Date of Award
8-22-2025
Date Published
September 2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biomedical and Chemical Engineering
Advisor(s)
Ian Hosein
Keywords
energy storage;ion coordination;ion transport mechanisms;molecular dynamics simulations;multivalent batteries;polymer electrolytes
Subject Categories
Chemical Engineering | Engineering
Abstract
Multivalent metal-ion batteries, especially calcium (Ca²⁺) and magnesium (Mg²⁺) systems, are attractive alternatives to lithium-ion technologies owing to their high theoretical energy density, improved safety profiles, and abundant natural resources. Nevertheless, the successful commercialization of these technologies is impeded by challenges in electrolyte development, particularly related to cation solvation, ion transport efficiency, and interfacial stability. This dissertation addresses these challenges through comprehensive experimental investigations and molecular dynamics simulations of polymer-based electrolytes designed explicitly for multivalent cation conduction. In the first study, polymer gel electrolytes comprising poly(ethylene glycol) diacrylate (PEGDA) and low dielectric solvents—1,3-dioxolane (DOL) and dimethoxyethane (DME)—with calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)₂) were developed and characterized. Spectroscopic analyses revealed strong Ca²⁺–solvent coordination, minimal interaction with the polymer host, and solvent-dominated ion transport. Conductivity measurements showed a non-monotonic dependence on salt concentration, reaching optimum values (10⁻⁴–10⁻³ S/cm at room temperature) balanced between enhanced charge-carrier density and ion pairing. Electrochemical characterization demonstrated effective calcium plating/stripping cycles, though increasing overpotentials indicated interfacial passivation. The second investigation extended electrolyte design by incorporating PEGDA-based gel polymer electrolytes (GPEs) utilizing Ca(BF₄)₂ salt and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) ionic liquid. These GPEs exhibited significantly enhanced ionic conductivities (up to 2.16 mS/cm), wide electrochemical stability windows (approximately 4 V), and thermal stability above 200 °C. Cycling tests demonstrated low initial overpotentials and verified stable Ca plating/stripping behavior, confirming their suitability for high-performance calcium-metal batteries. In the third project, a preliminary molecular dynamics study probing how salt concentration—expressed as oxygen-to-metal ratios (O\:M = 10 and 44)—governs solvation structure and ion transport in PEO-based polymer electrolytes was presented. Structural analyses (radial distribution functions and cluster-size distributions) showed that concentrated conditions (O\:M = 10) promote larger ionic aggregates and more frequent multi-chain coordination, whereas dilute conditions (O\:M = 44) favor greater ionic dissociation and more localized polymer coordination. These early results provide molecular-level guidance for tuning salt loading to balance structural stability and transport in solid-state polymer batteries. Collectively, these projects provide comprehensive insights into multivalent polymer electrolyte systems, emphasizing critical molecular interactions, electrolyte composition optimization, and practical electrochemical performance. This work lays a foundation for developing efficient, stable, and safe electrolytes, accelerating the realization of advanced multivalent metal-ion battery technologies.
Access
Open Access
Recommended Citation
Wang, Xinlu, "Calcium-Ion Transport in Gel and Solid Polymer Electrolytes: From Solvent-Solute Interactions to Molecular Simulations for Next-Generation Calcium Batteries" (2025). Dissertations - ALL. 2180.
https://surface.syr.edu/etd/2180
