Boot and shoe making
Patent
1990-06-08
1991-12-31
Skapars, Anthony
Boot and shoe making
429104, B23P 1900, H01M 204
Patent
active
050759574
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for constructing an alkali metal energy conversion device, for example an alkali metal cell and particularly a sodium sulphur cell. Such cells typically employ a solid electrolyte element separating cathodic and anodic reactants which are liquid at the cell operating temperature.
A known construction of device comprises an external casing, a solid electrolyte element dividing the interior of the casing into two electrode regions, an electrically insulating element joined to the electrolyte element, and at least one metal member sealed to the insulating element. This structure typically forms part of the sealing arrangement for the device, sealing off the two electrode regions both from each other and from the ambient environment. For example, the external casing of the device may be of metal, so that any sealing of an electrode region requires a seal to be made between the metal of the casing and the electrolyte element. However the metal of the casing must be electrically insulated from the electrolyte element and the insulation is provided by the intervening electrically insulating element.
An example of such an arrangment applied to a sodium sulphur cell is shown in GB-A-2102622 which has an alpha alumina lid closing a tubular electrolyte element. A centrally located current collector is mounted in an aperture through the alpha alumina lid and insulated by the lid from the electrolyte element. The outer electrode region, on the outside of the electrolyte element, is sealed by means of a metal closure member welded about its periphery to a metal casing for the cell, and sealed about an inner periphery to the alpha alumina lid. This latter seal between the metal closure member and the alpha alumina lid has sometimes been made by compression bonding using an intermediate layer, between the metal closure element and the ceramic lid, of a soft material, e.g. aluminium, to provide the necessary bonding.
Such bonding is carried out after the insulating element, i.e. the alpha alumina ceramic lid, is attached to the electrolyte element since this attachment is effected by glazing at elevated temperatures which would destroy seals manufactured by thermocompression bonding using an intermediate layer between the metal closure element and the ceramic lid.
Alternatively, EP-A-0166605 discloses the techniques of directly thermocompression bonding the metal member to the insulating ceramic lid to provide a seal between the two which is not adversely effected by subsequent temperature cycling such as may be employed if the insulating element is subsequently joined to the electrolyte element by glazing. The ability to form such a seal between the metal member and the insulating element before the latter is joined to the electrolyte element greatly facilitates the making of this seal. For instance, a stack of metal members and insulating elements may be simultaneously sealed to one another to provide a plurality of sealed pairs.
It will be appreciated that the sealing of sodium sulphur cells and other alkali metal energy conversion devices is of critical importance in the manufacture of the cell to ensure good performance and safety and is a particularly difficult problem because of the high operating temperatures of these cells, typically 350.degree. C. Bonding techniques using cements have not proved practical.
The insulating ceramic element is typically formed of alpha alumina and is quite strong enough to withstand the substantial pressures exerted on it during the thermocompression bonding process. However, the electrolyte element, typically beta alumina, is relatively fragile and can easily be damaged during a thermocompression bonding process on an insulating element fastened thereto. Consequently, the bonding techniques used hitherto to secure the metal closure element or elements to the insulating element have of necessity been dependent upon whether the insulating element is itself joined to the solid electrolyte element as is the case when an intermediate layer, placed betw
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Patent Abstracts of Japan, vol. 10, No. 134 (M-479) (2191), May 1, 1986.
Allen Jeffrey
McLachlan Stuart
O'Neil Bell Christopher
Pender John A.
Rampton Stephen C.
Chloride Silent Power Limited
Skapars Anthony
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