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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)

During lithium-ion battery electrode fabrication, slurry drying conditions influence the resulting microstructure of electrodes. It has been found that the drying conditions can result in non-uniform cathode microstructures and material distributions. Accelerated drying, for example, is widely assumed to cause the binder in an electrode to migrate within the slurry, which can contribute to adhesion failure, and ultimately capacity fade and reduced battery life. While there are some conflicting studies regarding the aspects of accelerated drying that cause binder migration, there is not a widely used standard metric for measuring the gradient of binder across the thickness of an electrode. In this work, the vertical heterogeneity of electrodes, as measured using energy-dispersive X-ray spectroscopy (EDX), is correlated with different drying methods and rates. An improved metric for measuring the binder gradient in electrodes is proposed. For the electrodes in this study, binder migration is minimally affected by the drying method and the normalized binder gradient does not increase with increased drying rate. The results are compared to a drying physics model, and it is shown that further development of current models that predict binder gradient as a function of drying rate will need to be modified to more fully capture the physics of slurry drying.

With the increasing usage of electronics powered by lithium ion batteries, it is more and more importantto improve the recycling process. The current study is focused on reducing graphite content of disposedlithium batteries to aid the further treatment of the batteries. In larger picture, an increase of efficiencyleads to a less cost and less loss of material in recycling process. The approach used is to reduce graphitecontent by the agglomerated flotation, using the natural hydrophobicity of graphite. This approach candecrease the percentage of this mineral in the further recycling process of LIBs where the actual focus arethe valuable metals as lithium, cobalt, nickel and manganese. The results and conditions of flotation arecompared in cases where flotation feed material is the bulk material or thermally treated one.

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