Facile synthesis and electrochemical sodium storage of CoS2 micro/nano-structures

We report the synthesis and electrochemical sodium storage of cobalt disulfide (CoS2) with various micro/nano-structures. CoS2 with microscale sizes are either assembled by nanoparticles (P-CoS2) via a facile solvothermal route or nano-octahedrons constructed solid (O-CoS2) and hollow microstructures (H-CoS2) fabricated by hydrothermal methods. Among three morphologies, H-CoS2 exhibits the largest discharge capacities and best rate performance as anode of sodium-ion batteries (SIBs). Furthermore, H-CoS2 delivers a capacity of 690 mA.h.g(-1) at 1 A.g(-1) after 100 cycles in a potential range of 0.1-3.0 V, and similar to 240 mA.h.g(-1) over 800 cycles in the potential window of 1.0-3.0 V. This cycling difference mainly lies in the two discharge plateaus observed in 0.1-3.0 V and one discharge plateau in 1.0-3.0 V. To interpret the reactions, X-ray diffraction (XRD) and transmission electron microscopy (TEM) are applied. The results show that at the first plateau around 1.4 V, the insertion reaction (CoS2 + xNa(+) + xe(-) -> NaxCoS2) occurs; while at the second plateau around 0.6 V, the conversion reaction (NaxCoS2 + (4 - x) Na+ + (4 - x) e(-) -> Co + 2Na(2)S) takes place. This provides insights for electrochemical sodium storage of CoS2 as the anode of SIBs.