Recently, we have developed techniques using the combination of a high intensity synchrotron x-ray beam and fast detectors (image plate or position sensitive detectors) to do in-situ X-ray diffraction (XRD) during charge-discharge cycling and time resolved X-ray diffraction during the thermal decomposition of charged cathode materials. We have also developed synchrotron based in-situ X-ray absorption (XAS) techniques to study the changes of oxidation states and coordination of the transition metal elements during cycling. The in-situ and ex-situ soft x-ray absorption spectroscopy techniques we have developed allow us to distinguish the structural differences between the surface and bulk of electrodes using both electron yield (EY) and fluorescence yield (FY) detectors simultaneously. In this presentation, we will report our studies on the structural changes of various cathode materials such as layered LiMO2 (M=Co, Mn, Ni) and olivine structured LiMPO4 (M=Fe, Mn, Co, Ni) with and without surface coating, during charge-discharge cycling as well as during thermal decompositions. The results of these studies provide very important information for synthesizing new cathode materials with improved properties. Preliminary results of studies using in-situ transmission electron microscopy and high-resolution analyses will also be reported. ACKNOWLEDGMENT This work done at Brookhaven National Lab. was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-AC02-98CH10886