Ionic states associated with extraction/infusion of Li ions at LiFePO sub(4) thin film cathode surface

A 100-nm-thick lithium iron phosphate (LiFePO sub(4)) film was deposited by sputtering, and charge-discharge cycle tests were performed using LiFePO sub(4) films as cathodes in electrochemical cells. After removing the electrolyte, the charged and discharged LiFePO sub(4) thin film cathodes were investigated using XPS. XPS results revealed that the peak area intensity of Fe super(2+) state increases for charged cathodes, while that of Fe super(3+) increases for discharged cathodes. In addition, the variation of Fe super(3+) and Fe super(2+) peak area intensities gradually attenuated as the number of charge-discharged cycles increased. The results reflect the performance of the battery and its degradation. Copyright copyright 2014 John Wiley & Sons, Ltd.