Carbon shell encapsulated cobalt phosphide nanoparticles embedded in carbon nanotubes supported on carbon nanofibers: A promising anode for potassium ion battery.

Despite transition metal phosphide (TMP)-based hybrid structures demonstrating desirable results for potassium ion battery applications, most of their preparation methods require complex multi-step procedures. Herein, a three-dimensional (3D) structural material in which amorphous carbon (AC) encapsulated CoP nanoparticles are embedded at the top of nitrogen-doped carbon nanotubes derived from ZIF-67/ZIF-8 grown on the surface of carbon nanofibers (AC@CoP/NCNTs/CNFs) is reported for the first time. The CoP acts as a core and the amorphous carbon layer acts as a shell, which restrains the volume expansion of active materials during charging and discharging. Furthermore, the carbon nanofiber network can improve the conductivity, and doped nitrogen can increase active sites. As a result, the electrochemical properties of the potassium ion battery are enhanced when an AC@CoP/NCNTs/CNFs nanocomposite is used as the anode electrode, and the electrode exhibits a reversible capacity of 247 mA h g after 1000 cycles at 0.8 A g in a potassium ion battery.