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Title:Structural evolution of α-Fe2O3 nanowires during lithiation/delithiation and electrochemical property improvement
Author(s):Huang, Bo
Advisor(s):Dillon, Shen J.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):Conversion Reaction
Mechanism
Lithium Ion Battery
Nanowires
Abstract:Hematite Fe2O3 exhibits great potential in lithium ion battery area as anode material, due to high capacity, elemental abundance, low cost and biocompatibility. Its reaction with lithium ion is accepted as conversion reaction. In this paper, single crystal α-Fe2O3 nanowires were prepared by an electrical resistive heating method under ambient conditions. Transmission electron microscopy characterized the anode material at various stages of lithiation and delithiation. The phase and morphological evolution demonstrate the conversion reaction process in α-Fe2O3. The process was initiated through the reduction of Fe2O3 to Fe3O4 nanocrystals, which form 4-nm-nanoparticles within the nanowire. Further lithiation converted all of the iron oxides to BCC Fe nanocrystals with the significant growth up to 21 nm. During delithiation, the reactions proceeded in the reverse order, Fe0-Fe2+-Fe3+. However, the initial single crystalline α-Fe2O3 nanowires were replaced by nanocrystalline ones after first cycle. The delithiated electrode maintains the nanowire geometry over many cycles due to the nature of the short-range cation diffusion that facilitates the process. Besides, nanowires covered with continuous carbon film exhibited much better electrochemical properties, such as cycle capacity, stability and conductivity, than the uncoated ones. The intrinsic conductivity improvement from α-Fe2O3 to Fe3O4 can further enhance the electrochemical performance.
Issue Date:2013-05-24
URI:http://hdl.handle.net/2142/44162
Rights Information:Copyright 2013 Bo Huang
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05


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