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<p> In the pursuit to enable the rapid charging of lithium-ion batteries, lithium plating at the anode  poses one of the most significant challenges. Additionally, the heat generation that accompanies  high rate battery operation in conjunction with non-uniform cooling and localized heating at tabs  is known to result in thermal inhomogeneity. Such thermal anomalies in the absence of proper  thermal management can instigate accelerated degradation in the cell. This work seeks to elucidate  the link between thermal gradients and lithium plating in lithium-ion batteries using a combined  experimental and simulation-based approach. First, we experimentally characterize the lithium  plating phenomenon on graphite anodes under a wide variety of charging rates and temperatures  to gain mechanistic insights into the processes at play. An in operando detection method for the  onset of dendritic lithium plating is developed. Lithium plating regimes are identified as either  nucleate or dendritic, which exhibit vast differences in reversibility. An operando method to  quantify lithium stripping based on the rest phase voltage plateau is presented. Next, a model is  employed to provide fundamental insights to the thermo-electrochemical interactions during  charging in scenarios involving an externally imposed in-plane and inter-electrode thermal  gradient. The relative importance of in-plane vs. inter-electrode thermal gradients to charging  performance and cell degradation is necessary to inform future cell design and cooling systems for  large-format cells, which are crucial for meeting the energy requirements of applications like  electric vehicles. While in-plane thermal gradients strongly influence active material utilization,  the lithium plating severity was found to be very similar to an isothermal case at the same mean  temperature. By contrast, inter-electrode thermal gradients cause a shifting on the solid phase  potential at each electrode during charging, related to the increase or decrease in overpotential due  to local temperature variation. An experiment is then performed on a commercial multi-layer  pouch cell, in which it was found that applied thermal gradients provide a slight reduction in  lithium plating severity and degradation rate when compared to an isothermal cell at the same  mean temperature. The presence of a thermal gradient causes heterogeneous lithium plating  deposition within the cell, with colder regions experiencing higher quantities of plating and larger  thermal gradients leading to more severe heterogeneity.   </p>

This study has two parts. In the first part we develop a computational approach to the solution of an inverse modelling problem concerning the material properties of electrolytes used in Lithium-ion batteries. The dependence of the diffusion coefficient and the transference number on the concentration of Lithium ions is reconstructed based on the concentration data obtained from an in-situ NMR imaging experiment. This experiment is modelled by a system of 1D time-dependent Partial Differential Equations (PDE) describing the evolution of the concentration of Lithium ions with prescribed initial concentration and fluxes at the boundary. The material properties that appear in this model are reconstructed by solving a variational optimization problem in which the least-square error between the experimental and simulated concentration values is minimized. The uncertainty of the reconstruction is characterized by assuming that the material properties are random variables and their probability distribution estimated using a novel combination of Monte-Carlo approach and Bayesian statistics. In the second part of this study, we carefully analyze a number of secondary effects such as ion pairing and dendrite growth that may influence the estimation of the material properties and develop mathematical models to include these effects. We then use reconstructions of material properties based on inverse modelling along with their uncertainty estimates as a framework to validate or invalidate the models. The significance of certain secondary effects is assessed based on the influence they have on the reconstructed material properties. / Thesis / Doctor of Philosophy (PhD)

