Rational design of freestanding necklace-like ZnSe with double N-doped carbon layer protection for efficient sodium storage

ZnSe, as a promising electrode material for sodium storage, has a high theoretical capacity, low cost, and excellent physicochemical properties. The poor reaction kinetics and huge volume variation of ZnSe hinder its practical applications. Therefore, in this study, ZnSe electrode materials embedded in carbon nanofibers (ZnSe@NC@NCNFs) were synthesized through electrospinning and selenization using a Zn-based metal-organic framework (Zn-MOF) precursor. During the calcination process, the MOF-derived porous N-doped carbon layer wraps the ZnSe nanoparticles, and the one-dimensional (1D) carbon nanofiber forms a second N-doped carbon protective layer. The interwoven nanofibers can be severed as a freestanding electrode for sodium storage without conductive and binder agents. In situ X-ray diffraction (XRD) demonstrates the formation of irreversible NaZn₁₃ during the initial discharge process, which can act as sodiophilic sites and buffering matrices for subsequent Na⁺ insertion/extraction. The ZnSe@NC@NCNFs exhibit significant electrochemical performance for sodium storage with high reversible capacity and desired rate performance.