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

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 PF₆ ^- 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.