Date of Award
Summer 8-15-2022
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Electrochemical energy systems rely on particulate porous electrodes to store or convert energies. While the three-dimensional porous structures of the electrodes were introduced to maximize the interfacial area for better overall performance of the system, spatiotemporal heterogeneities arising from materials thermodynamics localize the charge transfer processes onto a limited portion of the available interfaces. These reaction heterogeneities may cause local hot and cold spots, and early battery failures. This dissertation focuses on the following three aspects of the dynamic reaction heterogeneities in the particulate cathodes and anodes in the lithium-ion batteries: (i) the real-time evolution of reaction heterogeneities in graphite anodes, (ii) the origin of reaction heterogeneities and their interplay with the phase transformation mechanisms in graphite anodes, and (iii) the quantification method of reaction heterogeneities in solid-solution cathodes. The dissertation also concentrates on the systematic electrochemical investigation of the graphite cathodes in aluminum-ion batteries for their coherent design.A simple but precision method has been developed that can directly track and analyze the operando (i.e. local and reacting) interfaces at the mesoscale in a practical graphite porous electrode to obtain the true local current density. The seemingly random reaction heterogeneities are actually controlled by the interplay between the non-equilibrium material thermodynamics and the electrochemical kinetics. The combined theoretical and experimental analyses revealed that unlike other phase-transforming porous electrodes, not all phase separation processes in graphite electrodes can be suppressed by high currents. The results shed light on the long-standing discrepancies in kinetics parameters derived from electroanalytical measurements and from first principles predictions and highlight the necessity to examine the concentration-dependent exchange current density for intercalation electrodes undergoing complex phase transformation processes. While optical microscopy revealed the subtleties of spatiotemporal heterogeneities in graphite electrodes, their identification in solid-solution materials posed challenges. A Raman spectroscopy tool has been developed to map and quantify the spatiotemporal heterogeneities in Ni-rich layered oxide cathode materials (NMC532). The results revealed a significantly high true current density than the widely-accepted globally-averaged one. Incorporating nonequilibrium thermodynamics into classical electrochemical models and electroanalytical techniques will ensure self-consistent understandings of practical porous electrodes toward precision design and management. Lithium-ion batteries rule the energy storage market owing to their overall high performance, which, however, deteriorate severely at temperatures below -10°C. Emerging aluminum-ion batteries (AIBs) can deliver higher reversible capacities at low temperatures down to even -30°C. A systematic electrochemical characterization of the AIBs using classical electroanalytical methods at five temperatures selected between -20°C and room temperature, has been performed to assess the fundamental kinetics. The temperature-insensitive fast kinetics could be attributed to the high availability and easy access of active species at the inner Helmholtz plane near the electrode surface. The results revealed the governing mechanisms facilitating the high performance of AIBs in a wide temperature range and demonstrated the necessity of electrolyte optimization with a focus on the inner Helmholtz plane of the electric double layer structure to ensure high-rate electrode performance at low temperatures.
Language
English (en)
Chair
Peng Bai
Committee Members
Pratim Biswas, Rohan Mishra, Vijay Ramani, Elijah Thimsen,