Consumers use batteries daily, and the lithium-ion battery has undergone a lot of engineering advances in the last few decades. There is a need to understand and improve the cathode chemistry to adapt to the rapidly growing electronics and electric vehicle market that is continually demanding more energy from batteries. Nickel-rich layered LiNi_1-x-yMn_xCo_yO₂ (1-x-y ≥ 0.6, NMC) cathodes could potentially provide the necessary energy to meet the demand of the high energy applications. Overcoming the stability issues from oxygen activation in nickel-rich materials is one of the largest challenges facing the commercial incorporation of NMCs. This thesis focuses on, LiNi_0.8Mn_0.1Co_0.1 (NMC811). Using surface sensitive techniques, such as Xray Absorption (XAS), our research reveals that degradation of NMC811 occurs during cycling, regardless of temperature, and that oxygen activation plays a role in the overall surface changes and degradation observed in NMC811. The thesis then explores the role of substituting a transition metal in the NMC811. Then we used a gradient addition of titanium to the NMC811 material to stabilize the battery performance. Theoretical techniques, such as Finite Difference Method Near Edge Structure, and experimental techniques, such as XAS, revealed how transition metal substitution, specifically titanium, stabilized the lattice. The results indicated that titanium deactivates oxygen by limiting the nickel and oxygen covalency that typically leads to oxygen activation upon charging. We observed that the titanium substitution increases cycling reversibility after hundreds of cycles. Overall, the work indicates that a more stable nickel-rich material is possible. It identifies the reasons why substitution can work in cathode materials. Additionally, the methods described can provide a guideline to further studies of stabilization of the cathode. / Master of Science / Consumers across the world use lithium-ion batteries in some fashion in their everyday life. The growing demand for energy has led to batteries dying quicker than consumers want. Thus, there are calls for researchers to develop batteries that are longer lasting. However, the initial increase in battery life over the years has been from better engineering and not necessarily from making a better material for a battery. This thesis focuses on the understanding of the chemistry of the materials of a battery. Throughout the chapters, the research delves into the how and why materials with extra nickel degrade quickly. Then, it investigates a method of making these nickel-rich materials last longer and how the chemistry within these materials are affected by the addition of a different metal. Overall, the findings indicate that the addition of titanium creates a more stable material because it mitigates the release of oxygen and prevents irreversible changes within the structure of the material. It determines that the chemistry behind the failings of nickel-rich lithium-ion batteries and a potential method for allowing the batteries to last longer. It also provides insight and guidance for potential future research of stabilization of lithium-ion materials.

Indiana University-Purdue University Indianapolis (IUPUI) / In the last years, lithium-ion batteries (LIBs) have become the most important energy storage system for consumer electronics, electric vehicles, and smart grids. The development of lithium-ion batteries (LIBs) based on current practice allows an energy density increase estimated at 10% per year. However, the required power for portable electronic devices is predicted to increase at a much faster rate, namely 20% per year. Similarly, the global electric vehicle battery capacity is expected to increase from around 170 GWh per year today to 1.5 TWh per year in 2030--this is an increase of 125% per year. Without a breakthrough in battery design technology, it will be difficult to keep up with the increasing energy demand. To that end, a design methodology to accelerate the LIB development is needed. This can be achieved through the integration of electro-chemical numerical simulations and machine learning algorithms. To help this cause, this study develops a design methodology and framework using Simcenter Battery Design Studio® (BDS) and Bayesian optimization for design and optimization of cylindrical cell type 18650. The materials of the cathode are Nickel-Cobalt-Aluminum (NCA)/Nickel-Manganese-Cobalt-Aluminum (NMCA), anode is graphite, and electrolyte is Lithium hexafluorophosphate (LiPF6). Bayesian optimization has emerged as a powerful gradient-free optimization methodology to solve optimization problems that involve the evaluation of expensive black-box functions. The black-box functions are simulations of the cyclic performance test in Simcenter Battery Design Studio. The physics model used for this study is based on full system model described by Fuller and Newman. It uses Butler-Volmer Equation for ion-transportation across an interface and solvent diffusion model (Ploehn Model) for Aging of Lithium-Ion Battery Cells. The BDS model considers effects of SEI, cell electrode and microstructure dimensions, and charge-discharge rates to simulate battery degradation. Two objectives are optimized: maximization of the specific energy and minimization of the capacity fade. We perform global sensitivity analysis and see that thickness and porosity of the coating of the LIB electrodes that affect the objective functions the most. As such the design variables selected for this study are thickness and porosity of the electrodes. The thickness is restricted to vary from 22microns to 240microns and the porosity varies from 0.22 to 0.54. Two case studies are carried out using the above-mentioned objective functions and parameters. In the first study, cycling tests of 18650 NCA cathode Li-ion cells are simulated. The cells are charged and discharged using a constant 0.2C rate for 500 cycles. In the second case study a cathode active material more relevant to the electric vehicle industry, Nickel-Manganese-Cobalt-Aluminum (NMCA), is used. Here, the cells are cycled for 5 different charge-discharge scenarios to replicate charge-discharge scenario that an EVs battery module experiences. The results show that the design and optimization methodology can identify cells to satisfy the design objective that extend and improve the pareto front outside the original sampling plan for several practical charge-discharge scenarios which maximize energy density and minimize capacity fade.

Effects of mould flux contaminant on scale-steel adhesion and hydraulic descaling of scale formed on slabs were investigated. In this investigation, stainless steel type 304 (austenitic with 18% Cr and 8% Ni) and specific mould fluxes were used when growing the scale on contaminated samples under simulated industrial reheating conditions, with subsequent high pressure water hydraulic descaling. The basic hypothesis was that the steel-scale adhesion depends on the microstructure of different phases present in the scale, the segregation of specific elements at the interface and the interfacial morphology of the scale after reheating. It was found that mould flux contaminant decreases scale-steel adhesion and therefore improved the descaling effectiveness significantly compared to non contaminated stainless steel. The descaling effectiveness of contaminated and uncontaminated slab was dependent to the presence of metal free paths (chromite layers along the austenite grains boundaries) and the presence of unoxidized metal in the scale due to nickel enrichment at the interface. Compared to the uncontaminated samples, the descaling of contaminated samples was efficient which could be due to the fact that some mechanisms which increase scale– steel adhesion (notably nickel enrichment at the interface) were considerably reduced. For all contaminated samples, the descaling effectiveness after visual observation were close to 100% and it was found that mould flux type 832 ( low basicity) gave a high descaling efficiency with better steel surface quality after descaling compared to mould fluxes type 810 and RF1. / Dissertation (MSc)--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted