Electron Microscopy Study of the LiFePOsub 4 to FePOsub 4 Phase Transition

The mechanism by which is transformed into isostructural has been elucidated using electron microscopy on large, hydrothermally grown crystals following chemical delithiation. Lithium is extracted at narrow, disordered transition zones on the crystal surface as the phase boundary progresses in the direction of the -axis. The substantial lattice mismatch along (ca. 5%) causes crack formation in the plane. Despite considerable disorder in the transition zone, the general structural arrangement is preserved, leading to good crystallinity in the newly created domains. Implications for improved electrode performance are discussed.