Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-06-19
2003-06-03
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S072000, C429S206000
Reexamination Certificate
active
06573008
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a battery for the production of electric energy by reaction between hydrogen peroxide (H
2
O
2
) or oxygen, and aluminium or lithium or a mixture thereof, and which utilizes electrodes of bottle brush shape, and which can mechanically be charged by inserting metal anodes. The advantages of the invention are a battery with high utilization of the reactants combined with the possibility of quick mechanical charging.
The main object of the invention is a battery which can be utilized for the energy supply of small unmanned underwater vehicles (UUV), but the invention is not limited for this use only. The battery is going to have pressure-compensated operation, i.e. the battery does not have to be encapsulated in a pressure tank. The cells are based on an alkaline electrolyte with H
2
O
2
or oxygen as the oxidant, and metal anodes. The oxidant is added to the electrolyte, and the electrolyte is pumped through the cells in the battery. The anode material are alloys which form soluble reaction products by anodic dissolution in alkaline electrolyte.
RELATED PRIOR ART
“Bottle brush” electrodes are known from NO 171 937, (Garshol and Hasvold), where there is described electrodes formed as bottle brushes. The purpose of these bottle brush electrodes are to obtain maximum area of the electrodes combined with good conductivity, low resistance to flow and a sufficiently mechanically stable solution.
Batteries which utilize oxygen or hydrogen peroxide, where a circulation of electrolyte takes place, are known from U.S. Pat. No. 4,305,999 (Zaromb). The anode is made of consumable metal, especially zinc, magnesium or aluminium. The purpose of the '999 Patent is to regulate the electrolyte level in the battery cell in relation to the power consumption in such a way that unnecessary corrosion is prevented.
U.S. Pat. No. 4,910,102 describes a battery and a process for operating the battery, where bipolar electrodes are included consisting of an inert cathode which works as a hydrogen peroxide electrode, and an anode plate of aluminium, magnesium or alloys thereof. (In the abstract for U.S. Pat. No. 4,910,102 there seems to be an error: There is referred to a hydrogen electrode, but it seems to be a hydrogen peroxide electrode. Further there is referred to bipolar cathodes; the correct term seems to be bipolar electrodes). The electrolyte flows through the battery, and H
2
O
2
is added in concentrations between 0.5% and 30% as volume part of the electrolyte. The electrolyte is, for example, sea water.
Expected time of discharge for such a battery for an unmanned underwater vehicle is long, typically more than 10 hours. The long time of discharge gives low current densities which subsequently allows for relatively large electrodes and a large distance between the electrodes in the cells of the battery. The battery comprises one or more cells. Anode materials of current interest are alloys which form soluble reaction products by anodic dissolution in an alkaline electrolyte. The rate of corrosion of the metal in the electrolyte has to be relatively low, which excludes the alkaline metals, except for lithium. Most appropriate are probably alloys of aluminium such as utilized earlier in FFI's alkaline aluminium/air battery and as described in Hasvold: “Development of an alkaline aluminium/air battery system”. Chemistry and Industry (1988), pp 85-88, and Størkersen: “Development of a 120 W/24V Mechanically Rechargeable Aluminium-Air Battery for Military Applications”. Power Sources 13, (1991), Ed.: Keily, T. and Baxter, B. W., pp 213-224.
Galvanic cells, which utilize hydrogen peroxide (HP) as oxidant (“cathodic depolarizer”), have been known for long. In some systems, HP is utilized directly in the cell, while in other systems, HP is used as a storage medium for oxygen, i.e. as an oxygen carrier. In the last case, one lets H
2
O
2
decompose in a reactor and supplies the cells with oxygen from this reactor:
2H
2
O
2
=2H
2
O+O
2
(1)
The oxygen is consumed in a gas cathode in a fuel cell or in a metal/oxygen battery. A typical example of such a technology is Alupowers's alkaline aluminium/oxygen battery for operation of unmanned underwater vehicles and is described in Deuchars, G. D. et al.: “Aluminium- hydrogen peroxide power system for an unmanned underwater vehicle” Oceans 93 (1992), Vancouver, pp 158-165. In other cells, as e.g. described by Zaromb in U.S. Pat. No. 4,198,475, HP is added directly to the cathode in an aluminium/hydrogen peroxide battery with alkaline electrolyte. Whether HP decomposes in the electrolyte under formation of oxygen which in turn is reduced on the cathodes, or HP is reduced directly on the electrode surface, makes little difference in practice.
The advantage of utilizing HP as oxidant instead of oxygen is that the storage is substantially easier. Further, HP is miscible with water and can be added directly to the electrolyte in the desired concentration. In a UUV, the storage can also, if desired, be made outside the pressure hull. According to equation (1), 1 kg pure HP equals 0.471 kg oxygen. Pure HP implies a handling risk, as HP is unstable and the decomposition of HP releases a considerable amount of energy. This risk is considerably reduced by increasing the contents of water. 70% HP can be handled by attention to special precautionary measures, and at 50%, the heat of decomposition is no longer sufficient for complete vapourization of the water forming. In 70% HP, the “oxygen part” of the weight constitutes approx. 33% and in 50% HP approx. 24%. Liquid oxygen, LOX, provides effective storage based on weight, but cryogenic storage of oxygen demands a certain thickness of the isolation, so that one for small systems gets very voluminous tanks in relation to the useful volume. The demand for insulation increases with the time the oxygen is to be stored. Further, a cryogenic storage tank is basically not suitable at large external pressures. For this reason, the storage in a UUV has in practice to be carried out in a pressure tank, which makes the system not very well suited for application in small vehicles.
The last and most common storage form for oxygen is under pressure in cylindrical- or spherical pressure tanks (bottles). This is very practical as long as the pressure of the battery is less than the bottle pressure, as the oxygen supply can be regulated by operating a valve. The tanks can be exposed to external pressure and be arranged on the outside of the pressure hull. Traditional metal tanks are heavy, typically an empty weight of 15 kg can store 4 kg oxygen, but fibre reinforced tanks can be made considerably lighter, and a storage capacity of 40-50% is not unlikely in the future.
At 300 bar, oxygen has a density of approx. 0.4 kg/litre and a system density by utilizing fibre-reinforced tanks of approx. 0.2 kg oxygen/litre. This provides somewhat more voluminous storage by utilizing pressure tanks than by oxygen storage in the form of 50% HP. Further, it has to be taken into consideration that with UUV batteries which operate at ambient pressure, the oxygen has to actively be pumped out of the bottles when external pressure is higher than the bottle pressure. This is a considerable problem for UUV's which are to operate at great depths. In comparison, a HP storage will normally have ambient pressure independent of depth. Finally, it should be mentioned that while HP can directly be mixed in the electrolyte in the desired concentration, the solubility of oxygen in the electrolyte is low. Even if the solubility increases proportionally with pressure, the rate of dissolution is relatively slow, which can entail a complex system for the mixing of oxygen into the electrolyte. For the above mentioned reasons, one has primarily considered the use of HP in UUV batteries, but an oxygen-based battery which operates at a pressure of more than 5 to 10 bar, will have almost identical properties.
A problem with batteries where the oxidant is dissolved in the electrolyte is th
Den Norske Stats Oljeselskap A.S.
Foley & Lardner
Maples John S.
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