Synchrotron-based x-ray absorption near-edge structure (XANES) spectroscopy is applied to investigate the variation of Ti valence in the discharge and charge processes of Li4 Ti5O12.Through analysis of the XANES data,the average valence of Ti can be calculated,which allows quantitative determination of the ratios of Ti3+ /Ti4+ as a function of Li content in the electrodes.It is found that the ratios in the composites of Li4 Ti5O12/acetylene black (AB)-carbon are larger than those in Li4TisO12/Ag/AB-carbon after the discharge to 1.1 V,indicating a larger amount of Li inserted into the former than that into the latter.This finding provides a good explanation for the fact that the Li4 Ti5 O12/AB-carbon samples exhibit larger storage capacities than the Li4 Ti5 O12/Ag/AB-carbon ones prepared in this work,conceing the larger Ti3+/Ti4+ ratio and the larger amount of Li+ inserted in the electrode for satisfying the charge neutralization requirement.