Thermodynamics analysis of LiFePO4 pecipitation from Li-Fe(II)-P-H2O system at 298 K

Thermodynamics of the precipitation from Li-Fe(II)-P-H2O system at 298 K was investigated. The results demonstrate that LiFePO4 can be formed at room temperature under pH value of 0-11.3, and the impurities Li3PO4 and Fe(OH)(2) will be yielded at pH value above 11.3 and 12.9, respectively. The optimum pH value for LiFePO4 precipitation is 8-10.5. Considering the low rate of phase transformation kinetics, metastable Li-Fe(II)-P-H2O system was also studied. The results indicate that equimolar ratio of co-precipitation precursor Fe-3(PO4)(2)center dot 8H(2)O and Li3PO4 cannot be obtained at the initial molar ratio 1:1:1 and 1:1:3 of Li:Fe:P. In contrast, equimolar ratio of the co-precipitation precursor can be yielded by adjusting the pH value to 7-9.2, matching the molar ratio 3:1:1 of Li:Fe:P, meaning that Li+-excess is one of the essential conditions for LiFePO4 preparation by co-precipitation method.