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 elec