Cleverly embedded CoS2/NiS2 on two-dimensional graphene nanosheets as high-performance anode material for improved sodium ion batteries and sodium ion capacitors

The CoS 2 /NiS 2 -RGO composite with excellent electrochemical performance is first used as an anode material for sodium-ion capacitors (SICs) and sodium-ion batteries (SIBs). CoS 2 /NiS 2 -RGO is prepared by one-step hydrothermal process. In half-cell tests, CoS 2 /NiS 2 -RGO exhibits a remarkably high reversible capacity of 473.7 mA h g −1 after 50 cycles at the specific current of 100 mA g −1 . SICs show an impressive energy density of 139.1 W h kg −1 at the power density of 14,000 W kg −1 , which has great advantages compare to the commercial lithium ion batteries. SIBs also show a good capacity of 50 mA h g −1 at a rate of 5 °C. The excellent electrochemical performance of CoS 2 /NiS 2 -RGO is mainly attributed to the heterostructure formed by CoS 2 and NiS 2 , which effectively improves the electrical conductivity. On the other hand, there is a good synergistic effect between RGO and CoS 2 /NiS 2 . The large specific surface area of RGO makes CoS 2 /NiS 2 disperse uniformly on the surface of RGO, preventing agglomeration and reducing particle size of CoS 2 /NiS 2 . In turn, CoS 2 /NiS 2 acting on the surface layer of RGO hinders the secondary overlap and increases the electrical conductivity of RGO. The mixed bimetallic sulfide/RGO system is expected to promote the rapid development of sodium storage devices.