Cleverly embedded CoS_2/NiS_2 on two-dimensional graphene nanosheets as high-performance anode material for improved sodium ion batteries and sodium ion capacitors

摘要

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 syner-gistic 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.