The effects of in‑plane strains on the electrochemical properties of Li adatoms on the ZrS2 monolayer : a first-principles study

Abstract

In this study, we use density functional theory (DFT) with a Hubbard (U) parameter, implemented in the Quantum Espresso code, to investigate the interactions between Li-ions and the ZrS2 monolayer under the influence of in-plane uniaxial and biaxial strains, specifically within the context of lithium-ion batteries. This is to ensure the ZrS2 monolayer is more robust against the Coulomb forces arising from interactions between multiple lithium ions. This study objectively examines the impact of tensile and compressive strains ranging from − 5% to 5% on the energetic stability and electrochemical properties of the lithiated ZrS2 electrode monolayer. For a single Li adatom on a 3 × 3 ZrS2 monolayer, the compressed structure (at − 5% strain) becomes more energetically favorable, exhibiting a low adsorption energy of − 1.41 eV. In contrast, the stretched structure (at + 5% strain) has a higher adsorption energy of − 0.95 eV compared to the unstrained structure (− 1.16 eV), although exothermic interaction is maintained. The ZrS2 electrode monolayer has a shallow energy barrier of 0.23 eV for Li-ion diffusion, indicating greater mobility, which is slightly enhanced by compressive strain. The application of − 5% (compressive strain) resulted in an average OCV of 0.93 V, and 0.78 V for unstrained, while + 5% (tensile strain) yielded an OCV of 0.69 V, which is in the range of commercial anode materials. The tensile strain on a ZrS2 electrode monolayer would be more effective in mitigating the dendrite formation. The introduction of a Li adatom rearranged the conduction band minimum, leading to the hybridized Zr d orbital states crossing the Fermi level and becoming more populated as the number of Li adatoms increases, leading to a more conductive electrode. Additionally, the strain reduced the band gap, causing the induced electronic states to be continuous from the VBM to the CBM edges, which enhances the electronic conductivity of the material, ensuring the excellent LIBs operation during the charge and discharge processes.