Molecularly Tailored Deep Eutectic Electrolytes for Safe Elevated-Temperature Sodium-Ion Batteries

Sodium-ion batteries are pivotal for energy storage due to their scalability and cost efficiency, although they face safety challenges arising from unstable interfaces, parasitic reactions, and thermal or mechanical stresses. Here, we present a universal electrolyte design strategy that incorporates elevated-dielectric-constant solvents, N-methylacetamide (NMA) and vinylene carbonate (VC), to optimize succinonitrile (SN)-based deep eutectic electrolytes. This approach enhances the compatibility of SN with Lewis bases while simultaneously improving the intrinsic safety at elevated temperatures. The robust hydrogen bonding network (C=O···H–C) between NMA and SN effectively immobilizes free SN molecules and reduces Na+ coordination. Through competitive preferential adsorption at the electrode interface, NMA and VC exclude SN from the Helmholtz plane, thereby establishing an anion-rich interfacial phase that mitigates electrolyte consumption, dendrite growth, phase transitions, and gas evolution. As anticipated, Prussian blue||hard carbon pouch cells demonstrate enhanced flame-retardancy, improved shear resistance, and a capacity retention of 71.0% after 500 cycles.