Lithium-ion LiCoO2/graphite batteries have been studied using synchrotron, high-energy X-rays to obtain diffraction patterns on complete multilayer battery packages containing electrodes, separators, current collectors, and electrolyte vacuum sealed in a plastic bag. Reflections associated with both the LiCoO2 cathode and graphite anode were observed so that both phases could be monitored in detail as a function of the charging and discharging process. The charge-discharge behaviors of cycled batteries were also investigated and compared with fresh ones: for the cycled battery, there is a measurable loss of Li intercalation at the graphite anode on charging and incomplete reintercalation of the LiCoO2 cathode on discharging. Furthermore, the microstructure of the Li-ion batteries was investigated by cross-sectional electron microscopy. The anode contained spherical particles of mesocarbon microbeads which were composed of a mixture of graphitic plates and many smaller carbon spheres. (C) 2003 The Electrochemical Society.