Solvent molecular branching drives synergistic solvation and antifreezing for ultra-low-temperature anode-free sodium metal batteries

Molecular branching triggers synergistic solvation to achieve “weak + weak = strong” electrolyte behavior. The binary system stays liquid to −80 °C, enabling anode free full cell cycling at −60 °C and 123 Wh kg −1 in Ah-scale pouch cells at −40 °C.