Cu(2)Se Nanoparticles Encapsulated by Nitrogen-Doped Carbon Nanofibers for Efficient Sodium Storage

Cu(2)Se 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 Cu(2)Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu(2)Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu(2)Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu(2)Se 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 Cu(2)Se-NC for SIBs.