WO1992010864A2

WO1992010864A2 - Metal/oxygen battery constructions

Info

Publication number: WO1992010864A2
Application number: PCT/GB1991/002212
Authority: WO
Inventors: Handel Meirion Thomas
Original assignee: Rolls-Royce And Associates Limited
Priority date: 1990-12-12
Filing date: 1991-12-12
Publication date: 1992-06-25
Also published as: AU9080891A; GB9026927D0; WO1992010864A3; EP0561938A1

Abstract

The cells of a multicell metal/oxigen battery construction each contain a potassium hydroxide electrolyte, a metal anode plate and a pair of oxygen permeable cathode panels, one on each side of the anode. Each cell has an electrically non-conducting housing comprising opposed faces and a peripheral rim region, with an aperture in each of the opposed faces, to which the cathode panels are sealingly fixed so as to obturate the aperture. The faces of adjacent housings are sealed to each other in confronting fluid-tight manner so as to define therebetween oxygen feeds and electrolyte drains, both the oxygen feeds and the electrolyte drains communicating externally of the cells with the cathodes.

Description

METAL/OXYGEN BATTERY CONSTRUCTIONS

This invention relates to metal/oxygen battery constructions, both the construction of individual cells and of a stack of such cells electrically connected together in series externally of the cells.

Metal/oxygen batteries are also known as metal/air batteries, and in this specification use of the former term should be taken to include the latter, except where the context requires otherwise. Such batteries are becoming well known as, e.g., small emergency sources of power for use at sea or on land. For examples of background technology the reader is referred to the following United States patent specifications: Niksa et al, US4925744; Hunter et al, US4942100; Hoge, US4885217; Strong et al, US4871627; and Ha len et al, US4626482.

Such batteries rely on the combination of waterproof sheet-like gas-permeable oxygen cathodes and consumable metal anodes in an aqueous electrolyte.

One known type of cathode material comprises several layers of different sheet materials laminated together by hot rolling. The innermost layer, in contact with the electrolyte, comprises a non-woven web of carbon fibre. This is bonded to a nickel mesh which acts as a current collector, which in turn is bonded to another carbon fibre web layer. The outermost layer, on the oxygen side of the cathode, is a microporous layer of TEFLON (RTM). The carbon fibre webs are impregnated with a carbon/TEFLON/silver catalyst slurry which is dried before the hot rolling process.

It has been found that aluminium alloy anodes as disclosed in the above-mentioned prior art are particularly advantageous to use.

With optimisation of the cell concept, aluminium/oxygen batteries can give a very high energy density and a power density which is adequate for many applications.

Known chemical optimisation of the cells includes the use of an alkaline electrolyte, particularly potassium hydroxide, to achieve formation of aluminium hydroxide precipitate instead of a passivating gell in the space between the anode and the cathode. Known physical optimisation includes:

-the doubling of active cathode area by arranging that the anode is located between two sheet-like oxygen cathodes, each of which is exposed to air or oxygen through a window in its own side of the cell;

-the use of a cell containing a large overall volume of electrolyte relative to the volume of electrolyte being actively used in the space between the cathodes and the anode; and

-achieving circulation of fresh electrolyte to the space between the cathodes merely by thermal convection currents rather than pumping or stirring, thereby ensuring that the aluminium hydroxide precipitate falls to the bottom of the cell instead of remaining in suspension.

The latter two measures help to ensure that, despite the production of large amounts of aluminium hydroxide as a precipitate, the reaction can proceed for a relatively large number of amp-hours without serious loss of efficiency.

It is an overall object of the present invention to further improve metal/oxygen battery design to achieve long running times at currents sufficient to power submersible vehicles, such as remote controlled undersea survey vehicles.

A related object is to provide a submersible vehicle making use of such improved batteries.

A further object is to provide simple but efficient cooling of a multi-cell metal/oxygen battery when situated in a submersible vehicle.

Another object of the invention is to improve the supply of oxygen to individual cells in metal/oxygen batteries.

Another object of the invention is to provide more effective separation of precipitating aluminium hydroxide from the circulating electrolyte. Yet another object of the invention is to provide a way of improving circulation of electrolyte within cells without disturbing the precipitated aluminium hydroxide.

A further object of the invention is to enable the sharing of electrolyte between cells in multicell metal/ oxygen batteries in order to maintain a common level of electrolyte while also substantially maintaining electrical isolation between cells.

Accordingly, in a first aspect the present invention provides a metal/oxygen battery construction having a plurality of separate elecrolyte-holding cells each containing metal anode means and oxygen cathode means, each cell having an electrically non-conducting housing comprising opposed faces and a rim region, each housing having aperture means in at least one of the opposed faces, to which aperture means the cathode means are sealingly secured, the faces of adjacent housings being sealed to each other in confronting fluid-tight manner so as to define therebetween oxygen feed means and electrolyte drainage channel means, both the oxygen feed means and the electrolyte drainage channel means communicating with the cathode means.

Preferably, the oxygen feed means comprises an oxygen supply space in direct communication with the cathode means, and at least one oxygen feed channel leading to the oxygen supply space.

For optimum efficiency, each cell contains a metal anode plate located between two oxygen cathodes and each face of the housing has an aperture with a corresponding one of the cathodes sealingly secured thereto, the oxygen supply space being adjacent to confronting cathodes of adjacent housings.

Conveniently, the oxygen feed channels between the adjacent housings are connected to an an oxygen delivery manifold. Preferably, the oxygen supply spaces, the oxygen feed channels and the electrolyte drainage channel means are defined by depressions in the adjacent confronting faces of the housings.

Although the oxygen permeable sheetlike cathodes are substantially waterproof, there is inevitably some seepage of electrolyte through them and out of the cells, hence the need for an electrolyte drain. To prevent eventual filling of this drain and of the oxygen supply space, we prefer that the lowest portion of the drain incorporates electrolyte drainage means for transport of the seepage away from the sealed areas between the housings. We further prefer that the drainage means comprises electrolyte recirculation means for injecting drainage electrolyte back into the interior of an adjacent cell.

