Cathode Electrolyte Interphase Engineering by Quaternized Chitosan for Stabilized Li–SPAN Batteries

Abstract Sulfurized polyacrylonitrile (SPAN) represents a highly promising cathode material for lithium–sulfur (Li–S) batteries, leveraging a solid‐solid sulfur conversion mechanism. However, persistent interfacial side reactions and sluggish redox kinetics in SPAN cathodes compromise the electrochemical performance. Here, quaternized chitosan (QCS) is employed as a functional agent to stabilize the SPAN cathode electrolyte interphase (CEI). The positively charged quaternary ammonium groups selectively adsorb PF ₆ ^– anions, modifying the Helmholtz layer structure and facilitating the formation of an anion‐derived CEI enriched with LiF. Consequently, the SPAN@QCS‐1.0% cathode delivers a high discharge capacity of 1499 mAh g ⁻¹ at 0.2 C, an outstanding rate capability of 902 mAh g ⁻¹ at 10 C, and a prolonged cycle life exceeding 1500 cycles at 1 C. Under practical conditions of high sulfur loading (12.0 mg cm ⁻² ) and lean electrolyte (E/S ratio = 5 µL mg ⁻¹ ), the SPAN cell achieves a high areal capacity of 17.1 mAh cm ⁻² , surpassing that of conventional lithium–ion batteries (≈4 mAh cm ⁻² ) by more than fourfold. Furthermore, a 0.9 Ah pouch‐cell prototype demonstrates stable cycling for over 30 cycles. The interface strategy provides a facile and effective approach to developing high‐performance SPAN‐based Li–S batteries.