Synthesis and characterization of LiFePO4/C composite obtained by sonochemical method

Abstract

Lithium iron phosphate has become of great interest as storage cathode for the next generation of rechargeable lithium batteries. Olivine structure LiFePO4/C composite powder was prepared by ultrasound assisted synthesis. A polyvinyl alcohol solution was used as the source of an in situ formed carbon. X-ray powder diffraction confirmed the phase purity. X-ray powder diffraction data were used for the crystal structure refinement, based on Rietveld full profile method. All relevant structural and microstructural crystal parameters that could be significant for electrochemical intercalation/deintercalation processes were determined. The Rietveld refinement also showed additional electron density on the lithium sites, indicating 3 at.% iron on the lithium site. Electrochemical characteristic of the composite was evaluated by using galvanostatic charge/discharge tests. While cycling at C/3 (C/10) rate the discharge capacity increases, starting from the value of 94.1 (116.0) mAh/g and reaching 99.5 (124.0) mAh/g at the end of the cycling. Particle morphology was revealed by both scanning and transmission electron microscopies. On the thin particle edges carbon film with a typical thickness of several nanometers can be observed, as well as small carbon agglomerates (typical size < 6 nm) at certain spots on the substrate surface.