To provide the rim region of the cells with an enlarged external surface area for enhanced transfer of internal cell reaction heat to the environment, it may be advantageous to make the rim regions of the housings with a stepped configuration rather than a plain cylindrical or outwardly tapered shape. This stepped configuration may occupy only part of the periphery of the housings if the heat dissipation obtained by such an arrangement is sufficient.

In a second aspect, the invention provides a submersible vehicle comprising a hull, pressurised oxygen supply means, a multi-cell metal/oxygen battery, power conditioning means and propulsion means, at least the battery being contained in free-flooded compartment means whereby the battery operates at ambient pressure and circulation of water around the battery effects cooling of the cells. Such circulation of the water around the battery may be forced or unforced.

Preferably, at least part of the pressurised oxygen supply means is also contained in the above-mentioned free-flooded compartment means. There may be two separate free-flooded compartments for containing said at least part of the oxygen supply means and the battery respectively. Preferably, the free-flooded compartment means has at least one removable vehicle external wall portion to allow removal and replacement of the battery and/or said at least part of the oxygen supply means.

The pressurised oxygen supply means may comprise a pressurised oxygen tank, an oxygen supply manifold for distribution of oxygen to the cells comprising the battery, an oxygen supply pipe extending between the tank and the manifold, and flow control means in the supply pipe, the flow control means comprising isolating valve means to allow disconnection of an aft portion of the supply pipe from the oxygen tank, vent/fill valve means to allow venting and filling of the tank from outside the vehicle and flow regulator means between the isolating valve means and the manifold for control of flow of oxygen to the manifold.

In a preferred embodiment the pressurised oxygen tank is integral with the hull of the vehicle and an aft portion of the oxygen supply pipe with associated flow control means is disconnectable from the tank for removal from the vehicle together with the battery, the free-flooded compartment means being to ithe rear of the tank and forward of the power conditioning equipment.

A third aspect of the invention provides a metal/oxygen cell construction comprising an electrically non-conducting housing for holding therein anode means, oxygen cathode means and an electrolyte, the housing comprising opposed faces and a stepped rim region for providing the cell with an enlarged external surface area for enhanced transfer of heat to the environment. This construction is particularly advantageous where a metal/oxygen battery comprises a plurality of cell housings whose faces are sealingly engaged to each other to form a stack of cells, thereby restricting the surface area of the housings available for radiative and convective dissipation of heat generated by electrochemical reactions within the cells. In this case the stepped rim region considerably increases the surface area available for heat exchange with the environment. This aspect of the invention is particularly intended for use in the above-described battery powered submersible, the stepped rim region being exposed to the water in the free-flooded compartment means.

Preferably, the stepped rim region comprises a plurality of steps.

The stepped rim region may comprise only a portion of the circumference of the housing.

In a fourth aspect, the invention provides a metal/ oxygen battery cell construction in which an electrically non-conducting housing contains metal anode means and oxygen cathode means in fixed spaced-apart relationship to each other, each housing comprising opposed faces thereof and a peripheral rim region, the cell interior comprising an electrolytic reaction region containing the anode and cathode means, a precipitate collection region for retaining reaction product particles precipitated from the reaction region, and electrolyte circulation channel means for facilitating circulation of electrolyte within the cell without disturbing the precipitated particles, the channel means having intake means and exit means adjacent different parts of the reaction region, the channel means between the intake means and the exit means extending around at least part of the periphery of the precipitate collection region. In one preferred embodiment of the invention, the exit means is situated such that the part of the channel means leading thereto extends through the precipitate collection region from the periphery of the cell towards the reaction region. To prevent blockage of the exit means, the exit means should be shielded from deposition of precipitate particles thereinto from the reaction region.

It is thought that natural convective circulation of the electrolyte through the channel means will be maximised and disturbance of the precipitate particles minimised if the exit means is situated directly beneath_^ and centrally of the reaction region and the intake means is situated near at least one of the extremities of the reaction region. In our presently preferred arrangement, the extremities of the reaction region are near the peripheral rim region of the housing and the channel means comprises a central channel portion extending centrally through the precipitate collection region from the periphery of the cell to an exit situated directly beneath and centrally of the reaction region and two peripheral channel portions each extending from a respective intake near an extremity of the reaction region, around a part of the periphery of the precipitate collection region, and joining the central channel portion at the periphery of the cell.

Preferably, the precipitate collection region comprises a plurality of elongate baffles extending widthwise between the opposed faces of the housing and lengthwise from the rim region towards the reaction region, the baffles being spaced from each other to define compartments open near the reaction region into which the precipitate is deposited during normal operation of the cell. Conveniently, if the part of the channel means leading to its exit extends through the precipitate collection region, that^' part of the channel means is defined between adjacent baffles and may be shielded from deposition of precipitate particles thereinto by baffle means located between the exit of the channel means and the reaction region.

In a fifth aspect, the present invention provides a metal/oxygen battery construction having a plurality of separate electrolyte-holding cells each containing metal anode means and oxygen cathode means, adjacent cells being connected together in electrical series, each cell having an electrically non-conducting housing comprising opposed faces and a rim region, each housing having aperture means in at least one of the opposed faces, to which aperture means the cathode means is sealingly secured, confronting faces of adjacent housings being sealed to each other in fluid-tight manner so as to define therebetween oxygen feed means and electrolyte drainage channel means, both the oxygen feed means and the electrolyte drainage channel means communicating with the cathode means, the oxygen feed means being connected to an an oxygen supply manifold for distribution of oxygen to the cells comprising the battery, the electrolyte drainage channels being connected to electrolyte recirculation means for injecting drainage electrolyte back into the interiors of the cells.

