Lithium iron phosphate/carbon nanocomposite film cathodes for high energy lithium ion batteries

This paper reports sol–gel derived nanostructured LiFePO₄/carbon nanocomposite film cathodes exhibiting enhanced electrochemical properties and cyclic stabilities. LiFePO₄/carbon films were obtained by spreading sol on Pt coated Si wafer followed by ambient drying overnight and annealing/pyrolysis at elevated temperature in nitrogen. Uniform and crack-free LiFePO₄/carbon nanocomposite films were readily obtained and showed olivine phase as determined by means of X-Ray Diffractometry. The electrochemical characterization revealed that, at a current density of 200 mA/g (1.2 C), the nanocomposite film cathodes demonstrated an initial lithium-ion intercalation capacity of 312 mAh/g, and 218 mAh/g after 20 cycles, exceeding the theoretical storage capacity of conventional LiFePO₄ electrode. Such enhanced Li-ion intercalation performance could be attributed to the nanocomposite structure with fine crystallite size below 20 nm as well as the poor crystallinity which provides a partially open structure allowing easy mass transport and volume change associated with Li-ion intercalation. Moreover the surface defect introduced by carbon nanocoating could also effectively facilitate the charge transfer and phase transitions.