A High Energy Density Vanadium Redox Flow Battery with 3 M Vanadium Electrolyte

In this paper, a high energy density vanadium redox battery employing a 3 M vanadium electrolyte is reported. To stabilise the highly supersaturated vanadium solutions, several additives were evaluated as possible stabilizing agents for the thermal precipitation of supersaturated V(V) solutions at elevated temperatures. The Blank 3 M V(V) solution in a sulfuric acid supporting electrolyte containing 5 M total sulfates, showed thermal precipitation after 3 days, while the solution containing 1 wt% H3PO4 additive increased the induction time for precipitation to over 47 days at 30°C. After 32 days, 3 M V(V) solutions containing 1 wt% sodium pentapoIyphosphate, 1 wt% K3PO4 and 2 wt% (NH4)2SO4 + 1 wt% H3PO4 showed final V(V) concentrations of 2.7, 2.7 and 2.6 M respectively, compared to 2.4 M V(V) in the Blank solution. From the screening tests, selected additives were used in vanadium redox flow cell cycling studies employing a 3 M vanadium electrolyte. The cell was subjected to 90 charge-discharge cycles and no precipitation or capacity loss was observed in the presence of 1wt% H3PO4 + 2 wt% ammonium sulfate. These results demonstrate that a significant enhancement in the energy density of the VRB can be achieved in the presence of additives that act as precipitation inhibitors for the vanadium ions.