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Rich Self-Generated Phase Boundaries of Heterostructured VS4 /Bi2 S3 @C Nanorods for Long Lifespan Sodium-Ion Batteries.

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 VS4 /Bi2 S3 @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 VS4 /Bi2 S3 @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.