Sole-Solvent High-Entropy Electrolyte Realizes Wide-Temperature and High-Voltage Practical Anode-Free Sodium Pouch Cells.

Anode-free sodium batteries (AFSBs) hold great promise for high-density energy storage. However, high-voltage AFSBs, especially those can stably cycle at a wide temperature range are challenging due to the poor electrolyte compatibility toward both the cathode and anode. Herein, high-voltage AFSBs with cycling ability in a wide temperature range (-20-60 °C) are realized for the first time via a sole-solvent high-entropy electrolyte based on the diethylene glycol dibutyl ether solvent (D2) and NaPF salt. The sole-solvent high-entropy electrolyte with unique solvent-ions effect of strong anion interaction and weak cation solvation enables entropy-driven electrolyte salt disassociation and high-concentration contact ion pairs, thus simultaneously forming stable anion-derived electrode-electrolyte interphases on cathode and anode. Moreover, the wide liquid range of D2 further extends the temperature extremes of the battery. Consequently, ampere-hour (Ah)-level anode-free sodium pouch cells with cyclability in a wide temperature range of -20-60 °C are realized. Impressively, the pouch cell achieves a leadingly high cell-level energy density of 209 Wh kg and a high capacity retention of 83.1% after 100 cycles at 25 °C. This work provides inspirations for designing advanced electrolytes for practical AFSBs.