Study on dynamics of structural transformation during charge/discharge of LiFePO4 cathode

Structural transformation taking place during charge/discharge of the LiFePO4 electrode in an organic Li-ion electrolyte has been studied by in situ synchrotron X-ray diffraction (XRD) concurrently with electrochemical analysis. The data reveal complex structural transformation patterns which result from significantly delayed structural transformation, even at low to moderate current rates (C/10 ∼ 1 C). The extent of the deviation is affected by charge/discharge conditions as well as history, and strong deviation appears detrimental to electrode cycle life. Furthermore, the two-phase characteristic of the Li+ insertion/extraction reactions is found to persist even within one metastable crystal structure. The result suggests the presence of domain structures that are probably caused by the strong electron/ion site coulombic interaction as previously suggested.