Conductive Short‐Chain Sulfur Composites with Ultra‐High Sulfur Content as High‐Capacity Anode Materials for Na/K‐Ion Batteries

Abstract Short‐chain sulfur species with high redox activity have significant applied implications as electrode materials for Na/K‐ion batteries. However, the synthesis of short‐chain sulfur composites that simultaneously feature high sulfur content and high conductivity remains a significant challenge. Herein, the facile fabrication of conductive short‐chain sulfur composite with ultra‐high sulfur content (42.5 wt%) for efficient Na/K‐ion storage is reported. The protocol relied only on the industrial pitch and elemental sulfur as precursor via a simple heat treatment at low temperature (e.g. 450 °C). Rich delocalized C═C and C═S bonds are introduced into the carbon skeleton, forming the spatial π‐electron conjugation and spatial sp 2 ‐hybridization, and resulting in a six‐order‐of‐magnitude enhancement of the electronic conductivity compared to the pitch‐derive carbon. The short‐chain sulfur species demonstrate superb reactivity with both Na‐ion and K‐ion without dissoluble polysulfide formation. A surface‐dominated storage mechanism enables outstanding electrode kinetics with diminished electrode deformation. As anodes, this composite delivers extraordinary reversible capacities for both Na‐ion (848 mAh g −1 ) and K‐ion (699 mAh g −1 ) storage with superior rate and promising cyclability. Moreover, this anode could even deliver impressive battery performances for K‐ion storage at a high mass loading (10.2 mg cm −2 ) of the active composite.