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Lithium iron phosphate (LiFePO 4 ) powders were prepared by hydrothermal reactions under a nitrogen atmosphere or an air atmosphere, and the microstructure and electrochemical properties of the LiFePO 4 powders were investigated. The LiFePO 4 powder prepared under the nitrogen atmosphere (LiFePO 4 -N 2 ) had a small particle size in the range of 300-500 nm, whereas the powder prepared under the air atmosphere (LiFePO 4 −air) had a large particle size in the range of 1-5 μm. Although the Fe 2+ /Fe 3+ ratio was not significantly different in both LiFePO 4 powders, the Fe 2+ /Fe 3+ ratio in the precursor suspension prepared under the nitrogen atmosphere was much higher than that prepared under the air atmosphere, thereby resulting in the small particle size of the LiFePO 4 -N 2 powder. The discharge capacity of a LiFePO 4 -N 2 electrode was 149 mAh g −1 at a low current density of 10 mA g −1 , whereas that of a LiFePO 4 −air electrode was 83 mAh g −1 . Impedance analyses indicated that the charge transfer resistances normalized to the surface area of LiFePO 4 particles for the LiFePO 4 -N 2 and LiFePO 4 −air electrodes were 4.6 and 4.8 Ω m 2 , respectively. These values were not significantly different. This revealed that the factor dominating the electrochemical properties of LiFePO 4 -N 2 and LiFePO 4 −air powders was particle size and not crystalline lattice or Fe 2+ concentration.

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