Research On The Electrolyte For All Vanadium Redox Flow Battery

The vanadium redox flow battery (VRB) developed in recent years is a kind of new rechargeable battery. It is with excellent advantages, such as low cost, high security, simply technological process and power rating and energy rating being independent. For these reasons, much research and development has been concentrated on it.The electrolyte is the active substance in VRB electrochemical reactions. Its characteristics have a direct impact on the battery performance. This paper used vanadium pentoxide as the original electrolyte materials. Vanadium pentoxide was reverted to vanadium trioxide by hydrogen at high temperature. Then, the electrolyte with trivalent and tetravalent vanadium ion which mole ratio is 1:1 was made by adding a certain amount of vanadium pentoxide and vanadium trioxide to sulfuric acid solution. This paper also introduced a kind of method called Coulomb Titration which can be used to ascertain the concentration of the electrolyte. We optimized the preparation method of the electrolyte on the basis of titration result. In order to investigate the diffusion behavior of vanadium ions in Nafion membrane, the electrolyte was used in VRB to test the penetrability in the membrane. After running single cell of VRB using home-made electrolyte, we found that the optimum flow rate of the electrolyte was 12 times as much as the theoretical one and the cell showed high electric power efficiency at the charge-discharge testing.As the active materials of VRB, there were different concentrations of vanadium ions in the sulfuric acid solution. For this reason, stability is very important to VRB. In the paper, 5 kinds of additives for vanadium battery were investigated by crystallization experiment and single-cell experiment. Urea, ammonium oxalate and ethylene glycol inhibited the crystallization of the trivalent vanadium ions, so that the decreasing rate of the electrolyte concentration was reduced. The efficiency and discharge capacity of the battery were decreased with Ethylene glycol as additive. The efficiency of the battery using Urea and ammonium oxalate as negative additive was reduced slightly but the voltage efficiency and columbic efficiency of the battery exceeded 85% and 98% under the current density of 60 mA/cm~2.