CoS2/N-doped Hollow Spheres as Anode Material for High Performance Sodium-Ion Batteries.

In this work, we first synthesized polyacrylic acid (PAA) spheres and used PAA as a template to load Co(OH) 2 particles on its surface. The product of CoS 2 nanoparticles dispersed in N-doped hollow spheres (N-HCS) was prepared through sulfurization treatment (CoS 2 /S@N-HCS). During the sulfuration process, S will penetrate into the PAA and be embedded in the graphite layer along with the carbonization process. It was found that during the charging and discharging process, the S in the carbon layer will gradually dissolve out, thereby forming new ion diffusion channels in the carbon spheres and exposing more CoS 2 active sites. CoS 2 /S@N-HCS composite exhibits a specific capacity of 729.6 mAh g -1 after 500 cycles at a current density of 1 A g -1 . The sodium storage mechanism and reaction kinetics of the materials were further measured by in-situ electrochemical impedance spectroscopy, ex-situ X-ray diffraction, capacitance performance evaluation and galvanostatic intermittent titration technique. The excellent cycling performance and rate capability demonstrated that the CoS 2 /S@N-HCS is a potential and prospective anode material for sodium-ion batteries.