A first-principles study of TiA2P4 (A = Si and Ge) monolayers as excellent electrode materials for Na-ion batteries

Abstract

Two-dimensional (2D) materials have shown excellent application prospects in energy storage technologies due to the extraordinary physical and chemical properties. In this work, TiA2P4 (A = Si or Ge) monolayers, that members of MA2Z4 family, are selected as electrode materials for lithium/sodium-ion batteries. Their structural stabilities, mechanical properties, electronic structures, and energy storage performances are investigated by using first-principles calculations. Satisfactorily, TiA2P4 monolayers have good thermodynamic stability and mechanical properties. Meanwhile, low diffusion barriers, suitable open circuit voltages and significant theoretical capacities prove that TiA2P4 are suitable electrode materials for Li/Na storage, except for TiGe2P4 that lack the ability to store lithium. The theoretical capacity of TiSi2P4 monolayer is up to 470.33/705.50 mA h g−1 for Li/Na storage, and that of TiGe2P4 monolayer is 507.24 mA h g−1 for Na-ions, which are better than many metal-like 2D layered materials. Our research indicates that both of TiA2P4 are potential electrode material for sodium-ion batteries, and inspire the future design of other MA2Z4 family in energy storage technologies.