Oxygen Vacancy Engineering in Na3V2(PO4)3 for Boosting Sodium Storage Kinetics

Improving Na-ion diffusion kinetics is an effective strategy to boost the sodium storage performance of electrode materials for sodium ion batteries (SIBs). Herein, an oxygen vacancy engineering is reported to evidently enhance Na-ion diffusion kinetics of Na3V2(PO4)(3) and accordingly boost sodium storage performance. Na3V2(PO4)(3)/C with different molar contents of Cu doping (0%, 2.5%, 4%, 5%, and 6%) are synthesized using a simple sol-gel method followed by an annealing treatment. The experimental results show that Cu2+ successfully replaces the V3+ sites of Na3V2(PO4)(3) and that does not change its phase composition. The introduction of Cu2+ not only results in the formation of V4+ to maintain charge balance, leading to a shorter V-O bond, but also promotes the generation of oxygen vacancies and accordingly facilitates Na-ion diffusion kinetics. As expected, the optimal sample displays a stable capacity of 111.4 mA h g(-1) with capacity retention of 90.4% over 300 cycles at 1 C and a high rate capacity of 83.8 mA h g(-1) at 20 C. The studies demonstrate that the Cu doping is favorable for the electrochemical enhancement of Na3V2(PO4)(3), which provides a promising prospect for Na3V2(PO4)(3) as a cathode for SIBs.