Enhancement of Electrical Conductivity of LiFePO4 by Controlled Solution Combustion Synthesis

LiFePO4 has been synthesized by a solution combustion method at different oxidant-to-fuel ratios. At stoichiometric oxidant-to-fuel ratio (1:2), Fe2O3 formed in addition to LiFePO4 during combustion. Hence, reducing atmosphere was generated by increasing the ratio from stoichiometric to 1:4 and 1:8, named as 1-LFP, 2-LFP, and 4-LFP, respectively. Furthermore, as-prepared powders were calcined in inert atmosphere to avoid oxidation of LiFePO4 to Fe2O3 and Li3PO4, as confirmed by x-ray diffraction (XRD) and thermogravimetric and differential thermal analyses. The calcined powders were characterized by XRD analysis, Raman spectroscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. X-ray photoelectron spectroscopy ascertained oxidation state of +2 and +5 for Fe and P, respectively. With increasing oxidant-to-fuel ratio, the binding energies of 2p (3/2) and 2p (1/2) levels of Fe shifted downwards and showed increased splitting. According to Raman spectroscopy results, the residual carbon is amorphous with sp (2) C-C bond. The conductivity of 1-LFP, 2-LFP, and 4-LFP measured at 313 K was 0.15 x 10(-6) S/cm, 8.46 x 10(-6) S/cm, and 1.21 x 10(-3) S/cm, respectively. The enhanced conductivity of 4-LFP is due to presence of residual carbon and Fe2P.