Morphological investigation of sub-micron FePO4 and LiFePO4 particles for rechargeable lithium batteries

Microstructural variations of amorphous FePO4 and LiFePO4 (the latter obtained by chemical lithiation of the former) as a result of the annealing temperature have been studied by Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), chemical analysis, Brunauer-Emmet-Taylor (BET) and Scanning Electron Microscopy (SEM) techniques. Round-shaped amorphous FePO4 particles 40-80 nm in size are obtained after heating (at 400 degreesC) amorphous FePO4.2H(2)O in air (previously prepared by a precipitation route). On further heating at 650 degreesC, in air, crystalline trigonal FePO4 of crystallite size <200 nm is formed. Round-shaped amorphous LiFePO4 particles 40-80 nm in size crystallize by heating at 550 degreesC in Ar + 5%H-2 for 3 h. After thermal treatment, LiFePO4 particles are interconnected by necks, which resembled a sintering process. The particle size of LiFePO4 increases with an increase of temperature up to 750 degreesC, but an abnormal growth is evident at annealing temperatures above 650 degreesC. DTA analysis showed two exothermic peaks at 547 and 768 degreesC for FePO4 due to phase transitions, whereas for LiFePO4 two exothermic effects at 496 and 567 degreesC are shown. (C) 2003 Elsevier Science Ltd. All rights reserved.