China Nonferrous Metallurgy

As a large-scale energy storage technology, all-vanadium redox flow batteries (vanadium batteries) have received widespread attention because of their high safety, stability, long service life, design flexibility and low environmental impact. However, vanadium batteries are limited in their development and commercial application because of solubility of vanadium compounds and stability of vanadium ions. In this paper, to improve the capacity, energy density and high-temperature stability of vanadium batteries, the main components of the vanadium electrolyte of the sulfuric-phosphoric mixed acid system and their performance effects were investigated. Through stability, electrochemical performance and battery performance of the electrolyte testing and analysis, the study shows that the sulfuric-phosphoric mixed acid system significantly improves the high-temperature stability of V(V) electrolyte, and the stabilization time is extended by 68h at 50℃. However, when the phosphoric acid concentration exceeds 0.2mol/L, a new precipitate of VOPO4 is formed, and the original V2O5 gradually disappears. When the sulfuric-phosphoric mixed acid electrolyte concentration composition is vanadium ion concentration of 2.0mol/L, sulfuric acid concentration of 3.0mol/L, phosphoric acid concentration of 0.15mol/L keeping stable after 100 times charge and discharge at 50℃, and without any precipitation, its capacity is 16.9Ah/L, energy density is 21.5Wh/L, coulomb efficiency is 94.0%.