Sulfurized Polyacrylonitrile for High-Performance Lithium-Sulfur Batteries: In-Depth Computational Approach Revealing Multiple Sulfur's Reduction Pathways and Hidden Li

Like no other sulfur host material, polyacrylonitrile-derived sulfurized carbon (SPAN) promises improved electrochemical performance for lithium-sulfur batteries, based on its compatibility with carbonate solvents and ability to prevent self-discharge and shuttle effect. However, a complete understanding of the SPAN's lithiation mechanism is still missing because its structural features vary widely with synthesis conditions, and its electrochemical performance deviates from elemental sulfur. This study continues our research on the elucidation of the SPAN's structural characteristics and lithiation mechanisms via computational approaches. Our models reproduce most experimental data regarding carbon's graphitization level and conjugated ordering, sulfur-carbon covalent bonding, sulfur loading, and elemental composition. Our simulations emulate the discharge voltage observed in experiments for the first discharge, which reveals that sulfur follows multiple reduction pathways based on its interaction with the carbon backbone. Sulfur reduction takes place above 1.0 V vs Li/Li