Fabrication of Porous Carbon with Controllable Nitrogen Doping as Anode for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are a potential alternative for lithium-ion batteries (LIBs) due to the abundant reserves of potassium and the low redox potential of K+/K. Nonetheless, the practical application of PIBs is hampered by the fact that K+ has a large ion radium and cannot smoothly and reversibly insert/extract into the existing electrode materials. Herein, a series of nitrogen-doped porous carbon materials with varied N content are synthesized and the effect of nitrogen content on the performance of PIBs is investigated. It is demonstrated that the N content is not in direct proportion to the K-storage capacity of porous carbon considering the irregular change of specific surface area. Porous carbon with 12.44 at% N content (NPC-2) exhibits the best performance among the synthesized samples on account of its large specific surface area associated with the superior porous structure as well as abundant defects. It delivers a high reversible capacity of 385 mAh g(-1) at 0.05 A g(-1), remarkable rate performance of 218 mAh g(-1)at 2 A g(-1), and long-term cycling stability maintaining 242 mAh g(-1) after 800 cycles at 0.5 A g(-1). The quantitative kinetics analysis verify that the K-storage mechanism is mainly dominated by surface-driven capacitive controlled process, which explains the superior rate capability. The theoretical simulation of different types of nitrogen adsorption and density of states (DOS) prove that pyridinic-N and pyrrolic-N exhibit higher affinity to K atoms and thus N-doping is beneficial to the adsorption of K+ on the surface of electrode. This work provides a basic reference for the subsequent development of carbon anode materials for potassium-ion batteries.