Understanding the influence of different carbon matrix on the electrochemical performance of Na3V2(PO4)3 cathode for sodium-ion batteries

Abstract

Na-superionic conductor-structured Na3V2(PO4)3 is extensively investigated as a promising cathode material for sodium-ion batteries. Unfortunately, the Na3V2(PO4)3 cathode suffers from low rate capability due to its inherent low electric conductivity. One of the general solutions to this dilemma is to embed the Na3V2(PO4)3 nanoparticles uniformly within carbon matrix, however, the effect of carbon matrix categories on the sodium storage performance of Na3V2(PO4)3 is unclear. Here we systematically compare the influence of different carbon matrix on the electrochemical properties of the Na3V2(PO4)3 cathode and find that expanded graphite outperforms carbon nanotubes and carbon black as carbon matrix. As a result, the as-synthesized Na3V2(PO4)3/expanded graphite composite delivers a high reversible capacity of 111.4 mAh g−1 at 1C, superior rate capability (105 mAh g−1 at 50C), and ultralong cycle life (48 mAh g−1 after 20,000 cycles at 50C), which are better than most Na3V2(PO4)3-based composites reported previously. Moreover, the remarkable electrochemical performance of Na3V2(PO4)3/expanded graphite in symmetric cells further advances the practical application of sodium-ion batteries.