Phase Transitions of Li₃PO₄ Solid Electrolyte for Secondary Batteries: A Real-Time Synchrotron X-ray Scattering Study

The phase transitions of Li 3 PO 4 solid electrolyte for secondary batteries during heating and isothermal annealing in air have been studied by using real-time synchrotron X-ray scattering. As results of the heating annealing in air, the crystal β-Li 3 PO 4 phase only existed from RT to 440 °C. The crystal γ-Li 3 PO 4 phase appeared at 450 °C and the crystal β-Li 3 PO 4 phase disappeared at 480 °C. The transition from the β-Li 3 PO 4 to the γ-Li 3 PO 4 phases occurred mainly at 450 °C. In the early hours of the isothermal annealing at 450 °C in air, the β-Li 3 PO 4 and the γ-Li 3 PO 4 phases existed together. As the annealing time increased to 12 hours, the β-Li 3 PO 4 phase was wholly transitioned to γ-Li 3 PO 4 phase. Our study revealed the detailed transition behavior from β-Li 3 PO 4 to γ-Li 3 PO 4 phases during real-time annealing in air.