Lightweight Electrolyte Design for Li/Sulfurized Polyacrylonitrile (SPAN) Batteries

Abstract Sulfurized polyacrylonitrile (SPAN) recently emerges as a promising cathode for high‐energy lithium (Li) metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. Besides, the large volume changes of Li metal anode and SPAN cathode require inorganic‐rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design where lightweight dibutyl ether (DBE) is used as a diluent for concentrated lithium bis(fluorosulfonyl)imide (LiFSI)‐triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04 g mL⁻¹) is 40%–50% lighter than conventional localized high‐concentration electrolytes (LHCEs), leading to 12%–20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent‐diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion‐derived inorganic‐rich interphases, minimize electrolyte consumption, and improve cell cyclability. The electrolyte also exhibits low volatility and offers good protection to both Li metal anode and SPAN cathode under thermal abuse.