Dual anionic doping strategy towards synergistic optimization of Co9S8 for fast and durable sodium storage

Cobalt sulfides with high capacities and excellent redox activities have attracted comprehensive attention as promising anode materials for sodium-ion batteries (SIBs). However, the poor conductivity and large volume change during sodium storage render them an unprecedented challenge to rate capability and cycling stability. Herein, a dual anionic (N and Se) doping strategy is first proposed in the preparation of Co9S8 (N,Se-Co9S8) with structural and electronic optimization as anode material for SIB. It has been revealed that N doping can increase the electron density of Co9S8 at the Fermi level while Se doping could expand the lattice spacing and lower Co-S binding energy; the synergistic combination of N and Se enables Co9S8 to possess high conductivity, good Na+affinity, and effective Na+diffusion, leading to fast reaction kinetics and energetically stable performance upon charging/discharging. In consequence, the N,Se-Co9S8 delivers an exceptionally high capacity of 550 mAh g−1 at a current density of 0.1 A g−1, conspicuous rate performance of 411 mAh g−1 at 5 A g−1, and good cycling stability with a retained capacity of 406 mAh g−1 over 3000 cycles at 5 A g−1, among the best results of reported SIB anodes. The dual anionic doping strategy provides an efficient way to synergistically manipulate electrode materials for high-performance sodium ion storage.