GB2134698A

GB2134698A - Power storage battery

Info

Publication number: GB2134698A
Application number: GB08401357A
Authority: GB
Inventors: Roger John Wedlake; Philip James Johnson
Original assignee: South African Inventions Development Corp
Current assignee: South African Inventions Development Corp
Priority date: 1983-01-26
Filing date: 1984-01-19
Publication date: 1984-08-15
Also published as: GB8401357D0; GB2134698B; FR2539919A1; JPS59143281A; DE3401794A1

Abstract

There is disclosed a power storage battery made up of a plurality of electrically interconnected secondary electrochemical cells 12 located in a thermally insulating housing which has one or more heat pipes 22 at least partially located in the interior of the housing, one or more of said heat pipes being provided with a catalytic converter for the flameless catalytic combustion of hydrocarbon fuels, each converter forming a heat source for the supply of heat via the associated heat pipe or pipes to the interior of the housing. <IMAGE>

Description

SPECIFICATION Power storage battery This invention relates to a power storage battery. In particular it relates to a power storage battery made up of a plurality of secondary or rechargeable electrochemical cells and suitable for use in an electric vehicle.

According to the invention, a power storage battery is made up of a plurality of electrically interconnected secondary electrochemical cells located in a thermally insulating housing which has one or more heat pipes at least partially located in the interior of the housing, one or more of said heat pipes being provided with a catalytic converter for the flameless catalytic combustion of hydrocarbon fuels, each converter forming a heat source for the supply of heat via the associated heat pipe or pipes to the interior of the housing.

Each catalytic converter may be mounted on or in the housing, and in one embodiment at least one said heat pipe may project through the housing from the interior thereof to the outside thereof, the catalytic converter being provided outside the housing. It will, however, be appreciated that the catalytic converter may be mounted inside the housing, either with the cells or, as described hereunder, in a separate compartment in the housing, the associated heat pipe acting to convey and distribute heat therefrom to at least some of the cells.

Cells of the type in question require electrical feed-throughs through the thermally insulating housing of the battery, to carry electrical current during heating of the battery by means of a heater in the housing, or to the battery terminals during charging and discharging.

In accordance with one particular aspect of the invention, at least one said heat pipe may thus be associated with an electrical feed-through from the interior of the battery housing to the outside thereof, the feed-through passing through the housing at the same position as the associated heat pipe.

The electrical feed-through may thus comprise electrically conducting material which forms an external sheath around said heat pipe, eg a copper coating for the heat pipe. Instead the electrical feed-through may comprise electrically conducting material, such as copper, located in a longitudinal passage or external groove in the heat pipe, where it forms an electrical conductor remote from the interior of the heat pipe, or the feed-through may merely be a conductor which extends longitudinally alongside the heat pipe through the housing.

The feed-through may be connected inside the housing to one of the terminals of the battery, or to an electrical heater for the battery.

Each catalytic converter may contain as its catalyst a metal selected from the group consisting in platinum and palladium and the catalyst may be contained in the pores of a porous ceramic substrate.

It is contemplated that the batteries in accordance with the invention will typically be used for power storage as in electric vehicle batteries, and will be made up of high temperature secondary electrochemical cells. Such cells are of the type which usually employ alkali metals such as sodium as the active anode material, with liquid eletrolytes comprising molten metal halide salts, and they frequently employ solid electrolytes such as beta alumina.For the cells to operate for reversible charging and discharging, the anode material and liquid electrolyte must be molten, necessitating operating temperatures generally of 1 000C or more, typically above 1 500C. Thus, for example, when sodium aluminium chloride (NaAICI4) is used as a liquid electrolyte, the temperature should preferably be above about 15000. For sodium sulphur cells, the minimum temperature is the freezing temperature of sodium polysulphide, which is about 27500. In such cases a safety margin of about 2500 should preferably be provided, above the minimum of freezing temperature of the cell component in question.

Furthermore, with cells employing beta alumina as a solid electrolyte, the cell internal resistance provided by the beta alumina reduces with increasing temperature, the typical operating temperature for such cells being in the range of about 3000 to 40000.

The upper operating temperature for the cells in question is usually determined by the temperature ,characteristics of the various cell components.

