Phenolic resin-based carbon microspheres for potassium ion storage

Potassium ion batteries (PIBs) have received widespread attention nearly four years due to sufficient potassium resources and similar chemical properties of potassium to lithium. Several works reported that N-doping on the carbon electrodes could efficiently improve the storage capacity of potassium ions. Herein, we synthesized two series of carbon spheres with the main difference is with or without N-doping. It is found that the storage of potassium ions is mainly determined by the crystal structure instead of N-doping. N-doping seems to affect the ion diffusion process, but the total capacity is still determined by the (0 0 2) lateral size of the carbon materials ( L a ). The specific capacity increases as L a increases. The N-doped carbon sphere with larger L a of 8.32 nm, delivers a higher reversible capacity of 241 mAh g −1 at a current density of 25 mA g −1 . And it still remains 121 mAh g −1 after 100 cycles at a current density of 100 mA g −1 .