In situ X-ray absorption spectroscopy of germanium evaporated thin film electrodes

The understanding of germanium Li-ion insertion/extraction reaction mechanism is drawing more and more attention in the field of Li-ion batteries. When a germanium thin film electrode is inserted with Li ions, the material remains amorphous until it crystallizes into Li15Ge4 as evidenced by X-ray diffraction. The local coordination environment of the Ge atoms of the intermediate amorphous phases was investigated by in situ X-ray absorption spectroscopy. Li-ion insertion and extraction were electrochemically controlled by continuous and intermittent galvanostatic methods. The evolution of the coordination number and interatomic distance of Ge-Ge and Ge-Li shells was determined as a function of Li composition. From a short range ordering perspective, it was observed that the first Ge-Ge interatomic distance increases and the Ge-Ge coordination number decreases with increasing Li content. The opposite is observed for the first Li-Ge interaction. Moreover, it was found that electrochemical lithiation is reversible at the atomic scale. (C) 2010 Elsevier Ltd. All rights reserved.