MSE Thesis Defense: “High-Resolution Characterization of Solid-Liquid Interfaces in Energy Storage Materials Using Microscopy: From Lithium Metal Anodes to Liquid Sodium-Potassium”

Battery technologies are crucial for reducing greenhouse gases by enabling the use of renewable energy and facilitating the transition to electric vehicles, thereby lowering emissions. Lithium metal anodes are ideal for next-generation batteries in automotive applications due to their high energy density. However, issues such as dendrite formation and solid electrolyte interphases (SEI) affect their long-term stability and reliability. Conversely, liquid metal batteries, like liquid Na-K anodes, show promise for large grid storage systems due to their fast kinetics, low cost, and potentially long cycle life. Despite these benefits, the development of liquid metal anodes has not been fully explored, making the feasibility of Na-K anodes uncertain. This thesis aims to address these challenges using cryogenic electron and ion beam microscopy. We developed a technique to create electron transparent battery samples for characterization by cryogenic transmission electron microscopy (cryo-TEM). Through this method, we discovered short-range ordering in the SEI of Li-metal batteries using cryogenic four-dimensional scanning transmission electron microscopy (4D-STEM). We propose that the structural ordering in SEIs is crucial for suppressing Li dendrites, thereby enhancing battery performance. Although SEIs were previously thought to be a mix of inorganic precipitates and organic matrix, our data suggest that their true morphology is largely amorphous, indicating significant electron beam damage in earlier analyses. We also investigated the behavior of liquid Na-K anodes with Na-ion electrolytes. Characterizing liquid metals is challenging due to their fluidic properties and high surface tension. However, cryogenic focused ion beam/scanning electron microscopy (cryo-FIB/SEM) and various characterizations revealed the dissolution of K, making these anodes unsuitable for Na-ion electrolytes. Our findings highlight the potential of cryogenic microscopy techniques in advancing battery technology and addressing key challenges in the development of next-generation energy storage systems.