Stable cycling performance of lituium-doping Na3−xLixV2(PO4)3/C (0 ≤ x ≤ 0.4) cathode materials by Na-site manipulation strategy.

The effect of Li+ doping on the structure and properties of the material and the reaction mechanism are fully explained by practical experiments combined with theoretical calculations. When the doping amount of Li+ is 0.2, Na 2.8 Li 0.2 V 2 (PO 4) 3 /C can provide a reversible capacity of 116.9 mAh/g, almost reaching the theoretical capacity (117 mAh/g). After 500 cycles, it shows an amazing capacity retention rate (99.82%). [Display omitted] • Based on the carbon coating, we discuss the Li+ substituted of Na 3−x Li x V 2 (PO 4) 3 /C (x = 0, 0.1, 0.2, 0.3, 0.4) series materials to achieve SIBs cathode materials comparable to the theoretical capacity. • The optimum doping amount is 0.2, Na 2.8 Li 0.2 V 2 (PO 4) 3 /C can provide a reversible capacity of 116.9 mAh/g, almost reaching the theoretical capacity (117 mAh/g). After 500 cycles, it shows an amazing capacity retention rate (99.82 %). • The effect of Li+ doping on the structure and properties of the material and the reaction mechanism are fully explained by practical experiments combined with theoretical calculations. Na 3 V 2 (PO 4) 3 (NVP) has become a hot material in the research field of sodium-ion batteries (SIBs) as a result of its unique structural advantages. Unfortunately, the poor electronic conductivity and ion diffusion ability fundamentally limit the practical development of NVP. Considering the above defects, a series of Li+ doped Na 3−x Li x V 2 (PO 4) 3 /C cathode materials for SIBs are synthesized through hydrothermal assisted sol–gel method. The cell volume steadily decline with the raise of Li+ doping amount, which is consistent with the usual doping effect. Moreover, with the increase of lithium doping amount, Li+ preferentially occupies Na (2) site and then occupies Na (1) site. Through the first principles calculation, it is clear that the introduction of Li+ can significantly reinforce the conductivity of the material system and diminish the electron localization phenomenon. The analysis of (1 1 6) crystal plane by TEM shows that Li doping will reduce the interplanar spacing. The change of V valence during the charge–discharge process of Na 2.8 Li 0.2 V 2 (PO 4) 3 /C is consistent with that of NVP by V element XANES characterization. There is no conventional phase transition phenomenon in the ex-situ XRD high-voltage charging state. The above facts indicate that lithium doping obtains a stable solid solution NVP. The electrochemical test results show that Na 2.8 Li 0.2 V 2 (PO 4) 3 /C can provide an amazing reversible capacity of 116.9 mAh/g (theoretical capacity of 117 mAh/g) and capacity retention rate of 99.82 % after 500 cycles. GITT results show that Li+ can significantly increase the Na+ diffusion coefficient of the material. Such excellent electrochemical performance is attributed to the fact that the doping of Li+ activates the activity of Na+ in Na (2) site and improves the reaction efficiency. [ABSTRACT FROM AUTHOR]