A high current density and long cycle life iron-chromium redox flow battery electrolyte

The electrolyte in the flow battery is the carrier of energy storage, however, there are few studies on electrolyte for iron-chromium redox flow batteries (ICRFB). The low utilization rate and rapid capacity decay of ICRFB electrolyte have always been a challenging problem. Herein, the effect of Fe/Cr molar ratio, and concentration of HCl on the performance of ICRFBs at high current density (140 mA cm⁻²) are investigated. The average energy efficiency of the optimal electrolyte (1.25 M FeCl₂, 1.50 M CrCl₃, 3.0 M HCl) increases by 5.99% in the first 20 cycles, and the discharge capacity increases by 15.72% in the first cycle compared to the original commercial electrolyte (1.0 M FeCl₂, 1.0 M CrCl₃, 3.0 M HCl). This electrolyte also shows a longer cycle life. In addition, the COMSOL simulation on the concentration change of electrolyte in ICRFB is proposed, the effect of physical properties on the electrolyte is further explained. Through the simulation and analysis of this complex system, researchers can better understand the performance of flow battery systems. It is important to consider various challenges and constraints that might be encountered in practical applications. This work effectively saves the cost of ICRFB and further provides data support for their engineering applications.