In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.

Surface reactivity of LiMn2O4 spinel cathode material towards ethylene carbonate (EC) electrolyte solvent using density functional theory (DFT).

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.

Lithium manganese oxide (LiMn2O4) is one of the promising cathode material for lithium-ion batteries (LIBs), however, it suffers from capacity fading mainly due to surface manganese (Mn2+) ion dissolution during Charge/discharge processes. Although many studies focused on reducing Mn-dissolution, surface modification has proven to be an ideal method of reducing Mn2+ ion dissolution in secondary Li-ion batteries. In this study, the density functional theory calculations were carried out to study the bulk properties and investigate the effect of Nb surface doping on major LiMn2O4 spinel surfaces. Upon surface Nb doping, we observed a decrease in surface free energy as compared to the surface energies of pure surfaces, indicating that the surface stabilizes upon doping. However, the (001) surface remained the most stable facet, with a similar trend of increasing energies and decreasing stability, i.e. (001) < (011) < (111). Due to the stronger binding energy of Nb-O as compared to Mn-O, doping with Nb can suppress the Mn dissolution during intercalation and hence improve the electrochemical performance.

Cationic doping has played an important role in the improvement and development of more efficient cathode materials for secondary lithium-ion batteries. In lithium manganese oxides, it was recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn 3+) ions that undergo disproportionation reaction. In the quest to meet the increasing demand for cheap, renewable, and clean energy, an in-depth understanding of surface doping and the reactivity towards the electrolyte is crucial. Here, we present a detailed DFT study of the effect of Nb doping on the major (001), (011), and (111) LiMn 2 O 4 surfaces and their interactions with the electrolyte components, ethylene carbonate (EC), and hydrogen fluoride (HF). Our calculations show that Nb doping in the sub-surface layers greatly enhances the (111) plane in the morphology, which is of significant interest since it has been reported in the literature that the exposed (111) surface promotes the development of stable solid electrolyte interface which can reduce Mn dissolution. Introducing the EC/HF on the Nb second surfaces further enhances the expression of the (111) surface.