Crystalline iron oxide nanotube arrays with high aspect ratio as binder free anode for Li-ion batteries

A comprehensive electrochemical study of crystalline iron oxide nanotube arrays grown in a highly ordered form with a high aspect ratio is presented. Nanotube arrays, thickness of similar to 5 mu m and tube diameter similar to 100 nm, were synthesized through an optimized two-step anodization technique. The morphology and the chemical composition of the resulting materials were characterized by field-emission scanning electron microscopy, X-ray diffraction, Rietveld analysis and Raman spectroscopy. The electrochemical response was evaluated by cyclic voltammetry, galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy on cells with Li metal as the counter and reference electrodes. The results have shown an excellent electrochemical response in terms of charge/discharge capacity (2775 mu Ahcm(-2) at 100 mu Acm(-2)) and rate capability (150 mu Ahcm(-2) at 800 mu Acm(-2)). Cyclic performance was also exceptional as a high reversible capacity (350 mu Ahcm(-2) at 200 mu Acm(-2)) was retained for 100 charge/discharge cycles. Such an enhanced electrochemical response is attributed to the unidirectional morphology of the nanotubes with high aspect ratio, favoring fast Li+ ion diffusion and improved electron transport. Also, avoiding use of binder and conductive carbon agents contribute towards high energy density of the anode material. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim