In-situ X-ray absorption spectroscopy (XAS) at the Fe K-edge X-ray absorption near edge was used to investigate the chemical change of LiFePO 4, which is a candidate cathode material for lithium ion batteries, during charge-discharge cycles. The relative amount of FePO4 formed in the LiFePO4 by the charge-discharge cycles was estimated from the XAS spectra. The results show that the amount Of FePO4 in the LiFePO4 increased with charging and decreased with discharging. While a linear relationship between the relative amount of FePO4 and electrical capacity was observed during the initial charging, it deviated from linearity during the charge-discharge cycles. This may be attributed to the irreversible diffusion paths of lithium ions and/or the partial formation of inactive FePO4 in the LiFePO4 during the charge-discharge cycles. It is shown that in-situ XAS has sufficient potential to nondestructively characterize heteroseneous electrochemical reactions in electrode materials during charge-discharge cycles.
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