Study On Anode Electrolyte Stability And Battery Performance Of Vanadium Redox Flow Battery

With low pollution and safe advantage, vanadium redox flow battery has been widely studied and received considerable attention on power system. Due to supersaturation, V(Ⅴ) ion would be precipitated from anode vanadium electrolyte when the electrolyte concentration excesses 2moL/L on high temperatures. Increasing the concentration of sulfuric acid could increase the solution of V(Ⅴ), but reduce the solubility of V(Ⅳ), besides high concentration of sulfuric acid could increase the electrolyte corrosion. So it is very important to screen effective additives to improve the stability of anode vanadium electrolyte.The V(Ⅳ)-H2SO4 solutions were prepared by oxidate reduction method in sulfuric acid. The effect of different additives, such as sodium bisulfate, potassium bisulfate and acetic acid and potassium sulfate on the solubility and stability of anode vanadium electrolyte were investigated, the stabilization mechanisms of the anode electrolyte with different additives were also discussed. The results showed that the stability of the anode vanadium electrolyte added sodium bisulfate, potassium bisulfate or acetic acid was better than that of potassium sulfate. The effect of additives on the electrochemical performance of the positive V-H2SO4 solution was investigated by cyclic voltammetry, UV-Vis absorption spectra and electrochemical impedance spectroscopy (EIS). The results indicated that there was not unfavorable effect of additives on the electrochemical properties of the anode vanadium electrolyte, and the electrolyte conductivity improved slightly compared to that without additives.By optimizing the electrolyte tank design, a single vanadium redox flow battery in laboratory level was assembled, and the battery performance with various electrolyte added different additives (such as potassium bisulfate and acetic acid) was investigated. The newly designed electrolyte tank could solve the inconsistency of the anode and cathode charging state caused by the oxidation of low vanadium ion, the permeation of different vanadium ions and water caused by the imbalance of pressure and membrane aging issues, thus the ion-exchange membrane life would extended and the battery efficiency and life would also improved. The effect of treatment temperature and time of the graphite felt electrodes, charge and discharge current density, and the number of cycles on the battery performance were investigated. It showed that the graphite felt electrode have showed the highest activity and the battery had the minimum inner resistance by treated at 600℃for 4h. With increasing charge current density, the current efficiency of the vanadium redox flow battery reduced. The voltage efficiency of battery decreased with the increasing of charge/discharge current density. In the early charge-discharge process, the current efficiency of battery increased with the number of cycles. There was not unfavorable effect of additives on the battery resistance and the charge-discharge peculiarity of battery when the additives were added in the anode electrolyte.