Understanding the solid electrolyte interface (SEI) on alloying anodes: development of a methodology for SEI sample preparation and x-ray photoelectron spectroscopy characterization and studies of the SEI on electrodeposited thin film intermetallic anodes for Li-ion batteries
Date
2020
Authors
Kraynak, Leslie A., author
Prieto, Amy L., advisor
Shores, Matthew, committee member
Strauss, Steven, committee member
Bandhauer, Todd, committee member
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Abstract
The solid electrolyte interface (SEI) is an important component of Li-ion rechargeable batteries that forms due to the potential stability limits of the organic electrolyte falling within the large operating potential window of the battery. It plays a crucial role in battery performance by passivating the electrode surface; it also affects the safety, Li-ion consumption/inventory, and Li-ion transport rates of the battery. Despite decades of study, there is still much that is unknown about the SEI, especially how to intentionally modify the composition and properties of the SEI in order to obtain better performance as measured by metrics that include reversible capacity and cycle lifetime. The gaps in understanding of the SEI are even more pronounced for alloying anode materials, and the mechanical and chemical instability of electrode surfaces and the SEI formed from conventional secondary battery electrolytes is one of the bottlenecks in the development of next generation battery technologies. The first chapter of this dissertation is an overview of studies from the past two decades concerning the SEI formed on metallic alloying anodes, examining SEI formation, the evolution of the SEI over long term cycling, and improvements to the SEI through the use of additives and novel electrolytes. Compared to the body of literature on the SEI on other anode materials such as graphite, Li metal, and silicon, there has been relatively little published about the SEI on metallic alloying anodes such as tin, antimony, and intermetallics, especially considering the scope of these types of anode materials. However, a comparison of the existing literature concerning the SEI on alloying anodes reveals interesting similarities and difference between the SEI formation and evolution on metallic alloying anodes and highlights some critical gaps in knowledge for the field. The second chapter concerns the development of a methodology to study the SEI formed on alloying anodes, and in particular binder- and additive-free thin film electrodes. The formation, composition, and properties of the SEI are dependent on a number of experimental variables, which makes it difficult understand the factors that affect SEI performance and limits progress towards the goal of more controlled or intentional SEI formation for better battery performance. One of the first steps towards this goal is to be able to make and characterize SEI samples in a reproducible manner. This chapter outlines some of the important considerations for SEI sample preparation that are not widely discussed in the battery community in addition to some of the important considerations for using X-ray photoelectron spectroscopy to characterize the SEI. The third and fourth chapters are about using the methodology described in Chapter 2 to characterize the SEI formed on intermetallic thin film anodes. The third chapter examines the role that vinylene carbonate, a conventional SEI-improving electrolyte additive, plays in passivating the surface and extending the cycle lifetime of Cu2Sb electrodes. The fourth chapter is concerned with understanding what role the SEI plays in the cycle performance of pure phase SnSb thin film electrodes. Studying changes in the SEI on SnSb over different stages of cycling can help elucidate whether the SEI plays a role in the capacity retention and long cycle lifetime of SnSb and whether it ultimately contributes to the failure of the electrode.
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Subject
thin films
intermetallics
XPS
surface characterization
Li-ion batteries