Improvement of electrochemical properties of LiFePO4 fine particles synthesized in ethylene glycol solution resulting from heat treatment

Fine crystalline LiFePO 4 particles with an average secondary size of about 200 nm were synthesized in ethylene glycol (EG) solution at 393 K. Their molar ratio of Li:Fe:P was about 1.3:1:1, implying the precipitation of an impurity containing extra Li ions. The unit cell volume of crystalline LiFePO 4 in heat-treated particles was larger than that in as-synthesized particles. The Fe K absorption edge in the X-ray absorption spectrum was shifted toward a lower energy position by heat treatment. These results suggest that the composition of crystalline LiFePO 4 in fine particles is modified by heat treatment because of the reaction with extra Li ions. Additionally, in the radial structural function obtained by Fourier transform of the extended X-ray absorption fine structure oscillation, the Fe–P correlation and Fe–Fe correlation peaks became high due to the heat treatment, implying the rearrangement of FeO 6 octahedra and PO 4 tetrahedra. In consequence of the above-mentioned structural changes, the electronic capacity of fine particles precipitated in EG solution was enhanced to about 150 mA/h by heat treatment at 673 K.