Iodine-doped sulfurized polyacrylonitrile with enhanced electrochemical performance for lithium sulfur batteries in carbonate electrolyte

Sulfurized polyacrylonitrile (S@pPAN), as a promising high-capacity cathode material, can completely solve the shuttling effect of lithium polysulfide and deliver reliable electrochemical performance in ester-based electrolyte. Until now, the inferior sulfur content, sluggish reaction kinetics and obscure reaction mechanism of the S@pPAN cathodes are still the critical hurdles for attaining their practical application. Herein, the iodine-doped sulfurized polyacrylonitrile (I-S@pPAN) prepared by a simple co-heating method exhibits good electrochemical performance in ester electrolyte. The electrochemical measurements and DFT calculation demonstrate that iodine-doping can effectively promote the electron and Li⁺ migration of S@pPAN. In-situ EIS spectra reveals the generated cathode electrolyte interface (CEI) layer, containing LiF and LiI, is beneficial to enhance the reaction kinetics. Ex-situ solid state NMR and XPS results demonstrate both -S_x- short-chain oligomers and double bonds (such as C[dbnd]N) in the composites can react with Li⁺ ions to provide capacity. The I-S@pPAN delivers a high reversible capacity of 1267 mAh g⁻¹ and good capacity retention of 85% after 1000 cycles at 2C. At a high C-rate of 8C (20.35 mA), the I-S@pPAN still achieves a reversible capacity of 1085 and 792 mAh g⁻¹ after 300 cycles. The proposed simple iodine-doping modification method and exploration of reaction mechanism may facilitate the practical application of S@pPAN cathodes.