Electrochemical studies of the LiFePO thin films prepared with pulsed laser deposition

Thin films of LiFePO4 have been prepared on stainless steel substrates with pulsed laser deposition utilizing an Ar atmosphere. Films were characterized with XRD, SEM, Raman spectroscopy and electrochemistry in liquid electrolyte. Raman spectral analysis revealed the presence of carbon in the films, even though the targets contained less than a few percent residual carbon. The Raman spectra also suggest the presence of various iron oxide species on the surface of the film. The 75nm film showed reversible cycling of more than 90 mAh/g for 60 cycles and a coulombic efficiency close to 1. Variable sweep rate cyclic voltammetry showed a diffusion-controlled reaction with an effective diffusivity of about 10-12 cm2/s. The performance of the thicker film was poor with a coulombic efficiency much less than 1.