Using antimony as a model anode to study the chemical and mechanical stability of electrodes in Li-ion and next generation batteries
Date
2019
Authors
Schulze, Maxwell Connor, author
Prieto, Amy, advisor
Shores, Matthew, committee member
Neilson, James, committee member
Weinberger, Chris, committee member
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Abstract
As humanity grapples with the ever-increasing global demand for electrical energy, we are concurrently trying to curb global greenhouse gas emissions on massive scales to avoid potentially catastrophic changes in the global climate. Strategies to address these problems include transitioning away from a fossil fuel powered society where electrical grid energy is instead generated from renewable sources and internal combustion engine vehicles are replaced with electrified ones. Both of these transitions require energy storage technologies that can deliver high efficiencies, large energy densities, large power outputs, long lifetimes, and good safety factors all while remaining affordable and sustainable to produce. Li-ion batteries have already proven their merit as an effective energy storage technology with high enough energy densities, low enough costs, and long enough lifetimes to be ubiquitous in powering portable electronic devices. While the performance metrics of Li-ion batteries have also started to allow all-electric vehicles and grid-level energy storage to become commercially feasible, limitations in their cycle lifetimes and safety concerns arising from their flammable nature still limit their widespread implementation for these application. Ultimately, the interactions between constituent materials of a battery and the modes of their degradation limit a battery's performance. As such, research to understand and mitigate the degradation of battery materials, including those that move beyond Li-ion battery chemistry, is necessary to promote the widespread, tunable, and diverse use of batteries in overcoming the challenges discussed. Herein, I present a study that uses antimony as a model anode material to develop an understanding of the critical limiting factors of next-generation battery materials. Antimony-based anodes exhibit degradation and concomitant short cycle-lifetimes that are typical of many promising next-generation battery materials, including those that move beyond Li-ion chemistries. Thus, antimony-based model anodes can be used to study such degradation, which is primarily due to chemical and mechanical instability of the electrode and its interfaces with other battery cell components. In the following chapters, strategies to improve the chemical or mechanical stability of the antimony-anode and its interfaces are developed and can be more generally applied to other promising next-generation electrode materials. The following is a journal format dissertation, with each chapter being a document that is published, submitted, or in preparation to a peer-reviewed journal. The first chapter reviews the basic operating principles of rechargeable batteries as well as critically discusses the electrochemical experiments that are common in battery materials research. In particular, the first chapter emphasizes the limits of testing half-cell configurations in representing the cycle lifetimes of full-cell batteries, the key metric needed for long cycle lifetimes in full-cells being extremely high coulombic efficiencies. Chapter two explores and develops mitigation strategies for detrimental mechano-chemical interactions at the interface between the active Cu-Sb anode and the current collector that arise from the existence of a ternary Li-Cu-Sb phase with structural similarity to both Cu2Sb and Li3Sb. While the existence of the ternary phase results in good reversibility of Cu-Sb electrodes when cycled in Li-ion batteries, it also results in the formation of voids at Cu-Sb interfaces that exacerbates delamination during cycling to result in short cycle lifetimes. Chapter three develops a procedure for the electrodeposition of antimony carbon nanotube composites as a strategy to address the bulk mechanical instability of the anode during cycling in Li- and Na-ion batteries. Results of chapter three reveal significant chemical instability at the anode-electrolyte interface and motivate much of the work performed in chapter four, which departs from focusing on antimony as an anode material and instead uses antimony to explore the properties of anode coatings. Chapter four is a systematic study that explores how annealing conditions affect properties of polyacrylonitrile coatings relevant to the chemical stabilization of the electrode-electrolyte interface. This study reveals that ion diffusion in annealed polyacrylonitrile films is correlated to the delocalization of electrons in conjugated domains within the polyacrylonitrile films. Finally, chapter five reviews the materials properties that have made the Li-ion battery so successful, such as the mechanically and chemically stable interfacial layers that form at the electrode-electrolyte interfaces. The chapter additionally highlights some recent progress in the battery materials field and suggests that electrolyte additives, interfacial coatings, and solid-state electrolytes as the most impactful types of materials to continue researching and developing for the future.
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Subject
antimony
Li-ion
anode
Na-ion
battery