Sudden olivine LiFeP04 Nanocrystallisation by progressive introduction of li into ferrous phosphate structure

Abstract

Homogeneous sub-micron sized particles of surface carbon coated phase pure LiFeP04are synthesised by a novel non-aqueous oxalate-based sol-gel route. X-ray diffractogram of LiFeP04 reveals nanocrystals with average crystallite size 32(7) nm. The very large QS (nearly five times greater than that of Fe3+) value observed from Mossbauer spectrum is due to high spin configuration of 3d electrons and the asymmetric local environment at Fe site in LiFeP04. A uniform particle size distribution with grain size 100 - 150nm was observed in SEM with few irregular growths. Our synthetic route successfully overcomes the incidence of Fe3+, effectively controls undesirable particle growth and has the potential for upscaling and application as Li-ion battery cathodes. Progressive evolution of olivine structure by the interlock of Fe06octahedra and PO 4tetrahedra with Li concentration is studied by introducing lithium in to LixFeP04( 0.0≤x≤1.0 ). A fairly abrupt phase transformation from monoclinic Fe3(P04)2to orthorhombic LiFeP04 shows up for x∼0.2 accompanied by structural disorder which gets stabilized at x≈0.35. A systematic study of X-ray diffractograms shows nanocrystal nucleation and growth from an unstable low symmetry crystalline phase with considerable disorder. Copyright© 2007 Materials Research Society.