Aluminium, which is often used for seals and current collectors in the cells in question, has a softening point in the region of about 55000, and this is regarded, for pratical purposes, as the upper limit of the operating temperature for the cells in question, once again with a safety margin of about 2500 to 500C, leading to a design upper limit of about50000to52500.

When batteries of the type in question are being charged or discharged, they can be maintained at their operating temperatures, by virtue of heating caused by their internal resistance, together with the use of suitable thermal insulation, and when charging power, eg from electrical mains, is available, maintaining such batteries at their operating temperature presents no difficulty. However, when the batteries are used for electrically propelled road vehicles, maintaining battery temperature, particularly for extended periods, without discharging the battery can cause difficulty at low; ambient temperatures, in spite of the use of efficient thermal insulation for the battery.It is in these situations that it is contemplated that the batteries in accordance with the invention, employing heat pipes associated with catalytic converters for hydrocarbon fuels will have particular utility. Safe, flameless combustion of the fuels will take place in the catalytic converters, and each associated heat pipe will conduct heat in an extremely efficient fashion into the interior of the battery in question through the thermally insulated holder, acting to level out any temperature fluctuations in the heat source.

Thus, in accordance with a particular embodiment of the invention, the cells may be high-temperature cells having an operating temperature in the range 1 00#500OC, each heat pipe having as its active vaporizable material a substance selected from the group consisting in sodium and potassium.

Operation of the catalytic converter can- be continuous or intermittent, as required, to maintain battery temperature, and the rate of catalytic conversion or combustion of the fuel can be controlled to maintain the battery at its operating temperature, or at a suitable lower temperature at which the battery is operable, and can quickly attain its operating temperature after discharging thereof is initiated. Even if the battery has been allowed to cool down completely to ambient temperature (although this is undesirable owing to stressing of solid components of the battery by freezing of its liquid components), the heat pipe and catalytic converter can be used quickly and effectively to heat it either to its minimum operating temperature, or to its design or intended operating temperature.

During rapid charging or discharging of batteries of the type in question, particularly at high ambient temperatures, excessive temperatures may be reached in the interior of the battery. In such cases, the heat pipes can have utility as safety devices, operating in reverse to conduct heat from the interior of the battery, outwardly through the thermally insulated battery holder, to the exterior thereof.

Although different heat pipes or different sets of heat pipes may be used for battery heating and for battery cooling, conveniently the same heat pipes are used both for battery heating and for battery cooling. Thus, the active material of the heat pipes, ie that which is evaporated and condensed in the heat pipes, should evaporate at a temperature above the design operating temperature of the battery, but below the temperature at which components of the battery can become damaged by overheating. In any event, the heat pipes should be inoperative at the design operating temperature of the battery or below, otherwise they would lead to considerable undesirable heat leakage from the battery.

For batteries of the type in question, operable typically over a temperature range from a minimum between, say 100 and 3000C to a maximum between, say, 500 and 5000C, heat pipes employing potassium as the active material, as mentioned above, are extremely suitable. Thus, in accordance with the invention, the heat pipes may comprise preferably potassium as active material in a corrosion-resistant or stainless steel pipe, or nickel pipe, with a porous or fibrous wicking material also of similar steel or nickel in the interior of the pipe, as the case may be. Such heat pipes can be designed to have operating temperatures of from about 5250C to about 9750C, making them ideal for emergency cooling of batteries and also for heating of batteries by means of catalytic converters for hydrocarbon fuels, which operate in this temperature range.

Similarly, heat pipes with sodium as active material with a nickel or stainless steel, may be employed for use in heating, but as their possible working temperature range is from about 62500 to 1 275 OC, they may not be entirely suitable for emergency cooling, if their minimum operating temperature is above the maximum permitted working temperatures encountered for the cells in question.

The cooling zone and the catalytic converter may be provided in separate compartments in the housing which are separated from a compartment in the housing in which the cells are located.

Naturally, however, the cooling zone, which may be a part of the heat pipe provided with fins or the like to promote eg air-cooling, and the catalytic converter, may each be located totally outside the housing. Instead, it is possible in principle to have the cooling zone and the catalytic converter inside the housing with eg a cooling air line passing into the housing to the cooling zone and out again from the housing and, similarly, a fuel line passing in through the housing to the catalytic converter with a combustion gas line passing out through the housing from the converter. In this case the heat pipe or pipes will act to distribute heat from the converter to other parts of the interior of the housing and/or to collect excess heat from said parts of the housing and convey it to the cooling zone.

