Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1997-10-23
2000-11-07
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429188, 4292315, 429326, H01M 624, H01M 808, H01M 1008
Patent
active
061434434
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for stabilising an electrolyte for use in a redox cell, in particular for stabilising an electrolyte for use in an all-vanadium redox cell, a stabilised electrolyte, in particular an all-vanadium stabilised electrolyte, a redox cell, in particular an all-vanadium redox cell, comprising the stabilised electrolyte, a redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte, a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte, a process for the production of electricity from a charged redox battery, and in particular a charged all-vanadium redox battery, comprising the stabilised electrolyte, a redox battery/fuel cell and a process for the production of electricity from a redox battery/fuel cell.
BACKGROUND OF THE INVENTION
Since the energy density available from batteries based on oxidation/reduction reactions of ions in the electrolyte is directly proportional to the concentration of redox ions undergoing oxidation or reduction in the electrolyte, the energy density available from batteries based on redox electrolytes is limited generally by the maximum solubility of redox salts of the various oxidation states in the electrolyte, and in particular the redox component with the lowest solubility. It follows that if there was a way of increasing the solubility of the redox ions beyond their normally considered maximum solubility and if there was way of preventing or reducing precipitation of redox ions from the redox electrolyte, the maximum energy density available from the battery containing such an electrolyte would increase in proportion (which may be a linear proportion or a non linear proportion depending on the redox system) to the increase in solubility of the redox components. Consider for example the case of the all-vanadium redox battery. Vanadium can exist in aqueous solution in several oxidation states which are readily interconvertible under appropriate conditions. For this reason, and because of the relatively low atomic weight of vanadium, vanadium electrolyte systems have desirable properties for their use in batteries including redox batteries. Lithium/vanadium and all-vanadium batteries, for example, are known. Experiments conducted on the stability of V(V) solution have also shown that concentrated solutions (greater than 1.8M Vanadium) when subjected to temperatures greater than 40.degree. C., slowly precipitate.
FUNDAMENTAL PRINCIPLE OF INVENTION
In the vanadium cell however, you cannot use normal chelating or complexing methods to increase the concentration of vanadium in a vanadium electrolyte since V(V) is strongly oxidizing and will oxidize most of these compounds eventually to CO.sub.2, producing gas in the system which stops the pumps and can cause the whole stack to burst if not able to escape.
Surprisingly, however, it has been found by inventors that if used in low concentrations, these type of compounds have a stabilising ability and inhibit precipitation in highly supersaturated solutions of vanadium by adsorbing on the nuclei and preventing ions from approaching the nuclei, therefore stopping crystal growth.
At such low concentrations, these additives do not have sufficient reducing power and can thus not be oxidized by the V(V) in the positive half cell electrolyte. The solutions are thus stable for long periods and over so much wider temperature range than unstabilised solutions.
For example of a 2M V(V) solution are exposed to temperatures of 30.degree. C., a slight precipitate will start to form after 2 days, with heavy precipitation evident after only 4 days. At 40.degree. C., a heavy precipitate will form after 2 days in a 2M V(V) solution. Even a 1.8 M V(V) solution will precipitate after 3 days at 40.degree. C.
This problem in use can be avoided by reducing the vanadium ion concentration to less than 1.8 M for applications where the temperature is likely to e
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Kazacos Maria Skyllas
Kazacos Michael
Nuzzolillo Maria
Pinnacle ARB Limited
Ruthkosky Mark
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