Scalable synthesizing nanospherical Na4Fe3(PO4)2(P2O7) growing on MCNTs as a high-performance cathode material for sodium-ion batteries

An iron-base phosphate Na4Fe3(PO4)2(P2O7) nano-sphere growing on the multi-walled carbon nanotubes (MCNTs) is scalable synthesized via a convenient spray drying way. The Na4Fe3(PO4)2(P2O7)@MCNTs composite as cathode material for sodium-ion battery (SIBs) exhibits a high discharge capacity of 115.7 mA h g−1 at 0.1 C and an outstanding cycle stability with a with a capacity retention of 95% after 1200th at 2 C rate. It also shows an excellent rate capability with a capacity of 62.8 mA h g−1, even at high rate of 20 C. The outstanding electrochemical performance of Na4Fe3(PO4)2(P2O7)@MCNTs cathode are attributed to its' particular P2O7 dimers for reducing the rotation/distortion and higher electronic conductivity improves by MCNTs. A sodium-ion battery using the Na4Fe3(PO4)2(P2O7)@MCNTs cathode and the hard carbon anode shows a working voltage of 3.04 V with a specific energy of 210 Wh Kg−1 bases on the total weight of both electrode materials.