One of the questions arising as regards to structured materials is how one can compute their cluster concentrations. Specifically, we are interested in deriving the concentrations of the micro-structures in the NMC (Nickel-Manganese-Cobalt) layer of the cathodes of Li-ion batteries. A simulated annealing approach has been used lately for detecting the structure of the whole lattice which is computationally heavy. Here we propose a mathematical model, called cluster approximation model, in the form of a dynamical system for describing the concentrations of different clusters inside the lattice. However, the dynamical system is hierarchical which requires to be truncated. Truncation of the hierarchical system is performed by the nearest-neighbor closure scheme. Also, a novel framework is proposed for an optimal closure of the dynamical system in order to enhance the accuracy of the model. The parameters of the model are reconstructed by the least square approach as a constrained optimization problem by minimizing the mismatch between the experimental data and the model outputs. The model is validated based on the experimental data on a known Li-ion battery cathode and different approximation schemes are compared. The results clearly show that the proposed approach significantly outperforms the conventional method. / Thesis / Master of Science (MSc)

The wide applications of energy storage systems in consumer electronics, electric vehicles, and grid storage in the recent decade has created an enormous market globally. The electrochemical flow system has many applications in Li-ion battery recycling and energy storage system design. First, research work on a scalable electrochemical flow system is presented to effectively restore the lithium concentration in end-of-life Li-ion cathode materials. An effective recycling process for end-of-life lithium-ion batteries could relieve the environmental burden and retrieve valuable cathode battery materials. The design is validated in a static configuration with both cathode loose powder and cathode electrode sheet. Materials with comparable electrochemical performance to virgin cathode materials are produced after post heat treatment. Second, research contributions in sulfur-based flow battery systems for long-duration energy storage are presented. Sulfur-based redox flow batteries are promising due to their high theoretical capacity, low cost, and high abundance. The speciation of aqueous sulfur solutions with different nominal concentrations, sulfur concentrations, and pH are studied by Raman spectroscopy. Next, a promising aqueous manganese catholyte to couple with the sulfur anolyte for a full flow battery is investigated. Test protocols and quantification metrics for the catholyte are developed. The stability of the catholyte, including self-discharge rate and precipitation rate, is measured via ex-situ characterizations. The electrochemical performance of the catholyte is investigated and optimized via in-situ experiments. The reaction pathway for the precipitation of catholyte is discussed and several mitigation strategies are proposed. Finally, a semi-solid sodium-sulfur flow battery is developed. The electrochemical performance of the sodium-sulfur battery is studied first in a static configuration at an intermediate temperature (150°C). Then a Na-S semi-solid flow cell is assembled and cycled under the two-aliquots and three-aliquots intermittent flow. / Doctor of Philosophy / The market of energy storage systems has been expanding dramatically in recent years due to their wide applications in portable electronics, electric vehicles, and large-scale grid storage. First, the research on the development of an electrochemical flow system in the Li-ion batteries (LIB) recycling process is presented. The improper disposal of end-of-life LIBs will generate flammable hazardous waste. Recycling spent LIBs could ease the environmental burden and replenish valuable resources such as lithium, cobalt, and nickel, and reduce the cost of battery manufacturing. In this study, an electrochemical flow system is designed to restore the end-of-life cathode materials in LIBs. The design has the potential to scale up and is validated with a static configuration. The recycled materials show comparable electrochemical performance to virgin battery cathode materials. Life cycle analysis shows that the recycling process consumes less energy and is more environmentally friendly. Second, the research contribution in sulfur-based flow battery systems for long-duration energy storage is presented. The aqueous sulfur solutions with different nominal concentrations, sulfur concentrations, and pH are studied by Raman spectroscopy. Next, a promising aqueous manganese catholyte to couple with the sulfur anolyte for a full redox flow battery is investigated. The chemical stability of the catholyte, including self-discharge rate and precipitation rate, is measured via ex-situ characterizations. The electrochemical performance of the catholyte is studied and optimized via in-situ experiments. The reaction mechanisms for the precipitation of aqueous manganese solutions are discussed. Finally, a semi-solid sodium-sulfur (Na-S) flow battery is developed. The electrochemical performance of the sodium-sulfur battery is studied first in a static cell at intermediate temperature. Then a Na-S semi-solid flow cell is demonstrated and cycled under the two-aliquots and three-aliquots intermittent flow.

