Influence Of Impurity Ions On The Electrolyte Stability And Electrochemical Performance Of Vanadium Redox Flow Battery

As a kind of new rechargeable battery，the vanadium redox flow battery (VRB)posseses a lot of advantages, such as low pollution,electrodes not involving reaction,power rating and energy rating being independent. For these reasons, it has developedrapidly in recently years. China is abundant in Vanadium resource，so VRB has moredevelopment space.The electrolyte is the active material for VRB electrochemical reactions. Itscharacteristics have a direct impact on the battery performance. The influence ofimpurity ions on the electrolyte performance were rarely studied. Due to the differentvalence states of vanadium electrolyte stability and electrochemical performance can beinfluenced by different factors, the influence of impurity ions on trivalent, tetravalent,pentavalent vanadium electrolyte performance was studied respectively in this paper.In this paper，the trivalent,tetravalent,pentavalent vanadium electrolyte of differentvanadium and sulfuric acid concentration were prepared by Electrolysis.The effects ofvanadium concentration and sulfuric acid concentration on vanadium electrolytestability and electrochemical performance were studied by CV and Stability test. Hereby,the optimum concentration ratio of vanadium and sulfuric acid were obtained. Theoptimum value were3~4mol·l-1containing1.6~2mol·l-1sulfuric acid. The coulombicefficiency of single cell charge-discharge test for vanadium electrolyte at thisconcentration range was up to94%and the energy efficiency was up to85%. The singleperformed good cycling property.In low concentration vanadium and sulfuric acid electrolyte, microimpurity ionsmain influence the stability of quinquevalent vanadium electrolyte at high temperature,Fe2+、Co2+、Ni2+、Cu2+、Zn2+、AlO2-、SiO32-、NO3-、Cr2O72-、MnO4-can significantlyreduce the stability of quinquevalent vanadium electrolyte. In high concentration vanadium and sulfuric acid electrolyte, microimpurity ions main influence the stabilityof trivalent and tetravalent vanadium electrolyte at low temperature. Mg2+、Al3+、Ti4+、Cr3+can significantly reduce the stability of trivalent and tetravalent vanadiumelectrolyte, but PO43-、 Cl-can improve the stability of trivalent and tetravalentvanadium electrolyte. Microimpurity has no no obvious effect on the electrochemicalperformance of tetravalent and pentavalent vanadium electrolyte, however certainMicroimpurity can significantly influence the reversibility in electrochemistry reactionof trivalent vanadium electrolyte,such as Li+、Al3+、Cr3+、PO43-、Cl-can improve thereversibility in electrochemistry reaction of trivalent vanadium.After total comparing the influence of impurity ions on the electrolyte stability andelectrochemical performance of vanadium redox flow battery, we got the followingconclusions. Fe2+、Co2+、Ni2+、Cu2+、Zn2+、AlO2-、SiO32-、NO3-、Cr2O72-、MnO4-mustbe removed from the vanadium electrolyte. Mg2+、Al3+、Ti4+、Cr3+、Mn2+should try toavoid in vanadium electrolyte.An appropriate amount of Li+、Na+、K+、NH4+、PO43-、Cl-can exit in vanadium electrolyte, besides Li+、PO43-、Cl-can have a further study asadditives for vanadium electrolyte.