Nanoscale reaction, transport, and phase transformation in LixFePO4 battery electrodes
- Interfacial reaction, transport, and phase transformations are the primary mechanisms by which materials change. Understanding these processes, especially on the nanoscale, is key to understanding how material properties change through external physical and chemical stimuli. To obtain a holistic understanding, it is also necessary to study how these mechanisms are coupled to one another. The lithium-ion battery is an ideal model system for studying the coupling of reaction, transport, and phase transformations on the nanoscale. Not only do batteries use all three mechanisms during charge and discharge, it is also possible to precisely control the lithium composition, an extrinsic variable, at the nanoscale by controlling the electrochemical current. Fundamental studies of Li-ion battery materials, especially phase transforming ones, are hindered by the porous electrode architecture. Such porous electrodes contain an ensemble of nanoparticles with nonuniform electronic and ionic connectivities. With heterogeneous current densities and lithium compositions, it is very difficult to correlate macroscopic current-voltage or structural measurements to microscopic, single-particle phenomena. My thesis overcomes this problem by using nanoscale imaging study individual battery particles. By being able to probe the lithium composition and current density of single battery particles on the nanoscale, I obtain a local, microscopic measurements of reaction, transport, and phase transformation dynamics. While I initially conduct these experiment ex situ by cycling and disassembling the battery electrodes, I also develop in situ techniques that enable me to track the evolution of the lithium composition and current density on the nanoscale as the battery charges and discharges. I specifically aim to understand four different ways that reaction, transport, and phase transformation are coupled on the nanoscale. First, I study how transport at the porous electrode affects reaction and phase transformation within individual particles. Second, I investigate how ion insertion reaction rate affects the phase transformation pathway. Third, I examine how the lithium composition and phase affects the ion insertion reaction rate. Finally, I study how diffusion affects the ion insertion rate. I developed a coherent model that quantitatively explains how the rate of ion insertion reaction and the rate of diffusion ultimately affect the phase transformation pathway, both within individual battery particles and in a many-particle electrode. This model shows how reaction, transport, and phase transformation are coupled together to determine how this battery electrode undergoes charge and discharge.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Materials Science and Engineering.
|Statement of responsibility
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2016.
- © 2016 by Yiyang Li
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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