Electron Microscopy Study of the LiFePO4 to FePO4 Phase Transition

The mechanism by which LiFePO 4 is transformed into isostructural FePO 4 has been elucidated using electron microscopy on large, hydrothermally grown LiFePO 4 crystals following chemical delithiation. Lithium is extracted at narrow, disordered transition zones on the ac crystal surface as the phase boundary progresses in the direction of the a-axis. The substantial lattice mismatch along a (ca. 5%) causes crack formation in the bc plane. Despite considerable disorder in the transition zone, the general structural arrangement is preserved, leading to good crystallinity in the newly created FePO 4 domains. Implications for improved electrode performance are discussed.

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