Facile synthesis and electrochemical properties of alpha-phase ferric oxide hematite cocoons and rods as high-performanc
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Nutan Gupta School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798; and TUM-CREATE Center for Electromobility, Nanyang Technological University, Singapore 637459
Raghavan Prasanth School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798; and Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Singapore 637553
Huey Hoon Hng School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798
Srinivasan Madhavia) School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798; Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Singapore 637553; and TUM-CREATE Center for Electromobility, Nanyang Technological University, Singapore 637459 (Received 30 October 2012; accepted 2 January 2013)
Unique cocoon- and rod-shaped alpha-phase ferric oxide, hematite (a-Fe2O3) is prepared by a simple, scalable and surfactant-free chimie douce synthesis. The structure and morphology is confirmed by x-ray diffraction, field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical properties of a-Fe2O3 anodes are investigated using cyclic voltammetry, galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The mesoporous a-Fe2O3 exhibited an initial discharge capacity .1741 mAh/g with excellent cycling performance and rate capabilities. The solvent used for the preparation of a-Fe2O3 plays a key role in determining the morphology of the materials, which greatly influenced its electrochemical properties.
I. INTRODUCTION
Rechargeable lithium-ion batteries (LIBs) have been commonly used as a power source for numerous portable electric devices due to their high energy density. Carbonaceous materials like graphite is widely used as anodes in commercial LIBs because of their stable voltage profile, good capacity and reasonable cost.1 However, graphite suffers high irreversible capacity loss and poor cycling life due to which its overall performance is inadequate to satisfy the demands for the high power and/or energy densities applications such as electrical/hybrid vehicles and miscellaneous power devices. In recent years, metal oxides (MOx, M 5 Co, Ni, Mn and Fe etc.) have been widely investigated as anode materials for LIBs, owing to their high theoretical capacity (greater than that of commercial graphite, 372 mAh/g). Among them, iron oxides are extensively studied because of many advantages such as low cost, nontoxicity, ecofriendliness, natural abundance and good a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.7 824
J. Mater. Res., Vol. 28, No. 6, Mar 28, 2013
structural stability.2,3 Alpha-phase ferric oxide hematite (a-Fe2O3) is capable of lithium ion (Li1) insertion/extraction in excess of 6 Li1 per formula unit resulting in a significantly higher reversible capacity. The mechanism of Li-ion intercalation/deintercalation
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