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

A 100‐nm‐thick lithium iron phosphate (LiFePO 4 ) film was deposited by sputtering, and charge–discharge cycle tests were performed using LiFePO 4 films as cathodes in electrochemical cells. After removing the electrolyte, the charged and discharged LiFePO 4 thin film cathodes were investigated using XPS. XPS results revealed that the peak area intensity of Fe 2+ state increases for charged cathodes, while that of Fe 3+ increases for discharged cathodes. In addition, the variation of Fe 3+ and Fe 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 © 2014 John Wiley & Sons, Ltd.