Stability and reaction thermodynamics of boron-doped nitrogenated holey graphene (NHG) monolayers and their energy storage properties for Li, Na and K-ion batteries: A first principles investigation

Abstract

A comprehensive first principles investigation is performed to address the stability, reaction thermodynamics and the electrochemical properties C2N1−xBx and C2B monolayers for the use as the anodes in alkali metal ion batteries (Li, Na and K). The formation of C2N1−xBx structures in terms of the substituting of N in C2N monolayer by B atom is found to the thermodynamically spontaneous above the room temperature. The reaction thermodynamics in the combination with the first principles molecular dynamics simulations confirm the optimal experimental conditions for the preparation of C2N1−xBx or C2B should be a reaction directly between C2N and B element at the moderately high temperature in the range from 500 K to 900 K in the vacuum. For the electrochemical properties, the B-doped C2N show a systematic improvement on theoretical capacities, open circuit voltages and ion diffusion dynamics over those of C2N especially for B-rich C2N1−xBx structures. Nevertheless, owing to its small molar mass and less prominent adsorption site preferences, the overall electrochemical performances of C2B are much superior to those of C2N and ternary C2N1−xBx. Specifically, the theoretical capacities of C2B are predicted to be Li (1546 mAh/g), Na (663 mAh/g) and K (411 mAh/g), respectively. The migration energy barrier heights of C2N1−xBx and C2B are found to be much lower than those of C2N monolayer for the favorable diffusion pathways. Overall, the C2B monolayer is considered as a new 2-D structural platform to provide the high theoretical capacities and small migration energies as the anodes for the alkali metal ion batteries.