Ion Migration‐Induced Capacity Evolution in Iron–Chromium Redox Flow Batteries during Cycling

This article focuses on the iron–chromium redox flow batteries (ICRFBs), systematically investigating the effects of different states of charge (SOCs) on electrolytes, the correlation between detection conditions and capacity, ion migration mechanisms, joint estimation of component migration and capacity loss, as well as the significance of ion migration for system operation. The results reveal that during charging, the volume and ion concentration of positive/negative electrolytes exhibit regular changes, with chromium ion and hydrated hydrogen ion migration being the key factors affecting the charging process. Under detection conditions, SOCs calculated by concentration and voltage show deviations from theoretical values, highlighting the need for precise control of electrolyte charging depth in practical applications. Ion migration is driven by combined effects of potential difference, concentration gradient, and osmotic pressure. In the initial stage, ion diffusion delays capacity decay, while water molecule migration leads to normal capacity decline in the later stage. Utilizing a capacity recovery system combined with ion enrichment can enhance battery capacity beyond the design value. These findings provide critical theoretical support for the practical application and optimized design of ICRFBs.