Na-ion batteries are becoming comparable to Li-ion batteries because of their similar chemical characteristics and abundant sources of sodium. However, the materials production should be cost-effective in order to meet the demand for large-scale application. Here, a series of nanosized high-performance cathode materials, Na-3(VO1-xPO4)(2)F1+2x (0 <= x <= 1), has been synthesized by a solvothermal low-temperature (60-120 degrees C) strategy without the use of organic ligands or surfactants. The as-synthesized Na-3(VOPO4)(2)F nanoparticles show the best Na-storage performance reported so far in terms of both high rate capability (up to 10C rate) and long cycle stability over 1200 cycles. To the best of our knowledge, the current developed synthetic strategy for Na-3(VO1-xPO4)(2)F1+2x is by far one of the least expensive and energy-consuming methods, much superior to the conventional high-temperature solid-state method.