Ultrahigh Nitrogen Doping of Carbon Nanosheets for High Capacity and Long Cycling Potassium Ion Storage

Potassium-based energy storage devices (PESDs) are promising candidates for large-scale energy storage applications owing to potassiums abundant in nature, the low standard redox potential (−2.93 V for K/K⁺ vs the standard hydrogen electrode) of potassium (K), and high ionic conductivity of K-ion based electrolytes. However, lack of proper cathode and anode materials hinder practical applications of PESDs. In this work, carbon nanosheets doped with an ultrahigh content of nitrogen (22.7 at%) are successfully synthesized as an anode material for a K-ion battery, which delivers a high capacity of 410 mAh g⁻¹ at a current density of 500 mA g⁻¹, which is the best result among the carbon based anodes for PESDs. Moreover, the battery exhibits an excellent cycling performance with a capacity retention of 70% after 3000 cycles at a high current density of 5 A g⁻¹. In situ Raman, galvanostatic intermittent titration, and density functional theory calculations reveal that the ultrahigh N-doped carbon nanosheet (UNCN) simultaneously combines the diffusion and pseudocapacitive mechanisms together, which remarkably improves its electrochemical performances in K-ion storage. These results demonstrate the good potential of UNCNs as a high-performance anode for PESDs.