Comparative Study of Li and Na Electrochemical Reactions with Iron Oxide Nanowires

This study emphasizes optimization of Fe2O3 and Fe3O4 nanowire conversion electrodes by directly-growing them on current collectors, preparing them as single crystals, and coating their surfaces with conductive carbon coatings. The systems with the least polarization during Li-ion cycling are then tested as electrodes for Na-ion chemistry. Precipitation of nanograined material during the first cycle reduces the polarization associated with Li insertion upon subsequent cycles. After the first cycle, delithiation primarily contributes to polarization associated with the conversion reaction with lithiation occurring close to the equilibrium potential. The initial reduction reaction does not proceed to completion for Na chemistries. Electron microscopy reveals significant Na insertion that occurs along with the formation of defect networks. However, the results indicate that an insufficient amount is present to form critical nuclei necessary to induce the conversion reaction. (C) 2013 Elsevier Ltd. All rights reserved.