GB2271018A

GB2271018A - Drive system for a road vehicle incorporating an electric motor driveable by a battery and by a fuel engine driven generator

Info

Publication number: GB2271018A
Application number: GB9319219A
Authority: GB
Inventors: Roger John Wedlake; Julia Sandra Weaving
Original assignee: Programme 3 Patent Holdings
Current assignee: Programme 3 Patent Holdings
Priority date: 1992-09-16
Filing date: 1993-09-16
Publication date: 1994-03-30
Also published as: FR2695597A1; GB9319219D0; JPH06223870A; DE4331569A1; FR2695597B1

Abstract

In a drive system 10 comprising a prime mover in the form of a turbine 16 drivable by the combustion of a fuel, an electrical generator 22 drivingly connected to the engine and driveable by the engine, an electrochemical power storage battery 28 electrically connected via a charge controller 25 to the generator and chargeable by the generator, and an electric motor 32 electrically connected to the battery via a power controller 31 and driveable by the battery, wherein the generator, battery, controller and electric motor are interconnected together such that the generator can charge the battery and drive the electric motor both separately and simultaneously, and such that the electric motor is driveable by the battery and generator both separately and simultaneously, the battery comprises a plurality of electrically interconnected high temperature electrochemical power storage cells each having a cathode comprising as active material Fe, Ni, Co, Cr, Mn, Cu dispersed in a matrix impregnated with alkali metal aluminium halide molten salt, the matrix being a laterally compressed plate of thickness 0.5 - 5 mm and the cathode having a volumetric energy density of 0.2 - 0.6 Ah/cm<3>. <IMAGE>

Description

22771018 Drive System for a Road Vehicle THIS INVENTION relates to a drive

system for a road vehicle. The invention also relates to a road vehicle incorporating the drive system; and to a method of driving such vehicle using said system.

According to the invention a drive system for a road vehicle comprises:

a prime mover in the form of an engine drivable by the combustion of a fuel; an electrical generator drivingly connected to the engine and drivable by the engine; an electrochemical power storage battery electrically connected via a charge controller to the generator and chargeable by the generator; and an electric motor electrically connected to the battery via a power controller and drivable by the battery, the battery comprising a plurality of electrically interconnected high temperature electrochemical power storage cells each having a cathode in the form of an electronically conductive electrolyte-permeable porous matrix impregnated with an alkali metal aluminium halide molten salt electrolyte which is molten at the operating temperature of the cell, an electrochemically active cathode substance in the form of a halide of a transition metal selected from the group consisting of Fe, Ni, Co, Cr, Mn, Cu and mixtures thereof being dispersed in the porous interior of the matrix, the cell having an alkali metal active anode substance which is molten at the operating temperature of the cell and the anode substance being separated from the cathode and molten salt electrolyte by a separator which is a conductor of the alkali metal of the anode, the generator, battery, controller and electric motor being interconnected together such that the generator can charge the battery and drive the electric motor 2 both separately and simultaneously, and such that the electric motor is drivable by the battery and generator both separately and simultaneously, the cells of the battery having cathode matrixes in the form of laterally compressed panels or plates of a thickness of 0,5 5 mm and said matrixes having a volumetric energy density of 0,2 - 0,6 Ah/cm3.

The battery may have a capacity of 20-40 kWh, the generator having a power output rating of 20-40 W, the plates having a thickness of 2 - 5 mm and said matrixes having a gravimetric energy density of 0,2 - 0,4 Ah/g.

Preferably the plate thickness is 1 - 4,5 mm, and said volumetric energy density may be 0,225 - 0,525 Ah/cm3. On a plot of matrix volumetric energy density in Ah/cm3 against matrix thickness in mm, said matrixes may be characterised by falling is inside the boundary of a triangle whose corners have the coordinates:

Matrix Volumetric Energy Matrix Thickness (mm) Density (Ah/cm3) 0,6 0,5 0,2 0,5 0,2 5,0 Preferably, on said plot, said matrixes are characterized by falling inside the boundary of a triangle whose corners have the following coordinates:

Matrix Volumetric Energy Matrix Thickness (mm) Density (Ah/cm3) 0,525 1,0 0,225 1,0 0,225 4,5 In other words, the plates are characterised by having a thickness and volumetric energy density such that on a plot of plate thickness in mm against volumetric energy density in 3 Ah/cm3, said plates fall inside the boundary of a triangle whose corners have the coordinates:

