Solvation‐Equilibrium Locking Enables Ultrawide‐Temperature Operation of High‐Voltage Lithium‐Metal Batteries

High‐energy lithium metal batteries are promising for space, polar, deep‐sea, and other extreme environments, but their operation is constrained by temperature‐sensitive ion transport, Li + solvation, and interfacial chemistry. A solvation‐equilibrium‐locked electrolyte (SELE) is reported by combining dimethyl sulfite (DMS), a low‐freezing weakly solvating solvent, with Pyr 13 DFOB (1‐methyl‐1‐propylpyrrolidinium difluoro(oxalato)borate) as an ionic‐liquid co‐solvent. Cooperative ion–dipole and weak C–H⋯O interactions between DMS and Pyr 13 + regulate the free‐solvent reservoir, while TFSI − (bis(trifluoromethanesulfonyl)imide) and DFOB − enrich the primary Li + coordination shell. Variable‐temperature 7 Li NMR, Raman, and molecular dynamics simulations show that solvent‐separated ion pairs, contact ion pairs, and aggregates remain nearly invariant from −60°C to 60°C, unlike the strongly temperature‐responsive Pyr 13 DFOB‐free electrolyte. This locked anion‐rich solvation structure reduces solvent coordination around Li + , mitigates solvent‐derived interfacial decomposition and gas evolution, and promotes LiF‐ and borate‐rich interphases on Li metal and NMC811. Consequently, Li||NMC811 cells deliver discharge capacity at −85°C and operate up to 120°C, while pouch cells remain functional after cooling to −122.9°C. A 6.6 Ah Li||Ni90 pouch cell further achieves 565 Wh kg −1 under lean‐electrolyte conditions, establishing solvation‐equilibrium locking as a molecular design principle for lithium metal batteries operating over a broad temperature range.