Synergistic Dual-Confinement Effect: Merit of Hollowly Metallic Co9S8 in Packaging Enhancement of Electrochemical Performance of Li–S Batteries

Abstract

Lithium–sulfur (Li–S) batteries have become a powerful alternative for lithium-ion batteries due to their high energy density and high specific capacity. However, several problems still hinder its practical application, such as poor electron conductivity, large volumetric expansion, and severe shuttle effect. To overcome these obstacles, a metallic and polar sphere-like Co9S8 with high electron conductivity is designed and prepared. Merited from a large chemical affinity and improved integration with polar polysulfides (LiPSs), Co9S8 enables chemically immobilizing LiPSs effectively with an improved cycle life of Li–S batteries. Besides, the hollow sphere structure can physically block the diffusion of LiPSs into electrolyte. Sufficient internal space can accommodate more active materials and mitigate the volume expansion. The high electron conductivity of Co9S8 facilitates improving of electrochemical reaction kinetics. Thus, serving as host material for Li–S batteries, the Co9S8 electrode exhibits a high initial specific capacity of ∼1200 mAh/g at 0.1 C and the discharge specific capacity retains 570 mAh/g after 100 cycles at 0.5 C.