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Electrochemical Energy Storage Systems are a viable and popular solution to fulfill energy storage requirements for energy generated through sustainable energy resources. With the increasing demand for Electrical Vehicles (EVs), Lithium-ion batteries (LIB) are being widely and getting popular compared to other battery technologies due to their energy storage capacity. However, LIBs suffer from disadvantages such as battery life and the degradation of electrode material with time, that can be improved by understanding these mechanisms using experimental and computational techniques. Further, it has been experimentally observed and numerically determined that lithium-ion intercalation induced stress and thermal loading can cause capacity fading and local fractures in the electrode materials. These fractures are one of the major degradation mechanisms in Lithium-ion batteries. With LixMn2O4 as a cathode material, stress values differ widely especially for intermediate State Of Charge (SOC), and very few attempts have been made to understand the stress distribution as a function of SOC at molecular level. Therefore, the estimates of mechanical properties such as Young’s modulus, diffusion coefficient etc. differ, especially for partially charged states. Further, the effect of temperature, particularly elevated temperatures, have not been taken into the consideration. Studying these parameters at the atomic scale can provide insight information and help in improving these materials lifetime. Hence, molecular/atomic level mathematical modelling has been used to understand capacity fade due to Lithium-ion intercalation/de-intercalation induced stress. Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [1], that is widely used for atomic simulations, has been used for the simulation studies of this dissertation. Thus, the objective of this study is to understand the fracture mechanisms in the Lithium Manganese Oxide (LiMn2O4) electrode at the molecular level by studying mechanical properties of the material at different SOC values using the principles of molecular dynamics (MD). As part of the model validation, the lattice parameter and volume changes of LixMn2O4 as a function of SOC (0 < x < 1) has been studied and validated with respect to the experimental data. This validated model has been used for a parametric study involving the SOC value, strain-rate (charge and discharge rate), and temperature. Based on the validated MD setup, doping and co-doping studies have been undertaken to design and develop new and novel cathode materials with enhanced properties. In the absence of experimental data for the new engineered structures, validation with Quantum Mechanics generated lattice structures has been done. The results suggest that lattice constant values obtained from both MD and QM simulations are in good agreement (∼ 99%) with experimental values. Further, Single Particle Model (SPM) based macro scale Computational Fluid Dynamics findings show that co-doping has improved the material properties especially for Yttrium and Sulfur doped structures which can improve the cycle life anywhere between 600-7000 cycles. Further in order to reduce the required computational time to obtain minimum potential energy ionic configuration out of millions of scenario, Artificial Neural Network (ANN) technique is being used. It improved the processing time by more than 88%. / Thesis / Doctor of Philosophy (PhD)

The surface tension of liquid metals is an important and scientifically interesting parameter which affects many metallurgical processes such as casting, welding and melt spinning. Conventional methods for measuring surface tension are difficult to use for molten metals above temperatures of 1000 K. Containerless methods are can be used to measure the surface tension of molten metals above 1000 K. Oscillating drop method is one such method where a levitated droplet is allowed to undergo damped oscillations. Using the Rayleigh’s theory for the oscillation of force-free inviscid spherical droplets, surface tension and viscosity of the sample can be calculated from oscillation frequency and damping respectively. In this thesis, a numerical model is developed in ANSYS Fluent to simulate the oscillations of the molten metal droplet. The Volume of Fluid approach is used for multiphase modelling. The effect of numerical schemes, mesh size, and initialization boundary conditions on the frequency of oscillation and the surface tension of the liquid are studied. The single-phase model predicts the surface tension of zirconium within a range of 13% when compared to the experimental data. The validated single phase model is extended to predict the interfacial tension of a core-shell structured compound drop. We study the effect of the core and shell orientation at the time of flow initialization. The numerical model we developed predicts the interfacial tension between copper and cobalt within the range of 6.5% when compared to the experimental data. The multiphase model fails to provide any conclusive data for interfacial tension between molten iron and slag.