Phytic acid assisted synthesis of carbon-coated Na3V2(PO4)3 as a superior cathode material for sodium ion batteries

Abstract

Na3V2(PO4)3 with NASICON (sodium superionic conductor) structure, has been considered as a potential cathode material for sodium ion batteries (SIBs). Herein, sustainable phosphorus sources of phytic acid is adopted to synthesize carbon coated Na3V2(PO4)3 (Na3V2(PO4)3/C-1) nanoparticles. Phytic acid can chelate with VO2+ ions and in-situ transform into tightly coated carbon. As a result, the dispersivity and size-distribution of Na3V2(PO4)3/C-1 particles are ideal, which will provid an enhanced conductivity and structure stability as cathode material for SIBs. For the rate performance, when the current increases from 0.05 A g−1 to 5.0 A g−1, a capacity of 70.7 mA h g−1 is maintained, corresponding to a capacity retention of 73.7 %. For the long-term cycling at current of 5.0 A g−1, there is only 0.0027 mA h g−1 capacity decay per cycle, giving a high capacity retention of 83.9 % after 5000 cycles. The high rate capability and cycling stability is attributed to the lower charge transfer resistance and higher diffusion coefficient of sodium ion, proved by the galvanostatic intermittent titration technique and electrochemical impedance spectroscopy.