UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

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    HIGH-SAFETY ELECTROLYTES DESIGN FOR HIGH ENERGY DENSITY BATTERY DEVICES
    (2021) Zhang, Jiaxun; Wang, Chunsheng CW; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Recently, the market share of lithium-ion batteries (LIBs) increase rapidly in the global energy market, while accidents related to fires and explosions of LIBs reported worldwide in the past several years, thus battery safety is a vital prerequisite for battery application in our daily life. The flammable organic solvent in the electrolyte of the battery is the main source that leads to fires and explosions of batteries. Designing intrinsically safe electrolytes is the key to enhancing the safety properties of batteries. Fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes are attractive due to their inherent non- or less-combustibles. However, the energy density, cycle stability, and battery cycle life of the LIBs using the above electrolyte systems are far from commercial batteries due to poor solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In this dissertation, we designed SEI/CEI on anode/cathode surfaces in fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes to enhance battery performance. Specifically, 1. By building a highly stable CEI on a high-voltage LiCoO2 cathode, we improved the energy density of fluorinated organic electrolyte batteries. 2. By introducing UV-curable polymer into the organic electrolytes, we lowered the flammability of the sodium batteries and enhanced the energy density of the sodium battery system with stable CEI on sodium cathode. 3. By limiting the water activity in the bulk electrolyte and constructing an effective SEI layer on anode surface, we expanded the electrochemical stability window of the aqueous electrolytes. We seek to understand the working mechanism of SEI/CEI in different high-safety electrolyte systems. The corresponding electrochemistry, thermodynamics, kinetics, and reaction reversibility are studied in this work.
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    Comprehensive Calorimetry and Modeling of the Thermally-Induced Failure of a Lithium Ion Battery
    (2016) Liu, Xuan; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A lithium ion battery (LIB) subjected to external heat may fail irreversibly. Manifestation of this failure include venting of potentially combustible gases and aerosols followed by a rapid self-heating accompanied by ejection of the battery materials. Quantification and simulation of the dynamics and energetics of this process are important to ensure LIBs’ safety. Here we report on development of a new experimental technique for measuring the energetics of the thermally-induced failure of LIBs as well as a new thermo-kinetic model to predict battery failure behaviors. The newly developed experimental technique, Copper Slug Battery Calorimetry (CSBC), was employed to investigate a widely utilized form factor of LIB (i.e. 18650) with 3 different battery chemistries: lithium cobalt oxide (T-Energy ICR18650, LCO), lithium nickel manganese cobalt oxide (Panasonic CGR18650CG, NMC) and lithium iron phosphate (K2 18650E, LFP), at various states of charge (SOCs). This technique can yield time resolved data on the rate of heat production inside the failing battery. The heat capacity of these LIBs was evaluated to be 1.1±0.1 J g-1 K-1 for all three cathode types. It was shown that the total heat generated inside the batteries increases with increasing amount of electrical energy stored. The maximum total internal heat generated by fully-charged LIBs was found to be 37.3±3.3, 34.0±1.8 and 13.7±0.4 kJ/cell for LCO, NMC and LFP LIBs, respectively. Additionally, experiments were carried out in which the CSBC technique was combined with cone calorimetry to measure the heat produced in flaming combustion of vented battery materials. The released combustion heat did not show a clear dependence on the stored electrical energy; this heat varied between 35 and 63 kJ/cell for LCO LIBs, 27 and 81 kJ/cell for NMC LIBs, and 36 and 50 kJ/cell for LFP LIBs. Beyond the experimental work, detailed modeling of heat transfer in the CSBC experiments was carried out, by utilizing COMSOL Multiphysics software, to evaluate thermal conductivities of the LIBs and demonstrate the satisfactory accuracy of CSBC experimental analysis in the determination of the battery failure energetics for all examined battery types. Moreover, it is presented in this study a general methodology to develop a thermo-kinetic model of thermally-induced failure of lithium ion batteries (LIBs), using COMSOL and experimental data collected by CSBC. This methodology is demonstrated specifically on LCO LIBs (T-Energy ICR18650), but it can be easily extended to other battery types. The model was parameterized based on Arrhenius’ Law and via an iterative inverse modeling analysis of CSBC test results using COMSOL. These model parameters are dependent on the cells’ states of charge (SOCs) and they can effectively represent the tested cells’ heat production energetics during failure. The fully-parameterized thermo-kinetic model was then validated against CSBC tests that were not utilized in the model parameterization: CSBC tests on 100% SOC LIB cell with non-standard heating rates ranging from 40 W to 100 W; and CSBC tests on 75% SOC LIB cell with a standard heating rate of 20 W. The agreements between the experimentally measured and the simulated copper slug temperature histories in these tests were found within in 5% on average. Last but not least, this model was applied to predict the thermally-induced failure of LIB cells in a more complex scenario – cascading LIB failure of 6 LIB cells in a billiard battery pack. The simulated onset time of thermal runaway of each LIB cell in the battery pack were found of excellent agreements with experimental observations.
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    Heterogeneous Ordered Mesoporous Carbon/Metal Oxide Composites for the Electrochemical Energy Storage
    (2015) Hu, Junkai; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The combination of high electronic conductivity, enhanced ionic mobility, and large pore volume make ordered mesoporous carbons (OMCs) promising scaffolds for active energy storage materials. However, mesoporous structures and material morphology need to be more thoroughly addressed. This dissertation discusses the effects of mesoporous structures and material morphologies on the electrochemical performance of OMC/Fe2O3 composites. In the first approach, Fe2O3 was embedded into 1D cylindrical (FDU-15), 2D hexagonal (CMK-3), and 3D bicontinuous (CMK-8) symmetries of mesoporous carbons. These materials were used as supercapacitors for a systematic study of the effects of mesoporous architecture on the structure stability, ion mobility, and performance of mesoporous composite electrodes. The results show that the CMK-3 and CMK-8 synthesized by hard template method can provide high pore volume, but the instability of their mesostructures hinders the total electrode performances upon oxide impregnation. In contrast, the FDU-15 from the soft template method can provide a stable mesostructure. However, it contains much smaller pore volume and surface area, leading to limited metal oxide loading and electrode capacitance. Based on these results, anodized aluminum oxide (AAO) and triblock copolymer F127 are used together as hard and soft templates to fabricate ordered mesoporous carbon nanowires (OMCNW) as a host material for Fe2O3 nanoparticles. The synergistic effects in the dual template strategy provide a high pore volume and surface area, and the structure remains stable even with high metal oxide loading amounts. Additionally, the unique nanowire morphology and mesoporous structure of the OMCNW/Fe2O3 facilitate high ionic mobility in the composite, leading to a large capacitance with good rate capability and cycling stability. I further evaluated this OMCNW/Fe2O3 as a lithium-ion battery (LIB) anode, which showed that the porous symmetry, material morphology, and structure stability are even more important in the rate and cycling performances of LIBs. This work helps further the understanding and optimization of porous structures and morphologies of heterogeneous composites for next generation electrochemical energy storage materials.