Plastic and nonmetallic article shaping or treating: processes – Reactive gas or vapor treatment of work – Work is organic material
Patent
1996-12-03
1998-07-28
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Reactive gas or vapor treatment of work
Work is organic material
429176, B29C 7100, H01M 200
Patent
active
057859124
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the fabrication of an electrochemical cell and in particular, to a method for the fabrication of an electrochemical cell which has long term chemical resistance and stability to anolyte and catholyte solutions having pH's of less than 1 and/or above 12 at temperatures from ambient to 60.degree. C. and which can be formed from thermally processable materials by conventional techniques.
U.S. Pat. No. 4,485,154 discloses an electrically rechargeable anionically active reduction-oxidation electric energy storage-supply system using a sulfide/polysulfide reaction in one half of the cell and an iodine/polyiodide, chlorine/chloride or bromine/bromide reaction in the other half of the cell. The specification suggests that the cell may be operated with the anolyte and catholyte being maintained at slightly basic but near neutral pH's. We have found that when operating the system with a bromine/bromide couple, very low pH's are encountered on the bromine side of the cell and very high pH's on the sulfur side of the cell.
Polytetrafluoroethylene (PTFE) is highly resistant to the action of chemicals including strong acids and strong alkalis. However, it is not a thermally processable material.
Polyvinylidene fluoride (PVDF) is a thermoplastic fluorocarbon polymer which can be processed by conventional techniques such as compression moulding, injection moulding, extrusion, vacuum forming, rolling and welding. Whilst PVDF is fairly resistant to strong acids it is not stable in strong alkalis.
We have now developed a method for the fabrication of an electrochemical cell having chemical resistance and long term stability at both high and low pH's from a thermally processable polymeric material.
Accordingly, the present invention provides a method for the fabrication of an electrochemical cell which has long term chemical stability to anolyte and catholyte solutions at pH's of less than 2, preferably less than 1, and above 12, which method comprises the steps of: transition and/or melting thermal transition to form the cell structure or components of the cell structure, and structure which, in use, will be in contact with the anolyte and catholyte solutions, to a post halogenation process, whereby the polymeric material forming the said surfaces undergoes halogen substitution to form a chemically stable halogen modified polymeric material.
The polymeric material which is used in step (i) of the present invention may be any material which (a) is thermally processable and exhibits a glass transition and/or melting thermal transition. The polymeric material preferably has a Newtonian melt viscosity at 150.degree. C. and 400 Pascals of less than 1000 Pascal seconds, more preferably less than 600 Pascal seconds, and (b) when halogenated forms a chemically stable modified polymeric material at its surface. Examples of suitable polymers are high or low density polyethylene, polypropylene or ethylene-propylene copolymers.
The polymeric material may be made into the desired cell structure or components of the cell structure by any of the well known techniques, such as machining of preformed sheets or plates, injection moulding, transfer moulding or compression moulding.
The halogenation process is preferably a fluorination process, although bromination or chlorination processes may also be used. The fluorination is preferably effected by exposing the surfaces which, in use, will be in contact with the anolyte and catholyte solutions to fluorine gas. The treatment with fluorine gas will preferably be carried out by contacting the surfaces with fluorine gas at a temperature of below 50.degree. C. A fluorination process for the production of fluorinated polyethylene film and fluorinated polyethylene containers is disclosed in U.S. Pat. No. 2,811,468 and a similar process may be used in the present invention.
The fluorination may be carried out using an atmosphere containing 100% fluorine, or the fluorine may be diluted with an inert gas such as nitrogen.
When the halogenation process is a
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Cooley Graham Edward
Nix Kevin John
Eashoo Mark
National Power PLC
Silbaugh Jan H.
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