High-temperature batteries of the type in question typically exhibit a temperature profile, having their highest temperatures in their central zones, and their lowest temperatures at their peripheral or surface zones, adjacent their thermally insulating housings. Effective emergency cooling dictates at least one heat pipe passing through a central position in the battery, optionally provided with heating fins, branch pipes, or the like, passing in turn through the peripheral portions of the battery, and such branch pipes, fins, or the like, can also act effectively, during battery heating, to transmit heat to the peripheral zones of the battery.However, instead, several heat pipes may be provided, leading frorn eg the same catalytic hydrocarbon fuel converter or several such converters, to various positions in the battery, both central and peripheral, to provide for even heating, even cooling or even temperature maintenance in the battery. Each heat pipe, even when inoperative, will, if it extends through the housing, lead to unavoidable heat leakage from the cell during normal operation, and this disadvantage will have to be borne in mind when selecting the number and location of the heat pipes used.

To guard against heat losses and to improve the efficiency of heat retention, the dimensions of the battery may conveniently be selected, depending on the shape of the battery used, so that its external surface area is at a minimum, having regard to its volume. The shape of the battery will in turn affect the shape, geometry and arrangement of the heat pipe or heat pipes used.

To control the temperature at which heat is applied to the battery to a more or less constant value, while providing for variation of the rate of heat imput into the battery, the heat pipes may be gas-control led or variable-conductance heat pipes.

Such heat pipes are as described in the Kirk Othmer Encyclopaedia of Chemical Technology, John Wiley 8 Sons, 3rd Ed. Vol. 12, at-pages 191-201, and in an article by G. Yale-Eastman entitled 'Heat Pipe', in ECT, Ind Ed. Suppl. Vol. at pages 448-499 Such heat pipes contain a suitably inert gas under pressure, and during use of the heat pipe to transfer heat into the battery, the volume occupied by such gas varies inversely with the rate of heat transfer, the smaller the volume of the gas, the greater the area of heat pipe inside the battery available for heat transfer to the interior of the battery, and the greater the rate of heating consequently effected.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing, in which Figure 1 shows a schematic sectional side elevation of a battery in accordance with the invention; and Figure 2 shows a sectional schematic side elevation of a heat pipe.

In Figure 1 of the drawings, a battery in accordance with the invention is generally designated by reference numeral 10. The battery comprises an assemblage 12 of electrically interconnected electrochemical cells. The assemblage has a passage 14 therethrough which, in use, as shown in the drawing, extends upwardly. The assemblage 12 is circular or hexagonal in plan view outline, the passage 14 being centrally located. The assemblage 12 is located in a thermally insulating holder or housing 16 of a suitable thermal insulating material. The housing 16 has, in its insulating wall, an upper compartment 18 above the passage 14 and a lower compartment 20, below the passage 14. A heat pipe 22 extends from the lower compartment 20, upwardly along the passage 14, and into the upper compartment 18.In the upper compartment 18, the heat pipe 22 has a cooling zone 23 provided with a plurality of cooling fins 24. In the lower compartment 20, the lower end of the heat pipe 22, which forms a heating zone 25 of the heat pipe, is located in the interior of a catalytic converter 26 for the flameless catalytic combustion of a hydrocarbon fuel. The assemblage 12 is thus located in a separate compartment, designated 27, separate from the compartments 18, 20.

The compartment 18 has a cooling air inlet line 28 connected to a fan or blower (not shown) and an air outlet line 30. A hydrocarbon fuel inlet line 32 leads to the converter 26, which converter in turn has a combustion gas outlet line 34. An annular electric heater 36 surrounds the assemblage 12, and the heat pipe 22 has, above and below said assemblage 12, a plurality of equally circumferentially spaced radially projecting branch pipes 38. The interior of the holder 1 6, excluding the compartment 18 and including the compartments 20 and 27, is filled with a suitable particulate fibrous material, which may have thermal insulating properties, and/or may have sorbent properties, for safety in sorbing escaping cell contents from the battery assemblage 12, eg in a crash situation.

