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

Abstract

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.