Impact of Vacancies and Chemistry on Iron-based Electrodes for Alkali-ion Batteries

Thesis (Ph.D.)--University of Washington, 2020The exponential growth in population and worldwide prosperity during the last century is reciprocal with energy consumption. Recent environmentalism and government regulation have produced greater demand for green energies and electric vehicles. Associated with these technologies is growing demand for battery materials to support power grid operation and transportation. Conventional lithium ion batteries are at risk of supply instability of cobalt and lithium precursors, potentially making them economically unfit for certain applications. Iron-based materials for lithium-ion and sodium-ion batteries are an attractive alternative for niche applications and grid level storage due to their abundant and inexpensive precursors. Material chemistry and structure have a strong influence on the electrochemical properties of battery electrodes such as redox potential and diffusion kinetics. Vacancy control via synthesis was investigated as a means of improving the kinetic and thermodynamic limitations of jarosite and iron hexacyanoferrate. Incorporation of divalent ions into the jarosite structure introduced cation vacancies that facilitated lithium-ion diffusion and reduced structural transformation. Cation chelation during synthesis of iron hexacyanoferrate retarded particle nucleation leading to highly crystalline structures with low vacancy concentration. Cation substitution of jarosite and iron hexacyanoferrate was investigated for its beneficial electrochemical effects. Doping of iron hexacyanoferrate with zinc increased the redox activity of low-spin iron species, while doping of manganese increased the redox potential of high-spin iron species. These findings demonstrate the importance of materials chemistry, defects, and structure on the properties of electrode materials for alkali-ion batteries, and the same fundamentals able to be implemented in other electrochemical material systems