An energy storage composition can be used as a new Na-ion battery cathode material. The energy storage composition with an alluaudite phase of AxTy(PO4)z, NaxTy(PO4)z, Na1.702Fe3(PO4)3 and Na0.872Fe3(PO4)3, is described including the hydrothermal synthesis, crystal structure, and electrochemical properties. After ball milling and carbon coating, the compositions described herein demonstrate a reversible capacity, such as about 140.7 mAh/g. In addition these compositions exhibit good cycling performance (93% of the initial capacity is retained after 50 cycles) and excellent rate capability. These alluaudite compounds represent a new cathode material for large-scale battery applications that are earth-abundant and sustainable.