Interfacial synergy in twinborn CoS2/CoS1.097 heterojunction to promote sulfur conversion kinetics in lithium-sulfur batteries

Abstract

The rational design of sulfur hosts is essential for mitigating the shuttle effect of lithium polysulfides (LiPSs) and improving the sluggish conversion kinetics of sulfur during multi-step phase transition. Herein, a twinborn CoS2/CoS1.097 heterojunction encapsulated in N-doped hollow carbon polyhedrons and in-situ generated CNTs (CoS2/CoS1.097@NC/CNT) was elaborately synthesized and utilized as the electrocatalyst in sulfur cathodes. The CoS2/CoS1.097 heterojunction provides abundant chemisorption sites that facilitate the formation of chemical bonds with polysulfides, thereby effectively adsorbing LiPSs. More importantly, the spontaneously generated internal electric field at the CoS2/CoS1.097 interface accelerates electron transfer, which promotes the reversible transformation between LiPSs and Li2S. Additionally, the hollow carbon polyhedrons and grafted CNTs not only effectively confine sulfur, but also provide extra buffer space for the sulfur evolution reaction. Benefiting from these characteristics, the battery assembled with CoS2/CoS1.097@NC/CNT/S cathode exhibits a remarkable initial capacity of 1454.4mAh/g at 0.1C), excellent rate capability of 674.7mAh/g at 4C, and outstanding capacity retention of 604.7mAh/g over 500 cycles at 2C (∼73.1 % of initial capacity).