Surface coating is one of the techniques used to improve the electrochemical performance and enhance the resistance against decomposition of cathode materials in lithium-ion batteries. Despite several experimental studies addressing the surface coating of secondary Li-ion batteries using α-Al₂O₃, the reactivity of the material toward the electrolyte components is not yet fully understood. Here, we have employed calculations based on the density functional theory to investigate the adsorption of the organic solvent ethylene carbonate (EC) on the major α-Al₂O₃(0001) surface. During adsorption of a single EC molecule, it was found that it prefers to bind parallel to the surface through its carboxyl oxygen. As the surface coverage (θ) was increased up to a monolayer, we observed larger adsorption energies per EC molecule (E_ads/N_EC) for parallel interactions and a reduction for perpendicular interactions. We also noted that increasing the surface coverage with both parallel and perpendicularly interacting EC molecules led to a decrease of the surface free energies and hence increased stability of the α-Al₂O₃(0001) surface. Despite the larger E_ads/N_EC observed when the molecule was placed parallel to the surface, minimal charge transfer was calculated for single EC interactions and at higher surface coverages. The simulated scanning tunneling microscopy images are also presented for a clean corundum α-Al₂O₃ surface and after adsorption with different coverages of parallel and perpendicularly placed EC molecules.

Surface reactivity of LiMn₂O₄spinel cathode material towards ethylene carbonate (EC) electrolyte solvent using density functional theory (DFT).

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn ³⁺ ) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn ₂ O ₄ ) lithium-ion batteries. However, the effect of surface doping on the major LiMn ₂ O ₄ 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 LiMn ₂ O ₄ (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 LiMn ₂ O ₄ (011) surface doped on the Nb _second site and for HF on the LiMn ₂ O ₄ (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.

Rechargeable metal-air batteries are considered the next generation energy storage devices with the highest energy density of ~200 Wh/kg (which is much higher than the Li-ion batteries with ~150 Wh/kg). However, their practical applications are widely affected by the formation of unstable discharge products (like Na/LiO2, Na/Li2O, and Na/LiO) which react with electrolyte or the porous electrode material leading to either fire or explosion. Here, we explore the stability of the bulk pyrite and marcasite lithium/sodium superoxide (Li/NaO2) discharge products produced in Li and Na-air batteries using density functional theory calculations. The calculated lattice and heats of formations are consistent with available reported data. The electronic properties of show the Pnmm LiO2 as the most stable structure with the least density of states at the Fermi. The vibrational properties also show no imaginary vibrations in all directions for Pnmm LiO2. This finding can help direct and give an insight into the stability of major discharge products and give research direction towards controlling the formation of desired M-O discharge products in the batteries.