Electronic structural changes of the electrochemically delithiated LiFe0.5Co0.5PO4 cathode material studied by X-ray absorption spectroscopy

In order to study the electronic structure changes of the electrochemically delithiated Li 1− x Fe 0.5 Co 0.5 PO 4 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 Fe 2+ ions at lower potential plateau (∼3.6 V) and the oxidation of Co 2+ ions at higher potential plateau (∼5.0 V). 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 Fe 3+ O bonds via the inductive effect. From the observation of pre-edge peaks, it is concluded that the electrochemical delithiation of Li 1− x FePO 4 result in the hybridization of P 3p states with the metal 3d states.