Spray-drying synthesized lithium-excess Li4+xTi5-xO12-δ and its electrochemical property as negative electrode material for Li-ion batteries

Li4Ti5O12 (Fd-3m space group) materials were synthesized by controlling the lithium and titanium ratios (Li/Ti) in the range of 0.800-0.900 by using a spray-drying method, followed by calcination at several temperatures between 700 and 900 degrees C for large-scale production. Chemical and structure studies of the final products were done by X-ray diffraction (XRD), neutron diffraction (ND), X-ray photon electron spectroscopy (XPS), scanning electron microscopy (SEM) and inductively coupled plasma mass spectrometry (ICP-MS). The optimum synthesis condition was examined in relation to the electrochemical characteristics including charge-discharge cycling and ac impedance spectroscopy. It was found that when the spray-drying precursors at the Li/Ti ratio of 0.860 were calcined at 700-900 degrees C for 12 h in air, a pure Li4+xTi5-xO12-delta (x = 0.06-008) phase with a lithium-excess composition was obtained. Based on the structural studies, it was found that the excess lithium is located at the lithium and titanium layer of the 16d site in the spinel structure (Fd-3m). These pure Li4+xTi5-xO12-delta (x = 0.06-0.08) phase materials showed a higher discharge capacity of similar to 164 mAh g(-1) at 1.55 V (vs. Li/Li+), between the cut-off voltage of 1.2-3.0, with an excellent cyclability and superior rate performance in comparison with the Li4Ti5O12 phase containing impurity phases. (C) 2009 Elsevier Ltd. All rights reserved.