A first-principles comparative study of lithium, sodium, potassium and calcium storage in two-dimensional Mg₂C

Two-dimensional (2D) materials have recently emerged as potential candidates for high-capacity lithium-ion batteries anode materials because of their compelling physicochemical and structural properties. In the present study, we use first-principles calculations to investigate the performance of 2D Mg₂C as anode materials for Li, Na, K and Ca-ions batteries. The calculated average open-circuit voltage are 0.37, 0.50, 0.03 and 0.06 eV vs Li, Na, K, Ca. No significant structural deformations are observed on the 2D Mg₂C upon the adsorption of Li, Na, K or Ca and the metallic characteristic of the 2D Mg₂C is retained. The metallic behaviour of both pristine and adsorbed Mg₂C ensures the desirable electric conductivity, implying the advantages of 2D Mg₂C for batteries. The Na and K atoms show an extremely high diffusivity on the 2D Mg₂C with a low energy barrier of 0.08 and 0.04 eV respectively, which is about an order of magnitude smaller than that of Li atom. For the Na and K atoms, the theoretical storage capacity can reach up to 1770 mAh g^-1, nearly two times that of the Li atom of 885 mAh g^-1. Our study suggests that the 2D Mg₂C is a promising anode material which offers a fast ion diffusion and high storage capacity.