Cu₂Se Nanoparticles Encapsulated by Nitrogen-Doped Carbon Nanofibers for Efficient Sodium Storage

Cu₂Se with high theoretical capacity and good electronic conductivity have attracted particular attention as anode materials for sodium ion batteries (SIBs). However, during electrochemical reactions, the large volume change of Cu₂Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu₂Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu₂Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu₂Se with a short Na⁺ diffusion path and provides a protective matrix to accommodate the volume variation. The kinetic analysis and D_Na+ calculation indicates that the dominant contribution to the capacity is surface pseudocapacitance with fast Na⁺ migration, which guarantees the favorable rate performance of Cu₂Se-NC for SIBs.