2025 Theses Doctoral

Physics-Based Modeling for Phenomenological Discovery in Secondary Battery Systems

Bernard, John C.

This doctoral thesis focuses on leveraging physics-based modeling, in conjunction with advanced electrochemical characterization and parameter estimation techniques, for phenomenological discovery in secondary battery systems. The research addresses critical challenges in understanding and optimizing both established lithium-ion batteries (LIBs) and emerging aqueous rechargeable zinc-manganese dioxide (Zn/MnO₂) batteries.

For LIBs, the study investigates the often-overlooked influence of polymer binders (PVDF) on liquid-phase Li-ion transport and tortuosity in NMC111 cathodes. A pseudo-two-dimensional (P2D) model, electrochemical impedance spectroscopy (EIS) on TiO₂ blocking electrodes, and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) was employed. Results reveal that increasing binder content significantly elevates electrode tortuosity beyond traditional Bruggeman predictions, attributed to a "choke-point" mechanism where binder constricts ion pathways. An empirical correlation linking binder volume fraction to tortuosity is proposed.

For aqueous Zn/MnO₂ systems, a multi-faceted approach was adopted to unravel their complex electrochemical behavior.
 First, a physics-based continuum model was developed, incorporating three primary reaction pathways: irreversible dissolution of pristine α-MnO₂, reversible dissolution/deposition of a zinc-manganese oxide (ZMO) species coupled with zinc-hydroxide-sulfate (ZHS) precipitation, and reversible Zn₂+ insertion/extraction into ZMO. Parameter estimation against experimental data identified electrolytic zinc depletion, driven by ZHS formation, as a key capacity-limiting factor.


Second, Galvanostatic Intermittent Titration Technique (GITT) was utilized to differentiate "fast" (kinetic/IR) and "slow" (transport/pH-driven) voltage relaxation processes. This analysis highlighted the critical role of pH dynamics, modulated by ZHS precipitation and solvation effects, in controlling cell potential and reaction kinetics, particularly for the ZMO dissolution/deposition pathway.

Third, electrolyte engineering strategies were systematically investigated, focusing on the effects of initial electrolyte pH (via H₂SO₄ addition), ZnSO₄ concentration, and MnSO₄ concentration on the performance and degradation of both 𝛼-MnO₂ and 𝛽-MnO₂ based cells. Operando pH measurements and continuum modeling linked capacity fade to the evolution of spatial gradients and potential material redistribution, influenced by ZHS precipitation and non- uniform MnO₂ utilization. Optimal ZnSO₄ levels were found to mitigate Zn²⁺ depletion, while initial acidification offered transient benefits, and increased MnSO₄ appeared to accelerated degradation.

Overall, this work provides significant mechanistic insights into the internal workings of these battery systems. The findings offer actionable principles for electrode design in LIBs and for electrolyte formulation and operational strategies in aqueous Zn/MnO₂ batteries, contributing to the development of more efficient and durable energy storage solutions.