Facile In Situ Construction of SiO2–Coated Graphite Felt Electrodes Enabling 1350 Cycles in All-Iron Flow Batteries

Abstract All-iron flow batteries offer low cost and environmental friendliness. The alkaline system circumvents the corrosion and cross-contamination issues of acidic systems. However, graphite felt electrodes suffer from strong hydrophobicity and limited specific surface area, which constrain battery performance. Herein, we propose a modification method for graphite felt based on instantaneous impregnation with SiCl4, constructing a SiO2 coating on the electrode surface. Characterization shows that the modified electrode exhibits significantly enhanced hydrophilicity, increased specific surface area, and higher surface defect density. The assembled battery achieves an average energy efficiency increase from 70.42% to 79.39% at 60 mA cm–2, with Coulombic efficiency stabilized above 99%, and maintains 76.92% energy efficiency after 1350 cycles, demonstrating excellent cycling stability and high-current-density adaptability. Theoretical calculations and simulations reveal that surface functionalization enhances interfacial adsorption of iron species, promotes uniform ion distribution, and alleviates concentration polarization. This method provides a new avenue for simple and efficient modification of flow battery electrodes.