Optimization of the electrolyte ratio for the vanadium flow battery and its effect on the battery performance

Electrolyte of vanadium flow battery (VFB) is the key component of the energy storage unit, which plays an important role in the energy conversion efficiency and cycle stability performance of VFB. Considering the volume ratio of the catholyte and anolyte, also the electrolyte valence state, the effect of the excess of negative active reactant on the electrochemical performance of VFB is systematically investigated. The results show that the increasing the volume of the anolyte with the same catholyte improves the discharge capacity for VFB, but has less effect on the energy conversion efficiency. The increasement of the electrolyte valence lead to a reduced discharge capacity of VFB in some extent, while the energy conversion efficiency increases at first and then decreases, conforming to a parabola law. Increasing of the volume of anolyte and electrolyte valence state result in the excess of the negative active reactant, the latter has more significant effect on the battery performance of VFB. However, the effect of anolyte volume will be enlarged with the existence of exec valence state.