The Effect Of Compound Additives On Electrolyte Performance Of Vanadium Batteries

With the increasing energy and ecological problems,the development and utilization of renewable energy has become the pursuit of all countries in the world.The Vanadium redox flow battery?VRB?has become the first choice of the large-scale energy storage because of its large capacity,low cost,flexible design and fast response.Electrolyte is the core of the battery.As the medium of energy storage and conversion,the performance of the electrolyte determines the overall performance of the battery.In this paper,the positive and negative electrolytes of vanadium batteries were prepared by chemical reduction and electrochemical methods.The effects of three composite additives on the stability and electrochemical performance of vanadium batteries were studied,and the mechanism was discussed.By calculating the?G at different temperatures during the electrolyte preparation process with hydrazine hydrate as the reducing agent,the?G-T diagrams of the reaction was obtained,and the E-pH diagrams of V-H₂O system and V-S-H₂O system were drawn,which provided a theoretical basis for determining the reaction temperature and the existing form,the stable region and the changing trend of vanadium ions in acidic solution at different temperatures.It is found that elevated temperature can promote the reduction process,and as the temperature increases,the stable region of V₂O₅ gradually decreases.According to thermodynamic studies,it was determined that the temperature at which the hydrazine hydrate reduced V₂O₅ to prepare an electrolyte was 90°C.The cmc concentration of surfactants SDBS,CTAB,D-sorbitol and 1%KHSO₄ in the positive and negative electrolyte was obtained by the critical micelle concentration method.According to the ratio of composite additives obtained,the addition of composite additive to the negative electrode electrolyte showed that the introduction of the additive did not change the phase of vanadium ions.After the addition of 1%KHSO₄+3 mmol/L SDBS,the concentration of vanadium ion remained high after stationary for the same time.The peak current ratio of cyclic voltammetry was 1.07,and the peak potential difference was 0.239 V,which significantly improved the stability and electrochemical performance.The XRD analysis of the precipitate proved that the precipitate was V₂O₅.The crystallinity of precipitates varies with the types of additives.The positive electrode electrolyte was prepared by constant current charging of the negative electrode electrolyte at a current density of 60 mA/cm².Three kinds of composite additives were added into the positive electrolyte respectively.The results showed that the addition of additives does not cause changes in the phase of vanadium ions.The electrolyte containing 1%KHSO₄+2 mmol/L CTAB had better stability at 45?.The concentration of vanadium ion was higher than that of the blank electrolyte after standing the same time,and the precipitate composition is V₂O₅.The results of electrochemical tests show that the peak current ratio decreases to 1.288 and the peak potential difference is 0.038V with the increase of peak current,which improves the stability and electrochemical performance.The results show that the change of the conductivity of the electrolyte is mainly due to the addition of KHSO₄,which increase the conductive ions.The addition of long chain organic compounds will cause the relative increase of electrolyte viscosity,and the effects of three kinds of composite additives on the positive and negative electrolytes are also different.