Thus, preferably, the plates have a thickness and volumetric energy density such that said plates fall inside a triangle whose corners have the coordinates:

Matrix Volumef:ric Energy Matrix Thickness (mm) Density (Ah/cm3) 0,6 0,5 0,2 0,5 0,2 5,0 Matrix Volumetric Energy Matrix Thickness (mm) Density (Ah/cm3) 1,0 0,2;5 1,0 0,225 4,5 The controller may be the usual type which adjusts voltage and/or current provided by the battery to the motor to control the power fed to the motor, and is preferably of the type which permits regenerative braking. as known in the art; and it can.

if desired, convert a direct current supply from the battery to alternating current feed to the motor, and vice versa during said regenerative braking.

In this specification, the term 'generator' is used broadly to cover also alternators.

Turning to the battery, for use on its own as in urban or suburban use of a passenger sedan,, it should have a useful capacity of 15-25 kWh. In a battery of cells of the type in question this is preferably available at a depth of discharge of up to 70% and at a maximum power delivery rating of 40-80 kW sustainable for at least 15 minutes. In other words, the battery may have a capacity of 15 - 25 kWh which it is capable of 4 delivering before it reaches a depth of discharge of 70 Accordingly, the battery should preferably have a theoretical capacity of 20-35 kWh, having a maximum power delivery rating of 40 - 80 kW sustainable for at least 15 minutes. For vehicles of the type in question, said capacity is expected to provide an adequate range of at least 100-150 km, with the electric motor driven solely by the battery and to a depth of discharge of 070%, when the turbine is out of use eg because of pollution considerations.

As indicated above the rate at which the battery is capable of being charged, is related to the generator power output power rating. Small passenger sedans of the type in question, for out of town use on the level, require a range of about 5 hours at a cruising speed of about 120 160 km/hr. This sets the size of is the fuel tank and indicates that a generator output rating of 20 - 40 kW would be acceptable, with the generator alone driving the electric motor directly. The battery should thus be capable of accepting charge at a rate of 20-40 M. A battery of cells of the type described above can in principle achieve this charging rate, particularly for cathode matrixes of 1 - 5 mm, preferably 2 - 4,5 mm thickness and having a volumetric energy density of 0,225 - 0,525 Ah/CM3, at least at a depth of discharge of up to 70%.

Thus the battery may be capable of accepting charge at a rate of - 40 kW at a depth of discharge of up to 70 %.

It follows that the electric motor should be capable of accepting an electric power supply (from the generator) of 20 kW (for sustained cruising on the level). For hill climbing, it should be capable of accepting both the maximum electric power output from the generator and that from the battery, so that it would be rated for a 40-80 kW electric power supply.

While the engine may be selected from suitable internal combustion engines and external combustion engines, typically employing a carbonaceous liquid fuel such as a fossil fuel, the engine being constructed to run or operate at a constant speed for high efficiency, and low cost, weight, volume and pollution, the engine is preferably a turbine employing a liquid fuel. Such turbines can be constructed or selected, for a suitable power output, to be of acceptably low mass and volume for road vehicle use for small passenger sedans having a mass of about 1 000 - 1 500 kg. Thus, the engine may be a turbine constructed to run at a constant speed of at least 100, 000 rpm while burning a liquid hydrocarbon fuel.

For small passenger sedans, the Applicant believes that a generator with a power output rating of 20-40 kW will be suitable, the power output of the turbine being rated accordingly, bearing in mind the efficiency of the generator and the charging characteristics of the battery.

The invention extends to a road vehicle having a drive system as described above, the vehicle having at least one drive wheel and a power transmission whereby the power output of the electric motor is connected to each drive wheel of the vehicle.

The road vehicle may be a passenger sedan having a mass of 1000 - 1500 kg.

The invention extends also to a method of driving a road vehicle as described above, which comprises burning a combustible fuel to drive the ei.gine, the engine driving the generator, the generator supplying electric power to at least one of the battery and electric motor, and the electric motor receiving electric power from at least one of the battery and generator, the electric motor finally driving at least one drive wheel of the vehicle via the vehicle power transmission.

Usually the vehicle will have a plurality of drive wheels which are driven.

