Hierarchical Nitrogen-Doped Graphitic Carbon Spheres Anchored with Amorphous Cobalt Nanoparticles as High-Performance and Ultrastable Anode for Potassium-Ion Batteries

As one of the most promising electrochemical energy-storage devices after lithium-ion batteries, potassium-ion batteries (KIBs) have been restricted by the limited capacity of carbon-based anodes. Herein, we design and prepare three-dimensional nitrogen-doped graphitic carbon spheres anchored with cobalt nanoparticles (CoNC) via self-sacrifice template method. The CoNC spheres exhibit a uniform spherical morphology with an inner hierarchical structure. The final calcination temperature is changed to obtain CoNC-700, CoNC-800, and CoNC-900, in which CoNC-700 is verified to combine amorphous cobalt nanoparticles with graphitic carbon spheres successfully and presents excellent rate capability and good potassium-storage performance. Nitrogen-doping and amorphous cobalt nanoparticle-loading can effectively introduce rich defects to the CoNC electrode, enhance electrical conductivity, and accelerate potassium-storage kinetics, which leadto a reversible specific capacity of 382 mA h g–1 at a current density of 0.5 A g–1 and 330 mA h g–1 at a current density of 1 A g–1 after 1000 cycles, suggesting the potential of the high-capacity, ultrastable anode for potassium-ion batteries.