Ionic states associated with extraction/infusion of Li ions at LiFePO4 thin film cathode surface

A 100‐nm‐thick lithium iron phosphate (LiFePO4) film was deposited by sputtering, and charge–discharge cycle tests were performed using LiFePO4 films as cathodes in electrochemical cells. After removing the electrolyte, the charged and discharged LiFePO4 thin film cathodes were investigated using XPS. XPS results revealed that the peak area intensity of Fe2+ state increases for charged cathodes, while that of Fe3+ increases for discharged cathodes. In addition, the variation of Fe3+ and Fe2+ 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.