Mo2N quantum dots decorating N-doped carbon nanosheets for kinetics-enhanced Li-S batteries

Abstract

Lithium-sulfur (Li-S) batteries face two main challenges, which are the severe shuttle effect of lithium polysulfides (LiPSs) and the slow redox kinetics of LiPSs. Herein, monodispersed Mo2N quantum dots decorating N-doped carbon nanosheets (Mo2N@NCNS) are rationally engineered via a simple and cost-effective method and used as an effective host for sulfur in high-performance Li-S batteries. Mo2N@NCNS presents enhanced intrinsic conductivity, superior catalytic capability, and improved LiPSs redox kinetics. The 3D N-doped carbon nanosheet networks endowed with abundant catalytic sites can heighten physically confined and chemically adsorptive LiPSs by strongly polar-polar interactions, further regulating the disordered motion of LiPSs. In the meanwhile, the highly dispersed Mo2N quantum dots with powerful adsorptive-catalytic properties anchor the soluble LiPSs and facilitate high-efficiency diffusion-conversion kinetics for the nucleation and deposition of Li2S2/Li2S, thus promoting the complete utilization of sulfur and the overall enhancement of electrochemical performance. Owing to these fascinating features, the Mo2N@NCNS-based sulfur cathodes demonstrate substantial enhancement in electrochemical performance, including remarkable capacity performance (1221 mAh g−1 at 0.2 C) and exceptional cyclability over 800 cycles at 2 C with a minimal decay rate (0.03 % per cycle). This work highlights the great potential of rational design of advanced composite materials for promoting the practical viability of Li-S batteries in energy storage systems.