Carbon-coated mesoporous Co9S8 nanoparticles on reduced graphene oxide as a long-life and high-rate anode material for potassium-ion batteries

Carbon-coated mesoporous Co9S8 nanoparticles supported on reduced graphene oxide (rGO) are successfully synthesized by a simple process. This composite makes full use of the protection of the carbon layer on the surface, the good conductivity and three-dimensional (3D) structure of rGO, the mesoporous structure and nanoscale size of Co9S8, thereby presenting the excellent electrochemical performances in potassium-ion batteries, 407.9 mAh center dot g(-1) after 100 cycles at 0.2 A center dot g(-1) and 215.1 mAh center dot g(-1) at 5 A center dot g(-1) in rate performances. After 1,200 cycles at 1.0 A center dot g(-1), this composite still remains a capacity of 210.8 mAh center dot g(-1). The redox reactions for potassium storage are revealed by ex-situ transmission electron microscope (TEM)/high-resolution TEM (HRTEM) images, selected area electron diffraction (SAED) patterns and X-ray photoelectron spectroscopy (XPS) spectra. The application of this composite as the host of sulfur for Li-S batteries is also explored. It sustains a capacity of 431.8 mAh center dot g(-1) after 800 cycles at 3 C, leading to a degradation of 0.052% per cycle. These results confirm the wide applications of this composite for electrochemical energy storage.