Phase and Microstructure Development in the Conversion Type Electrodes for Li-Ion Batteries Based on the Cu-Fe-O System

The phase and microstructure development in conversion-type electrodes for Li-ion batteries was investigated using X-ray and electron diffraction, transmission electron microscopy and X-ray spectroscopy. The study was focused on copper iron oxides (CFO) with different compositions, synthesized by the self-combustion method and lithiated in several steps during the first discharge against a Li counter electrode. Appropriate reduction steps for detailed structural investigations of the electrochemically lithiated CFOs were identified by characteristic features in galvanostatic measurements. It was found that the reduction of the starting CFO material is accompanied both by a change of the phase composition and by a strong fragmentation of the original crystallites, while the active material remained nanocrystalline during the whole first discharge. The observed lack of a full amorphisation is discussed with respect to the crystallographic similarity of some involved phases that develop during the discharge process by displacement reactions. (C) 2013 The Electrochemical Society. All rights reserved.