Advantageously, the connections between the oxygen supply manifold and the oxygen feed means are used to provide the required electrolyte recirculation means. This is achieved by using the flow of oxygen between the oxygen supply manifold and the oxygen feed means to entrain electrolyte from the drainage channels into mixed electrolyte/oxygen flow which is then passed into the tops of the housings and empties into the interiors of the cells where the mixed electrolyte/oxygen flow separates into its constituent components, an oxygen head space thereby being created in each cell, from which head space oxygen passes to the oxygen feed means and thence to the cathode window means.

Preferably, the oxygen head space is created in the upper closed end of a dip tube within each cell, the dip tube having a lower open end for the injection of the recirculated elecrolyte into the main body of electrolyte within the cell.

Preferably, the oxygen feed means defined between the confronting faces of adjacent housings comprises an oxygen supply space in direct communication with the cathode means, and an oxygen feed channel connected to the oxygen supply space and to the oxygen head space. We further prefer that the electrolyte recirculation means comprises oxygen feed lines each having one end connected to the oxygen supply manifold and the other end connected to a mixed oxygen/ electrolyte flow line at a 'T' junction, the oxygen feed line being the stem of the *T' and the oxygen/ electrolyte flow line being the cross-bar of the 'T*, one side of the cross-bar being connected to an electrolyte drainage channel through non-return valve means and the other side of the cross-bar being connected to an oxygen head space in the interior of the cell.

Conveniently, drainage electrolyte from each drainage channel (being seepage from two adjacent cells defining the drainage channel therebetween) is recirculated to only one of the two adjacent cells, that is, the first of the two cells in a designated direction lengthwise along the stack of cells, comprising the battery. In this case, the drainage channel on the outer face of the last cell in the stack is connected to the drainage channel on the outer face of the first cell in the stack, the latter drainage channel being connected to the electrolyte recirculation means. This ensures that there is a nominally correct amount of seepage returned to each cell.

A sixth aspect of the invention is directed to ensuring that the electrolyte level in different cells remains substantially similar in spite of differing leakage rates through the cathodes, and differing rates of recirculation of drainage electrolyte back into the cells, provision therefore being made for the interiors of adjacent cells to be connected for the interchange of electrolyte in such a way that no substantial shunt currents occur between cells. This may be achieved by connecting the interiors of adjacent cells through capillary tubes.

Exemplary embodiments of the above inventive concepts will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram showing a propulsive system for a submersible vehicle incorporating a metal/ oxygen battery;

Figure 2 is a pictorial view of a multi-cell metal/- oxygen battery according to the present invention, one end cell of the battery being shown with half the front wall of the cell removed to reveal internal structure;

Figure 3 is an end elevation of a typical one of the metal/oxygen cells in the battery shown in Figure 2, the cell again being shown with half the front wall of the cell removed to reveal internal structure;

Figure 4 is an enlarged detail of the top part of the cell shown in Figure 3;

Figure 5 is an enlarged detail of the bottom part of the cell shown in Figure 3;

Figures 6A and 6B are top and bottom portions respectively of a sectional view taken on the line joining points ABCDEF in the cell of Figure 3;

Figure 6C is an enlargement of the portion of Figure 6A within the outlined box;

Figure 7 is a view on arrow VII in Figure 3; and

Figure 8 is a view on arrow VIII in Figure 3.

The designs shown in the above-mentioned drawings are based on the use of a particularly simple form of aluminium/oxygen battery technology in which circulation of the electrolyte within individual cells relies on convection currents produced by the heating effect of the electrolytic reaction within the cell. The preferred elecrolyte is potassium hydroxide and the reaction product is a precipitate of aluminium hydroxide particles. Since circulation of the electrolyte is not forced, the precipitate particles are more likely to fall towards the bottom of the cells instead of being entrained in the circulation of the electrolyte. This keeps the cathode/anode space relatively free of reaction products and thereby facilitates maintenance of the maximum power output of the cell for a longer period during operation of the cell.

This type of cell has a high energy density and a power density which is suitable for many applications, such as emergency or stand-by power or electrically powered vehicles.

Figure 1 shows how such an aluminium/oxygen battery can be integrated into the power system of a ship, such as a remotely controlled undersea survey vehicle. A pressure vessel or oxygen tank 101, capable of holding gaseous oxygen at a pressure of two hundred atmospheres or higher, is linked through an oxygen supply line 102 to the battery 103, which comprises a number of individual cells 105. The cells 105 are externally linked together in electrical series so that two electrical output lines 107 and 109 are connected respectively to the anode of the first cell of the battery and the cathode of the last cell. In turn the electrical output lines 107 and 109 are connected in parallel to power conditioning equipment 111. This comprises two units, namely a constant voltage output DC/DC converter 113 for supplying power to vehicle services such as guidance and manoeuvring systems, and a variable output DC/DC converter 115 for powering an electric motor and gear unit 117 which drives a propeller 119.

Assuming that the above described power system is for a submersible vehicle, it is convenient if the vehicle is constructed as a monocoque chassis. The oxygen tank 101 forms part of the hull of the vessel, because the tank 101 must be very strong anyway to perform its oxygen containment function. Provision can be made for the tank 101 to have a duct 126 on its axial centreline through which electrical cables or other services can pass. Overall longitudinal stiffness of the vehicle can be provided by suitable chassis members (not shown), which also provide further fore-and-aft access for services.

The battery 103 is contained in a free-flooding compartment 127 within the hull so that the battery operates with its immediate surroundings at ambient seawater pressure and with circulation of water around the battery to effect cooling of the cells. Such circulation of the water around the battery may be forced, using pumps or the like, or unforced, utilising merely natural circulation induced by passage of the vehicle through the water.

It is a characteristic of batteries of the type described here that they produce a small amount of parasitically generated hydrogen. Immersion of the battery in water which is continuously interchanging with that outside the vehicle facilitates safe disposal of this hydrogen by entrainment with the through-flowing water.

