Study On The On-line Monitoring System And Application Of SOC In The Vanadium Flow Battery

The state of charge(SOC) is the important parameters of evaluating the vanadium flow battery(VFB) capacity and the battery performance. In this paper,to monitor the SOC of VFB,redox potential method and open-circuit voltage method were studied. The main points can be summarized as following.By using potential measurement method,the potential stability of five different reference electrode in the positive and negative electrolyte were studied. The results showed that the best of potential stability is the silver/silver sulfate solid state reference electrode. Therefore,this reference electrode suitable for monitoring the SOC of VFB by using the redox potential method.Several kinds of vanadium electrolyte were investigated by the potentiometric titration method. At this same time,measuring the oxidation-reduction potential of the electrolytic solution,to establish the relationship between ORP-SOC equation. The results showed that the relationship between ORP and ln(1/SOC-1) shoud be characterized by different fitting curve equation in charging and discharging process of the battery. For the cathode electrolyte,the goodness of fit for linear model and quadratic model is not very different. For the negative electrolyte,the goodness of fit for quadratic model was better than the linear model.Several kinds of vanadium electrolyte were investigated by the potentiometric titration method. At this same time,measuring the open-circuit voltage of battery,to establish the relational between OCV and SOC. The results showed that the SOC of positive electrolyte and negative electrolyte are not equal,thus the relationship between OCV and ln(1/SOC-1) were separately established for positive electrolyte and negative electrolyte. Besides the correlation coefficients were greater than 0.95.Developing of the on-line monitoring system of SOC in the vanadium flow battery,to achieve the SOC of positive and negative electrolyte on-line monitored. The results showed that the SOC measurement error is less than 4% by ORP potential method and less than 5% by open-circuit voltage method for negative electrolyte. And the SOC measurement error is less than 5% by ORP potential method and less than 10% by open-circuit voltage method for positiveative electrolyte. Thus, the SOC measurement error of ORP potential method is slightly less than the open circuit voltage method. Using the ORP potential method to monitor the SOC of battery is higher reliability.