Nitrogenated holey graphene C2N monolayer anodes for lithium- and sodium-ion batteries with high performance

Abstract

The experimentally synthesized layered nitrogenated holey graphene (C2N) nanosheets possess intriguing properties, having broad applications such as in metal-ion batteries and catalysis. However, its impurity and lack of C2N monolayers in experiments and the failed classic method of one single atom searching the stable adsorption site(s) of metal ions on C2N in simulations greatly hinder their mechanistic study, limiting their further development. Herein, by proposing a new particle pair adsorption model and employing first-principles calculations, we investigated mechanisms of the C2N monolayer as a high-performance anode material for sodium-(Na-) and lithium-(Li-) ion batteries. The maximum theoretical capacities of Na and Li ions approach to 2469 and 2939 mA h g−1, respectively, which are 6–8 times larger than those of graphite. A stable multilayer adsorption behavior was found. Based on the results of charge density difference, electron localization function and Bader charge analysis, the microscale mechanism is that the channels between C2N and metal atoms are built up for electron transfer, increasing their interactions. We proposed a new particle (atom) pair diffusion model and found that the metal ions have two stage diffusions. The metallic feature of the monolayer/metal ions complex and the low diffusion barriers of metal ions on the monolayer are the origins of the fast charge/discharge process in the battery. The C2N monolayer also possesses advantages of low average open-circuit voltages (~ 0.45 V) and excellent cycling stability. The work provides fundamental insights for the design and innovation of high-performance energy storage materials.