| Abstract
| - Changes in the local electronic structure at atoms around Li sites in the olivine phase of LiFePO4 were studiedduring delithiation. Electron energy loss spectrometry was used for measuring shifts and intensities of thenear-edge structure at the K-edge of O and at the L-edges of P and Fe. Electronic structure calculations wereperformed on these materials with a plane-wave pseudopotential code and with an atomic multiplet codewith crystal fields. It is found that both Fe and O atoms accommodate some of the charge around the Li+ ion,evidently in a hybridized Fe−O state. The O 2p levels appear to be fully occupied at the composition LiFePO4.With delithiation, however, these states are partially emptied, suggestive of a more covalent bonding to theoxygen atom in FePO4 as compared to LiFePO4. The same behavior is found for the white lines at the FeL2,3-edges, which also undergo a shift in energy upon delithiation. A charge transfer of up to 0.48 electronsis found at the Fe atoms, as determined from white line intensity variations after delithiation, while the remainingcharge is compensated by O atoms. No changes are evident at the P L2,3-edges.
|
