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

## TL;DR

This paper introduces quaternized chitosan to stabilize the cathode-electrolyte interface in lithium-sulfur batteries, significantly improving their performance and cycle life.

## Contribution

The novel use of quaternized chitosan to selectively modify the cathode-electrolyte interphase in Li–SPAN batteries is introduced.

## Key findings

- SPAN@QCS-1.0% cathode achieves 1499 mAh g−1 discharge capacity and 902 mAh g−1 at 10 C.
- SPAN cells with high sulfur loading and lean electrolyte deliver 17.1 mAh cm−2 areal capacity.
- A 0.9 Ah pouch-cell prototype cycles stably for over 30 cycles.

## 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 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.