Insight into MoS2–MoN Heterostructure to AcceleratePolysulfide Conversion toward High-Energy-DensityLithium–Sulfur Batteries

摘要

Lithium-sulfur batteries are deemed as optimal energy devices for the next generation of high-energy-density energy storage. However, several problems such as low energy density and short cycle life hinder their application in industry. Here, MoS2-MoN heterostructure nanosheets grown on carbon nanotube arrays as free-standing cathodes are reported. In this heterostructure, MoN works as a promoter to provide coupled electrons to accelerate the redox reaction of polysulfides while the MoS2, with a two-dimensional layered structure, provides smooth Li+ diffusion pathways. Through their respective advantages, both MoN and MoS2 could mutually boost the process of "adsorption-diffusion-conversion" of polysulfides, which have a synergy enhancement effect to restrain the lithium polysulfides from shuttling. The designed cathodes show excellent long-term cycling performances of 1000 cycles at 1C with a low decay rate of 0.039% per cycle and a high rate capability up to 6C. A high initial areal capacity of 13.3 mAh cm(-2) is also achieved under a low electrolyte volume/sulfur loading (E/S) ratio of 6.3 mL g(-1). This strategy of promoting polysulfide conversion by heterostructure MoS2-MoN as presented in this work can provide a more structured design strategy for future advanced Li-S energy storage systems.