PhD defense - Kaitlin Garman (Ban group)

About this event

Title: Solid State Synthesis, Mechanistic Insight, and Design of Electrochemical Materials

Abstract:

The increasing demand for batteries with improved energy density, rate capability, lifetime, safety, and cost has driven the development of next-generation battery technologies. However, the advancement of these technologies depends on overcoming challenges associated with the synthesis and electrochemical performance of their constituent materials. Developing a fundamental understanding of the mechanisms governing materials synthesis and electrochemical behavior can provide strategies for improving materials processing, performance, and design. This dissertation investigates these mechanisms across three electrochemical material systems: garnet-type solid electrolytes, Chevrel-phase sodium-ion cathodes, and hybrid sodium sulfide conversion-intercalation cathodes. The solid-state synthesis reaction pathway of garnet-type Li₆.₅La₃Zr₁.₅Ta₀.₅O₁₂ (LLZTO) was investigated to develop a strategy for reducing the prolonged reaction times associated with conventional solid-state synthesis. Through ex situ and operando X-ray diffraction and surface and bulk characterization, the reaction pathway was elucidated, revealing the importance of lithium precursor availability in controlling reaction equilibria and suppressing impurity formation. By increasing lithium precursor availability, the reaction time was significantly decreased while maintaining important solid electrolyte properties. Next, the reversibility, structural evolution, and sodium-ion diffusion kinetics of Chevrel-phase Mo₆S₈ were investigated to evaluate its potential as a sodium-ion battery cathode. Electrochemical characterization and in situ X-ray diffraction revealed highly reversible sodium intercalation and structural stability following initial irreversible sodium trapping. Sodium-ion diffusion coefficients were determined through CV, confirming the high sodium mobility in the Chevrel-phase open framework. The material ultimately displayed excellent rate capability and cycling stability. Finally, a novel hybrid intercalation-conversion cathode incorporating Mo₆S₈ and Na₂S was proposed and synthesized to combine the favorable ionic and electronic transport properties of Chevrel-phase materials with the high theoretical capacity of sodium sulfide. The hybrid material demonstrated sodium-sulfur conversion behavior and capacity stabilization over 400 cycles, suggesting its potential as a cathode for sodium-sulfur batteries. Together, these studies demonstrate how mechanistic insight into materials synthesis and electrochemical reactions can guide the optimization and design of electrochemical materials, providing strategies to address challenges in next-generation battery technologies.