Pulse Laser Deposition and Electrochemical Characterization of LiFePO₄−C Composite Thin Films

Conductive carbon was codeposited with LiFePO 4 to enhance the electrical conductivity of the olivine-type LiFePO 4 thin films. In this approach, poly(vinyl alcohol) was used as the source for carbon as well as the binder for target densification. After a highly densified (>80%) LiFePO 4 −C target was fabricated, pulse laser deposition (PLD) technique was employed to deposit the LiFePO 4 −C composite thin films on the Si/SiO 2 /Ti/Pt substrates. The as-deposited LiFePO 4 −C composite films were characterized by techniques of X-ray diffraction, scanning electron microscopy, Raman scattering spectroscopy, X-ray photoelectron spectroscopy, DC conductivity measurement, as well as cyclic voltammograms, electrochemical impedance spectroscopy, and galvanostatics. The effects of carbon content and postdeposition annealing treatments on the electrochemical performances of the as-deposited film electrodes were carefully investigated. The results showed that the codeposited carbon was homogeneously distributed throughout the LiFePO 4 films. It was found that 2 mol% carbon was the optimized amount for the highest capacity. Postdeposition annealing at 600 °C for 6 h in the same vacuum chamber could considerably improve the Coulombic efficiency as well as the high rate capability of the PLD-deposited LiFePO 4 −C composite thin films. However, the specific capacity would be reduced.