Two-dimensional sheet of germanium selenide as an anode material for sodium and potassium ion batteries: First-principles simulation study

Recently, two-dimensional layered materials have come forth as encouraging candidates for advanced electronic and optoelectronic applications. Anode materials with high energy-density and diffusion rate are fundamental features for the development of non-lithium ion batteries. Based on the density functional theory calculations, we propose a two-dimensional (2D) sheet of germanium selenide (GeSe) as a promising anode material for a sodium (Na) or potassium (K) ion battery. The phonon dispersion and formation energy verify the dynamic and thermal stability of the GeSe sheet. A substantial charge transfer from the alkali metal atoms to the GeSe sheet enhances the electrical conductivity of GeSe, favorable for an anode material. The Na or K diffusion on the GeSe sheet has a low energy barrier of 0.10 eV, giving a rapid charge/discharge rate without metal clustering. The GeSe sheet has a high theoretical capacity for both Na (707 mAh g(-1)) and K (530 mAh g(-1)) ion batteries. The GeSe sheet also gives a low and stable electrode potential comparable to that of a commercial anode material.