Stable C-Se-Co interface of CoSe₂@N-doped carbon aerogels for efficient sodium storage

The storage characteristics of sodium ions in CoSe₂ are intricately linked to the doping species and concentrations of heteroatoms within the carbon matrix. However, a systematic study of the impact of heteroatom doping on the interfacial forces between the carbon matrix and CoSe₂ has not been systematically investigated. In this work, CoSe₂ nanoparticles coated with different heteroatom doping (N/S) carbon aerogels derived from sodium alginate (SA) were constructed to investigate the influence of dopant atoms on the interfacial forces at the C matrix and CoSe₂ interface. The confinement effect of Co-SA-NH₂ junction zones facilitates the formation of stable C-Se-Co interface. The higher pyridinic nitrogen can promote the reinforced interfacial connection of CSe bond, further decreasing the interface distance between CoSe₂ and N-doped carbon aerogels (NCA) to 3.00 Å, alleviating the interfacial volume expansion to 15 %, thus increasing the sodium ion migration rate and cycling stability. However, the addition of sulfur inhibits the transformation of other nitrogen species into pyridinic nitrogen. Furthermore, sulfur shares the same valence electron configuration as selenium, it replaces selenium in the CSe bond position, thereby reducing the conductivity and stability of the interface. As a consequence, CoSe₂@N-doped carbon aerogels (CoSe₂@NCA) exhibits the lowest sodium diffusion barrier (1.10 eV) and the highest sodium ion negative adsorption energy (-2.21 eV). As expected, CoSe₂@NCA delivers superior long-term cycling performance (519 mAh g^-1 at 1.0 A g^-1 after 800 cycles) and excellent reversible capacity at high current density (474 mAh g^-1 at 5.0 A g^-1).