Salt‐in‐Salt Mediated Weak‐Solvent Electrolyte Enabling Fast‐Charging and Wide‐Temperature Lithium‐Ion Batteries

ABSTRACT Realizing the practical application of spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathodes requires electrolytes with fast‐charging capability and wide‐temperature adaptability, which conventional electrolytes lack due to insufficient high‐voltage stability, sluggish ion transport, and unstable interphases. Herein, we propose a salt‐in‐salt mediated “strong‐weak synergy” strategy for fluorinated weakly solvating electrolytes (WSEs), distinct from conventional ether‐based or single‐component WSEs. Harnessing the moderate Lewis acidity of Mg 2+ from Mg(TFSI) 2 , we promote LiDFOB dissociation to enrich anion‐rich contact ion pair/aggregate (CIP/AGG) solvation structures, while concurrently inducing a “drag” effect on Li + ‐coordinated solvents/anions to synergistically accelerate Li + desolvation. Notably, Mg 2+ from inorganic MgF 2 dynamically captures interfacial anions, directing the formation of a thin, robust inorganic CEI. This dual‐regulation mechanism simultaneously optimizes bulk electrolyte ion conduction and interfacial stability, overcoming the intrinsic limitations of poor oxidation resistance and sluggish kinetics in traditional WSEs. Consequently, LNMO||Li cells exhibit exceptional fast‐charging capability and cycling stability across a wide temperature range (–30 to 70°C), with pouch cells retaining 88.9% capacity after 400 stable cycles. The developed electrolyte also exhibits non‐flammability and broad compatibility for nickel‐rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.92 Co 0.06 Mn 0.02 O 2 and olivine‐type LiFePO 4 cathodes. This work offers fundamental insights into solvation chemistry and interfacial engineering toward safe, high‐performance lithium‐ion batteries.