Research Update: Retardation and acceleration of phase separation evaluated from observation of imbalance between structure and valence in LiFePO4/FePO4 electrode.

LiFePO₄ is a potential positive electrode material for lithium ion batteries. We have experimentally observed an imbalance between the valence change of Fe ions and the structure change from the LiFePO₄ phase to the FePO₄ phase during delithiation by simultaneous in situ XRD and XANES measurements in an LiFePO₄/FePO₄ electrode. The ratio of structure change to valence change clearly indicates that the phase separation from LiFePO₄ to FePO₄ is suppressed at the beginning of delithiation, while it is accelerated at the latter stage, which is due to the coherent strain caused by the lattice misfit between the two phases. [ABSTRACT FROM AUTHOR]