Partially Ion-Paired Solvation Structure Design for Lithium-Sulfur Batteries under Extreme Operating Conditions

Achieving increased energy density under extreme operating conditions remains a major challenge in rechargeable batteries. Herein, we demonstrate an all-fluorinated ester-based electrolyte comprising partially fluorinated carboxylate and carbonate esters. This electrolyte exhibits temperature-resilient physicochemical properties and moderate ion-paired solvation, leading to a half solvent-separated and half contact-ion pair in a sole electrolyte. As a result, facile desolvation and preferential reduction of anions/fluorinated co-solvents for LiF-dominated interphases are achieved without compromising ionic conductivity (>1 mS cm^-1 even at -40 °C). These advantageous features were found to apply to both lithium metal and sulfur-based electrodes even under extreme operating conditions, allowing stable cycling of Li || sulfurized polyacrylonitrile (SPAN) full cells with high SPAN loading (>3.5 mAh cm^-2 ) and thin Li anode (50 μm) at -40, 23 and 50 °C. This work offers a promising path for designing temperature-resilient electrolytes to support high energy density Li metal batteries operating in extreme conditions.