New freeze-drying method for LiFePO4 synthesis

The freeze-drying method is proposed as an effective synthesis process for the obtaining of LiFePO4/C composites. The citric acid is used as a complexing agent and carbon source. After the low temperature annealing, the freeze-dried solution leads to a homogeneous carbon covered LiFePO4 sample. The chemical characterization of the material included ICP and elemental analysis, infrared spectroscopy, X-ray diffraction, magnetic measurements and thermal analysis. SEM and TEM microscopies indicate an aggregate morphology with tiny particles of lithium iron phosphate inside a carbon matrix. Impedance spectroscopy showed a 8.0 x 10(-7) S cm(-1) conductivity value. Cyclic voltammetry graphics displayed the two peaks corresponding to the Fe(II)/Fe(III) reaction and demonstrated the good reversibility of the material. The specific capacity value obtained at C/40 rate was 164 mAh g(-1), with a slight decrease on greater C-rates reaching 146 mAh g(-1) at C/1. The capacity retention study has evidenced good properties, with retention over 97% of the maximum values in the first 50 cycles, which allows an effective performance of the freeze-dried sample as cathodic material in lithium-ion batteries. (C) 2007 Elsevier B.V. All rights reserved.