Regulating hydrogen-bond network via a low-viscosity electrolyte for hydrogen evolution reaction-free aqueous...

Aqueous sodium-ion batteries (ASIBs) have emerged as one of the most promising candidates for large-scale energy storage devices, owing to their inherent non-flammability, abundant resources and low cost. However, the water-induced hydrogen evolution reaction (HER) on the anode surface usually leads to low Coulombic efficiency (CE) and limited cycling stability. In this study, we propose a novel aqueous electrolyte recipe composed of H₂O/DMF/TTE-NaTFSI to mitigate the issue of HER. On the one hand, the 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TTE), acting as a diluent, is highly hydrophobic. It disrupts the hydrogen-bonding network of H₂O, thereby enhancing solvation kinetics. Furthermore, the fluorinated moieties of TTE interact with H₂O molecules via strong dipole interactions, reducing solvent mobility and optimizing the Na⁺ solvation sheath. On the other hand, the N, N-dimethylformamide (DMF) serves as a co-solvent that promotes miscibility between aqueous phase and TTE while restructuring the hydrogen-bonding network within the solvation shell. DMF and TTE regulate synergistically the primary solvation structure, stabilizing Na⁺ ions via strengthened anion coordination and effectively suppressing HER. Consequently, the ASIB demonstrates exceptional cyclic stability, retaining 99.2% of its capacity after 1000 cycles at 1C and 96.3% after 100 cycles at 2C in Na₃V₂(PO₄)₃/C full cells. This work presents a promising strategy to suppress HER through the synergistic interaction between DMF and TTE, enhancing electrochemical performance.