Although not shown, the compartment or compartments aft of the battery compartment, containing the power conditioning equipment 111 and the motor unit 117, may be dry or oil-filled as a matter of design choice, according to the type of electric motor chosen for unit 117. This aft space may also contain the steering and trim gear and their controls (not shown) .

Returning forward to the oxygen supply system, the oxygen supply line 102 extends between the tank 101 and an oxygen distribution manifold 200 on top of the battery with connections 201 to the individual cells 105. To control oxygen flow to the manifold 200, the supply line 102 includes two isolating valves 121,123, a vent/fill valve 125 to allow venting and filling of the tank 101 from outside the vehicle, and two flow regulators R1,R2 in series between the isolating valve 123 and the manifold 200. Rl is for lowering the oxygen pressure from the very high tank pressure to an intermediate value, and R2 is for reducing it further to a lower battery supply pressure. The aim is to control the battery supply pressure to a constant 24.9 mbar, approximately, above the pressure of the seawater in the compartment 127. To this end, the regulators Rl, R2 automatically adjust themselves with reference to the pressures in compartment 127 and supply line 102. A low pressure relief valve (not shown) is also fitted to the supply line 102 near the battery, say in the oxygen manifold, to protect the battery cells from being overpressύrised in the unlikely event of one or both of the regulators Rl,R2 failing.

Two isolating valves in the supply line 102 are necessary so that valve 121 can be opened while valve 123 is closed, to allow filling and venting of the oxygen tank independently of the connection to the battery 103. Optionally, as shown by the dashed lines in Figure 1, the oxygen supply line 102, at least up to its isolating valve 123, can be included in an extended free flooded compartment 127.

For ease of servicing the vehicle, the battery 103 and any attached equipment can be removed from the vehicle through a removable hull panel or door 129 comprising a wall of the compartment 127.

If desired, the battery and its associated oxygen flow control devices can be contained in respective adjacent free-flooding compartments.

Refuelling the vehicle requires the following sequence of operations.

- Dry dock the vehicle.

Remove the cover 129 over the monocoque chassis section of the hull.

- Disconnect the battery electrically from the vehicle.

Shut off the oxygen supply using valve 123. Disconnect the oxygen manifold 200 from the battery. Fill a new battery with electrolyte.

- Remove the depleted battery and replace it with the new one.

Reconnect electrically.

- Recharge the oxygen cylinder through valves 121,125.

- Reconnect the oxygen manifold and open the supply valves 121,123.

- Purge the oxygen line, the manifold and the battery of air.

Replace the monocoque cover. The vehicle is now refuelled.

Referring now to Figures 2 to 8, the basic electrochemical elements of each working cell 105 comprise an aluminium alloy anode 205, a pair of oxygen cathode panels 207A,207B, one panel on each side of the anode but spaced apart therefrom, a supply of oxygen and an alkaline electrolyte (not shown), preferably a 3.5 mole solution of potassium hydroxide.

These elements produce the cell voltage and current. In accordance with the invention the continued operation of the cell in a battery stack of cells is acheived by the following:-

1. A suitable stackable cell housing for accomodating the electrolyte, the anode and the cathodes.

2. Enhanced removal of waste heat from the cell.

3. Provision for oxygen feed to each cell.

4. Return of electrolyte cathode seepage into the cells.

5. Collection of the generated current from the cathodes and prevention of short circuits between adjacent cells.

6. Sedimentation and compaction of aluminium hydroxide precipitate with restraint of sediment against movement due to vehicle motion.

7. Removal of hydrogen evolved by parasitic corrosion.

The cell housing 203 comprises two similarly featured half-housings or shells 209A,209B, see particularly Figures 7 and 8 in addition to Figures 2 and 3. Each shell is moulded from, for example, epoxy resin reinforced with a glass fibre filler, though other suitably rigid non-corroding and non-conducting materials could be used at the option of the designer. A suitable thickness for the specified material is 2mm. However, the shells 209A,B are moulded with integral top and bottom block portions 211A,B and 213A,B respectively, The blocks have smooth plane mutually parallel front and back faces which are continuous with the plane radially outturned edges 215A,B of the thin shell portions. This enables easy assembly of the shells together to form the individual cells and easy stacking of the cells together to form the battery. The top and bottom block portions of the shells, when bonded together on their faces to form top and bottom structural blocks 211,213 for^" the complete cell, also provide a convenient location for fluid ingress and egress holes to and from the interiors of the cells and for helping to define oxygen supply and electrolyte drainage channels between the cells. They further provide convenient sites for connections to external oxygen and electrical connections.

A complete cell housing is made by gluing confronting plane edges 215A,B of the two halves of the housing together after fitting the components of the cell into the two halves. An epoxy glue may be used. After gluing the two halves together, a suitable total thickness for the housing is about 25mm. After the glue has cured, the various holes are bored in the top and bottom blocks 211,213 as required.

Each smooth front and rear end face 217A,B of a housing is moulded complete with a cross-shaped depression 219A,B. When the cells 105 are stacked together to form the battery 103, the depressions in confronting cell walls are in registration with each other, so forming between adjacent cells a central oxygen chamber 221, an oxygen supply channel 223 leading to the chamber 221 from the top of the battery and an electrolyte drain channel 225 leading from the chamber 221 to the bottom of the battery for draining off the inevitable electrolyte seepage through the cathodes 207A,B.

The cathode sheets or panels 207A,B fit within and are coextensive with the laterally extending arms of the cross-shaped depressions 219A,B, except for a triangular area of the oxygen chamber 221 below the cathode panels, which connects with the electrolyte drain channel 225.

