CoS2@C nanospheres encapsulated in N-doped graphene oxide as high-performance anode for sodium-ion battery

Metal sulfides (MSs) exhibit great prospects as high-performance electrodes for sodium-ion batteries (SIBs), because of the excellent redox reversibility and relatively high theoretical capacity of the conversion-type electrochemical reaction. However, they suffer from intrinsic poor electrical conductivity and tremendous volume expansion during the Na+ insertion process, which would lead to sluggish reaction kinetic and severe capacity damping. Generally, designing hybrid structures with a secure framework, which could withstand the tension brought by the volume change, is an effective way to promote cycling stability. Besides, the carbonaceous material is considered to be an important additive, which can effectively elevate the electron/ion conductivity and realize the high-rate performance of the anode. Herein, a comprehensive 0-dimensional/2-dimensional (0D/2D) structure of carbon-coated CoS2 nanospheres encapsulated in reduced graphene oxide (denoted as CoS2@C/RG) is designed as anode material for SIBs. In the notable 0D/2D CoS2@C/RG structure, the nanoscale CoS2@C particles and RG nanosheets provide a high superficial area for Na+ insertion and shortened Na+ diffusion pathway. Furthermore, benefiting from the high conductivity and structural flexibility, the introduced RG supplies fast electron transportation channel and guarantees structural stability of the anode, which brings in improved reaction kinetic and structural stability. Consequently, the CoS2@C/RG electrode delivers a high specific capacity of 716.3 mAh/g at 0.2 A/g after 100 cycles, excellent rate performance, and stable cyclicity of 514.9 mAh/g at 5 A/g after 600 cycles. This work broadens the scope of rationally constructing comprehensive structures and may shed new light on MSs-based multidimensional anode material for SIBs.