up.

This provided cells having inserted electrode stack-ups supported on the bottom with foam blocks, having an electrolyte inlet tube running into a reservoir at the bottom of the cell. The space, shown as 44 in Figure 4, between edge sides of the stack-up and the 2" edge walls of the cell containers was unfilled.

A viscous, room temperature curable epoxy resin was then dispensed, from an injection gun, into this space 44 between each edge side of the stack-ups and each edge wall of the cell case, to act as a hermetic sealant and to encapsulate the stack-up between the foam blocks and the top of the electrode stack-up. The top and bottom of the stack-up remained unsealed.

This would force the pumped electrolyte, from the bottom reservoir, to run through the plate channels 43 to the top of the cell rather than around the plates.

The top of the cell was fitted with a 5/16" inside diameter polypropylene cell electrolyte outlet tube. This tube, shown as 21 in the drawings, is in a coiled configuration. It starts just above the electrode stack-ups, under the cell exhaust manifold and runs across the cell width, coiling around the cell electrolyte inlet tube, running back across the cell, and fitting into the cell exhaust manifold, as shown in Figures 2, 3 and 4.

In order to form a top on the cell, the cell electrolyte outlet tube was held in place, with the outlet opening just at the top of the cell stack-up, with polyvinyl chloride adhesive tape.

The tape had holes for the bottom portion of the electrolyte outlet tube, the positive and negative interconnection lugs and the top of the electrolyte inlet tube to fit through. A top reservoir volume was thus formed between the tape and the top of the stack-ups.

A viscous, room temperature curable epoxy resin was then dispensed, from an injection gun, on top of the tape to encapsulate the top portion of the cell electrolyte outlet and inlet tubes and the intercell connection lugs. Thus epoxy resin formed the top of the cell.

The iron plaque in the stack-up was still in unformed condition. An electrolyte solution containing 25 wt. % KOH and 15 grams/liter of Li(OH)2 was poured into the cell and "formation" of the iron plaques was accomplished by a series of charge-discharge cycles.

Cells were then matched and electrically connected to form a five cell battery module Four modules were placed in series and 1/2 inside diameter polyvinyl chloride cell inlet manifolds and 3/4 " inside diameter cell exhaust manifolds were connected to the cell electrolyte inlet tubes and cell electrolyte outlet tubes respectively with room temperature curable epoxy resin glue. Each module was similar to that shown in Figure 1, with the manifolds 13 and 14 in parallel on top of the cells. The modules were assembled as shown in Figure 6, only there were four banks of modules, each bank contain four connected battery modules, each module containing five cells. Thus, there were a total of 16 modules or 80 cells to form the high power battery.

Referring to Figure 6, the cell inlet manifolds 14 and exhaust manifolds 13 were connected to common 1" inside diameter polyvinyl chloride battery manifolds with flexible polyvinyl chloride hose and hose clamps. The pump manifolds were connected to a 1/4 H.P. pump and a 25 gallon electrolyte reservoir 61 made of polyvinyl chloride.

The reservoir had a closed top and a ceramic flame arrestor barrier vent 66, to exhaust hydrogen or oxygen present in the electrolyte due to charging, and an inlet 67 for adding water or electrolyte. The cooling coils 65 were made from 20ft of coiled l/2 " inside diameter stainless steel. Cold water was circulated through the coils to cool the circulating electrolyte.

The electrolyte solution used in the system contained 25 wt.% KOH and 15 grams/liter of Li(OH)2. No gases were added to the electrolyte. The pump and reservoir were connected to the battery modules through disconnect valves in the common pump manifolds so that the high power battery could be discharged without them.

The assembled high power battery was then bench tested through several 3 hour charge, 2 hour discharge test cycles to establish a capacity rating. Best results yielded about 17 KWH, or 20 Wh/pounds of cell. The

