Spatially Strengthened Ion-Dipole Electrolyte Enables High-Temperature Anode-Free Sodium Batteries

Practical anode-free sodium batteries (AFSBs) require high-temperature adaptability, e.g., stable operation at 45°C. However, current AFSBs are usually confined to room/low temperatures, and pouch cell-level AFSBs capable of stable cycling >25°C have rarely been reported. Here we report high-temperature AFSBs via spatially strengthened ion-dipole electrolyte chemistry. Specifically, a novel solvent, namely, ethyl tetrahydrofurfuryl ether (ETFE) is designed. The reversely anchored rigid cyclic head endows ETFE molecule with weakened steric hindrance effect and stronger cyclic ethereal O─Na⁺ interaction accordingly, hence spatially strengthening overall ion-dipole interaction. Consequently, less vulnerable free solvents, ameliorated electrolyte decomposition, and formation of stable electrode/electrolyte interphases enable highly reversible Na plating/stripping behaviors at elevated temperatures. Further, an ampere hour (Ah)-level pouch cell capable of 200 cycles at 45°C with a capacity retention of 89.1% is realized even after initial 300-cycle ageing at 25°C, featuring the first long-term HT evaluation toward pouch cell-level AFSBs. This work should expedite the practicability of AFSBs.