Pulsed laser deposition and electrochemical characterization of LiFePO 4-Ag composite thin films

A simple approach is proposed to enhance the electrical conductivity of olivine-structured LiFePO₄ thin films by uniformly dispersing small fractions of highly conductive silver (ca. 1.37 wt %) throughout the LiFePO ₄ film. In this approach, a highly densified (>85 %) LiFePO ₄-Ag target was first fabricated by coating conductive silver nanoparticles onto the surfaces of hydrothermally synthesized LiFePO₄ ultrafine particles by a soft chemical route. Pulsed laser deposition (PLD) was then employed to deposit LiFePO₄-Ag composite thin films on the Si/SiO₂/Ti/Pt substrates. The PLD experimental parameters were optimized to obtain well-crystallized and olivine-phase pure LiFePO ₄-Ag composite thin films with smooth surfaces and homogeneous thicknesses. X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectrometry (Raman), X-ray photoelectron spectroscopy (XPS), DC conductivity measurements, cyclic voltammetry(CV), as well as galvanostatic measurements were employed to characterize the as-obtained LiFePO₄-Ag composite films. The results revealed that after silver incorporation, the olivine LiFePO ₄ film cathode shows a superior electrochemical performance with a good combination of moderate specific capacity, stable cycling, and most importantly, a remarkable tolerance against high rates and over-charging and -discharging. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.