The major components which are fitted into a cell before bonding together of the shells as mentioned above comprise the anode plate 205, two anode support posts 230,231 (one on each side of the cell), four lateral restraint posts 240 - 243 (two on each side of the cell) for restraining the anode against lateral moveme 0nts, the two panels of laminated cathode material 207A,B (one on the front face of the cell and one on its rear face) which confront the central anode 205, the baffle members 250 in the bottom half of the cell, and the electrolyte dip tube 260, which is instrumental in returning electrolyte seepage to the cell interior.

As seen best in Figures 3 and 4, the bottom of each anode support post 230,231 has a threaded end which is screwed into a threaded hole in the top edge of the anode. The top of each post 230,231 also has a threaded end which passes through the top block 211 and is secured by a nut 265 against movement. The posts 230,231 are provided with an insulating coating layer 270, which may comprise polyethylene, P.V.C., or the like.

The restraint posts 240 - 245 underneath the anode likewise have upper threaded ends which are screwed into threaded holes in the lower edge of the anode. At their lower ends the restraint posts are provided with forwardly and rearwardly projecting bosses 275 which contact the front and rear internal faces of the cell housing for lateral restraint of the anode,

At their cathode current collecting ends 280 inside the cell, the cathode current collector cables 285A,B are soldered or otherwise electrically bonded to a copper strip 290 (see particularly Figures 2 and 6C), which runs the width of the cathode panels 207A,B. This copper strip is in turn soldered or otherwise electrically bonded to a nickel mesh 300 forming part of the laminated construction of the cathode panels. As best shown in Figure 3, the copper strip 290 and the ends of the cables 285 connected to it are embedded in the cell wall and are not in direct contact with the electrolyte within the cell. The cables 285 emerge through the cell wall and are connected to the top of the anode posts 230,231 of the next cell along the battery in order to connect adjacent cells in electrical series.

The two cathode panels 207A,B each cover a trapeizoidal aperture defined by edges 295A,B moulded into the shells 209A,B. Each aperture is the same shape as, but slightly bigger than, the anode plate 205 within the cell. Each cathode panel 207A,B is a laminated construction comprising a thin inner layer of carbon fibre web material 301, a thick layer of carbon fibre mat material 302, the nickel alloy mesh 300 adhered between the two carbon fibre layers to collect the electrical current, and an outer covering of waterproof but oxygen permiable microporous plastic 303. The thickness of the fibre mat layer 302 is such that the outer plastic layer 303 of each cathode is in approximately the same plane as the surfaces of the housing surrounding the cross-shaped depressions 219A,B. The inner web material 301 is hydrophillic for absorption of the electrolyte into the cathode. This provides intimate contact between the electrolyte and the oxygen permiating into the outer layers of the cathode. The carbon fibre mat material 302 is impregnated with a mixture of catalytic silver particles combined with activated carbon and polytetrafluoroethylene, the latter constituent rendering the mat hydrophobic. The complete multilayer cathode material is a proprietory product of Alupower Inc., of New Jersey, U.S.A. Alternatively, other known cathode materials having similar properties may be substituted, such as those disclosed in the previously mentioned prior patents.

The cathode panels 207A,B are assembled into the shells 209A,B by peeling a peripheral edge portion of the carbon fibre mat material away from its supporting nickel mesh 300 and gluing or otherwise bonding that edge portion of the mat over the outside of the edges 295A,B of the trapeizoidal aperture. The parted peripheral strips of nickel mesh, having been previously bonded to the copper strips 290A,B along their top edges, are bonded to the inside of the edges 295A,B of the trapeizoidal aperture. Thereafter, the soldered connections to the cathode current collector cables 285A,B are made as previously mentioned, and the parted edge of the nickel mesh, the copper strips and their connections to the cables are sealed into the front and back walls of the cell by the bonding of a reinforced plastic strip 310 thereover. The inside face of each cathode panel confronts the central anode plate 205 across an electrolyte gap, where production of aluminium hydroxide precipitate occurs as a byproduct of the electricity production. Hence, the anode plate gradually erodes and it should therefore be sufficiently thick to enable the cell to operate for a desired length of time despite the erosion.

Controlled circulation of the electrolyte within the cell must be established in order to ensure that depleted electrolyte between the anode and the cathodes is replaced by fresher electrolyte. The design of the cell ensures very slow natural circulation of the electrolyte, caused by the heat of reaction between the anode and cathodes. The circulation is sufficiently slow to ensure that the aluminium hydroxide particles produced in the interelectrode gap do not remain in suspension, but drop to the bottom of the cell as sediment. If the particles remained in suspension between the electrodes, they would inhibit the cell reaction.

The sediment is collected in a sump construction defined by two sets of stainless steel strip baffle members 250 in the bottom half of the cell. These baffle members completely span the internal gap between the flat inner faces of the shells 209A,B and are bonded thereto. Besides providing the cell walls with a degree of fore-and-aft stiffening, they define sump compartments 320 - 325, which are open at the top near the cell reaction region, but closed at the bottom to retain the sediment. The vertically oriented baffle members, which help define the compartments, help control sediment movement laterally of the cell due to rolling vehicle motion. Once the sediment has settled in the sump compartments, it tends to become compacted, thereby enhancing the useful life of the cell. The baffle members 250 are made of a heat conducting material to assist cooling of the sediment, because this is thought to aid the compaction process. The useful life of the cell ends when the sediment level reaches the top of the sump compartments. As can be seen, the stainless steel baffle members 250 are positioned and shaped so as to leave a free path for the thermally induced natural circulation of electrolyte around a channel 330 defined between the periphery of the cell and the sump compartments and then up a central channel 331 defined between the two sets of baffle members. The central channel is prevented from being filled with sediment by an inverted V-shaped deflector baffle 335 held between the bottom of the anode plate and the top of the central channel. Thus, electrolyte warmed in the reaction region rises upwards towards the top of the cell, cools at the cell periphery, and simultaneously is pushed outwards and downwards around the cell periphery by newly warmed and rising electrolyte so that it enters the peripheral circulation channel 330, where it cools further and sinks to the bottom of the cell, so in turn pushing electrolyte up the central channel 331 back to the reaction region.

