PRIMARY BATTERY SYSTEM

Technical Field

This invention relates to metal-water electro- chemical cells and in particular to means for con¬ trolling the electrolyte composition in such cells.

Background Art

One well-known form of metal-water electrochem¬ ical cell comprises a lithium/silver oxide cell. The electrolyte in such a cell comprises a solution of lithium hydroxide in water. In one marine applica¬ tion of such a cell, the lithium hydroxide is dis¬ solved in seawater.

The power developed by the cell is a function of several variables, such as temperature, electrolyte velocity, electrode area, electrode spacer configura¬ tion, voltage, gas-liquid volume ratio, and lithium hydroxide concentration in the electrolyte. Thus, by suitably controlling the amount of dissolved lithium hydroxide to desired varying values, while controlling the remaining variables to nearly constant values, variable power output may be obtained.

In the operation of such a cell, lithium hydrox¬ ide is generated as a by-product of the electrochem- istry, thus changing the concentration of lithium hy¬ droxide in the electrolyte. To control the concen¬ tration of lithium hydroxide in the circulated elec¬ trolyte, a portion of the electrolyte circulated from the cell having an increased lithium hydroxide con- centration is discharged and replaced with water, which, in the marine application discussed above, is seawater.

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The control of the lithium hydroxide in such an application is complicated by the fact that another by-product of the electrochemistry of the cell is hy¬ drogen gas. The hydrogen does not dissolve in the electrolyte to any great extent but forms a distribu¬ ted mixture therein, tending to pressurize the system.

It has been conventional in such systems to sep¬ arate the hydrogen gas from the electrolyte prior to ejection of a portion of the electrolyte having the increased concentration of lithium hydroxide. Such hydrogen gas separation subsystems are relatively ex¬ pensive, bulky, and require undesirable energy con¬ sumption in the operation of the battery system.

Disclosure of Invention The present invention comprehends an improved battery system which eliminates the need for separa- tion of the gaseous by-product produced in the elec¬ trolyte as a result of the electrochemistry of the cell by controlling the pressurization of the system - as a function of the rate of discharge of the- elec¬ trolyte suitable for maintaining the desired lithium hydroxide concentration for the desired power output.

In the illustrated embodiment, the system is caused to have a sufficient hydrogen gas pressure so as to provide a desired small gas-to-electrolyte volume ratio, permitting the use of a circulation pump of conventional design. The invention comprehends that the maintained hydrogen gas pressure is less than a preselected pressure so as to avoid the need for bulky and heavy structures in containing the pressurized hydrogen gas. It has been found that the provision of means to effect the desired pressurizing of the system permits the gas- to-electrolyte volume ratio in the system reservoir to rise at a decreasing rate so that during the normal op- eration of the battery system, the gas-to-electrolyte

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volume ratio in the reservoir becomes effectively constant at a pressure less than a preselected maximum.

The invention comprehends providing pressure reg¬ ulating means for discharging the electrolyte from the reservoir as an incident of the pressure thereof ex¬ ceeding the preselected operating pressure.

The invention further comprehends the provision of pressure control means permitting the pressure condition of the electrolyte to cause an increase in the density of the gaseous component in the electrolyte, resulting in a reduced ratio of the gaseous component volume to the liquid component volume of the gas-electrolyte mixture. The invention broadly comprehends the provision in a battery system including a battery cartridge producing a gaseous by-product and a solute by-product in a circu¬ lated electrolyte liquid as an incident of electrochemical operation thereof, of pressurizing means for placing the electrolyte mixture under a preselected pressure, and replacing a portion of the pressurized electrolyte mix- ture with water. The pressure is preselected to cause the ratio of the volume of gaseous by-product to volume of the liquid component to be reduced, thereby reducing the volume of the portion of the mixture being dis¬ charged, and, upon replacement of the ejected mixture with water, permitting the electrolyte mixture provided to the battery cartridge to have a desired solute con¬ centration and gas-to-liquid volume ratio, for desired operation of the battery.

Thus, broadly under a specific steady operation condition, the mass flow rate of the ejected gas and the mass flow rate of the ejected electrolyte remain substantially steady since the electro-chemical re¬ action is substantially steady. The effects of the increased system pressure as to increase the density of the gaseous portion of•the ejected gas-liquid mixture, reduce the volume of the gaseous portion of the ejected

gas-liquid mixture, thereby reducing the total volume of the ejected mixture, and reduce the ratio of gas volume to liquid volume in the system as well as the ejected gas-liquid mixture. The battery electrolyte control system of the present invention is extremely simple and economical of contruction while yet providing improved efficiency, size and weight reduction, and reliability.