Suitable electric leads (not shown) will extend from the battery terminals through the compartment 20, and outwardly from the holder 16, via a passage 40 around the outlet 34. For example, one of the leads may incorporate the heat pipe 22, which is connected to one of the battery terminals, and suitable leads may be provided, also entering the holder or housing 16 via the passage 40, for the electrical heater 36.

The electrochemical cells of the battery assemblage 12 are, by way of example, of the type comprising molten sodium anodes, molten sodium aluminium chloride liquid electrolyte and beta alumina solid electrolyte. The cells themselves conveniently have aluminium terminals, seals, etc., and the heat pipe 22 has stainless steel walls and wicking material, and potassium therein as active material. The battery 10 is intended for use in the propulsion of a motor vehicle.

In use, the battery 10 will have a normal operating temperature in the region of 300 to 4000 C, which will be maintained during normal operation by heating caused by the internal resistance of the cells, in conjunction with the insulation of the battery. This operating temperature will also be maintained, by controlling the rate of charging, during charging of the battery. In situations where the vehicle is stationary at a charging station, the heater 36 can be used to maintain the normal operating temperature of the battery, or at least a minimum temperature, say, about 1 750C, at which the battery is operable, and the vehicle can draw away while heating itself up to its normal operating temperature.The heater 36 can also be used to heat the battery up when, for any reason, its temperature has fallen substantially and its liquid components-have solidified.

The heat pipe 22 will, by way of example, be designed to have a minimum operating temperature of 5250C, which is safely below the maximum safe operating temperature of the battery 10, which is, say, 5500C. When this temperature is reached, eg by over-rapid charging or discharging and/or extremely high ambient temperatures, the heat pipe 22 will automatically commence operating to evaporate potassium in the branch pipes 38 and in the pipe 22 in the interior of the passage 14, with potassium being condensed at cooling zone 23 at the upper end of the heat pipe 22 in the compartment 18.

Simultaneously, a thermocouple provided at 42 at the hottest part of the assemblage 12, ie at the upper end of the passage 14, will act when a temperature of 52500 is reached, to start the blower feeding air via the inlet 28 into the compartment 18. This causes condensation of the potassium in the cooling zone 23 of the heat pipe adjacent the fins 24 in the compartment 18.

When, for some reason, the vehicle is stopped remote from a charging station, the converter 26 can be used for battery heating and/or battery temperature maintenance. A thermocouple provided at 44, at the lowermost outer periphery of the assemblage 12 which is its coolest position, will act to operate a pump (not shown) to pump a suitable organic fuel via the inlet 32 into the converter 26, which contains platinum, palladium, or the like catalyst, once the temperature at 44 has dropped to, say, below 1 750C.

The pump will be arranged to stop the supply of hydrocarbon fuel to the converter once the temperature at 44 exceeds say 2000 C, and, likewise, the blower will be arranged to stop the air supply to the compartment 18, once the temperature at 42 drops below say 500 C. The catalytic converter may also be used for heating, if for any reason the temperature of the battery 1 0 has fallen substantially, and its components have solidified, although, for reasons of stressing of the various components, it is naturally desirable to avoid such solidification.

Naturally, depending on the specific components used in the battery and its cells, and in the heat pipe, and other design considerations, the exact temperature at which heating by means of the converter 26 starts and stops, can be varied within limits, as desired, as can the starting and stopping of the blower during cooling by means of the heat pipe.

Although a single heat pipe containing potassium as active vaporizable material has been shown in Figure 1, adapted for both heating and cooling purposes, there may instead be several such heat pipes. Furthermore, separate heat pipes may be used for heating and cooling. Thus, a heat pipe containing potassium as active material may lead from the compartment 27, where it branches into the assemblage 12, particularly at the hotter parts, such as 42, to the compartment 18, in which this heat pipe has a cooling zone 23. A further heat pipe containing eg sodium as active material can in this case have its heating zone 25 in the compartment 20, and will branch into the assemblage 12, particularly at the cooler parts, such as 44.

In Figure 2, a typical heat pipe is shown schematically, by way of illustration, and the same reference numerals are used for the same parts as in Figure 1, unless otherwise specified, the heat pipe being generally designated 22, and the branch pipes 38 being omitted for ease of illustration.

