A DFT + U-D3 Study of the Adsorption of Hydrogen Fluoride and Ethylene Carbonate on the Niobium-Doped (001), (011), and (111) Surfaces of Lithium Manganese Oxide

Abstract

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn3+) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn2O4) lithium-ion batteries. However, the effect of surface doping on the major LiMn2O4 surfaces and their interactions with the electrolyte components is not yet fully understood. In this work, spin-polarised density functional theory-based calculations [DFT + U-D3 (BJ)] were employed to study the adsorption of the electrolyte components ethylene carbonate (EC) and hydrogen fluoride (HF) onto the Nb-doped major LiMn2O4 (001), (011), and (111) surfaces. During the substitution of niobium for manganese ions in the second surface layers (Nb second ), it was found that the (111) surface stability improves, resulting in an enhanced (111) plane on the morphology. However, replacing the first (Nb first ) as well as both top and sub-surface (Nb both ) layers of Mn atoms in the slabs maintains the same stability trend as in the pure pristine surfaces. Moreover, both adsorbates greatly preferred binding to the surfaces through the Nb instead of Mn atoms, and the largest adsorption energy was calculated for EC on the LiMn2O4 (011) surface doped on the Nb second site and for HF on the LiMn2O4 (111) surface doped on the Nb both site. Furthermore, the EC/HF adsorptions further enhance the stability of the Nb second (111) surface plane. However, minimal charge transfer was calculated for both HF and EC interacting with the pure and Nb-doped surfaces. Our findings are interesting, since exposing the (111) surface promotes the formation of a stable solid electrolyte interface (SEI), significantly reducing Mn dissolution and enhancing the adsorption of EC and HF.