Brief Description of the Drawing Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a schematic illustration of a battery system embodying the invention; and FIGURE 2 is a fragmentary schematic illustration of a modification of a portion of the system of Figure

I embodying the invention.

Best Mode for Carrying Out the Invention

In the illustrative embodiment of the invention as disclosed in the drawing, a battery system gener¬ ally designated 10 is shown to comprise a primary bat¬ tery system having a battery cartridge 11 disposed in a battery cartridge zone 12 within a housing 13. The housing is provided with a divider wall 14 separating zone 12 from a reservoir chamber 15.

In the illustrated embodiment, battery cartridge

II comprises a lithium/silver oxide battery cartridge utilizing an electrolyte comprising an aqueous solu¬ tion of lithium hydroxide. In the illustrative system, water is introduced into the electrolyte from the surrounding ambient seawater 16.

Water is drawn into reservoir 15 by means of a pump 17 having an inlet 18 opening to the ambient sea¬ water, and an outlet 19 opening to the reservoir 15.

The invention comprehends the pressurizing of the electrolyte in the reservoir and, in the illustrative embodiment, a pump 17 is provided for producing pres¬ sure in the reservoir chamber 15 greater than the ⁵ ambient pressure.

The pressure in chamber 15 is desirably main¬ tained at the preselected elevated pressure, such as approximately 25 psi absolute to 3500 psi absolute, and preferably in the range of approximately 100 psi 0 absolute to 1000 psi absolute, by a suitable pres¬ sure regulating valve 20. As shown, the valve is connected through an inlet 21 to the reservoir cham¬ ber 15 and through an outlet 22 to exteriorly of the housing 13. 5 As will be obvious to those skilled in the art, the valve inlet could also be connected to other locations within the electrolyte circulation path, such as to battery cartridge discharge 26, thermostatic by¬ pass valve discharge 29, heat exchanger paths 30 through ⁰ 31, heat exchanger discharge 32, or circulation pump discharge 25.

Circulation of electrolyte from reservoir 15 through the battery cartridge 11 and back to the res¬ ervoir 15 is effected by means of a main pump 23 having ^ an inlet 24 opening to the reservoir chamber 15. An outlet 25 of the pump 23 is connected to one side of the battery cartridge 11 for delivering the electro¬ lyte through the battery to outlet 26 thereof extending through the divider wall 14 to thermostat bypass valve ° 27. In the illustrated embodiment, the thermostat valve is located in reservoir 15, as seen in Figure 1, it being obvious to those skilled in the art that the thermostat valve can be provided .at other suitable lo¬ cations in the electrolyte circulation path.

The thermostat valve is selectively operable to deliver the returned electrolyte through a first out¬ let 28 directly to the reservoir chamber 15, or through second outlet 29 to a heat exchanger 30 pro- viding heat exchange between the electrolyte circu¬ lated therethrough and the ambient seawater 16 through the housing 13. As will be obvious to those skilled in the art, the heat exchange may be provided at any desired location in the electrolyte circulation path. As further shown in Figure 1, the heat exchanging means includes a second portion 31 also providing heat exchange between the electrolyte flowed therethrough and the ambient seawater 16 through the housing 13, with the outlet 32 of the heat exchanger portion 31 opening into the reservoir chamber 15.

In the battery system 10 illustrated in Figure 1, divider wall 14 is provided with suitable openings 33 providing communication between reservoir chamber 15 and zone 12 exteriorly of the battery cartridge 11 so as to place both the reservoir and zone 12 at sub¬ stantially equal pressure.

In a modified form of the invention, as illus¬ trated in Figure 2, a battery system generally desig¬ nated 110 is similar to battery system 10, but is provided with a dividing wall 114 which is imperfor- ate so as to effectively maintain the pressure in reservoir chamber 115 selectively different from the pressure in zone 112 surrounding the battery cart¬ ridge 111. The discharge conduit 125 from the main pump 123 includes a first outlet 134 opening to zone 112 and a second outlet 135 opening to the battery cartridge 111. Thus, zone 112 and the inlet to the battery cartridge are placed under equal pressures. In all other respects, battery system 110 is similar to and functions similar to battery system 10.