The heat pipe 22 shown has a stainless or corrosion-resistant steel closed-ended pipe or tube 46 which is lined along the interior of its curved portion by a stainless steel wicking material 48. The material 48 is fibrous and/or porous and provides, in its interior, capillaries for the transport by capillary action of molten active material, such as sodium, potassium, or the like.

The outside of the curved portion of the pipe 46 is shown provided with a sheath or coating 50 of copper. Electrical leads 52 and 54 are shown connected to opposite ends of the sheath 50, the lead 54 being connected to a terminal (not shown) of the cell assemblage 12 (Figure 1). The wicking material contains the active material sorbed in its pores and there is a vacuum in the heat pipe.

In use, the heating zone 25 obtains heat from a heat source (the converter 26 of Figure 1) which melts and then vaporizes the active material sorbed in the wicking material 48 there. The vaporized active material moves along the interior of the pipe in the direction of the arrows, and is condensed in the cooling zone 23 which acts as a heat sink. The condensing active material is sorbed in the wicking material 48 in the cooling zone 23 and is transported in liquid form by capillary action along the wicking material 48, back to the heating zone where it is again vaporized. There is thus a continuous process of vaporization in the zone 25 and condensation in the zone 23, with the active material flowing along the interior of the pipe as a vapour from the zone 25 to the zone 23, and back as a liquid in the wicking material from the zone 23 to the zone 25.

Heat is transported essentially as latent heat of vaporization from the zone 25 to the zone 23.

It will be appreciated that, with reference to the heat pipe 22 having branch pipes 38 shown in Figure 1 and during heating of the battery assemblage 12, each branch pipe will have wicking material 48 (although not necessarily a copper sheath). Furthermore, substantially the whole of the haat pipe 22 in the passage 14, and the whole of each branch pipe 38 will act as a cooling zone where condensation takes place. The cooling zone 23 in the compartment 18 and the associated blower will be inoperative. Similarly, during cooling, substantially the whole of the pipe 22 in the passage 14 and the branch pipes 38 will act as heating zones, with the blower and cooling zone 23 being operative and the converter 26 and heating zone 25 inoperative.

A development of the heat pipe 22 is shown in Figure 2 in broken lines, whereby it can be converted into a so-called gas-controlled or variable-conductance heat pipe. The heat pipe 22 in this form has an extension or additional chamber 56 connected to its end having the cooling zone 23 by a passage 58. The chamber 56 is of stainless steel and is integral with the tube 46 of the pipe 22. The pipe 22 and extension 56 in this embodiment contain a suitably inert gas, inert to the other materials used, and at a suitable pressure.

In use, as described above, vaporized active material will move along the interior of the pipe 22 from the heating zone 25 to the cooling zone 23.

This moving vapour will sweep the inert gas along the pipe 22 towards the extension 56 until the extension 56 is filled with inert gas which also fills the passage 58 and a portion of the pipe 22 adjacent the passage 58. There is a sharp interface between the inert gas and the vapour, and the gas in the pipe 22 prevents access by the vapour to at least part of the walls of the pipe 22 in the cooling zone. The interface is shown at 60 in Figure 2, and it will be appreciated that, during steady-state operation of the heat pipe, only that portion of the cooling zone 23 on the same side of the interface 60 as the heating zone 25, is available for use in condensing vaporized active material.

In use, an increased heating load in the heating zone, ie an increased input of heat into the heating zone 25, will lead to increased evaporation rate and to an increase in pressure in the pipe 22. The increased pressure tends to compress the inert gas into the extension 56 and to move the interface 60 towards said extension 56, thereby exposing an increased area of the cooling zone 56 to the vapour on the opposite side of the interface 60 from the extension 56. The capacity of the cooling zone 23 is thereby increased.The nature and pressure of the inert gas in the heat pipe 22 can be selected, bearing in mind the nature of the active material and the temperature at which it is to be vaporized, together with the volume and linear dimensions of the pipe and its extension 56, so that a slight temperature increase arising from an increased heating load in the heating zone 25, is associated with a substantial movement of the interface 60 away from the heating zone and a substantial increase in capacity of the cooling zone 23. Correspondingly, a drop in heat load at the zone 25 moves the interface 60 to the left and reduces the capacity of the cooling zone 23, again with a relatively small temperature change.Use of the inert gas and the extension 56 thus make provision for substantial variations in the capacity of the heat pipe 22, in terms of heat transfer from the zone 25 to the zone 23, with relatively small, and often negligible, changes in the temperature at which heat is transferred, ie at which heat is received at the cooling zone.

