The in situ electrolyte reduction induced construction of LiF-rich cathode electrolyte interphase synergizing with high sulfur loading cathode design for high cycle-stable lithium-sulfur batteries

Attaining both high energy density and prolonged cycle stability in lithium‑sulfur (Li[sbnd]S) batteries remains a persistent challenge, particularly for sulfurized polyacrylonitrile (SPAN) cathodes, owing to interfacial instability and restricted sulfur incorporation. Furthermore, elevated sulfur content in the electrode exacerbates capacity degradation in Li-SPAN cells. Herein, we report a pre-potentiostatic strategy to induce in situ reductive decomposition of LiPF₆ based carbonate electrolytes, with the formation of a compact and LiF-rich cathode electrolyte interphase (CEI) on a S₈@S₇Se/PAN composite cathode with a high sulfur loading content. The robust LiF-rich CEI effectively suppresses polysulfide dissolution, mitigates parasitic side reactions, and facilitates solid-phase sulfur redox reactions by providing a mechanically stable and ionically conductive interface. Unlike conventional organic-rich transient CEIs, the LiF-rich CEIs exhibit superior uniformity and long-term stability under lean electrolyte (E/S ≤ 4.5 μL mg⁻¹) and high mass loading (>4 mg cm⁻²) conditions. Electrochemical tests demonstrate a high initial capacity of 1622.68 mAh g⁻¹ at a current density of 0.2C and stable cycling performance with a reversible capacity of 714.7 mAh g⁻¹ over 5000 cycles under the lean electrolyte conditions (E/S = 3.5 μL mg⁻¹) in Li(~ 45 μm)||S₈@S₇Se/PAN(5.51 mg cm⁻²) cells. This study presents a universal and scalable CEI engineering strategy that effectively resolves the conventional trade-off between energy density and cycling stability in Li-SPAN systems. The progressive degradation of the CEI is a critical determinant of electrode performance decay at high active material loading, thereby providing a viable pathway toward the practical implementation of high-performance Li[sbnd]S batteries.