Electrochemical studies of the LiFePO4 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. 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 iron oxide species on the surface of the film. Though the film morphology became rough with cycling and thicker films were cleaved; the films showed good stability on cycling. The 75-nm-thick film prepared with a carbon-containing target showed a reversible cycling of more than 90 mAh/g for 60 cycles. The use of the low-carbon (< 1 wt %), green-colored target significantly lowered the carbon content of the LiFePO4 film. The low-carbon films cycled stable at moderate current density but with lower capacities such as 80 and 51 mAh/g for the 75 and 335-nm films, respectively. Film capacity and crystallinity improved significantly when the pulsed-laser-deposited target-substrate distance was reduced to less than 5 cm. The 156-nm-thick film produced in this way showed a layered texture in surface morphology and delivered more than 120 mAh/g, keeping its particle morphology on cycling. The excellent capacity retention, despite low-carbon content, can be attributed in part to the enhanced conductivity derived from the excellent adherence between pulsed-laser-deposited film and the substrate. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2128763] All rights reserved.