The Synthesis Of FePO₄·2H₂O By Precipitation And Its Application To LiFePO₄

Olivine-type LiFePO4cathode materials have been a hot research area for several years because of high specific capacity, good thermal stability, rich raw materials, low cost, safety and environmental protection. Carbonthermal reduction using FePO4·2H2O as precursor has promising application in the synthesis of LiFePO4/C.With Fe(NO3)3·9H2O and NaH2PO4·2H2O as the raw material, precipitation by dropping (negative and positive) and thermolysis of iron phosphate complexes were adopted to the preparation of FePO4·2H2O.Compared with precipitation of negative dropping, LiFePO4/C synthesized by precipitation of positive dropping had weaker electrochemical performance. In the synthesis of FePO4·2H2O by precipitation of negative dropping, LiFePO4/C prepared by FePO4·2H2O with small particle size and good dispersion had good electrochemical performance. Under optimum condition, tap density of FePO4·2H2O was0.50g/cm3, mean particle size was1.08μm. Tap density of LiFePO4/C was0.81g/cm3. The first discharge capacity of LiFePO4/C was159.0mAh/g at0.1C rate. At3C rate, the discharge capacity was122.3mAh/g.Crystalline FePO4·2H2O was synthesized by thermolysis of iron phosphate complexes. Under optimized condition, FePO4·2H2O had mesoporous structure. Tap density of FePO4·2H2O was0.95g/cm3. Pore size ranged from20nm to80nm. LiFePO4/C retained the structure and morphology of precursor. Tap density was as high as1.26g·cm-3. The first discharge capacity of LiFePO4/C was135.0mAh/g at0.1C rate. At3C rate, the discharge capacity was84.4mAh/g.By comparing the results of two methods, thermolysis was better than precipitation by dropping in pratical application.