Various features of cells suitable for batteries of the type in question, and their electrochemistry, are described in US 6 Patents 4 546 055, 4 529 676,, 4 560 627j, 4 592 969,, 4 722 875 and 4 772 449, 4 797 332, 4 797 333, 4 975 344 and 5 051 324; and in published British Patent Application 2193837A.

In particular the cathode matrix may be of a transition metal such as porous iron, nickel, chromium,, cobalt or manganese, and the active cathode substance may be FeCl., NiCl., CrC12. COC12 ff MnC12 or CuC12. The alkali metal of the anode is preferably sodium, the separator being 0-alumina, in particular 011-alumina or nasicon. Instead alkali metal ion-conducting polymeric membranes may be used as flexible panel separators selected to conduct the alkali metal of the anode. For reasons of cost, it is believed that the appropriate active cathode substance for the cells of the battery will be Fe/FeC12.

As the liquid electrolyte, an electrolyte of the type MA1Ha14. in which M is an alkali metal and Hal is a halogen will usually be used, eg NaA1C14. In these electrolytes the molar proportion of Al ions should not exceed the molar proportion of alkali metal ions, ie the molar ratio of Al:M should not be greater than 1:1. This can be achieved by ensuring that the cathode compartment contains a proportion of solid alkali metal halide [MHal) in contact with the liquid electrolyte during all states of charge of the cell.

With regard tc electrolytes of the MA1Ha14 type, such as NaA1C14. in which the Al:M molar ratio is not more than 1:1P it is a particular advantage that, in addition to providing for substantial insolubility therein of active cathode substances such as FeC12. N'C12. CrC12. COC12 or MnCl. when the Al:M ratio is 1: 1, such electrolytes also exhibit their minimum vapour pressure [which is substantially less than that of sulphur/sodium sulphide/polysulphide] when said Al:M ratio is 1:1, at the cell operating temperatures typically encountered. This is important from a constructional and safety point of view, as flat, thin plates of eg PHalumina, which will typically be used with the thin cathode matrixes of the cells of batteries suitable for the 7 present invention, can be brittle and prone to damage by high electrolyte vapour pressures, particularly during temperature excursions caused eg by cell malfunctions. Furthermore, such electrolytes exhibit relatively gentle freeze/thaw stresses on the separator plates; and a further feature of such electrolytes is that the alkali metal and electrolyte react, in the event of separator failure, to form solid reaction products at the temperatures in question, eg metallic Al and solid NaCl when Na reacts with NaA1C14 in which the Al:Na mole ratio is 1:1. All these features permit a plurality and indeed a multiplicity of cells to be arranged in batteries in which they are stacked faceto-face, employing relatively thin cathode structures and relatively thin separator plates with acceptable durability and resistance to separator failure, and acceptable safety, even in is the event of separator failure.

Naturally, other suitable liquid electrolytes, eg other molten salt electrolytes, may be employed, provided they contain cations of the alkali metal of the anode. Suitable electrolytes will usually contain halide anions such as chloride anions, being both chemically and electrochemically compatible with the separator and cathode and being incapable of poisoning the separator or of dissolving the active cathode substance, as such active cathode substances, when in solution in the electrolyte. are usually capable of poisoning the separator.

