All Vanadium Redox Flow Battery Development for Stationary Energy Storage Applications
All-vanadium RFB system enlists the same element, vanadium, in both the catholyte and anolyte. Researchers at PNNL have revisited the standard vanadium sulfate electrolyte chemistry used in this system and developed an novel mixed acid electrolyte (sulfate and chloride) that can stabilize all four vanadium cations at concentrations ≥ 2.5M within a temperature range of 5~50oC. Recently, PNNL recently demonstrated a kW/kWh scale prototype battery utilizing this electrolyte system in order to better understand the system benefits of the mixed acid electrolyte. The system consisted of ~ 20 cell stack with 780cm2 of active area/cell, ~ 30 liter electrolyte tanks, pumps and associated piping. The stack incorporated new interdigitated flow fields for reduced pressure drop and thinner Nafion membranes for improved performance. Results of stack testing under a wide range of current densities and temperature conditions will be reported along with resulting energy efficiencies.