Synergistic Heterointerface Coupling Enables Long‐Life Sn‐Based Anodes for Na‐Ion Batteries

Developing high‐capacity and high‐rate anodes for Na‐ion batteries (NIBs) is important for practical use. Conventional hard carbon (HC) anodes exhibit good cycling performance, but the low specific capacity and potential Na plating pose significant challenges for their use in high‐energy NIBs. Sn‐based anodes, with appropriate Na storage potential and high capacity, hold great promise for high‐performance NIBs. However, sluggish alloying kinetics and dramatic volume changes cause limited cycling life due to particle pulverization and repeated rupture of the solid electrolyte interphase (SEI). Here, a mechanical ball‐milling process is used to construct a coupling heterointerface in the Sn/HC composite anode. The chemical–electrochemical coupling between Sn and HC significantly lowers the alloying reaction barrier, enhances reversibility, and establishes additional rapid ion‐transport pathways at the interface, thereby boosting reaction kinetics and stability. Simultaneously, local electrochemical‐potential modulation effectively suppresses Sn volume expansion and stabilizes the SEI. As a result, the Sn/HC composite anode achieves over 12 000 cycles at current densities of 1.7 and 4.2 A g ⁻¹ . This study elucidates the role of constructing a rational chemical–electrochemical coupling heterointerface in addressing complex issues for alloy‐based anode materials in high‐energy applications.