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

In this work, quaternized chitosan (QCS) is reported as an additive optimizing the sulfurized polyacrylonitrile (SPAN) cathode/electrolyte interphase (CEI). Its high positive charge density adsorbs PF6− anions, enriching the Helmholtz layer with aggregates. This promotes rapid anion desolvation, forming an anion‐derived CEI enriched in LiF. The resulting robust, ion‐conductive CEI significantly enhances Li‐SPAN cell electrochemical performance. 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 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. In this work, quaternized chitosan (QCS) is reported as an additive optimizing the sulfurized polyacrylonitrile (SPAN) cathode/electrolyte interphase (CEI). Its high positive charge density adsorbs PF 6 − anions, enriching the Helmholtz layer with aggregates. This promotes rapid anion desolvation, forming an anion-derived CEI enriched in LiF. The resulting robust, ion-conductive CEI significantly enhances Li-SPAN cell electrochemical performance. 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. Advanced Science, EarlyView.