Materials modelling in the University of Limpopo.

This article provides insights into building research capacity in computational modelling of materials at the University of Limpopo (UL), formerly University of the North, in South Africa, through a collaboration with a consortium of universities in the United Kingdom (UK) through the support of the National Research Foundation (NRF), formerly the Foundation for Research and Development, and the Royal Society (RS). A background that led to the choice of building research capacity at historically disadvantaged universities in South Africa, including the UL, is given. The of the collaboration between the UL and several UK universities on computational modelling of materials is outlined, together with the scientific highlights that were achieved in themes of minerals, energy storage and alloy development.

Exploring the Phase Stability of LiMn TM O (TM = Ni, Co, Cr, Ru) Cathode Materials in Lithium-Ion Batteries via the Cluster Expansion Method.

LiMnO has garnered significant interest as a potential cathode material due to its high electrochemical capacity, cost-effectiveness, and eco-friendliness. Nonetheless, its practical utilization is hindered by structural deterioration, which results in rapid capacity and voltage decay during cycling. To mitigate these challenges, cationic dopants have been incorporated to minimize structural collapse and enhance cathode material performance.

Reconstruction of Cooperite (PtS) Surfaces: A DFT-D+U Study.

Cooperite (PtS) is one of the main sources of platinum in the world and has not been given much attention, in particular from the computational aspect. Besides, the surface stability of cooperite is not fully understood, in particular the preferred surface cleavage. In the current study, we employed computer modeling methods within the plane-wave framework of density functional theory with dispersion correction and the parameter to correctly predict the bulk and surface properties.

Analysing the Implications of Charging on Nanostructured LiMnO Cathode Materials for Lithium-Ion Battery Performance.

Capacity degradation and voltage fade of LiMnO during cycling are the limiting factors for its practical use as a high-capacity lithium-ion battery cathode. Here, the simulated amorphisation and recrystallisation (A + R) technique is used, for generating nanoporous LiMnO models of different lattice sizes (73 Å and 75 Å), under molecular dynamics (MD) simulations. Charging was carried out by removing oxygen and lithium ions, with oxygen charge compensated for, to restrain the release of oxygen, resulting in LiMnO composites.

First-Principles Study on the Effect of Lithiation in Spinel LiMnO (0 ≤ x ≤ 1) Structure: Calibration of CASTEP and ONETEP Simulation Codes.

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.

Unravelling the Catalytic Activity of MnO, TiO, and VO (110) Surfaces by Oxygen Coadsorption on Sodium-Adsorbed MO {M = Mn, Ti, V}.

Metal-air batteries have attracted extensive research interest owing to their high theoretical energy density. However, most of the previous studies have been limited by applying pure oxygen in the cathode, without taking into consideration the effect of the catalyst, which plays a significant role in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Adsorption of oxygen on (110) Na-MO is investigated, using density functional theory (DFT) calculations, which is important in the discharging and charging of Na-air batteries.

Density Functional Theory Study of Ethylene Carbonate Adsorption on the (0001) Surface of Aluminum Oxide α-AlO.

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-AlO, 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-AlO(0001) surface.

Ethylene carbonate adsorption on the major surfaces of lithium manganese oxide LiMnO spinel (0.000 < x < 0.375): a DFT+U-D3 study.

Understanding the surface reactivity of the commercial cathode material LiMnO towards the electrolyte is important to improve the cycling performance of secondary lithium-ion batteries and to prevent manganese dissolution. In this work, we have employed spin-polarized density functional theory calculations with on-site Coulomb interactions and long-range dispersion corrections [DFT+U-D3-(BJ)] to investigate the adsorption of the electrolyte component ethylene carbonate (EC) onto the (001), (011) and (111) surfaces of the fully lithiated and partially delithiated LiMnO spinel (0.000 < x < 0.

Thermodynamically accessible titanium clusters Ti, N = 2-32.

