Putting the reversibility of lithium batteries under the microscope : dissolved cathode species, water impurities, and artificial protection layers

This thesis presents a comprehensive examination of the critical components influencing the performance and longevity of lithium batteries, with a particular focus on the solid-electrolyte interphase (SEI) and its integral role in battery stability and functionality. Through a series of meticulous studies, the thesis leverages advanced characterization and analytical techniques to unravel the complex mechanisms at play within battery anodes and proposes innovative strategies to mitigate performance degradation. In Chapter 1, the thesis begins with a comprehensive introduction to rechargeable lithium battery technology, tracing its evolution from the foundational work of Goodenough, Yoshino, and Whittingham to the latest developments in advanced battery research. This historical perspective encompasses significant innovations like lithium metal, silicon anodes, and sulfur cathodes, illustrating the continuous pursuit of higher energy density, enhanced safety, and cost-effectiveness. The chapter not only introduces fundamental concepts, particularly emphasizing the pivotal role of lithium metal anodes, but also delves into the unique failure mechanisms inherent to different battery chemistries. Highlighting the advanced characterization and analytical tools play in identifying and understanding failure mechanisms of battery materials. This sets the stage for the subsequent in-depth investigations and establishes a framework for understanding the current state, challenges, and future prospects of lithium battery technology, underlining its significance in the broader context of electrification and sustainability efforts. Chapter 2 delves into the detrimental effects of dissolved transition metals, particularly nickel, from high-voltage cathodes on the performance and lifespan of lithium metal anodes. Through the use of cryogenic electron microscopy, the study unveils the intricate process of nickel incorporation into the SEI and its profound impact on the SEI's chemistry and nanostructure. This incorporation is shown to alter the transport properties of lithium ions and electrons within the SEI, expediting electrolyte decomposition, fostering the formation of "dead" lithium, and ultimately triggering battery failure. Chapter 3 shifts the focus to the formation of lithium hydride (LiH) within lithium batteries and its implications on battery efficiency and safety. The chapter presents groundbreaking findings on the formation mechanism of LiH, demonstrating that hydrogen gas, a byproduct of cycling in Li batteries, reacts with deposited lithium metal to form LiH, thus consuming active lithium and diminishing battery capacity. The discovery demonstrates that LiH, a wide-bandgap insulator, electrically isolates metallic lithium from the current collector adds a new dimension to understanding battery degradation. Furthermore, the identification of LiH on various anode chemistries, each with its distinct SEI layer, underscores the significance of this degradation pathway across different lithium battery systems. In Chapter 4, the thesis explores the potential of interfacial coatings, specifically nanometer-scale aluminum oxide (Al2O3) coatings on carbon negative electrodes, to enhance lithium-ion battery performance. The research delineates the transformative changes in the SEI's structure and chemistry induced by Al2O3 coatings during SEI formation at low potentials. The findings illuminate the critical role of the refined SEI structure, chemistry, and uniformity in elevating battery performance, challenging the prevailing notion that performance enhancements are solely attributable to the physical presence of the coatings. Finally, Chapter 5 combines the insights from the preceding chapters, offering a comprehensive summary of the thesis and projecting an outlook for the field. It emphasizes the importance of the interplay between electrolyte composition, SEI structure, and electrode material in determining the performance and durability of lithium batteries. The chapter proposes directions for future research, focusing on understanding failure mechanisms in extreme conditions and emerging battery chemistries. Overall, this thesis contributes significantly to the field of battery technology by providing a deeper understanding of the intricate interactions within lithium battery anodes and paving the way for the development of more robust, efficient, and safer battery systems.

Keywords: Engineering.
Materials Science and Engineering.
Advisor: Cui Yi
Dresselhaus-Marais Leora
Mannix Andrew J.