Rich Self‐Generated Phase Boundaries of Heterostructured VS4/Bi2S3@C Nanorods for Long Lifespan Sodium‐Ion Batteries

Abstract Rationally designing on sundry multiphase compounds has come into the spotlight for sodium‐ion batteries (SIBs) due to enhanced structural stability and improved electrochemical performances. Nevertheless, there is still a lack of thorough understanding of the reaction mechanism of high‐active phase boundaries existing between multiphase compounds. Here, a VS 4 /Bi 2 S 3 @C composite anode for SIBs with rich phase boundaries in heterostructure is successfully synthesized. In situ X‐ray diffraction analyses demonstrate a multistep redox mechanism in the heterostructures and ex situ transmission electron microscopy results confirm that tremendous self‐generated phase boundaries are obtained and well‐maintained during cycling, dramatically leading to stable reaction interfaces and better structural integrity. Combining experimental and theoretical results, a self‐built‐in electric field forming between phase boundaries acts as a dominate driving force for Na + transport kinetics. Benefiting from the fast reaction kinetics of phase boundaries, the heterojunction provides an efficient approach to avoid abnormal voltage failure. As expected, the VS 4 /Bi 2 S 3 @C heterostructure displays superior sodium storage performances, especially an excellent long‐term cycling stability (379.0 mAh g −1 after 1800 cycles at a current density up to 2 A g −1 ). This work confirms a critical role of phase boundaries on superior reversibility and structural stability, and provides a strategy for analogous conversion/alloying‐type anodes.