Making electricity grids smarter and facilitating them with integration of renewable energy sources (RES) and energy storage are fairly accepted as the necessary steps to achieve a sustainable and secure power industry. To enable Net-zero energy and optimize power management for future homes or buildings, DC electric distribution systems (DC Nano-grid) find feasibility and simplicity for integrating renewable energy sources and energy storage. However, integrating the sources and loads in a simple, robust and smart way is still challenging. High voltage lithium-ion battery should be seriously considered concerning the overcharge/over-discharge risk. Dissipative cell equalization and its performance are studied. Non-dissipative equalization methods are reviewed using an energy flow chart. Typical charging schemes and the related over-charge risk are illustrated. A Lithium-ion battery charging profile based on VCell_Max/Min monitoring is proposed and validated with experimental results in an 8.4kW bidirectional battery charger for DC future home. For the DC future home emulator testbed, a grid interface converter, i.e. energy control center (ECC) converter, is reviewed with functions identification. A PV system with different configurations is compared to further expand the common MPPT region, and a DC-DC converter is designed as the interface between PV panels and DC bus, facilitating maximum power point tracking (MPPT) as well as fulfill the system energy management requirement. An 8.4kW multi-phase bidirectional battery charger with Si IGBT in DCM operation is designed to achieve high efficiency and to be the interface converter between lithium-ion battery and DC bus, enhancing the battery system management as well as increasing the system reliability. To integrate all the sources and loads in a simple, reliable and smart way, this thesis proposes a distributed droop control method and smart energy management strategy to enhance the Net-zero electric energy cost. All of the control strategies are applied to the DC future home with interactions among the energy control center (ECC), renewable energy sources, energy storage and load within a day/24 hours. System level energy management control strategies for Net-zero electric energy cost are examined and illustrated. A 10kW future home emulator testbed is built and introduced for concepts validation. / Master of Science

This work reports the experimental and numerical study of the thermal management of Li-ion battery packs under the context of electric vehicle (EV) or hybrid EV (HEV) applications. Li-ion batteries have been extensively demonstrated as an important power source for EVs or HEVs. However, thermal management is a critical challenge for their widespread deployment, due to their highly dynamic operation and the wide range of environments under which they operate. To address these challenges, this work developed several experimental platforms to study adaptive thermal management strategies. Parallel to the experimental effort, multi-disciplinary models integrating heat transfer, fluid mechanics, and electro-thermal dynamics have been developed and validated, including detailed CFD models and lumped parameter models. The major contributions are twofold. First, this work developed actively controlled strategies and experimentally demonstrated their effectiveness on a practical sized battery pack and dynamic thermal loads. The results show that these strategies effectively reduced both the parasitic energy consumption and the temperature non-uniformity while maintaining the maximum temperature rise in the pack. Second, this work established a new two dimensional lumped parameter thermal model to overcome the limitations of existing thermal models and extend their applicable range. This new model provides accurate surface and core temperatures simulations comparable to detailed CFD models with a fraction of the computational cost. / Ph. D. / Li-ion batteries have been widely used today as power source of electric vehicles (EV) or hybrid electric vehicles (HEV). Thermal management represents an important issue for the safe and efficiency of Li-ion batteries in EVs and HEVs. Thermal issues can lead to decreased energy efficiency, reduced battery lifetime, and even catastrophic failures. However, effective thermal management of Li-ion batteries is challenging due to several reasons, including the highly dynamic operation of the batteries and the wide range of ambient conditions under with the vehicles operate. To address these challenges, this work studied the thermal management problem through both experimental and numerical methods. Experimentally, actively controlled strategies have been designed and tested on our customized experimental platforms, and the results demonstrated the effectiveness such strategies. Numerically, multidisciplinary models have been developed and validated to provide comprehensive information of battery operation, and furthermore to simulate operation under extreme conditions that are difficult study experimentally. This dissertation reports both the experimental and numerical results, with a detailed analysis of their implications and applications.

