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Access Type

WSU Access

Date of Award

January 2015

Degree Type

Thesis

Degree Name

M.S.

Department

Chemical Engineering and Materials Science

First Advisor

K.Y. Simon Ng

Second Advisor

Kwo-Hsiung Young

Abstract

Zr-Ni-based alloys as nickel-metal hydride battery anode materials offer low-cost, flexible and tunable battery performance. Zr7Ni10 is an important secondary phase found in multi-phased AB2 Laves-phase-based metal hydride alloys, and the synergetic effect between the Zr-Ni and the Laves phases allows access to the high hydrogen storage of the Zr-Ni phases despite the lower absorption/desorption kinetics. Zr7Ni10 displays a small solubility window for Zr-rich compositions, while Zr2Ni7, with no solubility window, shows poor capacity with good kinetics. Stability of point defects within the crystal structure allows Zr7Ni10 to maintain the same structure at off-stoichiometric compositions, thus it is theorized that defects may play a role in the difference between the electrochemical behaviors in Zr7Ni10 and Zr2Ni7. Defect models in Zr7Ni10 and Zr2Ni7 compounds computed using a combination of density functional theory and statistical mechanics offer a starting point for understanding the possible roles that point defects have on the performance of Zr-Ni based active negative electrode materials in Ni/MH batteries. Theoretical vacancy and anti-site defect formation energies are calculated and reported for Zr-rich, Ni-rich, and stoichiometric compounds of Zr7Ni10 and Zr2Ni7, and the implications of the defect models on nickel-metal hydride negative electrode active material design and performance are discussed.

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