In the various patents and patent applications mentioned above, various options are described regarding the microstructure and electrochemical properties of the various features of the cells of the present invention. Thus US Patent 4 546 055 describes the basic cell electrochemistry from which the cells suitable for the battery of the present invention are derived; US Patent 4 529 676 describes a method of making cathodes for cells suitable for the battery of the present invention from a transition metal-containing matrix and the alkali metal halide discharge reaction product of the cathode; US Patent 4 560 627 describes the use of Co/CoCl 2 or Ni/NiC12 as a cathode substance a in parallel with a Fe/FeC12 cathode to protect the Fe/FeC12 cathode from overcharging; US Patent 4 592 969 describes the use of fluoride anions as a dopant in an NaAlCl 4 electrolyte to resist progressive internal resistance rise of the cell with sustained cycling believed to arise from poisoning of a 0-alumina separator by A1C1 3 in the electrolyte; US Patent 4 722 875 describes a method of making cathodes for cells according to the present invention from discharge reaction products of the cathode in particulate for.m with electrolyte; US Patent 4 772 449 describes a method of making a cathode suitable for the cells of the present invention by making a transition metal [Fe, Ni, Cr, Co or Mn] cathode matrix with sodium chloride dispersed therein by oxidizing the metal in particulate form followed by reduction thereof; US Patent 4 797 332; describes doping the surface exposed to the alkali metal of the anode of a ceramic solidelectrolyte separator with a transition metal oxide to improve the wettability of the separator surface by molten anode alkali metal; US Patent 4 797 333 describes a method of making cathodes suitable for cells of the present invention by charging a cathode precursor comprising alkali metal aluminium halide molten salt electrolyte, alkali metal halide, aluminium and transition metal [Fe, Ni, Cr, Co or Mn]; published British Patent Application 2193837A describes using magnesium dissolved in a sodium anode suitable for the cell of the present invention, when used with a 0-alumina separator, the magnesium acting as a getter for dissolved impurities in the sodium which can accumulate at the sodium/separator interface; US Patent 4 975 344 describes cells and batteries of the type in question having thin cathode structures; and US Patent 5 051 324 describes methods of making cells having thin cathode structures.

It will accordingly be appreciated that, as far as the microstructure and electrochemical properties of the various features [anodes, siparators, cathodes, etc] of cells suitable for the battery of the drive system of the present invention are concerned, and methods of making them, a variety of combinations and possibilities are available; as described, for example, in 9 the abovementioned prior patents and patent applications; and combinations of these various options may be employed, where desirable and compatible. These prior art references also describe suitable separators and molten alkali metal anodes. In particular, cells h aving thin cathode matrixes which are in principle capable of suitable rates of charge and discharge. are described, as indicated above, in US Patent 4 975 344.

The invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which:

Figure 1 shows a block diagram of a vehicle drive system according to the invention; Figure 1A is a plot of cell cathode matrix volumetric energy density in Ah/cm:3 against cell cathode matrix thickness in mm; Figure 2 shows a schematic sectional side elevation of an is electrochemical ce12 suitable for a battery for the drive system of Figure 1; Figure 3 shows a sectional side elevation of a battery of cells according to Figure 2; and Figure 4 shows a view similar to Figures 2 and 3 of another electrochemical cell suitable for a battery for the drive system of Figure 1.

In Figure 1 of the drawings, reference numeral 10 generally designates a drive system in accordance with the present invention, for a sedan passenger road vehicle weighing about 1250 kg (not shown).

The system 10 comprises a fuel tank 12 connected by a flow line 14 to a turbine 16. The turbine is drivable by liquid hydrocarbon fuel and is mounted on a shaft 18 supported by bearings 20. The shaft 18 forms a power input to a generator 22.

The generator 22 is connected by electrical leads 24 via a suitable charge controller 25 to the terminals 26 of a rechargeable power storage battery 28. The terminals 26 are in turn connected by electrical leads 30 to a suitable power controller 31, which is in turn connected by said leads 30 to an electric motor 32. For a direct current motor the controller will comprise a DC converter; and for an alternating current motor the controller will comprise an inverter. The motor 32 has a power output shaft 34 leading to a gearbox forming part of the transmission (not shown) of said vehicle.

In the example illustrated by Figure 1, the turbine 16 has a rated output of about 30 kW and the generator 22 in turn has an electrical outptt of about 25 M, the generator having a design operating speed which is the same as that of the turbine 16.

The battery 28 in turn has a capacity of 30 kWh and is capable of being charged at a rate of 25 kW by the generator, at least at depths of charge of up to 70%. The battery 28 is capable of delivering electrical power upon discharge thereof, at depths of discharge of up to 70%, to the motor 32 at a rate of 50 W.

The motor 32 is capable of accepting an electrical power input of 75 W, ie the output of the generator 22 (25 M) together with the maximum output of the battery 28 (50 M).

The motor 32 is capable of driving the vehicle at 120 km on the level for at least 5 hours when receiving 25 kW from the generator 22, for a vehicle range of at least 600 km on the level when driven by the generator 22 alone. The battery in turn is capable by itself of driving the vehicle at 110 km/hr on the level, while supplying 25 kW to the motor, for at least 1 hour at depths of discharge of 0-90%.

