Theoretical investigation of zirconium carbide MXenes as prospective high capacity anode materials for Na-ion batteries

Abstract

Currently, MXenes have been identified as promising electrode material candidates because of their excellent energy storage and electrical conductivity. In the present study, Na adsorptions on 2D MXenes of Zr₂C, Zr₃C₂, Zr₂CO₂, and Zr₃C₂O₂ are explored by density functional theory (DFT) calculations. We have found that Zr₂CO₂/Zr₃C₂O₂ MXenes show metallic behavior after Na adsorption and exhibit a low diffusion barrier (0.29/0.32 eV) and high storage capacity (up to Zr₂CO₂Na₄/Zr₃C₂O₂Na₄ stoichiometry) for Na-ion batteries (NIBs). Zr₂CO₂/Zr₃C₂O₂ MXenes also exhibit excellent properties such as good electrical conductivity, low diffusion barrier, decreased equilibrium open circuit voltage (OCV), and high theoretical capacity of Na storage, due to which they can be used as promising anode materials for NIBs. In addition, the physical origin of adsorption behavior of Na atoms on Zr₂CO₂/Zr₃C₂O₂ as well as on Ti₃C₄, Ti₃C₂O₂ and Ti₃C₂S₂ MXenes is studied. Our results give insights into understanding the manner in which the theoretical capacity can be efficiently tuned by charge transfer and lattice mismatch factors, which will be useful for designing other 2D anode materials for NIBs.