Defective graphene coating-induced exposed interfaces on CoS nanosheets for high redox electrocatalysis in lithium-sulfur batteries

Abstract

Herein, we propose the construction of sandwich-structured hosts filled with continuous 3D catalysis-conduction interfaces. The RG@CoS@C-C-RG@CoS@C architecture enables fast electron and Li+ diffusion, strong adsorption of S/Li2Sx and high-efficiency conversion on two-sided RG@CoS surfaces. With detailed experimental and theoretical characterization, we reveal that although the conformal graphene coating largely shields the catalytic activity and adsorbing ability of CoS nanosheets, the exposed interfaces of CoS at the defective sites of the graphene coating exhibit especially strong lithium polysulfide (LiPSs) anchoring and high conversion efficiency, with high-flux Li+ and electron transfer from the circumjacent graphene coating and the buried carbon nanofibers. Furthermore, the exposed interfaces exhibit an effective decrease in Li2S decomposition by releasing Li+ onto the circumjacent graphene surface with a low Li+ diffusion barrier and anchoring the remaining Li-S bond on the exposed CoS interface with a high adsorption energy. The unique structure consisting of catalytic CoS nanosheets, defective RG coating, and interwoven C fiber interlayers enables not only the coupling of Li+ diffusion and electron transfer but also efficient regulation of the polysulfide reaction, thereby producing a synergistic catalyzing effect on both LiPS conversion and Li2S decomposition. As a result, the batteries with RG@CoS@C membranes as interlayers exhibit stable cycle performance and reversible capacities of 629.2 mA h g−1 after 420 cycles at 2.0 C. The proposed strategy will contribute to guiding the design of novel composite materials for high-performance Li-S batteries.