Decoupling Dual Regulatory Roles and Mechanisms of Bismuth in Low‐Carbon‐Content Sn Anode for Fast and Stable Sodium Storage

Sn/C nanocomposite with low carbon content is a promising anode for high‐energy density sodium‐ion batteries (SIBs), but suffers from Sn spillage from the carbon skeleton during annealing and the spontaneous agglomeration of Sn nanoparticles during cycling, resulting in poor cycling stability and rate performance. Herein, a bimetallic entanglement evolution strategy is proposed and a unique phase‐separated Sn/Bi heterostructures encapsulated by porous carbon skeleton (Sn/Bi@C) with a low carbon content of only ≈11.1% is rationally designed and synthesized. The introduced bismuth not only effectively inhibits nanoparticles from overflowing the carbon skeleton during annealing process by forming heterostructures and robust Bi─O─C bonds, but also reverses spontaneous nanoparticles agglomeration during cycling based on in situ nanosizing process due to the complex phase transitions and negative work of separation of heterostructures, which significantly improves the structural stability and accelerates reaction kinetics. Therefore, Sn/Bi@C exhibits excellent rate performance and long cycle life in half/full cell. The dual regulatory roles and mechanisms of bismuth for structure formation and evolution are studied in detail, providing a constructive view for the design of high‐performance alloy anodes for SIBs.