Effect of sodium phosphate on stability and electrochemical performance of the positive electrolyte for a vanadium redox flow battery at 50°C

Abstract

This report suggests that the addition of sodium phosphate (Na3PO4) into the electrolyte of vanadium redox flow battery (VRFB) can effectively enhance the thermal stability of the electrolyte and significantly improve the discharge capacity at high temperatures. The introduction of Na3PO4 enables the positive electrolytes with 2 M vanadium ions to maintain stability at 50 °C for over 7 days, while the electrolytes without Na3PO4 show significant precipitation on the first day. In addition, a cell containing 0.3 M Na3PO4 exhibits a capacity retention of 83.02% after undergoing 100 cycles, which is nearly 13.2% higher than the pristine cell. After investigating the electrochemical performance of a cell containing 0.3 M Na3PO4 at 50 °C, it is discovered that the energy efficiency of 80% can be maintained at 150 mA cm−2. Additionally, the capacity retention rate of the cell after 100 cycles is 28.47% higher than that of the pristine cell. Therefore, Na3PO4 is a potentially effective additive for VRFB in long-term thermal stability and capacity retention, thereby reducing the thermal management cost of energy storage systems and providing a broad prospect for the application of VRFB.