Macroscopic Mass Transfer Simulation And Performance Experiments Of All-Vanadium Redox Flow Batery

Vanadium redox flow battery(short for VRB) is a new environmental friendly and efficient energy-storage battery. It achieves to make a cycle of charge and discharge by the electrochemical reaction transformation of vanadium ions at different valence states. VRB have received widespread attention and application in solar energy, wind energy, hydro-power for its highlight advantages, such as long life, high efficiency, fast response, low cost, and can be charged instantaneously. In this paper, we studied the actual performance under different operating parameters and ions distribution during the normal operation through the performance test experiments and computer simulation. The purpose of this paper is to optimize battery performance and improve the energy efficiency and reduce the cost.Building up an energy-storage battery test system by using the fuel battery tester and the wide-range variable switching power supply, combined with a self-designed VRB monomer. Experimental tests and analyses the j-V curves and ac impedance characteristics under different electrolyte flow rates and charge and discharge current density of VRB. The results show that: after reaching the same charging state, the greater flow rate sets, the longer the duration lasts, the greater the discharge energy efficiency and the output of power exhibits during the discharge progress. And with the increase of flow rate and current density, the ac impedance of VRB decreases gradually; Compared with lower current density, the change of flow velocity has the greater influence on ac impedance under high current density.In this paper, a VRB three-dimensional single mass model was established to simulate the mass transfer of V2+, V3+, VO2+, VO2+ during the operation. Distribution in four kinds of ions at the diffusion layer of electrode under the steady state in the battery was got through the analysis of the results and data. The influences of different operation parameters on its mass distribution were analyzed by controlling the flow rate and electrolyte concentration. The results show that: the distribution of VO2+ and V2+ reduced gradually along the flow direction, while that of the VO2+ and V3+ increased. Distribution of the four ions in the flow field showed as " high ends and middle low". The variety of the electrolyte flow rate can only influence the ion mass fraction at the entrance and have little effect on electro-chemical reaction rate. But the variety of the concentration of the electrolyte can affect both the battery in the electro-chemical reaction rate and the ion distribution at the entrance as well.