Patent ID: 8541138

Claim:
A redox cell comprising: a positive half-cell in communication with a positive half cell solution that contains at least one vanadium ion selected from the group consisting of vanadium (III), vanadium (IV) and vanadium (V); a negative half-cell in communication with a negative half cell solution that contains at least one vanadium ion selected from the group consisting of vanadium (II), vanadium (III) and vanadium (IV); and a cast perfluorinated ionically conducting membrane located between the positive half cell and the negative half cell and in contact with the positive half cell solution and the negative half cell solution and wherein the perfluorinated membrane comprises a polymer selected from the group consisting of a PTFE, perfluorosulfonic acid and a perfluorosulphonic acid/PTFE copolymer, said membrane having isotropic swelling and tensile strength properties, a conductivity at 25° C. of between 0.01 and 1 S/cm, and having a linear expansion of less than 8% in both directions from 50% Relative Humidity at 23° C. to water soaked at 23° C.