Development of a novel redox flow battery for electricity storage system

A novel cylindrical battery which uses carbon fibres with high specific surface area as electrodes and a porous silica glass with high chemical stability as membrane has been fabricated. The results obtained from electrolysis of 0.5 M K₃Fe(CN)₆-0.5 M KCl and of 85 mM V(IV) M H₂SO₄ indicate that the cell possesses excellent electrolytic efficiency. As a redox flow battery (RFB) its performance was investigated by employing all-vanadium sulfate electrolytes. The results of the cyclic voltammetry measurements indicate that at a glassy carbon electrode the electrochemical window for 2 M H₂SO₄ solution could reach 2.0 ∼ 2.4 V. Constant current charging-discharging tests indicate that the batteries could deliver a specific energy of 24 Wh L^-1 at a current density of 55 mA cm^-2. The open-circuit cell voltage, after full charging, remained constant at about 1.51 V for over 72 h, while the coulombic efficiency was over 91%, showing that there was negligible self-discharge due to active ions diffusion through the membrane during this period.