Effect of phosphoric acid additive on the electrolyte of all-vanadium flow batteries.

A phosphoric acid additive with an optimal concentration of 0.1 M can vastly promote the diffusion kinetics of the redox reaction between V(IV) and V(V) without a significant decline in energy efficiency for 300 cycles, and maintain the high-temperature stability (55 °C) of an electrolyte at a high state of charge (SOC) of 70% over the course of 30 days.