We have performed a genetic algorithm search on the tight-binding interatomic potential energy surface (PES) for small TiN (N = 2-32) clusters. The low energy candidate clusters were further refined using density functional theory (DFT) calculations with the PBEsol exchange-correlation functional and evaluated with the PBEsol0 hybrid functional. The resulting clusters were analysed in terms of their structural features, growth mechanism and surface area.

Periodic modeling of zeolite Ti-LTA.

We have proposed a combination of density functional theory calculations and interatomic potential-based simulations to study the structural, electronic, and mechanical properties of pure-silica zeolite Linde Type A (LTA), as well as two titanium-doped compositions. The energetics of the titanium distribution within the zeolite framework suggest that the inclusion of a second titanium atom with configurations Ti-(Si)-Ti, Ti-(Si)-Ti, and Ti-(Si)-Ti is more energetically favorable than the mono-substitution. Infra-red spectra have been simulated for the pure-silica LTA, the single titanium substitution, and the configurations Ti-(Si)-Ti and Ti-(Si)-Ti, comparing against experimental benchmarks where available.

Origin of electrochemical activity in nano-Li2MnO3; stabilization via a 'point defect scaffold'.

Molecular dynamics (MD) simulations of the charging of Li2MnO3 reveal that the reason nanocrystalline-Li2MnO3 is electrochemically active, in contrast to the parent bulk-Li2MnO3, is because in the nanomaterial the tunnels, in which the Li ions reside, are held apart by Mn ions, which act as a pseudo 'point defect scaffold'. The Li ions are then able to diffuse, via a vacancy driven mechanism, throughout the nanomaterial in all spatial dimensions while the 'Mn defect scaffold' maintains the structural integrity of the layered structure during charging. Our findings reveal that oxides, which comprise cation disorder, can be potential candidates for electrodes in rechargeable Li-ion batteries.

Amorphization and recrystallization study of lithium insertion into manganese dioxide.

Various polymorphs of MnO(2) are widely used as electrode materials in Li/MnO(2) batteries. Electrolytic manganese dioxide (EMD) is the most electrochemically active form of MnO(2) and is very difficult to characterize. Their structural details are still largely unknown owing to the poor quality of X-ray diffraction (XRD) patterns obtained from most MnO(2) samples.

Simulating mechanical deformation in nanomaterials with application for energy storage in nanoporous architectures.

Central to porous nanomaterials, with applications spanning catalysts to fuel cells is their (perceived) "fragile" structure, which must remain structurally intact during application lifespan. Here, we use atomistic simulation to explore the mechanical strength of a porous nanomaterial as a first step to characterizing the structural durability of nanoporous materials. In particular, we simulate the mechanical deformation of mesoporous Li-MnO(2) under stress using molecular dynamics simulation.

Predicting the electrochemical properties of MnO2 nanomaterials used in rechargeable li batteries: simulating nanostructure at the atomistic level.

Nanoporous beta-MnO2 can act as a host lattice for the insertion and deinsertion of Li with application in rechargeable lithium batteries. We predict that, to maximize its electrochemical properties, the beta-MnO2 host should be symmetrically porous and heavily twinned. In addition, we predict that there exists a "critical (wall) thickness" for MnO2 nanomaterials above which the strain associated with Li insertion is accommodated via a plastic, rather than elastic, deformation of the host lattice leading to property fading upon cycling.

Generating MnO2 nanoparticles using simulated amorphization and recrystallization.

Models of MnO2 nanoparticles, with full atomistic detail, have been generated using a simulated amorphization and recrystallization strategy. In particular, a 25,000-atom "cube" of MnO2 was amorphized (tension-induced) under molecular dynamics (MD). Long-duration MD, applied to this system, results in the sudden evolution of a small crystalline region of pyrolusite-structured MnO2, which acts as a nucleating "seed" and facilitates the recrystallization of all the surrounding (amorphous) MnO2.