Claims

**WARNING** start of CLMS field may overlap end of DESC **. portion of the cell electrolyte outlet and inlet tubes and the intercell connection lugs. Thus epoxy resin formed the top of the cell. The iron plaque in the stack-up was still in unformed condition. An electrolyte solution containing 25 wt. % KOH and 15 grams/liter of Li(OH)2 was poured into the cell and "formation" of the iron plaques was accomplished by a series of charge-discharge cycles. Cells were then matched and electrically connected to form a five cell battery module Four modules were placed in series and 1/2 inside diameter polyvinyl chloride cell inlet manifolds and 3/4 " inside diameter cell exhaust manifolds were connected to the cell electrolyte inlet tubes and cell electrolyte outlet tubes respectively with room temperature curable epoxy resin glue. Each module was similar to that shown in Figure 1, with the manifolds 13 and 14 in parallel on top of the cells. The modules were assembled as shown in Figure 6, only there were four banks of modules, each bank contain four connected battery modules, each module containing five cells. Thus, there were a total of 16 modules or 80 cells to form the high power battery. Referring to Figure 6, the cell inlet manifolds 14 and exhaust manifolds 13 were connected to common 1" inside diameter polyvinyl chloride battery manifolds with flexible polyvinyl chloride hose and hose clamps. The pump manifolds were connected to a 1/4 H.P. pump and a 25 gallon electrolyte reservoir 61 made of polyvinyl chloride. The reservoir had a closed top and a ceramic flame arrestor barrier vent 66, to exhaust hydrogen or oxygen present in the electrolyte due to charging, and an inlet 67 for adding water or electrolyte. The cooling coils 65 were made from 20ft of coiled l/2 " inside diameter stainless steel. Cold water was circulated through the coils to cool the circulating electrolyte. The electrolyte solution used in the system contained 25 wt.% KOH and 15 grams/liter of Li(OH)2. No gases were added to the electrolyte. The pump and reservoir were connected to the battery modules through disconnect valves in the common pump manifolds so that the high power battery could be discharged without them. The assembled high power battery was then bench tested through several 3 hour charge, 2 hour discharge test cycles to establish a capacity rating. Best results yielded about 17 KWH, or 20 Wh/pounds of cell. The battery was then operated in several electrical vehicles in excess of 100 cycles. The 80 cell (96 volt) circulating electrolyte battery was charged using a C/2 (100 Amp.) charge rate for 3 hours. Total electrolyte flow was 9 gal. per min., at an average pressure drop across the cell inlet-exhaust manifolds of 5 psi. The initial reservoir electrolyte temperature was 250C. The temperature of the battery after a full charge was 32"C. If no electrolyte circulation was provided during charging, the battery temperature after a full charge would have been in excess of 70"C, which would be very detrimental to the operating life of the electrodes and separators. In operation, the epoxy resin sealing system at the edge sides of the plates in the stack-up and the top of each cell proved to be leakproof. Uniform and very efficient and effective cooling of the cells during charging was accomplished. No deleterious self-discharge was observed by electrical conductivity of the electrolyte circulation plumbing system. There was no excessive increase in pressure drop in a cell after 2,000 charge-discharge cycles. This shows evidence of no plugging of the plate channels due to plate swelling or loose active material. The use of 2 channels per nickel plate, constituting 4% of one side of the nickel plate surface area, provided adequate cooling for this system. More channels, up to 10% of plate surface area, could be added where more cooling and less active material volume is required. WHAT WE CLAIM IS:

1. A battery which comprises a plurality of cells each containing a stack-up of electrode plates comprising porous metallic plaques containing active battery material; an electrolyte cooling means containing alkaline electrolyte spaced from said cell; electrolyte pumping means connected to said cooling means; and electrolyte circulation means connected from the pumping means to the cell and from the cell to the cooling means; face and edge sides of said electrode plates being sealed and at least one surface channel being provided on one side of at least one electrode plate in each stack-up, along which the alkaline electrolyte flows from the bottom to the top of the stackup, the channel being on the surface of but not through the electrode plate and constituting from 0.5% to 10% of the electrode plate surface area so that pumped electrolyte flows only along the at least one channel in the stack-up to cool the battery.

2. A battery according to claim 1, wherein the stack-up is disposed within a cell case and comprises at least one flat positive electrode plate, each containing active material distributer upon the flat surface and disposed within the pore volume of the plate.

3. A battery according to claim 2, wherein the plates comprise 75 to 95 percent diffusion bonded metal fiber plaques, the negative plates comprising iron oxide active material and the positive plates comprising nickel hydroxide active material with a small amount of Co(OH)2

4. A battery according to claim 1, 2 or 3 wherein the plates in each stack-up have a separator therebetween, the stack-up is disposed within a cell case such that the face sides of the stack-up of electrode plates fit in intimate contact with the cell case and the edge sides of the stack-up of electrode plates are sealed by a curable sealant, to provide a hermetic seal

between the sides of the stack-up and the cell case.

5. A battery according to claim 4, wherein the at least one channel is pressed into the surface of the at least one electrode plate in each stack-up, the sealant is an epoxy resin and the cooling means comprises a reservoir containing means for venting hydrogen and oxygen gas from the electrolyte.

6. A battery according to any of claims 1 to 5, wherein the electrolyte circulations means comprise parallel inlet and exhaust means which are positioned on top of the battery cells and can be detached from the pumping and cooling means.

7. Batteries substantially as described herein with particular reference to the foregoing Example and/or either Figs. 1 to 4 or Figs. 1 to 5 of the accompanying drawings.

8. Assemblies of battery modules fed by a circulating electrolyte system and substantially as described herein with particular reference to the foregoing Example and/or Fig. 6 of the accompanying drawings.