Research on thermo-electrochemical behaviors and energy conversion in discharge process of vanadium-manganese flow battery associated with MnO2 precipitation

Abstract

• 2-D isothermal model describing thermo-electrochemical behaviors is established. • Temperature has great impact on the property of vanadium-manganese flow battery. • Power consumption and Joule heating loss are analyzed and compared. • Battery presents better performance at applicable operating conditions. Vanadium-manganese flow battery is a promising renewable energy storage system due to higher energy density as well as lower cost of Mn(II)/Mn(III) redox couple in the cathode than V(II)/V(III). The non-isothermal 2-D model describing the thermo-electrochemical behaviors in the main reactions of V(II)/V(III) and Mn(II)/Mn(III) along with the side reaction of Mn(II)/MnO 2 is established to investigate the energy loss including power consumption and Joule heating loss associated with parameter researches, and the simulations agree with the experimental data. The amount of MnO 2 precipitation in the side reaction is inverse proportional to the discharge current density and electrode porosity. While the temperature rises from T = 5 to 45 °C, more power consumption deriving from deposition reaction than dissolution reaction occurs in the discharge, and the Joule heating loss acts as a main factor to influence energy loss as well as it increases with the rise of current density at lower temperatures. The maximum energy density of 32.17Wh/L and voltage efficiency of 93.07% arise respectively with electrode porosities of ε = 0.8 and ε = 0.7 under the current density of i = 50 mA/cm 2 , and the larger voltage efficiency and less power consumption accounting for total energy loss can be obtained with the electrode porosity of ε = 0.8, thus, the better performances can be obtained in the vanadium-manganese flow battery with optimized electrode porosity under the applicable operating conditions proposed in this work.