Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1981-02-25
1983-01-18
Walton, Donald L.
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429101, H01M 1200
Patent
active
043692354
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electrochemical cell and to a means for the manufacturing thereof, namely a gas diffusion electrode of a completely new type. A primary application of the electrochemical cell according to the invention, containing the new gas diffusion electrode, is in a battery of the type in which an oxygen electrode is utilized as the positive pole and in which the negative electrode usually consists of a metal such as, iron, cadmium, zinc or copper. However, the invention is not limited to the above-mentioned metal electrodes, and the negative electrode can also combust supplied fuels, such as hydrogen or methanol. Sources of electric current which consist of oxygen electrodes and metal electrodes are hereinafter referred to as metal/oxygen-cells (batteries), while the latter type of current source is called a fuel cell. Furthermore, the gas diffusion electrode according to the invention is used in connection with the electrochemical combustion of hydrogen. In this case the positive electrode is usually a metal oxide, and this third type of cell (battery) will be hereinafter designated metal oxide/hydrogen battery.
The invention is, however, not limited to the three types of cells mentioned above. The present invention can be applied to every electrochemical cell containing electrodes in contact with liquid electrolyte and where at least one of the electrodes is a gas diffusion electrode, which is exteriorly provided with a catalyst for converting gas to electricity, and which has an electrically conductive material as well as a hydrophobic material, at least internally. For the sake of simplicity, the invention will hereinafter be described in conjunction with metal/oxygen batteries without being limited thereto.
BACKGROUND ART
The advantage of metal/oxygen batteries compared with conventional batteries, is that a comparatively high energy density can be obtained, which is of great importance, e.g. if the battery is to be used for driving a vehicle. It has thus been found possible to obtain values of over 100 Wh/kg, which can be compared with about 60 Wh/kg for alkaline nickel oxide/iron batteries and about 40 Wh/kg for lead batteries.
A great drawback of the metal/oxygen cells manufactured up to now, is that an extensive auxiliary system is required to obtain a well-functioning cell. It has thus been found necessary to circulate the electrolyte, to pump oxygen or air past the gas sides of the oxygen electrodes, and to introduce a special charging electrode or other means for charging the metal electrode without destroying the oxygen electrode.
A summary of the systems which have been developed, or are under development, has been presented in "Journal of Power Sources" 2 (1977/78) pp. 287-296.
An oxygen electrode is disclosed in Swedish lay-open print No. 391,609, which is characterized in that water diffuses from the gas side towards the electrolyte during the charging phase. This is achieved by the construction of a dual layer electrode, where the layer on the gas side contains a hydrophobic material, preferably of polytetrafluoroethylene, and a catalyst for oxygen dissolution, while the layer towards the electrolyte side is hydrophilic. When built up into cells, the air electrodes are fixed into frames, and for constructing a battery, two adjacent cells form an air chamber for supplying the air electrodes with oxygen from the air.
In German Offenlegungsschrift No. 2,129,045 another metal/air or metal/oxygen battery is disclosed. In that battery a biporous oxygen (or air) electrode is used, which is layered with finely porous separators and metal electrodes to form an electrode package, where the gas electrodes are connected to a gas conduit at one or more places along the edges thereof.
The above-mentioned systems, however, have gas electrodes assembled into a pocket which is provided with gas conduits for supplying the pocket with oxygen or air from outside the pocket.
Another type of gas diffusion electrode is described in the article "Nouveau type d'electr
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patent: 3096215 (1963-08-01), Voss et al.
patent: 3102059 (1963-08-01), Harmer
patent: 3600230 (1971-08-01), Stachurski et al.
patent: 3840406 (1974-10-01), Depoix
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Walton Donald L.
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