It should be noted that in order to aid cooling of the electrolyte at the periphery of the cell, it may be necessary to form the outer edges of the shells 209A,B in a number of steps 340, as best seen in Figures 2,3 and 7, in order to increase the cell's surface area in this region.

In the design of the cell it is ensured that the volume of electrolyte in the sump compartments is not too great compared with the volume in circulation within the cell. However, normal molecular diffusion and gradual filling of the compartments with sediment ensures eventual use of the electrolyte in the sump compartments. Furthermore the sump compartment volumes should not exceed that necessary for containment of the reaction products produced by complete consumption of the anode plate.

Referring now particularly to Figures 3,4 and 5, the oxygen supply line 350 to the cell comprises a tapping from the oxygen manifold 200. The oxygen supply line 350 first passes around the outside of the cell to a point near the bottom, where it makes a T-junction with an electrolyte return pipe 351. The bottom end of this pipe is connected to an electrolyte drain tube 352 through a non-return valve 353 or equivalent device to ensure electrolyte flows only in the direction of the arrow. As best seen in Figures 5 and 6B, the electrolyte drain tube 352 is connected to a small drilling 354 within block 213 at the bottom of the cell. Through another drilling 355, the drilling 354 receives the cathode seepage electrolyte which collects in the drain channel 225.

It is arranged that the pressure of the oxygen in the supply line 351 is less than that exerted by a column of seepage electrolyte of a certain height collected in the drain channel 225. Hence, whenever the pressure exerted by the head of seepage electrolyte on the non-return valve 353 exceeds that of the oxygen, electrolyte is passed through the valve and entrained in the flow of oxygen past the T-junction through a short, very small diameter section of tube 356 to form an oxygen/electrolyte mixture, This then passes up the electrolyte return pipe 357 from the T-junction to the top of the cell.

Referring now to Figure 4, the electrolyte return line

357 is connected to a small diameter tube 358 at the top of the cell, which passes through a small diameter laterally oriented drilling in the top block 211 of the cell. The end of the small diameter tube 358 projects into a small chamber formed in the interior of the block by a large diameter vertical through-drilling 360, the top end of the drilling being sealed by a plug 361. The free end of the small tube

358 is bent downward within the chamber, so that in combination there is formed a separator for the oxygen/electrolyte mixture coming from the electrolyte return line. The electrolyte therefore drips from the free end of the tube 358 into the top of the electrolyte dip tube 260, which is connected to a sleeve insert 362 projecting from a narrower part of the vertical drilling 360 at its lower end. The oxygen, however, exhausts from the oxygen/electrolyte separator chamber by means of a vent 370, which is a continuation of the small diameter lateral drilling containing the tube 358. This vent connects with a further fore-and-aft oriented drilling 375 which leads to the oxygen supply channel 223 formed between adjacent cells, and thence to the outside of the cathode panels 207A,B. By virtue of the delivery pressure of the oxygen in the electrolyte dip tube 260, which reaches the bottom of the cell, the electrolyte level in the dip tube is depressed relative to the level in the rest of the cell. As returned electrolyte collects in the top of the dip tube, an equivalent amount is expelled from the bottom end of the tube into the interior of the cell.

As best illustrated in Figure 4, there are three large drillings passing vertically through the upper block 211 of each cell. In addition to the drilling 360 which forms the oxygen/electrolyte separator already referred to, there is a drilling 380 which provides a means of filling the cell with electrolyte after the cell has been assembled into the battery stack. After the cell has been filled with electrolyte, the top end of the drilling 380 is sealed off with a plug 381. A third vertical drilling 390 has its top end sealed with a plug of microporous material 391 which is waterproof, but permeable with regard to hydrogen so that any hydrogen created in the cell reactions can be vented into the free-flooded chamber surrounding the battery and hence safely disposed of as mentioned previously.

Figure 8 shows the bottom block 213 of the cell having a vertical drilling 400 connecting with the interior of the cell and sealed by a plug 401. The plug is removable so that electrolyte can be drained from the interior of the cell as required.

In addition to the above entry and exit points to the interior of the cell, there are also simple vent valves (not shown) in the top and bottom blocks 211,213, connected to the oxygen supply channels 223 and the elect #rolyte drain channels 225 formed between the adjacent cells by the cross-shaped depressions 319A,B when the cells are stacked together. These are provided for the purpose of purging the channels and the oxygen chambers 221 of air when the battery is connected up to the oxygen supply before use.

When the individual cells are stacked together to form a battery as shown in Figures 2 and 6B, it is necessary to obtain a gas-tight seal between adjacent cells in the stack, namely around the cross-shaped depressions 219A,B. This can be obtained using a known suitable silicone elastomer sealant to seal between the flat mating faces 217A,B of adjacent cells.

Because adjacent cathodes in the battery stack differ in electrical potential by one cell potential difference, strips of open cellular plastic material 410 (Figure 3) are used to ensure they do not touch each other and cause an electrical short circuit. Adjacent cathodes are also separated by a sheet of tough impervious plastic material 420 (Figure 2), such as Mylar (RTM), to ensure that shunt currents are avoided in the event of excessive wetness due to excessive seepage of electrolyte through the cathode panels.

Cells are clamped together in the battery by means of long threaded bolts or studs 430, which pass through holes in the edges of the shells 209A,B, see Figures 2,3 and 7. Correct spacing and avoidance of distortion of the thin shells is ensured by spacers 431 on the bolts or studs extending between adjacent cell edges.

After stacking of the cells in this way, the oxygen manifold is installed on the top blocks 211 of the battery as shown and connections are made to the oxygen supply line 350 for each cell.

