ChE PhD Dissertation Defense: Dominick Guida

Dominick Guida

Title:

Characterizing and Modeling Heterogeneity in Alkaline Zn-MnO2 Batteries Using Synchrotron CT and EDXRD

Date:
11/25/2024

Time:
11:00:00 AM

Committee Members:
Prof. Joshua Gallaway (Advisor)
Prof. Leila Deravi
Prof. Richard West

Location:
EXP 610 and Teams

Abstract:
Alkaline Zn-MnO2 cells have dominated the primary battery industry for decades, enabled by their inherent safety, minimal environmental impact, and low cost. Despite their widespread use, the internal phenomena that occur within alkaline Zn anodes and MnO2 cathodes remain incompletely characterized. Within alkaline Zn anodes, unaccounted discharge phenomena result in an inability to predict active material distribution, internal resistance, and eventual cell failure. In the MnO2 cathode, heterogeneous protonation and subsequent gradient relaxation impacts cell performance, yet remains incompletely characterized. A robust understanding of the function of alkaline Zn-MnO2 batteries is a necessary step in further improving their performance and expanding on their usefulness.

To better understand Zn anodes, high resolution computed tomography (CT) was used to determine the material distribution and morphology of active phases in situ for Zn anodes discharged under various conditions. A novel algorithm was then developed to segment each individual phase from the CT data and obtain 1-D radial material distributions for direct comparison with computational modeling. The evaluation of material distributions and battery performance data provided invaluable insights on the function of alkaline Zn anodes, including percolation effects on the Zn particle network, maintenance of the electronic network through ZnO bridging, and solid phase mobility due to granular flow. Identifying these phenomena have been a significant step towards elucidating the functional mechanisms within alkaline Zn anodes, representing critical behaviors that had previously gone undetected. Not accounting for such pivotal electrode characteristics provides ample evidence as to why early modeling attempts failed to adequately capture Zn anode function. By incorporating these newly discovered phenomena, it is now possible to predict the behavior of alkaline Zn anodes with excellent accuracy.

In studying MnO2 cathodes, spatially resolved energy dispersive X-ray diffraction (EDXRD) was used to measure the heterogeneity in protonation of the active material. When using a pulsed discharge protocol, it was identified that a significant gradient in MnO2 proton content forms across the cathode thickness during a discharge pulse and partially relaxes during a subsequent rest. The rate of gradient relaxation suggested a redox-based mechanism for proton redistribution, which was not accurately predicted when using typical kinetic models. A fundamental kinetics experiment was performed on prismatic MnO2 electrodes, identifying that the core-shell discharge behavior of MnO2, where undischarged cores of MnO2 are surrounded by shells of MnOOH discharge products, has significant implications for the reaction kinetics. As a result, the kinetic expression used for MnO2 cathodes was modified to account for the effects of proton transport limitations induced from the MnOOH shell, as well as kinetic effects of the active particle surface. This new expression dramatically improved MnO2 cathode model accuracy, with simulated proton gradient formation and relaxation rates being in excellent agreement with EDXRD measurements.

The experimentally driven insights into alkaline Zn anodes and MnO2 cathodes have led to significant discoveries of previously unknown and uncharacterized phenomena that impact cell performance. These results were then incorporated into computational models to improve their accuracy and effectiveness, while also representing an improved overall understanding of alkaline Zn-MnO2 batteries.