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Title:In situ studies of surface reactions affecting Li-ion battery failure
Author(s):Tang, Ching-Yen
Director of Research:Dillon, Shen J.
Doctoral Committee Chair(s):Dillon, Shen J.
Doctoral Committee Member(s):Braun, Paul V.; Bellon, Pascal; Schleife, André
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Li-ion battery
Surface reactions
Abstract:Li-ion batteries dominate commercial use in economically important applications such as portable electronic devices and electric vehicles. Tremendous effort has been dedicated to improving the safety and cycle life of Li-ion batteries. Unfortunately, many of the mechanisms and fundamental atomistic processes governing the degradation and failure of Li-ion batteries remain poorly understood. Capacity fade in commercially relevant systems can broadly be traced back to the interfaces between the cell components and electrolyte where so-called side reactions occur; such as Li trapping in non-active regions, loss of active electrode material, gas evolution, electrolyte decomposition, and chemical reactions with packaging and current collectors. Particular side reactions dominating capacity fade vary with electrode and electrolyte chemistry. Many of the general trends and associated design principles have not been established and are not generally agreed upon. Investigating battery evolution is challenging as many structural and analytical characterization techniques are best suited for ex situ study. This can be problematic due to the sensitivity of such systems, particularly their surface chemistry, to the ambient environment, particularly H2O and O2. Since the surface reactions are also dynamic and can exhibit time dependent relaxations in situ study is better suited to elucidating surface reaction mechanisms. The work in this dissertation develops a novel cross-platform in situ open cell approach to carry out studies with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The cell was first utilized to study the mechanism of lithium dendrite growth, which imposed a safety concern for the current Li-ion battery. This study elucidated the underlying mechanism for lithium dendrite growth on carbon, which presents a significant safety risk in Li-ion systems. Second, the open cell configuration was used to study the conversion anode material CuO, demonstrating the first advanced in situ XPS/AES cell in the field of Li-ion battery research. This work shed lights on the inconsistencies in the published literature with respect to the reaction pathway of CuO during Li-ion cycling. Furthermore, the cell was applied to study the surface evolution of LiMn2O4 cathode material. A series of systematic experiments suggest that its poor cycle life results in part from the cyclic formation and decomposition of Li2CO3 that occurs upon cycling which in turn leads to CO/CO2 evolution. Finally, related experiments were performed on several cathode materials including LiCoO2, LiNiO2, LiMn2O4, LiFePO4 and LiNi1/3Mn1/3Co1/3O2. A relationship between carbon surface stability and cycle life was identified. This instability is hypothesized to be associated with CO2 evolution commonly observed in measurements of gas evolution from cathodes. To further investigate the role of these gases in affecting full cell cycle life, cycling experiments were carried out in flowing mixed gases of Ar, CO, and CO2. This dissertation deals with the detailed observation and description of the mechanism controlling the surface evolution of several cathode and anode electrodes, demonstrating the importance of surface reactions affecting the battery failure. The results provide new visions into the surface modification or functionalization for improved cycle life in the commercial Li-ion battery.
Issue Date:2017-10-17
Rights Information:Copyright 2017 Ching-Yen Tang
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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