The vehicle is arranged, for hill climbing, to permit the battery 28 to deliver 50 kW to the controller 31 and thence to the motor 32 for at least 15 minutes, in parallel with the generator's delivering 25 kW to the motor 32.

The vehicle is thus traffic compatible both in town and in open road driving. It has a range in excess of 500 km on the level on the open road when driven by the generator 22 and turbine 16; and a range in excess of 100 km in town when driven solely by the battery 28. A turbine can be used which requires several minutes to start up and reach its operating speed, during which time the vehicle can be driven by the battery. When the vehicle is being driven by the turbine at speeds below those (cruising speeds) at which it consumes the full 25 kW power output of the generator 22, the excess power from the turbine can be employed to charge the battery 28 and to keep it fully charged. Indeed, the system can be provided with electrical circuitry whereby, when the vehicle is being driven below its cruising speed and below the rated or design power output of the generator 22, the turbine 16 and generator 22 can be operated intermittently, eg only and whenever the battery falls below a predetermined depth of charge, fully to charge the battery from time to time, as required.

It is expected, for practical reasons, that the battery 28 will be made up of.lectrochemical cells of the type described broadly hereinabove, and having an active cathode material which is FeC12 in its charged state. The geometry of such cells can be of the type described with reference to Figure 2 hereunder, having cathode structures of the nature of flat plates, expected to have a thickness of about 0,5 - 5 mm. typically 1 4j5 mm.

As far as cathode loading with FeC12 in the charged state is concerned, the porosity in the cathode matrix and the amount of FeC12 therein in the charged state should be such as to provide a cathode capacity of 0,, 2 0,,6 Ah/cm3. typically 0,225 - 0,525 Ah/cm, which values are approximately, in gravimetric terms, respectively 0,2 - 0j6 Ah/g and 0,22 - 0,52 Ah/g, based on the volumes and masses respectively of the cathode matrixes. Excessively high values for energy density will not permit the cells and battery to achieve the necessary high power goals, whereas excessively low values will not permit achievement of the 12 necessary low mass and low volume goals, whereby the battery and cells have a sufficient power output coupled with a sufficiently low mass and volume. Suitable cell matrixes are, with reference to Figure 1A, characterized by having a combination of thickness and volumetric energy density falling inside the boundary of the triangle whose corners have the coordinates:

Preferably they fall inside the boundary of the triangle whose corners have the coordinates:

Matrix Volumetric Energy Matrix Thickness (mm) Density (Ah/cm3) 0,6 0,5 0,2 0,5 0,2 5,0 Matrix Volumetric Energy Matrix Thickness (mm) Density (Ah/cm3) 0,525 1,0 0,225 1,0 0,225 4,5 It is also desirable to design the 011-alumina solid electrolyte separator plates or sheets so that their area exposed to the flat plate cathodes is related to the cathode capacity according to the constraint whereby Ah/cm'<O, 2, preferably <l, 15 and more preferably at most 0,1 Ah/cm'.

The battery as a whole should have a volumetric energy density of >100 Wh/9, and a gravimetric energy density of >100 Wh/kg.

Referring now to Figure 2. a sectional side elevation is shown on the type of electrochemical cell contemplated for use in the battery 28 of the vehicle drive system of the present invention.

13 In Figure 2, the cell is generally designated 36. The cell 36 comprises a molten sodium anode 38; a P"-alumina solid electrolyte separator 40; and a cathode 42 in the form of a porous iron matrix having, in its charged state, FeC12 dispersed therein and a molten NaA1C14 electrolyte impregnated therein. The FeCl 2 is in finely divided and/or thin layer form; and the matrix in the charged state has a small amount of NaCl in solid form dispersed therein,, so that the NaCl:A1C13 mole ratio in the electrolyte is never less than 1:1. The cell 36 has a housing 44 of square outline when viewed in the direction of arrows 46, and the housing is provided with anode and cathode terminals (not shown) electronically connected respectively to the anode 38 and the matrix of the cathode 42. The matrix of the cathode 42 is in contact with the separator 40 and the cell is shown in its charged state with the sodium anode 38 substantially filling the compartment within which it is contained.

The housing 44 is divided by the separator 40 into an anode compartment 46 containing the sodium 38, and a cathode compartment 48 containing the cathode 42. The housing 44 is of mild steel and the part of the housing 44 in contact with the anode 38 is electronically insulted from the part of the housing 44 in contact with the cathode 42 by insulating material 50.

