A Coordinated-Anion-Enriched Electrolyte for Lean-Electrolyte Li–S Batteries

The solid electrolyte interphase (SEI) on Li and cathode electrolyte interphase (CEI) at sulfurized polyacrylonitrile (SPAN) formed in the commonly used liquid electrolytes cannot accommodate the large volume change of both Li anode and SPAN cathode, resulting in severe electrolyte and Li consumption and fast capacity decay under high mass loading and lean electrolyte conditions. Herein, a LiF-rich SEI and a LiF–Li x N y O z coenriched CEI are simultaneously formed by adding ionic liquid (Py13TFSI) in the localized high-concentration electrolyte (LHCE), which forms a coordinated-anion-enriched solvation structure. The LiF-rich interphase results in less stress/strain during large volume changes of Li and SPAN, therefore achieving obviously improved stability even at a high areal capacity. Consequently, Li (50 μm)||SPAN (6 mg cm–2) pouch cells under the lean electrolyte conditions (E/S ratio of 5 mL gSPAN –1) deliver a stable cycle life of 120 cycles with 79.2% capacity retention, demonstrating great promise for high-energy-density lithium–sulfur batteries.