Insights into the elevated electrochemical performance and kinetic characteristics of magnesium-substituted Na3V2−xMgx(PO4)3/C with superior rate capability and long lifespan

Na3V2(PO4)3 has been pursued to be a prospective cathode for SIBs because of its outstanding structural stability. Nevertheless, the extensive application of Na3V2(PO4)3 is impeded by its poor electronic conductivity and inferior Na+ migration ability. Herein, a promising Mg-doped Na3V2−xMgx(PO4)3/C composite is prepared by a facile carbon-thermal reduction route. The substitution of magnesium onto vanadium site downsizes the particle, providing shorter pathway for the migration of Na+ and electron. The introduction of Mg2+ generates beneficial holes to facilitate the electronic diffusion efficiently. A superior electrochemical performance of Na3V1.93Mg0.07(PO4)3/C sample can be achieved due to the multiple synergetic effects. It delivers a high specific capacity of 113.5 mAh g−1 at 0.1 C. A high reversible capacity of 95 mAh g−1 can be obtained at 10 C rate, and the retention is 84.6% after 1000 cycles. Moreover, a comprehensive GITT analysis is conducted to give a better understanding of the elevated electrochemical properties for Na3V1.93Mg0.07(PO4)3/C: The migration of Na+ suffers from the intense interactions arising from the phase transfer during the potential plateau (~ 3.4 V). The minimum values of DNa+ at ~ 3.4 V for Na3V1.93Mg0.07(PO4)3/C are one order magnitude higher than that of undoped sample, implying the improved kinetics from magnesium substitution.