The use of the heat pipe to heat the battery by means of the catalytic converter, has the advantage that the heat pipe flattens any nonuniform power output from the converter, and provides a power density at the cooling zone 23 which is less than the power density at which heat is supplied by the converter. Use of the catalytic converter has the advantage that no ignition system is required, temperatures are amenable to control, and no flames are produced, with combustion taking place to an acceptably complete degree, at acceptably low temperatures with low fuel/air ratios.The system is reliable, and as it is expected that the heat pipe would need to be used only a few times a year, the use of a suitable hydrocarbon fuel, such as gasoline, butane or propane, will be economically acceptable as it will be used in extremely small quantities, even though complete absence of catalyst poisons therein will be required, and it may be expensive. The platinum or palladium will typically be provided in a porous ceramic substrate.

Although the branch heat pipes 38 are described as being in the form of radially projecting spokes, they may naturally be of spiral or circular (having a diameter equal to that of the assemblage 12 with a radial leg connecting them to the upright heat pipe 22) or other suitable configuration. Indeed, it is contemplated that the single upright central pipe 22 may be all that is necessary. It will further be appreciated that having the upright central pipe 22 aids the wicking or capillary action of the heat pipe in returning condensed potassium in a downward direction, both during heating and during emergency cooling.

Claims

CLAIM-S

1. A power storage battery made up of a plurality of electrically interconnected secondary electrochemical cells located in a thermally insulating housing which has one or more heat pipes at least partially located in the interior of the housing, one or more of said heat pipes being provided with a catalytic converter for the flarneless catalytic combustion of hydrocarbon fuels, each converter forming a heat source for the supply of heat via the associated heat pipe or pipes to the interior of the housing.

2. A battery as claimed in Claim 1, in which each catalytic converter is mounted on or in the housing.

3. A battery as claimed in Claim 1 or Claim 2, in which at least one said heat pipe projects through the housing from the interior thereof to the outside thereof, the catalytic converter being provided outside the housing.

4. A battery as claimed in Claim 3, in which at least one said heat pipe is associated with an electrical feed-through from the interior of the battery housing to the outside thereof, the feedthrough passing through the housing at the same position as the associated heat pipe.

5. A battery as claimed in Claim 4, in which the electrical feed-through comprises electrically conducting material which forms an external sheath around said heat pipe.

6. A battery as claimed in Claim 4, in which the electrical feed-through comprises electrically conducting material located in a longitudinal passage or external groove in the heat pipe, where it forms an electrical conductor remote from the interior of the heat pipe.

7. A battery as claimed in any of Claims 4 to 6 inclusive, in which the feed-through is connected inside the housing to one of the terminals of the battery.

8. A battery as claimed in any of the preceding claims, in which each catalytic converter contains as its catalyst a metal selected from the group consisting in platinum and palladium.

9. A battery as claimed in Claim 8, in which the catalyst is contained in the pores of a porous ceramic substrate.

10. A battery as claimed in any one of the preceding claims, in which the cells are hightemperature cells having an operating temperature in the range of 1 0O-5000C, each heat pipe having as its active vaporizable material a substance selected from the group consisting in sodium and potassium.

11. A battery as claimed in Claim 10, in which each heat pipe has wicking material in its interior, the pipe having walls and wicking material selected from the group consisting in nickel and stainless or corrosion-resistant steel.

12. A battery as claimed in Claim 10 or Claim 11, in which the active vaporizable material is potassium, and in which the heat pipe, at a position remote from its associated catalytic converter, is provided with a cooling zone.

13. A battery as claimed in Claim 12, in which the cooling zone and the catalytic converter are provided in separate compartments in the housing which are separate from a compartment in the housing in which the cells are located.

14. A battery, substantially as described and as illustrated herein.