The vanadium solution was prepared by heating the mixture of vanadium trioxide and vanadium pentoxide in sulfuric acid solution, which utilized the autocatalytic effect of vanadium with mixed valence, to intensify the dissolving of the mixture of vanadium trioxide and vanadium pentoxide. The formations of vanadium ions were theoretically determined. Moreover, negative ?_rG_m and ?_rH_m of the reactions were calculated by thermomechanical analysis. The reactions was proved to be a spontaneous process (?_rG_m＜0). The results were confirmed by the UV-Vis analysis for the formation of ions. Its electrochemical performance was characterized by cyclic voltammetry and charge-discharge. The results showed that the prepared vanadium solution had an excellent electrochemical behavior, which indicated that the method was suitable for the industrial application. Our work may serve as the theoretical basis for industrial production of the electrolyte of vanadium redox-flow batteries.

Key words: redox-flow battery, vanadium solution, thermodynamic