DYNAMIC ATOMISTIC STUDY OF TUNNEL FUNCTIONS IN NANOSTRUCTURED TRANSITIONAL METAL OXIDES

Author

Yifei Yuan, Michigan Technological UniversityFollow

Date of Award

2016

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Reza Shahbazian Yassar

Advisor 2

Jun Lu

Committee Member 1

Stephen Hackney

Committee Member 2

Gregory Odegard

Abstract

Alpha (α-) MnO₂ is a well know transitional metal oxide possessing one dimensional 2×2 (4.6 × 4.6 Ų) 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.

Recommended Citation

Yuan, Yifei, "DYNAMIC ATOMISTIC STUDY OF TUNNEL FUNCTIONS IN NANOSTRUCTURED TRANSITIONAL METAL OXIDES", Open Access Dissertation, Michigan Technological University, 2016.

https://doi.org/10.37099/mtu.dc.etdr/228