The battery's electrical connections are also made on the blocks 211, As best shown in Figures 3,4 and 7, the two cathode collector cables 285A,B. on each side of each cell are joined together (optionally by means of a connector block 440 as alternatively shown in Figure 2) and a short cable 286 carrying their combined currents is connected to the top of the anode post 230 of the next adjacent cell along the battery stack so as to connect the cells together in series.

When the cells are stacked together, the seepage from two cathode panels in adjacent cells is collected by the electrolyte drain channels 225 between the cells and passed back into one of the cells. However, this arrangement creates the probability that the first and last cells in the battery stack will gradually attain unequal electrolyte volumes. To correct this, it is shown in Figure 6B that the first and last cells in the stack are suitably interconnected by a pipe 500 and extra drillings 501-503 in blocks 213 so that the cells' electrolyte volumes are automatically equalized.

Nevertheless, there remains the possibility that seepage amounts from different cathode panels will be unequal, or that one or more of the cathode panels may spring a leak. In that case, different amounts of seepage electrolyte will be returned to adjacent cells. This problem can easily be corrected by means of capillary tubes (not shown) connecting adjacent cells. However, care must be taken that the capillaries are of small enough bore and sufficiently long to ensure that shunt currents between cells are insignificant.

In addition to the above, an expansion bladder (not shown) is a necessary means of coping with small short term electrolyte volume changes caused by changes in cell temperature. It is also necessary for absorbing the long term electrolyte volume increase due to the net influx of oxygen atoms into the aluminium hydroxide precipitate in the cells. Such an expansion bladder may conveniently be connected to the interior of an end cell in the battery stack through a capillary tube and functions to maintain a pressure in the cells which is exactly the same as the ambient pressure.

Claims

CLAIMS : -

1. A metal/oxygen battery construction having a plurality of separate elecrolyte-holding cells each containing metal anode means and oxygen permeable hydrophobic cathode means, each cell having an electrically non-conducting housing comprising opposed faces and a peripheral rim region, each housing having an aperture in at least one of the opposed faces, to which aperture the cathode means is sealingly fixed so as to obturate said aperture, the faces of adjacent housings being sealed to each other in confronting fluid-tight manner so as to define therebetween oxygen feed means and an electrolyte drain, both the oxygen feed means and the electrolyte drain communicating externally of the cells with the cathode means.

2. A metal/oxygen battery construction according to claim 1, in which the oxygen feed means comprises an oxygen supply space in direct communication with the cathode means, and at least one oxygen feed channel leading to the oxygen supply space.

3. A metal/oxygen battery construction according to claim 1 or claim 2, in which each cell contains a metal anode plate located between two oxygen cathode panels and each face of the housing has an aperture and a corresponding one of the cathode panels sealed thereto, the oxygen supply space being adjacent to confronting cathode panels of adjacent housings.

4. A metal/oxygen battery construction according to any preceeding^'claim, in which the oxygen feed means between the adjacent housings are connected to an an oxygen delivery manifold.

5. A metal/oxygen battery construction according to any preceeding claim, in which the oxygen feed means and the electrolyte drains are defined by depressions in the adjacent confronting faces of the housings.

6. A metal/oxygen battery construction according to any preceeding claim, in which the lowest portion of the electrolyte drain incorporates electrolyte drainage means for transport of the seepage away from the sealed areas between the housings.

7. A metal/oxygen battery construction according to the preceeding claim, in which the electrolyte drainage means comprises electrolyte recirculation means for injecting drainage electrolyte back into the interior of an adjacent cell.

8. A metal/oxygen battery construction according to any preceeding claim, in which the rim region of the cells is provided with an enlarged external surface area for enhanced transfer of internal cell reaction heat to the environment.

9. A metal/oxygen battery construction according to the preceeding claim, in which the peripheral rim regions of the housings have a stepped configuration.

10. A metal/oxygen battery construction according to the preceeding claim, in which the stepped configuration occupies only part of the periphery of the housings.

11. A submersible vehicle comprising a hull, pressurised oxygen supply means, a multi-cell metal/oxygen battery, power conditioning means and propulsion means, at least the battery being contained in free-flooded compartment means whereby the battery operates at ambient pressure and circulation of water around the battery effects cooling of the cells.

12. A submersible vehicle according to the preceeding claim, in which circulation of the water around the battery is obtained merely by means of motion of the vehicle.

13. A submersible vehicle according to any one of the two preceeding claims, in which at least part of the pressurised oxygen supply means is also contained in the free-flooded compartment means.

14. A submersible vehicle according to any one of the three preceeding claims, in which there are two separate free-flooded compartments for containing at least part of the oxygen supply means and the battery respectively.

15. A submersible vehicle according to any one of the four preceeding claims, in which the free-flooded compartment means has at least one removable vehicle external wall portion to allow removal and replacement of the battery and/or at least part of the oxygen supply means.

16. A submersible vehicle according to any one of the five preceeding claims, in which the pressurised oxygen supply means comprises a pressurised oxygen tank, an oxygen supply manifold for distribution of oxygen to the cells comprising the battery, an oxygen supply pipe extending between the tank and the manifold, and flow control means in the supply pipe, the flow control means comprising isolating valve means to allow disconnection of an aft portion of the supply pipe from the oxygen tank, vent/fill valve means to allow venting and filling of the tank from outside the vehicle and flow regulator means between the isolating valve means and the manifold for control of flow of oxygen to the manifold.

1(7. A submersible vehicle according to the preceeding claim, in which the pressurised oxygen tank is integral with the hull of the vehicle.

18. A submersible vehicle ac ording to the preceeding claim, in which an aft portion of the oxygen supply pipe with associated flow control means is disconnectable from the tank for removal from the vehicle together with the battery, the free-flooded compartment means being to the rear of the tank and forward of the power conditioning means.

