Electrochemically Activated α→β Phase Transition in Space‐Confined MnO/MnSe‐Based Heterostructure Enabling Exceptional Li/Na‐Ion Storage

The advancement of conversion‐type anodes for Li/Na‐ion batteries necessitates innovative strategies to synergistically address sluggish kinetics and structural degradation. Herein, a rational multi‐scale engineering paradigm is proposed by constructing a MnO/MnSe‐based heterostructure space‐confined in a hierarchical carbon matrix. Such architecture synergizes oxygen vacancy (Vo) engineering, in situ phase‐transition‐driven heterointerface reconstruction, and dual‐carbon space confinement. Systematic selenization control enables the formation of Vo‐rich MnO coupled with metastable α‐MnSe, which undergoes irreversible electrochemical transformation to conductive β‐MnSe during initial cycling, creating dynamically stabilized heterointerfaces with optimized charge redistribution. First‐principles calculations reveal that the α→β phase transition is thermodynamically driven by interfacial energy minimization, and the newly formed β‐MnSe demonstrates robust structural stability and significantly enhanced Li/Na electrochemical kinetics. The space‐confined carbon (scC) framework, integrating pyrolytic carbon and graphene confinement, orchestrates ion/electron highways while alleviating mechanical stress. The optimized MnO‐Vo/β‐MnSe@scC delivers exceptional rate capability and cycling performance, surpassing current state‐of‐the‐art Mn‐based anodes. This work establishes a universal materials design philosophy that couples phase transition manipulation, defect modulation, and heterointerface engineering with space hierarchical carbon confinement, providing transformative insights into overcoming intrinsic limitations of conversion materials for next‐generation high‐power energy storage systems.