Dimethyl Sulfoxide/H 2 O Cosolvent Reconstructs Fe 2+ Solvation Sheath and Breaks Water H‑Bond Network for Stable Aqueous Iron Metal Batteries

Aqueous iron metal batteries are promising candidates for safe and low‐cost stationary energy storage, but their practical application remains hindered by poor Fe anode reversibility due to hydrogen evolution reaction (HER), by‐product formation, and poor low‐temperature operation. Herein, a dimethyl sulfoxide (DMSO)–water cosolvent electrolyte is developed to address these challenges through simultaneous reconstruction of the Fe 2+ solvation sheath and disruption of the intrinsic hydrogen‐bond network among water molecules. Molecular dynamics simulations and spectroscopic characterization reveal that DMSO preferentially coordinates with Fe 2+ ions, displacing water molecules from the primary solvation sheath and substantially reducing interfacial water activity. This solvation restructuring effectively suppresses parasitic HER and the associated irreversible formation of FeSO 4 (OH)·3H 2 O by‐products, as confirmed by X‐ray diffraction and in situ optical microscopy. As a result, the optimized electrolyte (DMSO/H 2 O = 2:8) enables stable Fe plating/stripping with a compact electrode morphology, achieving over 350 h of cycling stability in Fe//Fe symmetric cells at 1 mA cm −2 , and demonstrating a significantly enhanced Coulombic efficiency. Furthermore, the disruption of the hydrogen‐bond network by DMSO depresses the freezing point of the electrolyte from −2.8 to −20.9 °C, endowing the Fe//PBA full cell with stable cycling for over 400 cycles at −20 °C.