Graduate Defense: Eric Gabriel

Dissertation Information

Title: Stabilization Of Layered Transition Metal Oxides Sodium Ion Battery Positive Electrodes At High Potential

Program: Doctor of Philosophy in Materials Science and Engineering

Advisor: Dr. Hui (Claire) Xiong, Materials Science and Engineering

Committee Members: Dr. Elton Graugnard, Materials Science and Engineering; Dr. Eungje Lee, Materials Science and Engineering; Dr. Yuzi Liu, Materials Science and Engineering; and Dr. Chengjun Sun, Materials Science

Abstract

As global demand for energy storage rises in response to the proliferation of electric vehicles and intermittent renewable energy sources, the resources associated with popular energy storage systems are increasingly strained. Lithium ion batteries (LIBs) rely heavily on elements with low abundance and unstable supply chains, while sodium ion batteries (SIBs) are a promising alternative technology based on abundant, globally available elements such as iron and sodium. However, the electrochemical performance of SIBs must be improved to enable their commercial viability. In the class of layered transition metal oxide (LTMOs) materials that are strong candidates as positive electrode materials for SIBs, the process of desodiation during charge leads to a variety of degradation mechanisms. Irreversible phase transformations and the reactivity of the surface against electrolyte are particularly pernicious, which makes tools to mitigate these processes highly valuable.
The application of structural heterogeneity is evaluated in LTMOs as a means to mitigate the degradation of these materials at high voltage. First, the role of the transition metal composition in the degradation of the O3-type Na(NiMn)1-xFex system is investigated, identifying the interaction between Ni and Fe at high state of charge and Fe content that harms the reversibility of Ni redox. Next, it is shown that using Li as a dopant in NaxLiyNi0.4Fe0.2Mn0.4O2 can suppress the irreversible phase transformation observed in the undoped material by the mechanical reinforcement from the biphasic the Na-O3/Li-O’3 structure. However, the Li doping increases the side reaction at the surface, which can be partially mitigated by Al2O3 coating. An O3/P3 heterostructure can be promoted in NaNi0.5Mn0.5O2 by controlled thermal processing, which can bolster the reversibility of its high voltage redox process. Finally, by manipulating the Na/Li ratio in Na0.67-xLiyNi0.33Mn0.67O2, the location of Li within the structure can be controlled with significant influence on the cycling stability. Further, the Li can promote a heterogeneous interlayer ordering of transition metal ions that accelerates Na+ diffusion and yields superior high-rate capacity. Overall, it is found that the thermodynamic and kinetic control of heterogeneous LTMO structures is an effective means to influence their structural stability and other properties.