A First-principles Comparative Study of Lithium, Sodium, Potassium and Calcium Storage in Two-dimensional Mg2C.

Two-dimensional (2D) materials have recently emerged as ideal 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 for lithium-, sodium-, potassium- and calcium- ions batteries, respectively. 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 behavior 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 1 770 mAhg-1, nearly two times that of the Li atom of 885 mAhg-1. Our study suggests that the 2D Mg2C is a promising anode material which offers a fast ion diffusion and high storage capacity.