We demonstrate that a series of high-performance cathode materials, sodium vanadium polyanionic compounds, Na3(VO1-xPO4)2F1+2x (x = 0, 0.5 and 1), can be synthesized by a phase-transfer assisted solvo-thermal strategy at a rather low temperature (80-140 °C) in one simple step, exhibiting a high Na storage capacity of ca. 120 mA h g(-1) and excellent cycling performance. This study makes a significant step to extend this strategy to the synthesis of functional materials from simple binary to complex multicomponent compounds.