Lithium alloys with metallic or semi-metallic elements are attractive candidate materials for the next-generation rechargeable Li-ion battery anodes, thanks to their large specific and volumetric capacities. The key challenge, however, has been the large volume changes, and the associated stress buildup and failure during cycling. The chemo-mechanics of alloy-based electrode materials entail interactions among diffusion, chemical reactions, plastic flow, and material property evolutions. In this study, a continuum theory of two-way coupling between diffusion and deformation is formulated and numerically implemented. Analyses based on this framework reveal three major conclusions. First, the stress-to-diffusion coupling in Li/Si is much stronger than what has been known in other electrode materials. Practically, since the beneficial effect of stress-enhanced diffusion is more pronounced at intermediate or higher concentrations, lower charging rates should be used during the initial stages of charging. Second, when plastic deformation and lithiation-induced softening take place, the effect of stress-enhanced diffusion is neutralized. Because the mechanical driving forces tend to retard diffusion when constraints are strong, even in terms of operational charging rate alone, Li/Si nano-particles are superior to Li/Si thin films or bulk materials. Third, the diffusion of the host atoms can lead to significant stress relaxation even when the stress levels are below the yield threshold of the material, a beneficial effect that can be leveraged to reduce stresses because the host diffusivity in Li/Si can be non-negligible at higher Li concentrations. A theory of coupled chemo-mechanical fracture driving forces is formulated in order to capture the effect of deformation-diffusion coupling and lithiation-induced softening on fracture. It is shown that under tensile loading, Li accumulates in front of crack tips, leading to an anti-shielding effect on the energy release rate. For a pre-cracked Li/Si thin-film electrode, it is found that the driving force for fracture is significantly lower when the electrode is operated at higher Li concentrations -- a result of more effective stress relaxation via global yielding. The results indicate that operation at higher concentrations is an effective means to minimize failure of thin-film Li/Si alloy electrodes.

Une compréhension précise de la géométrie de coordination et de la structure électronique autour d’un ion métallique à l’intérieur des catalyseurs et des matériaux de batteries est essentielle pour contrôler ces systèmes complexes, modifier leur fonctionnement, et permettre la conception logique de sites améliorés. Cependant, la structure de ces systèmes n’est pas toujours accessible par des techniques de diffraction, et même si elle l’est, la structure électronique ne peut alors être déduite qu’indirectement des coordonnées atomiques. De ce fait, il est essentiel d’avoir une sonde directe de la structure électronique. L’objectif de cette thèse est l’étude des propriétés structurales et électroniques des sites mé- talliques de catalyseurs et de matériaux de batteries par Résonance Magnétique Nucléaire en rotation à l’angle magique (MAS NMR). La MAS NMR est une technique très performante pour l’étude des effets locaux dans les matériaux à l’état solide et permet de sonder directement la structure électronique des matériaux paramagnétiques à haute résolution. Néanmoins, cette ap- proche souffre d’une pauvre résolution et d’une sensibilité limitée pour les noyaux proches d’un site paramagnétique. Pour dépasser ces limitations, nous avons levé des verrous dans l’acquisition et l’interprétation de la MAS NMR en développant et appliquant de nouvelles méthodes pour l’étude de solides paramagnétiques basées sur des hautes fréquences de rotation (60-111 kHz MAS). Pour ce faire, un répertoire de séquences d’impulsion a été développé pour la détection et l’interprétation des effets paramagnétiques dans des solides cristallins et non cristallins. Le potentiel de cette méthodologie a été examiné pour l’élucidation de la géométrie locale et de la structure électronique autour des sites paramagnétiques de catalyseurs homogènes ou hétérogènes, et des matériaux de cathodes en phase mixte pour des batteries au Lithium. Nous voyons dans les méthodes présentées ici, un ensemble d’outils indispensables pour l’élucidation de nombreuses questions de la chimie moderne relatives à la structure et la fonction des sites métalliques. / A precise understanding of the coordination geometry and electronic structure around metal cen- ters in catalysts and battery materials is crucial in order to control these complex systems, modify their behavior, and allow rational design of improved sites. However, such systems are not al- ways amenable for diffraction-based structural determination, and even if they are, obtaining atom-specific electronic structure can only be inferred indirectly from the atomic coordinates. As such, a direct probe of the electronic structure is highly desired. The aim of the present thesis is the investigation of structural and electronic properties of metal sites in catalysts and battery materials by magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. MAS NMR is a powerful technique for the investigation of local effects in solid materials, and offers a direct probe of highly resolved electronic structures in paramagnetic solids. However, it suffers from limited sensitivity and resolution for nuclei lying close to a paramagnetic center in general. We address these limitations by first tackling some of the bottlenecks in the acquisition and interpretation of MAS NMR by developing and applying new methodologies to paramagnetic solids using ultra-fast (60-111) kHz MAS rates. A "toolkit" of suitably designed pulse sequences is assembled for broadband detection and interpretation of paramagnetic shifts in crystalline and non-crystalline solids. The potential of this methodology is explored for the elucidation of local geometry and electronic structure around paramagnetic metal sites in homogeneous and heterogeneous catalysts, and a set of mixed-phase Li-ion battery cathode materials. We anticipate that the approaches described herein form an essential tool to elucidate many outstanding questions about the structure and function of metal sites in modern chemistry.

