Tuning the Morphology and Electronic Properties of Single-Crystal LiNi0.5Mn1.5O4-δ
The commercialization of lithium-ion batteries has played a pivotal role in the development of consumer electronics and electric vehicles. In recent years, much research has focused on the development and modification of the active materials of electrodes to obtain higher energies for a broader range of applications. High voltage spinel materials including LiNi0.5Mn1.5O4-δ (LNMO) have been considered as promising cathode materials to address the increasing demands for improved battery performance due to their high operating potential, high energy density, and stable cycling lifetimes. In an effort to elucidate fundamental structure-property relationships, this thesis explores the tunable properties of single-crystal LNMO. Utilizing facile molten salt synthesis methods, the structural and electronic properties of LNMO can be well controlled. Chapter 2 of this thesis focuses on uncovering the effect of molten salt synthesis parameters including molten salt composition and synthetic temperature on the materials properties. A range of imaging, microscopic, and spectroscopic techniques are used to characterize structural and electronic properties which are investigated in tandem with electrochemical performance. Results indicate the Mn oxidation state is highly dependent on synthesis temperature and can dictate performance, while the molten salt composition strongly influences the particle morphology. In Chapter 3, we explore the concept of utilizing LNMO as a tunable support for heterogeneous metal nanocatalysts, where alteration of the support structure and electronics can have an influence on catalytic properties due to unique support effects. Ultimately, this work illustrates the tunable nature of single-crystal LNMO and can inform the rational design of LNMO materials for energy applications.