Thermally Stable Positive Electrolytes with a Superior Performance in All-Vanadium Redox Flow Batteries

A new positive electrolyte formulation for all-vanadium redox flow batteries (VFRB) with a significant improvement in electrochemical properties is reported in this communication. A 5 KDa poly(ethyleneimine)-based dendrimer (dPEI) demonstrates enhanced performance when used as an additive for positive electrolytes in VFRB. A thermal stability test at 40 degrees C shows that the dPEI additive prevents the precipitation of VO2+ over 720 h. The optimum concentration of the dPEI additive was as low as 0.6% (weight per volume of electrolyte), leading to a cost-effective solution in terms of a 38% increase in energy density (18 Wh L-1) with respect to the additive-free system (ca. 13 Wh L-1). Moreover, this innovative electrolyte performance remains stable at 88% in energy efficiency over a wider operational temperature (up to 60 degrees C) while retaining the energy density.