Boosted Sodium Storage Performance by Iron Doping in Hybrid Spheres of Cobalt Selenide/Carbon Composite Anode

Cobalt diselenide (CoSe 2 ) has stimulated increasing research interest in the field of sodium-ion batteries (SIBs) because of its relatively high theoretical capacity and affordable cost. Nevertheless, its sodium storage performance and practical application are largely hampered by inferior electrical conductivity, severe volumetric variation, and pulverization during the repeated cycling process. In this work, we report the fabrication of hybrid spheres of Fe-doped CoSe 2 embedded in a carbon shell (denoted as Fe-CoSe 2 /C), which uses a facile solvothermal and subsequent carbonization/selenization approach. The carbon shell produced from the precursor of CoFe-glycerate (CoFe-Gly) effectively enhances the electrical conductivity and mitigates the structural stress, while the modulated doping of certain amounts of Fe in CoSe 2 facilitates the transfer of electrons and the diffusion of ions in the composite. As a result, the optimal Fe-CoSe 2 /C-2 electrode exhibits good rate performance (388 mAh g −1 at 5 A g −1 ) and outstanding cycling durability (501 mAh g −1 at 1 A g −1 after 500 cycles, retention of 93.5%), suggesting the great potential of Fe-CoSe 2 /C hybrid spheres to serve as promising anode materials for high-performance SIBs. Graphical Abstract