Broad temperature adaptability of vanadium redox flow battery—Part 1: Electrolyte research

• Impact of temperature (-35 °C-50 °C) on properties of VRFB electrolyte is studied.
• V2+, V3+, V3.5+, V4+ (VO2+) and V5+ (VO2+) electrolytes are tested respectively.
• V2+, V3+ and V3.5+ precipitates at low temperature can redissolve when temperature increases.
• V5+ precipitates at high temperature cannot redissolve when temperature decreases.
• Conductivity and viscosity of the electrolytes are greatly affected by temperature.

The broad temperature adaptability of vanadium redox flow battery (VRFB) is one of the key issues which affects the large-scale and safety application of VRFB. Typically, five types of vanadium electrolytes, namely V2+, V3+, V3.5+ (V3+:VO2+ = 1:1), V4+ (VO2+) and V5+ (VO2+), are the most common electrolytes' status existing in VRFB system. In this work, the physicochemical and electrochemical properties of these vanadium electrolytes are studied in detail at a broad temperature range (-35 °C–50 °C). The results show that all types of vanadium electrolytes are stable between -25 °C–30 °C. The temperature fluctuation will largely influence the conductivity and viscosity of the electrolytes. Besides, the electrochemical properties of the positive (VO2+) and negative (V3+) electrolytes are greatly affected by the temperature; and the charge transfer process fluctuates more greatly with the temperature variation than the charge diffusion process does. These results enable us to better and more comprehensively evaluate the performance of the electrolyte changing with the temperature, which will be beneficial for the rational choice of electrolyte for VRFB operation under various conditions.

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