Regulating the Front-Line Orbital Energy Level Enables a High-Rate Performance for Lithium–Sulfur-Containing Polymer Batteries

Sulfur-containing polymers are promising cathode materials for lithium batteries, offering a novel pathway toward high-energy batteries. Moreover, tuning the frontier orbital energy levels of sulfur-containing polymers can accelerate the electrochemical reaction kinetics. Herein, an organic cathode material containing selenium is synthesized using a selenium sulfide solid solution via a previously proposed thiol-sulfur click chemistry reaction, which is a rubber-like material with good mechanical properties. According to front-line orbital theory, the introduction of a selenium group VI element like sulfur leads to sp3 hybridization and S–Se covalent bond formation. Owing to the electronegativity disparity between sulfur and selenium, electrons accumulate near sulfur atoms, creating nucleophilic sites and continuous negative regions that promote Li+ transport. As a result, the Li+ diffusion coefficient increases from 9.7 × 10–13 cm2 S–1 to 2.7 × 10–12 cm2 S–1. The bandgap narrows from 4.14 to 3.89 eV, facilitating the lithiation process and enhancing electrochemical performance. Among the cathode materials with different selenium contents, the fabricated materials exhibit a superior initial capacity of 580 mAh g–1 at 0.05 C and longer cycle stability. This study reveals how doping-modulated frontier orbital energy levels can be employed to enhance reaction kinetics, offering insights for improving sulfur containing polymers–lithium batteries’ performance.