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

Abstract 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 ₆ 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 ⁻¹ 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.