Synthesis of LiVOPO₄ by Emulsion Drying Method for Use as an Anode Material for Rechargeable Lithium Batteries

Highly crystalline β-LiVOPO₄ was synthesized from a water-in-oil emulsion. At 400 °C in ambient air, removal of the oil phase from the emulsion precipitates resulted in a poorly crystalline intermediate compound. On increasing the temperature to 750 °C under Ar, a single phase was formed. Rietveld refinement of the X-ray diffraction (XRD) data obtained from the product heated at 750 °C indicated that the product has an orthorhombic β-LiVOPO₄ olivine structure with no impurities. Although the β-LiVOPO₄ had an irreversible capacity in the first cycle, the electrode exhibited stable cyclability for 100 cycles, maintaining approximately 85.5% (573 mAh g^-1) of the first charge capacity (670 mAh g^-1). In addition, the β-LiVOPO₄ electrode had a high capacity even at high rates: 601 mAh g^-1 at 1C rate (670 mA g^-1) and 373 mAh g^-1 at 30C rates (20.1 A g^-1). Consolidating the results from XRD, X-ray photoelectron spectroscopy, and time-of-flight secondary mass spectroscopy, we suggest that the electrochemical activity of the β-LiVOPO₄ arises from the conversion reaction accompanied by the formation of Li₂O and Li₃PO₄. In addition, the ion-conducting Li₃PO₄ contributes to high capacity delivery at high rates up to a C-rate of 30.