Date of Award
Open Access Dissertation
Doctor of Philosophy in Materials Science and Engineering (PhD)
Administrative Home Department
Department of Materials Science and Engineering
Reza Shahbazian Yassar
Committee Member 1
Committee Member 2
Alpha (α-) MnO2 is a well know transitional metal oxide possessing one dimensional 2×2 (4.6 × 4.6 Å2) tunnels for accommodation of various ions. Such a characteristic tunneled structure has enabled the wide applications of α-MnO2 in the fields of ion exchange, molecular sieves, biosensor, catalysis and energy storage. This PhD dissertation focuses on the dynamic study of ion transport functionality of α-MnO2 at atomic level using an aberration corrected scanning transmission electron microscopy equipped with a special holder with a scanning tunneling microscopy probe.
The wide application of in situ TEM studying the dynamic behaviors/reactions in rechargeable lithium ion battery is first reviewed. Li+-tunnel interaction during lithiation of a single α-MnO2 nanowire was then systematically studied in situ at sub-Å resolution. An asynchronous tunnel expansion was for the first time captured with an ordered Jahn-Teller distortion theory proposed and confirmed further by DFT. Reversible Na+ insertion in the 2×2 tunnels of α-MnO2 is also explored and the tunneled structure is found to be less stable during sodiation than lithiation, which is explained by the larger Na+ ionic size and thus stronger Na+-tunnel interaction. The effect of large cations (K+) occupying the center of 2×2 tunnels on the electrochemical performance of α-MnO2 as a LIB cathode is systematically studied by controlling K+ concentration. It is found that the presence of K+ improves both the electronic conductivity and Li+ diffusivity of α-MnO2 nanowires, leading to superior discharge rate performance compared to the ones without K+ presence. The last project explores the oriented attachment (OA) growth mechanism of α-MnO2 in aqueous solution. The atomistic formation mechanism of the OA interface is demonstrated based on sub-Å analysis of the edge structures of related planes of α-MnO2. The tunnel-based nature of OA interface is evidenced by direct atomic imaging. The role of surface atomic arrangement at single-tunnel level in directing the self assembly of α-MnO2 nanowires is clearly illustrated with strong DFT theory support.
Yuan, Yifei, "DYNAMIC ATOMISTIC STUDY OF TUNNEL FUNCTIONS IN NANOSTRUCTURED TRANSITIONAL METAL OXIDES", Open Access Dissertation, Michigan Technological University, 2016.
Available for download on Thursday, June 01, 2017