Electrolyte Solvation Structure Regulation for Low-Temperature Sodium-Ion Battery

The development of high-performance sodium-ion batteries (SIBs) that can operate effectively in low-temperature environments is essential for large-scale energy storage systems. Due to the sluggish kinetics of Na⁺ desolvation at the electrode-electrolyte interface, the capacity of SIBs decays rapidly at low temperatures, which is one of the main challenges SIBs are facing at present. On the basis of diethylene glycol dimethyl ether (DEGDME) electrolyte, 1,3-dioxane (DOL) with a low melting point and low solvation energy is used as a cosolvent, and trimethylsilyl isocyanate (Si-NCO) with a low LUMO level is used as an additive to optimize the solvation structure. This optimization facilitates greater participation of PF₆^- anions in the inner shell of the solvation structure, thereby improving its stability over a certain temperature range. The designed electrolyte enables the Na||HC half-cell to maintain 88.57% of its room-temperature capacity at -40 °C, with a capacity retention of 94.50% after 100 cycles. Additionally, in the full cell composed of O3-type layered oxide sodium nickel iron manganese (NFMN) and hard carbon (HC), the capacity retention is 83.73% after 100 cycles at -40 °C. This work provides new insights into the development of electrolyte formulations for enhancing the electrochemical stability of SIBs at low temperatures.