Advanced Electrolyte Formula for Robust Operation of Vanadium Redox Flow Batteries at Elevated Temperatures.

Insufficient thermal stability of vanadium redox flow battery (VRFB) electrolytes at elevated temperatures (>40 degrees C) remains a challenge in the development and commercialization of this technology, which otherwise presents a broad range of technological advantages for the long-term storage of intermittent renewable energy. Herein, a new concept of combined additives is presented, which significantly increases thermal stability of the battery, enabling safe operation to the highest temperature (50 degrees C) tested to date. This is achieved by combining two chemically distinct additives-inorganic ammonium phosphate and polyvinylpyrrolidone (PVP) surfactant, which collectively decelerate both protonation and agglomeration of the oxo-vanadium species in solution and thereby significantly suppress detrimental formation of precipitates. Specifically, the precipitation rate is reduced by nearly 75% under static conditions at 50 degrees C. This improvement is reflected in the robust operation of a complete VRFB device for over 300 h of continuous operation at 50 degrees C, achieving an impressive 83% voltage efficiency at 100 mA cm(-2) current density, with no precipitation detected in either the electrode/flow-frame or electrolyte tank.