Harnessing iodine doping to unlock high-loading SPAN dry-electrode for practical Li–S batteries

Abstract

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for high-loading lithium–sulfur batteries owing to its inherent ability to suppress the shuttle effect. However, they undergo severe volume changes during cycling. Fabrication of dry electrodes can mitigate this issue by providing structural integrity and mechanical robustness while enabling high-loading electrodes without binder migration or conductive material aggregation due to the elimination of solvent evaporation. Despite these advantages, the nonpolar nature of the polytetrafluoroethylene (PTFE) binder limits Li⁺ affinity and ion transport. Herein, we introduce an iodine-doped SPAN (I-SPAN), in which the incorporation of iodine creates an electron-rich environment that enhances Li⁺ adsorption and diffusion. The dissolution of iodine into the electrolyte triggers nucleophilic substitution with PF₆^–, forming a LiF/LiI-rich cathode–electrolyte interphase (CEI) that lowers the interfacial resistance and improves structural stability. Consequently, solvent-free I-SPAN dry electrodes with 90 wt% active material deliver an areal capacity of 22.6 mAh cm^-2 at a loading of 42.4 mg_AM cm^-2 and a rate of 0.05 A g_AM^-1. In addition, at a loading of 8.8 mg_AM cm^-2, the dry electrode maintained a reversible capacity of approximately 4.0 mAh cm^-2 even at a high current density 0.5 A g_AM^-1.