Provision is made for changes in volume of the anode and cathode during charging/discharging by having the walls of the housing 44 flexible. Instead, inert gas spaces (not shown) can be provided in the compartments 46, 48.

In Figure 2 the separator 4 0 is in the form of a flat plate, as is the matrix of the cathode 42, which matrix fills the compartment 48.

In Figure 3 a battery of the cells 36 of Figure 2 is shown, generally designated 28. The cells 36 are shown arranged face-to face in series and the same reference numerals are used for the same parts in Figure 3 as in Figure 2. The housings 18 of the cells 36 in the battery 28 are provided by a common elongated box 14 structure 54 of square cross-section and having end walls and partitions, designated respectively 56 and -58. The partitions 58 form common walls of adjacent cell housings 44, and the end walls 56 form outwardly facing walls of the housings 44 of the cells 36 at opposite ends of the battery 28.

Turning to Figure 4, the cell shown is again designated 36, and, unless otherwise specified, the same reference numerals are again used for the same parts as in Figures 2 and 3. The cell 36 of Figure 4 has a mild steel housing 44 similar to the box structure 54 of Figure 3.

In the housing 44 a plurality (three) of anodes 38 are shown in opposed spaced face-to-face relationship in series. Between the anodes 38 are provided, alternating with the anodes 36, a plurality of cathode structures 42. Two structures 42 are shown between the anodes 38 and a structure 42 is shown at each end of the series, outwardly of the outermost anode 38 at that end. The structures 42 at the ends of the series are half the thickness of the structures 42 between the anodes 38.

Each cathode structure 42 is in the form of a f lat plate iron matrix, similar to that of the cathode 42 of Figure 2, and is similarly saturated with molten NaA1C14, also having FeC12 and NaCl dispersed therein.

Each of the anodes 38 is in turn in the form of a flattened box-like V'alumina holder containing molten sodium active anode material.

It should be noted that, for ease of illustration,. the structures 42 are shown spaced from the anodes 38, but in practice the structures 42 and anodes 38 are hard up against and in abutment with one another in series.

The housing 44 is, outside the structures 42 and anodes 38, filled with molten NaAM4 electrolyte 52, which immerses and saturates the structures 42.

Each structure 42 has a mild steel wire current collector (not shown) which connects its matrix to the housing 44, which housing forms the cathode terminal of the cell 36. Each anode 38 also has a mild steel wire current collector (also not shown) which passes through a sealed opening in the associated ON alumina holder of that anode. In the holder the current collector is connected to a suitable current collecting mesh or gauze which lines the holder, and, outside the holder it is electronically insulated from the LaAlCl 4 electrolyte and from the housing 44, through which it passes. The anode current collector wires are connected together outside the housing 44. so that the cell has its cathode structures 44 connected in parallel to form a single cathode, and its anodes 38 connected in parallel, to form a composite anode.

In practice, it is contemplated that the cathode matrixes will be relatively thin, those of Figures 2 and 3 being about 3,5 mm thick, as will be the structures 42 of Figure 4 which are located between the anodes 38. These matrixes will thus be in the form of sheets, and they will be provided with a porosity and with a loading of PeCl 2 in the charged state such that their capacity can be expressed as 0,3 Ah/g and 0,34 Ah/cm3.

The separators 40 of Figures 2 and 3 and the walls of the holders of the anodes 38 of Figure 4,, which holders also function in practice as solid electrolyte separators. each have and are directed at and opposed to the adjacent cathode matrix sheets.

such that the capacity of the cathode sheets can be expressed as 0,1 Ah/cm2 (this can be regarded as the overall capacity of the cathode matrixes divided by the total separator area exposed face-to-face with said cathode matrixes).

16 The Applicant has conducted tests which show that cells of the type shown in Figure 2 as described above are capable of receiving a charge over a period of 1 h amounting to 70% of the cell capacity, and can have an energy:sustained power ratio of 1:3.

These cells are accordingly suitable for the vehicle drive system 10 described with reference to Figure 1.