<p>Li-ion batteries is a system that dynamically couples electrochemistry and mechanics. The electrochemical processes occurring during battery operation induces a wealth of elemental mechanics such as deformation, plasticity, and fracture. Likewise, mechanics influences the electrochemical processes via modulating the thermodynamics of Li reactions and kinetics of ionic transport. These complex interrelated phenomena are far from being well understood and need to be further explored. This thesis studies the couplings between the mechanical phenomena and electrochemical processes in Li-ion batteries using integrated theories and experiments. </p> <p>A continuum model coupling the kinetics of Li diffusion and kinematics of large elasto-plastic deformation is established to investigate the coupling between Li transport and stress evolution in electrodes of Li-ion batteries. Co-evolutions of Li distribution, stress field and deformation in the electrodes with multiple components are obtained. It is found that the Li profile and stress state in a composite electrode are significantly different from <a></a><a>that </a>in a free-standing configuration, mainly due to the regulation from the mechanical interactions between different components. Chemomechanical behaviors of the heterogeneous electrodes in real batteries are further explored. Three-dimensional reconstructed models are employed to investigate the mechanical interactions of the constituents and their influence on the accessible capacity of batteries. </p> <p>Structural disintegration of the state-of-art cathode materials LiNi_xMn_yCo_zO₂ (x+y+z=1, NMC) during electrochemical cycling is experimentally revealed. Microstructural evolution of different marked regimes in electrodes are tracked before and after lithiation cycles. It is found that the decohesion of primary particles constitutes the major mechanical degradation in the NMC materials. Electrochemical impedance spectroscopy (EIS) measurement confirms that the mechanical disintegration of NMC secondary particle causes the electrochemical degradation of the battery. To reveal the reasons for particle disintegration, the dynamic evolution of mechanical properties of NMC during electrochemical cycling is explored by using instrumented nanoindentation. It is found that the elastic modulus, hardness, and interfacial fracture strength of NMC secondary particle significantly depend on the lithiation state and degrade as the electrochemical cycles proceed, which may cause the damage accumulation during battery cycling.</p> <p>Corrosive fracture of electrodes in Li-ion batteries is investigated. Li reaction causes embrittlement of the host material and typically results in a decrease of fracture toughness. The dynamics of crack growth depends on the chemomechanical load, kinetics of Li transport, and the Li embrittlement effect. A theory of coupled diffusion, large deformation, and crack growth is implemented into finite element program and the corrosive fracture of electrodes under concurrent mechanical and chemical load is simulated. The competition between energy release rate and fracture resistance as crack grows during both Li insertion and extraction is examined in detail, and it is found that the corrosive fracture behaviors of the electrodes rely on the chemomechanical load and the supply of Li to the crack tip. The theory is further applied to model corrosive behavior of intergranular cracks in NMC upon Li cycles. The evolving interfacial strength at different states of charge and different cycle numbers measured by in-situ nanoindentation is implemented in the numerical simulation.</p>