Abstract: As the core material for energy storage and conversion of vanadium redox battery,the composition of electrolyte,especially the impurity content in the solution,greatly affects the physicochemical properties of electrolyte,reversibility of electrode reactions and the charge-discharge performance of battery.The influence of Al concentration on the physicochemical properties of electrolyte was studied,and the effect of Al on the electrochemical performances of electrolyte and battery was analyzed by cyclic voltammetry and charge-discharge test.The results indicate that with the increase of Al/V（molar ratio）,both of the viscosity and density of the electrolyte increase,with the conductivity obviously decreased.At the molar ratio of Al to V of 1∶3.0,the viscosity and density of the electrolyte increase by 64% and 2.8% respectively,and the conductivity of the electrolyte decreases by 34%.Furthermore,Al reduces the reversibility of positive and negative electrode reactions.Meanwhile,with increase in the molar ratio of Al to V,coulombic efficiency of the battery increases,with its voltage efficiency and energy efficiency significantly decreased.In addition,the stability of negative electrolyte is decreased due to the existence of Al.