Date of Award

2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Materials Science & Engineering

First Advisor

Eric Detsi

Abstract

There is an urgent need to increase national use of clean, renewable energy. While resources such as solar energy are highly intermittent, renewable energy adoption can be extended by dramatically increasing the energy density of Li-ion battery (LIB) technology used to store renewable energy by replacing graphite with high-capacity nanostructured alloy anodes. However, there are many challenges to utilizing these materials in commercial LIBs, including: (1) limited sustainable and scalable nanomaterial fabrication methods, and (2) their poor cycling performance. In this work, we seek to better understand and help mitigate these two challenges. To address the first challenge, we demonstrate a methodology for fabrication of nanoporous Au (NP-Au) through electrolytic dealloying of a Au-Ag parent alloy with simultaneous recovery of the sacrificial Ag material. This sustainable electrolytic dealloying method is generalized to a procedure that can be used to fabricate a wide array of nanoporous metals including nanoporous Al (NP-Al), a promising high-capacity alloy anode material. We find that NP-Al fabricated through this methodology is nearly oxide-free and consists of a hierarchical, bimodal morphology with the smaller ligaments having a structure size of 10-20 nm. While NP-Al alloy anodes exhibit enhanced performance compared to bulk Al, NP-Al still has a short cycle life, prompting the need to explore the various morphological evolutions that occur during cycling that give rise to this poor performance. We address the second challenge by studying the solid-electrolyte interphase (SEI), microstructure, and phase evolutions that occur when cycling nanoporous alloy anodes. Using transmission electron microscopy (TEM), we find that the SEI formed on a NP-Au model anode becomes increasingly thick during lithiation and fractures during delithiation. Next, we investigate the microstructural evolution of NP-Au during cycling using TEM and small-angle X-ray scattering. The nanoporous structure degrades during lithiation as the ligaments expand and pulverize to form nanoparticles which become trapped in the SEI. During delithiation, SEI containing these particles fractures and a fine porous structure forms on the ligaments. From these insights, we develop a model for the degradation that occurs during cycling. The last morphology evolution process explored is the phase transformation pathways that occur in nanoporous alloy anodes compared to bulk alloy anodes. By comparing the voltage profile shape of bulk and nanoporous Ag (NP-Ag) model alloy anodes with X-ray diffraction data and the calculated Ag open circuit voltage, we can determine the phase transformation pathways that occur during cycling. While bulk Ag follows the pathway expected by the phase diagram, the NP-Ag alloy anode forms a non-equilibrium solid solution during lithiation. We develop models of the complex core-shell phase morphologies expected from both of these pathways. Lastly, we explore NP-Al as a candidate material for an alternative energy application: a water-reactive metal used to produce hydrogen gas on-demand to generate clean electricity using a fuel cell. From our conclusions, we suggest future work and show preliminary results for a fully electrochemical (de)alloying alloy anode fabrication process, and an operando TEM investigation of alloy anode degradation processes.

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Video2.1.mp4 (2656 kB)
Video2.2.mp4 (15732 kB)
Video7.1.avi (11044 kB)
Video7.2.avi (23500 kB)

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