SUMMARY

Monolithic aluminum foils are attractive candidates for replacing graphite in Li-ion batteries. However, fundamental challenges, including large volume changes, solid-electrolyte interphase (SEI) formation, and sluggish ion transport, require better understanding. This thesis investigates how aluminum alloy foils with different compositions behave electrochemically and chemo-mechanically during galvanostatic cycling. Different foil compositions exhibited a power-law dependence between electrochemical cycle life and the amount of material reacted per cycle. This relationship was termed “electrochemical fatigue,” as inspired by mechanical fatigue processes. High-purity foils also exhibited higher Coulombic efficiencies (CE) in the first cycles compared to Al alloy foils. Operando optical microscopy revealed different spatiotemporal reaction mechanisms, which affects CE behavior through lithium trapping. This thesis then investigates the role of microstructure, composition, and processing conditions on lithium alloying/dealloying, lithium trapping behavior, and damage evolution. Electrochemical measurements with cross-sectional SEM imaging helped visualize the distribution of reaction products and damage. Composition and heat treatment affects grain structure, mechanical properties, and defect concentrations, which influence morphology and distribution of the LiAl phase during lithiation. Upon delithiation, the reacted LiAl morphology affects the degree to which cracking vs. lithium trapping occur. It is speculated that the internal stress state plays a role in the degree of lithium trapping. Secondary precipitate phases also cause concentrated chemo-mechanical damage as voids that form and remain during cycling. This study advances understanding about the role of microstructure and processing on lithium trapping and fracture, paving the way for the rational design of foil anodes with enhanced stability and performance. Virtual link: https://bit.ly/3Tzh1ll