Structural Investigations of LiFePO4 Electrodes by Fe X-ray Absorption Spectroscopy

Fe K-edge X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) have been performed on LiFePO4, and on electrodes containing this material to determine the local atomic and electronic structure and their stability with electrochemical cycling (repeated charging and discharging). Comparison of the XANES data for the powder sample, uncycled electrode, and cycled electrodes 7SG and 9SG reveals that the Fe ions are octahedrally coordinated and in the Fe2+ state. Even after repeated charging and discharging, the structure of the LiFePO4 cycled electrodes (7SG, cycled 64 times, and 9SG, cycled 21 times) did not change and hence the material possesses very desirable characteristics for an electrode. This makes it an excellent choice for long cycle life Li-ion battery applications.