2D novel C5N2 allotropes: High-performance anode materials for alkali metal ion battery

Two-dimensional (2D) CN compounds have been extensively investigated for alkali metal ion batteries, and the known materials still manifest certain shortcomings when used as anode. Therefore, we predicted three novel 2D CN compounds, specifically C5N2 allotropes, and explored their potential as anode materials for alkali metal ion batteries by first-principles calculations. The calculated results of phonon spectrum and ab-initio molecular dynamics revealed that all three C5N2 allotropes are kinetic and thermodynamic stability. In addition, all the allotropes possess excellent mechanical properties (362.96–363.85 N m−1) and metallic properties, along with strong adsorption capabilities for Li, Na, and K. Crucially, they all exhibit good ion diffusion properties for Li, Na, and K, especially in C5N2-b and C5N2-c (the diffusion barrier of Li, Na, and K on C5N2 are 0.242 eV on C5N2-b, 0.166 eV on C5N2-c, and 0.146 eV on C5N2-c, respectively). Besides, the C5N2 allotropes show a high theoretical storage capacity (913.68 mAh g−1 for Li/Na, 837.54 mAh g−1 for K), along with a suitable voltage platform. These findings prove that the three novel C5N2 allotropes have great potential to be used as high-performance LIBs/SIBs/PIBs anode material and provide new insights into predicting new 2D materials.