Constructing abundant oxygen vacancies in NaVPO4F@C for boosting sodium storage kinetics

Abstract

NaVPO4F is attracting extensive attention as cathode material for sodium ion batteries owing to its advantages of stable structure, high voltage platform and high theoretical capacity. However, the poor electrical conductivity of NaVPO4F hinders its practical application. In this work, we propose a facile strategy to construct abundant oxygen vacancies in NaVPO4[email protected] by the introduction of Cr2+ to solve the problem associated with poor electronic conductivity. Density functional theory calculations and experimental studies indicate that the suitable Cr doping and abundant oxygen vacancies can significantly promote the electronic conductivity and Na-ion diffusion kinetics. Benefiting from the synergistic effects, the optimized Cr-doped NaVPO4[email protected] displays a high capacity of 121.3 mA h g−1 at 1 C and a high rate capacity of 98.8 mA h g−1 at 10 C with the capacity retention of 79.3% after 4000 cycles. Moreover, it also shows outstanding cycling performance and rate capability when assembled into full batteries (NaTi2(PO4)3@G film as the anode). This facile method proposed in our work may present a feasible approach to design the oxygen vacancies into other cathode materials for greatly improving the performance of sodium ion batteries.