Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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Item In-situ investigation of lithium dendrite growth and its interactions with a polymer separator in a lithium metal cell(2023) Kong, Lingxi; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium dendrites are metallic structures that initiate and grow inside a lithium battery duringcharging. Lithium dendrite growth can negatively affect battery cycle life and safety. Observing the dendrite growth process and revealing its interaction with other components is necessary to improve battery safety. This study uses a transparent optical cell to directly observe the dendrite growth process, explore the lithium dendrite growth modes under various current densities, evaluate the interactions between the dendrite and separator, and explore the effect of electrolyte additives on dendrite growth behavior. The dendrite growth under different current densities showed the transition of dendrite morphologies from a dense structure to a porous structure. The examination of the dendrite-separator interaction regions showed that dendrites can deform and penetrate the separator. We show that additives can enhance the uniformity of lithium dendrite distribution compared with the dendrite formed in the electrolyte without additives.Item DEGRADATION ANALYSIS AND HEALTH MONITERING OF LITHIUM ION BATTERIES(2011) Williard, Nicholas Dane; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Degradation and health monitoring of lithium-ion batteries is explored through life-cycle testing and failure analysis. Test samples comprised of four different battery types from two different manufactures underwent aging and charge/discharge cycling using a variety of load profiles including constant current discharge, pulsed discharge, and varying depths of discharge. Data from in situ monitoring of several parameters including current, voltage, temperature and internal resistance, was analyzed in order to find the best features that could be used to track and characterize battery performance degradation. Degraded samples were disassembled according to a newly developed disassembly methodology that considered the effects of the environment on post-disassembly failure analysis results. Several different failure analysis methods were used in order to gain an understanding of how degradation mechanisms propagate from a materials stand point. Battery electrodes were investigated to observe changes in their chemical and mechanical structures.