Porous Hollow Zno/Zns@N-Doped Carbon Heterostructures as Anodes for High Performance Sodium Ion Batteries

Abstract

Conversion-type anode, zinc oxide (ZnO), has been considered as one of the most promising materials for sodium ion batteries (SIB) because of its high theoretical capacities and an appropriate working potential. However, ZnO-based anodes suffer from huge volume change, poor electrical conductivity, and serious capacity decay during sodiation/desodiation process. Here, a hollow ZnO/ZnS heterostructure with nitrogen-doped carbon coating layer (ZnO/ZnS@NC) was rationally designed through a facile multistep strategy of template-involved sulfidation, etching, polydopamine (PDA) coating, and pyrolysis process. The heterostructure interface was demonstrated by HRTEM. XPS analysis indicated the existence of abundant covalent S-O bonds in ZnO/ZnS@NC, which might induce a built-in electric field in the heterostructure of oxide and sulfide. The N-doped carbon coating not only suppress zinc oxide aggregation, but also buffering volume change during charge/discharge process. Consequently, the ZnO/ZnS@NC heterostructures exhibit improved Na+ storage capacity compared with that of ZnO nanorods. Combined with in situ XRD, the conversation-alloy mechanism of ZnO/ZnS@NC heterostructure was disclosed. As anodes for SIBs, the hollow ZnO/ZnS@NC heterostructure exhibits better electrochemical performance than most reported zinc oxide-based anodes for SIBs. The in-situ disclosed reaction provides insights into electrochemcial sodiation mechanism of metal oxides and sulfides for sodium ion batteries.

Keywords: ZnO/ZnS heterostructure, Hollow structure, Anode material, Electrochemical performance, Sodium-ion batteries