Sugar gourd-like amorphous carbon coated CoS/Co9S8 nanoparticles anchored on carbon nanotubes for potassium-ion batteries

Transition metal sulfides (TMSs) with high theoretical capacity have been recognized as potential anode materials for potassium ion batteries (PIBs). However, TMSs undergo strong volume changes during charge/discharge, which can be solved by combining with carbon materials and rational structural design. Herein, sugar gourd-like amorphous carbon coated CoS/Co₉S₈ nanoparticles anchored on carbon nanotubes (CoS/Co₉S₈/CNTs-C) are prepared by constructing novel nanostructures. The amorphous carbon-coated layer as the “sugar coating” acts as a fixation to mitigate the volume expansion and agglomeration of the CoS/Co₉S₈ nanoparticles, while the carbon nanotubes as a support provide a robust framework that enhances conductivity, resulting in composites with strong structural stability and outstanding electrochemical performance. With the benefit of the unique sugar gourd-like structure, the CoS/Co₉S₈/CNTs-C-0.2 composites exhibit favorable cycling stability at 100 mA g⁻¹ with 331.7 mAh g⁻¹ after 500 cycles and impressive rate performance (653.7 mAh g⁻¹ at 50 mA g⁻¹ and 367.9 mAh g⁻¹ at 2000 mA g⁻¹). Moreover, density functional theory calculations indicate that the improved electrochemical reaction kinetics of CoS/Co₉S₈/CNTs-C comes from the stronger adsorption energy for K⁺. Furthermore, CoS/Co₉S₈/CNTs-C-0.2 exhibits favorable electrochemical performance in full cells, which proved the significance of its practical applications.