Anion Doping and Dual-Carbon Confinement Strategies to Synergistically Boost the Sodium Storage Performance of Cobalt-Based Sulfides.

Cobalt-based sulfides (CSs) are generally regarded as potentially valuable anode materials for sodium-ion batteries (SIBs) due to their excellent theoretical capacity and natural abundance. Nevertheless, their slow reaction kinetics and poor structural stability restrict the practical application of the materials. In this study, the dual-carbon-confined Se-CoS@NC@C hollow nanocubes with anion doping are synthesized using ZIF-67 as the substrate by resorcin-formaldehyde (RF) encapsulation and subsequent carbonization and sulfurization/selenization. RF- and ZIF-67-derived dual-carbon skeleton hollow structures with a robust carbon skeleton and abundant internal space minimize cyclic stress, mitigate volume changes and maintain the structural integrity of the material. More importantly, Se doping increases the lattice spacing of CoS, weakens the strength of Co-S bonds, and modulates the electronic structure around Co atoms, thereby optimizing the adsorption energy of the material. As a result, the hollow nanocubes of Se-CoS@NC@C demonstrates excellent electrochemical performance as the anode for SIBs, delivering a high reversible capacity of 549.4 mAh g at 0.5 A g after 100 cycles and a superb rate performance (541.1 mAh g at 0.2  A  g, and 393.3 mAh g at 5 A g). This study proposes a neoteric strategy for synthesizing advanced anodes for SIBs through the synergy of anion doping engineering and dual-carbon confinement strategy.