Industrial Applicability

In one embodiment of the invention, the battery cartridge 11 comprised a lithium/silver oxide battery cartridge. Pump 17 comprised a positive displacement pump with a variable output capacity of approximately 0 gpm to 60 gpm, operating at approximately 2 gpm to 20 gpm when the battery is required to deliver full power, suitable to place the reservoir chamber at a pressure of approximately 100 psi absolute to 1000 psi absolute, and more specifically, in the illustrated embodiment, at a pressure of approximately 200 psi ab¬ solute to 800 psi absolute. The main pump 23 provided a discharge of approximate 50 gpm to 500 gpm at full power, at a pressure differential of approximately 20 psi to 350 psi for providing the desired circulation of the electrolyte fluid.

By maintaining the pressure in reservoir 15 at approximately 200 psi absolute, or greater, the hydro¬ gen gas by-product produced by operation of the battery cartridge 11 was compressed in the electrolyte liquid ^' so as to have a ratio to the lithium hydroxide by-product produced by operation of the battery cartridge suitable to permit the mixture of the electrolyte and compressed hydrogen gas to be discharged through valve 20 while maintaining the molarity of the lithium hydroxide in the electrolyte in reservoir 15 suitable to provide de¬ sired operation of the battery cartridge 11 when recircu¬ lated thereto by pump 23.

It has been found that where the battery system is operated at a depth in the seawater of approximately 200' to 3,000* or more, sufficient pressure is produced by the ambient seawater to effect the desired compression of the hydrogen gas in reservoir 15. However, when the battery system is operated at lesser depths, the pump 17

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and regulating valve 20 maintain a minimum pressure within the reservoir 15 sufficient to permit ejection of suf¬ ficient quantities of hydrogen gas, while maintaining a desired low gas-to-liquid volume ratio in the circulated fluid mixture, so as to permit continuing operation of the battery system as a primary battery system, with a portion of the recirculated electrolyte being con¬ tinuously discharged by replacement with fresh seawater electrolyte through the inlet pump 17. Resultingly, the expensive and energy inefficient separation of hydrogen gas from the returned electro¬ lyte is effectively eliminated by the improved simpli¬ fied structure of the present invention providing im¬ proved efficiency and reliability in the operation of the primary battery system.

The heat generated by ^" operation of the battery cartridge is transmitted to the ambient seawater through the heat exchanger 30, 31, when necessary, under the control of thermostat valve 27. Where the temperature of the returned electrolyte mixture is below the setting of the thermostat valve, the mix¬ ture may be delivered directly back to the reservoir 15 through the outlet conduit 28 without the need for heat exchange. Where it is desired to maintain the pressure within the zone surrounding the battery cartridge substantially equal to the pressure at the battery cartridge inlet, the system 110 illustrated in Figure 2 may be employed. To initiate operation of the battery, a measured amount of lithium hydroxide is dissolved in seawater with the solution then being introduced into the bat¬ tery cartridge inlet. In one illustration embodi¬ ment, the starting solute was dry sodium hydroxide

stored in the reservoir area. As will be obvious to those skilled in the art, other suitable start-up means may be utilized within the scope of the invention. In summary, the invention comprehends a novel battery system wherein the gaseous by-product gener¬ ated by the battery cartridge in the electrochemical operation thereof is maintained in the fluid mixture at a preselected pressure so as to reduce the ratio of the volume of the gaseous component to the volume of the liquid component within the fluid mixture. Maintenance of the desired concentration of the solute is effected by introducing fresh solvent to replace a portion of the pressurized fluid which is discharged, thereby re¬ moving from the system a portion of the generated gas- eous by-product and reducing the solute concentration to the d,esired level. The invention is advantageously adapted for use in a lithium/silver oxide battery sys¬ tem. •

The invention comprehends any modification of the disclosed system wherein pressurizing all or any part of the system, permitting the gas and electro¬ lyte liquid to be ejected as a mixture, is desired. Thus, the invention is adapted for use wherein the recirculating electrolyte normally constitutes a gas/ liquid mixture.

The foregoing disclosure of specific embodiments is illustrative of the broad inventive concepts comprehended by the invention.