Thermal Stability of Concentrated V(V) Electrolytes in the Vanadium Redox Cell

The vanadium redox battery currently employs solutions of up to 2 M V(II)/V(III) and 2 M V(IV)/V(V) as the negative and positive half‐cell electrolytes. This concentration is limited by the solubility of the different vanadium ions in the temperature range of 10 to 40°C. Generally, the solubility of V(II), V(III), and V(IV) increases with an increase in temperature; however, the V(V) electrolyte suffers from the effect of thermal precipitation at temperatures of 40°C and above. While thermal precipitation is a serious problem in solutions of V(V) concentrations between 1.5 and 2.0 M , a surprising result was observed at concentrations above 3.0 M . As the results presented here show, at higher vanadium concentrations the V(V) solution demonstrated increased stability and there was no evidence of thermal precipitation over a 30 day period at temperatures above 40°C.