First-principles study on the regulation of vacancy defects in two-dimensional MoSi2N4 as an anode material for potassium-ion batteries

Abstract

Context

In this paper, the adsorption properties of K atoms on the surface of two-dimensional MoSi₂N₄ were investigated via density functional theory. It was found that the adsorption energies of K atom at the Mo-top, N-top and Si-top sites of pristine MoSi₂N₄ were − 0.03 eV, − 0.05 eV and − 0.08 eV, respectively. The diffusion barrier of K atom on the MoSi₂N₄ surface was calculated to be only 0.052 eV, indicating the excellent diffusion ability of K atom on MoSi₂N₄. With the increasing of adsorbed K atoms, stable adsorption of K atoms on the MoSi₂N₄ surface was no longer achievable. By introducing Si-vacancy defects, the adsorption energy of K atoms at the most favourable adsorption site on the MoSi₂N₄ surface reached − 3.92 eV. Compared with pristine MoSi₂N₄, the adsorption strength was enhanced by approximately 50 times. Meanwhile, the number of stably adsorbed K atoms increased from 1 to 6. Accordingly, a maximum theoretical K storage capacity of 773 mAh/g and an open-circuit voltage of 1.66 V were obtained. Moreover, the diffusion barrier of K atom on the V_Si-MoSi₂N₄ surface was calculated to be 0.053 eV. The modified two-dimensional MoSi₂N₄ combined excellent K atom transport capability with moderate adsorption strength, demonstrating its potential application as an anode material for potassium-ion batteries.

Methods

First-principles calculations based on density functional theory were performed to investigate the effects of vacancy defects on the potassium-storage properties of two-dimensional MoSi₂N₄. All calculations were performed using the Vienna ab initio Simulation Package. The generalized gradient approximation with the Perdew–Burke–Ernzerhof exchange–correlation functional was adopted for structural relaxation and energy calculation. The Heyd–Scuseria–Ernzerhof hybrid functional was utilized to calculate electronic band structures and acquire accurate band gap values. The projector augmented-wave method was employed to describe core–valence electronic interactions, and the DFT-D3(BJ) approach was used to account for van der Waals interactions. The CI-NEB method and AIMD simulations were separately adopted to evaluate the diffusion kinetics and thermal stability of the material system.