Facile synthesis of Co9S8@NC anode with enhanced sodium storage and long cycling life

Transition metal sulfides (TMSs) are presently under extensive research and have been regarded as the prospective anode candidates for sodium ion batteries (SIBs). However, the poor intrinsic electrical conductivity and huge volume expansion of metal sulfides electrodes during the discharge-charge process eventually cause pulverization of active materials and quick capacity decay, which severely limit their further practical application. In this study, ultrafine Co₉S₈ nanoparticles embedded in N-doped carbon layer (Co₉S₈@NC) were facilely synthesized via a simple one-step solid phase calcination method with glucose as the carbon source and thiourea served as N, S-containing precursor. The Co₉S₈@NC hybrid with small nanoparticle size could aid in the quick penetration of the electrolyte and shorten the pathway of Na ions diffusion; Meanwhile, the N-doped disordered carbon layer could maintain structural integrity and favor the electron transport of the nanocomposite during the electrochemical reaction. The Co₉S₈@NC composite is firstly investigated as anode for SIBs. They exhibit a satisfied discharge/charge specific capacity of 285.3/276.3 mAh g^-1 after 160 cycles at 170 mA g⁻¹, and its discharge/charge specific capacity is capable to maintain 160.8/158.5 mAh g⁻¹ even after 1000 cycles at 1000 mA g⁻¹. Further kinetics analyses based on CV demonstrate that the partial pseudocapacitive behaviors partially accounts for the remarkable Na storage performances.