ABSTRACT
Highly crystalline ß-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 ß-LiVOPO4 olivine structure with no impurities. Although the ß-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 ß-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 ß-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.
