Developing model architectures via atomic layer deposition to investigate interfacial electrochemical processes in lithium-ion batteries
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This dissertation describes the development of thin film electrodes with well-defined structures and geometries (architectures) to aid in the assessment of complex charge transfer processes in lithium ion battery systems. Titanium dioxide (TiO₂) anodes and vanadium pentoxide (V₂O₅) cathodes are synthesized via atomic layer deposition (ALD) onto transparent and opaque carbon films and used as model interfacial systems to investigate the chemical and electrochemical properties of lithium ion (Li-ion) coupled electron transfer processes at the electrode/electrolyte interface. The superior film quality and precise control over structure and chemistry afforded by ALD allow tuning of the electrode properties to facilitate coupling of analysis methods and provide new insights. A combination of analytical techniques, including cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF SIMS), and ultraviolet-visible (UV-Vis) absorption spectrophotometry, is used to elucidate mechanistic information about charge storage processes. Electrochemical investigations of TiO₂ lithiation coupled with high-resolution, spatially resolved surface analytical techniques demonstrate that in situ formation of hydrofluoric acid (HF) during cycling can alter the lithiation process and introduce partial lithiation by conversion reaction as a result of HF co-intercalation. The relationship between electrode material length scale (thickness) and the balance between charge storage via bulk intercalation versus surface pseudocapacitance is also determined for TiO₂. Combined CV and UV-Vis absorption spectrophotometry are used to investigate optical and electronic transitions in transparent V₂O₅ cathodes as a function of lithiation.