Dimethyl Sulfoxide/H2O Cosolvent Reconstructs Fe2+ Solvation Sheath and Breaks Water H‑Bond Network for Stable Aqueous Iron Metal Batteries.

Abstract

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 Fe2+ 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 Fe2+ 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 FeSO4(OH)·3H2O by-products, as confirmed by X-ray diffraction and in situ optical microscopy. As a result, the optimized electrolyte (DMSO/H2O = 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.

Abstract as supplied by the indexing source. © the authors / publisher.