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.

Ab initio density functional theory was used to investigate the adsorption of oxygen molecule on the nickel-rich pentlandite (110) surface, which is important for mineral extraction. The three most reactive adsorption sites: Fe-top, Ni-top, and fcc-hollow have been considered. Firstly, the non-adsorbed pentlandite surface reflects the Ni atoms relaxing inwards. Consequently, their electronic structure showed high Fe 3d-orbital contribution than the Ni 3d-orbitals at the EF (indicating that the Fe atoms are more reactive than Ni). Secondly, the O2-adsorbed surface predicted lowest adsorption energy for Fe-top (-1.902 eV), as a more spontaneous reaction is likely to occur than on fcc-hollow (-1.891 eV) and Ni-top (-0.040 eV) sites, suggesting Fe preferential oxidation. The density of states indicates that the O₂ show prevalence of electrons in the ^πp* antibonding orbitals, and are reduced to zero states at the valence band on metal-bonded oxygen (O₁). The ^πp* orbital is observed to reside just above the EF for Fe-top and fcc-hollow site, while on Ni-top is half-occupied for both metal-bonded oxygen (O₁) and terminal oxygen (O₂). Finally, the isosurface charge density difference showed electron (charge) depletion on Ni/Fe metals and accumulation on the O₂ molecule. Bader analysis indicated that the oxidized Fe and Ni atoms adopt more positive charge, while O₂ on Fe-top atoms possesses more negative charge than on Ni-top, resulting with O₁ possessing a smaller charge than O₂ atom.

Due to the outstanding power conversion efficiency (PCE), lightweight, flexible, and low manufacturing cost, perovskite solar cells (PSCs) attract a lot of attention as the most promising candidate for the next generation of solar cells. However, the issue of poor intrinsic stability of the absorber materials and operational stability of devices remains unsolved. In this study, first-principle calculations were performed on the CsPbX₃ (X = Br or I) perovskites to provide insight into the structural, mechanical, vibrational and electronic properties of CsPbBr₃ and CsPbI₃ for their applications as active layers of solar cells. It was found that the calculated lattice parameters are in good agreement with the experimental results. CsPbBr₃ and CsPbI₃ have negative energy of formation, which implies that the materials are thermodynamically stable. The calculated band structures indicate that CsPbBr₃ and CsPbI₃ are semiconductors with direct bandgaps along R-symmetry point. Furthermore, cluster expansion and simulations of Monte-Carlo were performed to identify new possible CsPbBr_1-xI_x structures and evaluate the effect of temperature on the system. The ground-state search generated 26 new multi-component CsPbBr_1-xI_x structures, and the temperature-profile showed that the system mixes well at ∼800 K. Thus, the phase stability insight is crucial for the development of these promising perovskite solar cells.

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

Lithium–manganese–oxide (Li-Mn-O) spinel is among the promising and economically viable, high-energy density cathode materials for enhancing the performance of lithium-ion batteries. However, its commercialization is hindered by its poor cyclic performance. In computational modelling, pivotal in-depth understanding of material behaviour and properties is sizably propelled by advancements in computational methods. Hence, the current work compares traditional DFT (CASTEP) and linear-scaling DFT (ONETEP) in a LiMn₂O₄ electronic property study to pave way for large-scale DFT calculations in a quest to improve its electrochemical properties. The metallic behaviour of Li_xMn₂O₄ (0.25 ≤ x ≤ 1) and Li₂Mn₂O₄ was correctly determined by both CASTEP and ONETEP code in line with experiments. Furthermore, OCV during the discharge cycle deduced by both codes is in good accordance and is between 5 V and 2.5 V in the composition range of 0 ≤ x ≤ 1. Moreover, the scaling of the ONETEP code was performed at South Africa’s CHPC to provide guidelines on more productive large-scale ONETEP runs. Substantial total computing time can be saved by systematically adding the number of processors with the growing structure size. The study also substantiates that true linear scaling of the ONETEP code is achieved by a systematic truncation of the density kernel.