Metal working – Method of mechanical manufacture – Electrical device making
Patent
1992-01-15
1994-01-18
Kalafut, Stephen
Metal working
Method of mechanical manufacture
Electrical device making
429104, H01M 1038
Patent
active
052796256
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a sodium/sulphur cell, and in particular to a method of closing the case of a sodium/sulphur cell.
Unlike conventional lead acid batteries in which a liquid electrolyte--dilute sulphuric acid--separates two solid electrodes, in a sodium/sulphur cell a solid electrolyte--generally beta alumina--separates two liquid electrodes, namely liquid sulphur and liquid sodium electrodes.
Such a sodium/sulphur cell is shown in FIG. 1 of the drawings which is a perspective view of the cell with part broken away.
As shown the cell comprises a case 1 of, for example steel with an internal anti-corrosion coating of aluminium or aluminium alloy, in the form of a right circular cylinder and containing a solid electrolyte cup 2 of beta alumina, the cup 2 containing a sodium electrode 3, while a space between the case 1 and the cup 2 contains a sulphur electrode 4. For use, the cell is maintained at a temperature of between 300.degree. C. and 400.degree. C. such that the sodium and sulphur electrodes 3 and 4 are in liquid form.
The open end of the cup 2 is closed by an insulating disc 5 of alpha alumina, while the case 1 is closed by an annular sealing closure disc 6 of steel again with an internal anti-corrosion coating of aluminium or aluminium alloy.
The case 1 serves as a terminal for the sulphur electrode 4, while the sodium electrode 3 contains an elongate metal current collector 8 which extends axially of the case 1 out through the disc 5 where it is connected to a centre terminal disc 7 mounted on the disc 5, the necessary connections being made by welding.
As sulphur is essentially non-conducting a means of making an electrical connection between the case 1 and the cup 2 has to be provided, and this is generally achieved by forming the sulphur electrode 4 as a carbon fibre mat impregnated with sulphur.
It will be appreciated that with such a cell the sodium and sulphur electrodes 3 and 4 can have their locations reversed.
With such a cell it is necessary for the alpha alumina disc 5 to seal the open end of the beta alumina cup 2 and this is generally effected by a glazing technique. It is also necessary for the disc 6 and the terminal disc 7 to be secured to the alpha alumina disc 5 to form seals, and since alpha alumina is both ionically and electronically insulating diffusion bonding is generally used.
It is also necessary for the disc 6 to be secured to the case 1, and this is generally affected using electron beam, laser or TIG fusion welding techniques.
However, a difficulty which arises when using such techniques is that the heat required can damage the corrosion resistant coating provided on the case 1 and on the closure disc 6, or can create a heat affected zone in the weld region, either of which can result in a more rapid than usual localised degradation in the cell due to corrosive attack by the cell electrode materials. Generally, it has been found difficult to produce a hermetic bond between the case and the closure member of prior are sodium/sulphur cells.
According to the present invention there is provided a method of closing the case of a sodium/sulphur cell by securing a closure member to the case, each of the case and the closure member being formed of a composite material consisting of a metal substrate and a deformable metal layer mechanically fixed to said substrate, said substrate being formed of a material which is harder than said deformable metal, the method comprising the steps of forming an outwardly extending annular flange at the open end of the case and securing the closure member to the annular flange by solid phase bonding thereby to close the case.
The provision of an outwardly extending annular flange at the open end of the case has at least two advantages, as follows contact with the electrode materials. Accordingly, any damage or weakening of the case or the closure member caused by the process of securing the case and the closure member together is not exacerbated by corrosive attack by the cell electrode materials. case and closure member together can b
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patent: 3294591 (1966-12-01), Jordan
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patent: 3841912 (1974-10-01), Kagawa et al.
patent: 4027075 (1977-05-01), Nakabayashi et al.
patent: 4048393 (1977-07-01), Heintz et al.
patent: 4332868 (1982-06-01), Anand et al.
patent: 4413043 (1983-11-01), Steinlettner et al.
Chloride Silent Power Ltd.
Kalafut Stephen
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