Engineering a Sulfur-Vacancy-Rich Binary Sulfides@Carbon Heterostructure Displaying Fast Reaction Kinetics in High-Performance Secondary Batteries.

Sodium-ion (Na-ion) batteries are currently restricted by nonideal anodes with poor reaction kinetics. Developing emerging anodes with vacancies and heterostructures would efficiently accelerate ion diffusion and electron transfer, thus improving the reaction kinetics, which still remains a big challenge. Herein, we develop a sulfur-vacancy-rich BiS/MoS@nitrogen-doped carbon (BiS/MoS@NC) heterostructure, which shows significantly improved kinetics and excellent performance as a Na-ion battery anode. The heterostructure working with sulfur vacancies enables high-speed ion diffusion and electron transfer by a synergistic effect of multiple regulations. The in situ Raman spectrum verifies the reversible conversion during charge-discharge, extended X-ray absorption fine structure (EXAFS) spectra show atomic dispersion and robust Bi-S bonds in the heterostructure, and electron paramagnetic resonance (EPR) spectra and density functional theory (DFT) calculations demonstrate the enhancement mechanism. The BiS/MoS@NC anode retains a high capacity of 304.5 mAh g after 1000 cycles at 1.0 A g and displays 273.3 mAh g after 3200 cycles at 10.0 A g, significantly exceeding the values of most reported sulfide anodes. The full cell constructed from a BiS/MoS@NC anode and a NaV(PO) cathode also displays good stability after 2000 cycles. Our findings provide a general approach to develop vacancy-rich heterostructures for high-performance batteries, and in-depth insights are important for uncovering mechanisms of some other energy-storage systems.