Crystal structure analysis of Li3PO4 powder prepared by wet chemical reaction and solid-state reaction by using X-ray diffraction (XRD)

Lithium phosphate (Li3PO4) is one of the promising solid electrolyte materials for lithium-ion battery because of its high ionic conductivity. A crystalline form of Li3PO4 had been prepared by two different methods. The first method was wet chemical reaction between LiOH and H3PO4, and the second method was solid-state reaction between Li2O and P2O5. Crystal structure of Li3PO4 white powder had been investigated by using an X-ray diffraction (XRD) analysis. The results show that Li3PO4 prepared by wet chemical reaction belongs to orthorhombic unit cell of beta-Li3PO4 with space group Pmn2(1). Meanwhile, Li3PO4 powder prepared by solidstate reaction belongs to orthorhombic unit cell of gamma-Li3PO4 with space group Pmnb and another unknown phase of Li4P2O7. The impurity of Li4P2O7 was due to phase transformation in solid state reaction during quenching of molten mixture from high temperature. Ionic conductivity of Li3PO4 prepared by solid-state reaction was similar to 3.10(-7) S/cm, which was higher than Li3PO4 prepared by wet chemical reaction similar to 4.10(-8) S/cm. This increasing ionic conductivity may due to mixed crystal structures that increased Li-ion mobility in Li3PO4.