17

Claims

Claims: 1 A drive system f or a road vehicle which syptem comprises: a

prime mover in the f orm of an engine drivable by the combustion of a fuel; an electrical generator drivingly connected to the engine and drivable by the engine; an electrochemical power storage battery electrically connected via a charge controller to the generator and chargeable by the generator; and an electric motor electrically connected to the battery via a power controller and drivable by the battery, the battery comprising a plurality of electrically interconnected high temperature electrochemical power storage cells each having a cathode in the f orm of an electronically conductive electrolytepermeable porous matrix impregnated with an alkali metal aluminium halide molten salt electrolyte which is molten at the operating temperature of the cell, an electrochemically active cathode substance in the form of a halide of a transition metal selected from the group consisting of Fe, Ni, Co, Cr, Mn, Cu and mixtures thereof being dispersed in the porous interior of the matrix, the cell having an alkali metal active anode substance which is molten at the operating temperature of the cell and the anode substance being separated f rom the cathode and molten salt electrolyte by a separator which is a conductor of the alkali metal of the anode, the generator, battery, controller and electric motor being interconnected together such that the generator can charge the battery and drive the electric motor both separately and simultaneously, and such that the electric motor is drivable by the battery and generator both separately and simultaneously, the cells of the battery having cathode matrixes in the form of laterally compressed plates of a thickness of 0, 5 - 5 mm and said matrixes having a volumetric energy density of 0,2 - 0, 6 Ah/cm.
2. A system as claimed in claim 1, in which the battery has a capacity of 20 - 40 kWh, the generator having a power output rating of 20 - 40kWh, the plates having a thickness of 2 - 5 mm and said matrixes having a gravimetric energy density of 0,2 0, 4 Ah/g.
3. A system as claimed in claim 2, in which the plate thickness is 1 - 4,5 mm, t he volumetric energy density being 0,255 - 0,525 Ah/CM3.
4. A system as claimed in any one of claims 1 to 3, in which the plates are characterised by having a thickness and volumetric energy density such that, on a plot of plate thickness in mm against volumetric energy density in Ah/cm3, said plates fall inside the boundary of a triangle whose corners have the coordinates:

MATRIX VOLUMETRIC ENERGY MATRIX THICKNESS (mm) DENSITY (Ah/CM3) 0,6 0,
5 0,2 0,'S 0,,2 5,0 5. A system as claimed in claim 4. in which the plates have a thickness and volumetric energy density such that said plates fall inside a triangle whose corners have the coordinates:

MATRIX VOLUMETRIC ENERGY MATRIX THICKNESS (mm) DENSITY (Ah/CM3) 0,525 1,0 0,225 1,0 0,225 4,5
6. A system as claimed in any one of the preceding claims, in which the battery has a capacity of 15 - 25 kWh which it is capable of deliverilg before it reaches a depth of discharge of 70 %.

19
7. A system as claimed in any one of the preceding claims, in which the battery has a theoretical capacity of 20 - 35 kWh, having a maximum power delivery rating of 40 - 80 kW sustainable for at least 15 minutes.
8. A system as claimed in any one of the preceding claims, in which the battery is capable of accepting charge at a rate of 20 - 40 kW at a depth of discharge of up to 70 %.
9. A system as claimed in any one of the preceding claims, in which the engine is selected from internal combustion engines and
10 external combustion engines employing carbonaceous liquid fuels. the engine being constructed to run at a constant speed. 10. A system as claimed in claim 9, in which the engine is a turbine constructed to run at a constant speed of at least 100,000 rpm while burning a liquid hydrocarbon fuel. 15
11. A road vehicle having a drive system as claimed in any one of the preceding claims, the vehicle having at least one drive wheel and a power transmission whereby the power output of the electric motor is connected to each drive wheel of the vehicle.
12. A road vehicle as claimed in claim 11, which is a passenger 20 sedan having a mass of 1000 - 1500 kg.
13. A method of driving a road vehicle as claimed in claim 11 or claim 12, which comprises burning a combustible fuel to drive the engine, the engine driving the generator, the generator supplying electric power to at least one of the battery and electric motor, and the electric motor receiving electric power from at least one of the battery and generator, the electric motor finally driving at least one drive wheel of the vehicle via the vehicle power transmission.
14. A drive system for a road vehicle substantially as herein described and illustrated.

0 4 1 1
15. A road vehicle substantially as herein described.
16. A method of driving a road vehicle substantially as herein described.