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 °C shows that the dPEI additive prevents the precipitation of VO 2 + 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 °C) while retaining the energy density.