Covalent sulfur/CoS2-decorated honeycomb-like carbon hierarchies for high-performance sodium storage with ultra-long high-rate cycling stability

Transition metal sulfides (TMSs) with high theoretical sodium storage capacity have been regarded as one of the most competitive and promising anode materials for sodium-ion batteries. Nevertheless, great chal-lenges still exist for TMS to achieve long-cycle life owing to the poor conductivity and volume expansion during the sodiation/desodiation process. The conventionally used pure carbon coating method can ef-fectively solve the above problems. However, the low sodium ion storage capability of carbon will decrease the capacity of the anode. Thus the functionalization of well-designed carbon nanostructures with exotic elements (e.g., sulfur) or high-specific-capacity materials has been regarded as an efficient route to enhance sodium storage performance. Herein, we developed a facile strategy to incorporate covalent sulfur and CoS2 nanoparticles into honeycomb-like carbon matrices (denoted as S/CoS2@C), where sulfur is vaporized under vacuum and reacted with the Co-decorated carbon hierarchies, leading to the formation of CoS2 nano-particles as well as the covalent C-Sx-C bonds. Consequently, the as-prepared S/CoS2@C composite de-monstrates excellent sodium storage performance, with high initial coulomb efficiency (ICE) of 83 % and capacity retention of 95 % (478.5 mAh g-1) after 700 cycles at 0.2 A g-1, and an outstanding high-rate long-term cycling stability with a high reversible capacity of 396.1 mAh g-1 after 5000 cycles at 2 A g-1 (an average decay rate of only 0.0014 %). Furthermore, electrochemical analyses reveal that both covalent sulfur and CoS2 contribute to the sodium storage capacity via a predominantly surface-induced capacitive process, and the well-designed S/CoS2@C composite with encapsulation of covalent sulfur and CoS2 into the highly interconnected porous carbon matrices efficiently buffer the volume changes and well maintain the elec-trode integrity/conductivity upon sodiation/desodiation cycling.(C) 2023 Elsevier B.V. All rights reserved.