Effect of hexanol-based additives on the performance of positive electrolyte for vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) are considered a highly promising large-scale energy storage technology due to their long lifespan, high safety, large capacity, and high efficiency. In practical applications, pentavalent vanadium in the positive electrolyte of vanadium batteries is prone to precipitation under conditions of high temperatures and concentrations, reducing the energy density and cycle life of VRFBs. Therefore, choosing appropriate additives to improve the stability of pentavalent vanadium ions is crucial. This study researched the effects of two hexahydric alcohols (inositol and galactitol) as electrolyte additives on the performance of vanadium-positive electrolyte through X-ray diffraction (XRD), Raman spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge–discharge tests. The results show that both inositol and galactitol can improve the electrochemical performance of vanadium-positive electrolyte. At a current density of 80 mA cm⁻², the energy efficiency of the battery groups with inositol and galactitol added increased by 1.24% and 3.28% respectively compared to the blank battery group. The capacity retention rates of the battery groups with inositol and galactitol added were both higher than that of the blank battery group after 50 cycles. Due to the different distribution spaces of hydroxyl groups, galactitol was more significant in enhancing electrochemical activity and increasing the stability of the electrolyte.