A Universal Additive Design Strategy to Modulate Solvation Structure and Hydrogen Bond Network toward Highly Reversible Fe Anode for Low‐Temperature All‐Iron Flow Batteries

Abstract Aqueous all‐iron redox flow batteries (RFBs) are promising competitors for next‐generation grid‐scale energy storage applications. However, the high‐performance operation of all‐iron RFBs in a wider temperature range is greatly hindered by inferior iron plating/stripping reaction and low solid–liquid transition temperature at Fe anode. Herein, a universal electrolyte additive design strategy for all‐iron RFBs is reported, which realizes a highly reversible and dendrite‐free Fe anode at low temperatures. Quantum chemistry calculations first screen several organic molecules with oxygen‐containing functional groups and identify N,N‐Dimethylacetmide (DMAc) as a potential candidate with low cost, high solubility, and strong interactions with Fe 2+ and H 2 O. Combined experimental characterizations and theoretical calculations subsequently demonstrate that adding DMAc into the FeCl 2 solution effectively reshapes the primary solvation shell of Fe 2+ via the Fe 2+ ‐O (DMAc) bond and breaks hydrogen‐bonding network of water through intensified H‐bond interaction between DMAc and H 2 O, thereby affording the Fe anode with enhanced Fe/Fe 2+ reversibility and lower freezing point. Consequently, the assembled all‐iron RFB achieves an excellent combination of high power density (25 mW cm −2 ), long charge‐discharge cycling stability (95.59% capacity retention in 103 h), and preeminent battery efficiency at −20 °C (95% coulombic efficiency), which promise a future for wider temperature range operation of all‐iron RFBs.