19. A metal/oxygen cell construction comprising an electrically non-conducting housing for holding therein anode means, oxygen cathode means and an electrolyte, the housing comprising opposed faces and a stepped peripheral rim region for providing the cell with an enlarged external surface area for enhanced transfer of heat to the environment.

20. A metal/oxygen cell construction according to the preceding claim, the stepped rim region comprising a plurality of steps.

21. A metal/oxygen cell construction according to either of the preceding two claims, the stepped rim region comprising only a portion of the circumference of the housing.

22. A metal/oxygen battery cell construction in which an electrically non-conducting housing contains metal anode means and oxygen cathode means in fixed spaced-apart relationship to each other, the housing comprising opposed faces thereof and a peripheral rim region, the cell interior comprising an electrolytic reaction region containing the anode and cathode means, a precipitate collation region for retaining reaction product particles precipitated from the reaction region, and electrolyte circulation channel means for facilitating circulation of electrolyte within the cell without disturbing the precipitated particles, the channel means having intake means and exit means adjacent different parts of the reaction region, the channel means between the intake means and the exit means extending around at least part of the periphery of the precipitate collection region.

23. A metal/oxygen battery cell construction according to the preceeding claim, in which the exit means is situated such that the part of the channel means leading thereto extends through the precipitate collection region from the periphery of the cell towards the reaction region.

24. A metal/oxygen battery cell construction according to either of the preceeding two claims, in which the exit means is provided with shield means to prevent deposition of precipitate particles thereinto from the reaction region.

25. A metal/oxygen battery cell construction according to any one of the preceeding three claims, in which the exit means is situated directly beneath and centrally of the reaction region and the intake means is situated near at least one of the extremities of the reaction region.

26. A metal/oxygen battery cell construction according to any one of the preceeding four claims, in which the extremities of the reaction region are near the peripheral rim region of the housing and the channel means comprises a central channel portion extending centrally through the precipitate collection region from the periphery of the cell to an exit situated directly beneath and centrally of the reaction region and two peripheral channel portions each extending from a respective intake near an extremity of the reaction region, around a part of the periphery of the precipitate collection region, and joining the central channel portion at the periphery of the cell.

27. A metal/oxygen battery cell construction according to any one of the preceeding five claims, in which the precipitate collection region comprises a plurality of elongate baffles extending widthwise between the opposed faces of the housing and lengthwise from the rim region towards the reaction region, the baffles being spaced from each other to define compartments open near the reaction region into which the precipitate is deposited during normal operation of the cell.

28. A metal/oxygen battery cell construction according to the preceeding claim, in which the part of the channel means leading to its exit extends through the precipitate collection region, that part of the channel means being defined between adjacent baffles and shielded from deposition of precipitate particles thereinto by baffle means located between the exit of the channel means and the reaction region.

29. A metal/oxygen battery construction having a plurality of separate electrolyte-holding cells each containing metal anode means and oxygen cathode means, adjacent cells being connected together in electrical series, each cell having an electrically non-conducting housing comprising opposed faces and a peripheral rim region, each housing having aperture means in at least one of the opposed faces, to which aperture means the cathode means is sealed in obturating manner, confronting faces of adjacent housings being sealed to each other in fluid-tight manner so as to define therebetween oxygen feed means and electrolyte drainage channel means, both the oxygen feed means and the electrolyte drainage channel means communicating with the cathode window means, the oxygen feed means being connected to an an oxygen supply manifold for distribution of oxygen to the cells comprising the batrery, the electrolyte drainage channel means being connected to electrolyte recirculation means for injecting drainage electrolyte back into the interiors of the cells.

30. A metal/oxygen battery construction according to the preceeding claim, in which the connections between the oxygen supply manifold and the oxygen feed means provide the required electrolyte recirculation means.

31. A metal/oxygen battery construction according to the preceeding claim, having means for entraining electrolyte from the drainage channels into the flow of oxygen between the oxygen supply manifold and the oxygen feed means to produce mixed electrolyte/oxygen flow, means for passing said mixed flow to the tops of the housings and means for separating said mixed flow into its constituent components, whereby leakage electrolyte is reinjected into the cells and an oxygen head space is created in each cell, and means connecting the head space to the oxygen feed means, whereby oxygen passes from the head space to the cathode means.

32. A metal/oxygen battery construction according to the preceeding claim, in which the oxygen head space is created in the upper closed end of a dip tube within each cell, the dip tube having a lower open end for the injection of the recirculated elecrolyte into the main body of electrolyte within the cell.

33. A metal/oxygen battery construction according to the preceeding claim, in which the oxygen feed means defined between the confronting faces of adjacent housings comprises an oxygen supply space in direct communication with the cathode means, and an oxygen feed channel connected to the oxygen supply space and to the oxygen head space.

34. A metal/oxygen battery construction according to claim 29, in which the electrolyte recirculation means comprises oxygen feed lines each having one end connected to the oxygen supply manifold and the other end connected to a mixed oxygen/ electrolyte flow line at a 'T* junction, the oxygen feed line being the stem of the 'T' and the oxygen/electrolyte flow line being the cross-bar of the 'T', one side of the cross-bar being connected to an electrolyte drainage channel means through non-return valve means and the other side of the cross-bar being connected to an oxygen head space in the interior of an adjacent cell.

35. A metal/oxygen battery construction according to the preceeding claim, in which the electrolyte recirculation means is arranged to recirculate drainage electrolyte from each drainage channel means to only one of the two adjacent cells defining the drainage channel means, said one of the two adjacent cells being the first of the two cells in a designated direction lengthwise along the stack of cells comprising the battery.

36. A metal/oxygen battery construction according to the preceeding claim, in which the drainage channel on the outer face of the last cell in the stack is connected to the drainage channel on the outer face of the first cell in the stack, the latter drainage channel being connected to the electrolyte recirculation means to ensure that there is a nominally correct amount of drainage electrolyte returned to each cell.