Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-07-24
2003-05-13
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S188000, C429S231500, C429S326000
Reexamination Certificate
active
06562514
ABSTRACT:
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° 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
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 lout 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 if a 2M V(V) solution are exposed to temperatures of 30° C., a slight precipitate will start to form after 2 days, with heavy precipitation evident after only 4 days. At 40° 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° 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 exceed 40° C. and where the systems will be maintained in fully charged state for long periods. However in many applications it is not desirable to reduce the vanadium ion concentration below 2.0M since such a reduction effectively reduces the capacity and energy density of the battery. Thus, there is a general need for redox electrolytes which contain higher concentrations of redox ions. Thus, there is a need for a vanadium-based redox electrolyte which contains a higher concentration of vanadium ions. There is also a need for redox electrolytes in which the precipitation of redox species from the redox electrolyte is prevented or reduced. In particular, there is a need for a vanadium-based redox electrolyte in which the precipitation of vanadium species from the vanadium-based redox electrolyte is prevented or reduced.
OBJECTS OF INVENTION
Accordingly, it is an object of the present invention to provide a method for stabilising an electrolyte for use in a redox cell or redox battery, in particular for stabilising an electrolyte for use in an all-vanadium redox cell or all-vanadium redox battery.
Other objects include: (a) providing a stabilised electrolyte, in particular a redox electrolyte and more particularly an all-vanadium stabilised electrolyte; (b) a redox cell, in particular an all-vanadium redox cell, comprising the stabilised electrolyte; (c) a redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte; (d) a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte; (e) a process for the production of electricity from a charged redox battery, in particular an all-vanadium redox battery; (f) processes for producing a stabilized vanadium electrolyte, optionally highly supersaturated; (g) an all-vanadium redox charge cell; and (h) a process for charging a charge anolyte and a charge catholyte of an all-vanadium redox charge cell.
It is a further object of the present invention to provide an improved all-vanadium redox cell and all-vanadium redox battery.
Another object is to provide a redox battery/fuel cell and a process for the production of electricity from a redox battery/fuel cell.
DISCLOSURE OF THE INVENTION
In this specification when reference is made to the electrolytes of the all-vanadium redox charge cell the positive and negative electrolytes are referred to as the catholyte and anolyte respectively. This is opposite to normal convention used in electrolytic processes but for convenience and consistency with nomenclature relating to batteries and other all-vanadium redox battery patent applications by the present applicant, the former convention has been adopted.
The inventors have found surprisingly that one possible approach to enabling the increase of the upper concentration of redox ions in a redox electrolyte (such as increasing the upper concentration of metal ions in an aqueous solution) is the addition of an effective stabilising amount of one or more stabilising agents to the solution. The inventors have also found surprisingly that the stabilising agent may also reduce precipitation of redox species from the redox electrolyte.
Throughout the specification the expression “stabilising agent” refers to a substance that enables the upper concentration of redox ions in a redox electrolyte to be increased by adding an effective stabilising amount of the stabilising agent to the redox electrolyte. The stabilising agent may permit preparation of supersaturated solutions of redox ions in the redox electrolyte. The stabilising agent may also reduce or prevent precipitation of redox species from the redox electrolyte.
In particular, in the case of vanadium electrolyte systems, it has been found that it is possible to achieve a substantial increase in the concentration of vanadium ions (especially V(II), V(III), V(IV) and, in particular V(V) ions, up to and including supersaturated concentrations, or 0.1 to 15M or 2 to 10M and in particular 5.001 to 7.5M) i
Kazacos Maria Skyllas
Kazacos Michael
Morgan & Finnegan , LLP
Pinnacle VRB Limited
Ruthkosky Mark
Ryan Patrick
LandOfFree
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