In order to Study the electronic structure changes of the electrochemically delithiated Li1-xFe0.5Co0.5PO4 system, in situ Fe and Co K-edge XAS and ex situ P K-edge XAS have been carried Out during the first charging process. The Fe and Co K-edge XAS results showed that the major charge compensation at the metal sites during charge is achieved by the oxidation of Fe2+ ions at lower potential plateau (similar to 3.6V) and the oxidation of Co2+ ions at higher potential plateau (similar to 5.0V). The gradual shift of main edge features in P K-edge XANES spectra showed that P-O bonds become less covalent during delithiation, due to the increased covalency of Fe3+-O bonds via the inductive effect. From the observation of pre-edge peaks, it is Concluded that the electrochemical delithiation of Li1-xFePO4 result in the hybridization of P 3p states with the metal 3d states. (C) 2008 Elsevier B.V. All rights reserved.