Slight Na-site Zn2+ doping in Na3V2(PO4)3 enhances rate capability for sodium-ion batteries

Na 3 V 2 (PO 4 ) 3 (NVP) is a promising NASICON-type cathode for sodium-ion batteries (SIBs) owing to its robust three-dimensional framework and multielectron redox activity. However, its practical application for SIBs is limited by sluggish Na + transport kinetics at high rates. Herein, we report a rational Na-site engineering strategy via low-level aliovalent Zn 2+ substitution to regulate the Na + migration landscape in Na 3-2x Zn x V 2 (PO 4 ) 3 /C (x = 0–0.05). All compositions crystallize in the rhombohedral R 3 ‾ c structure without secondary phases, confirming that Zn incorporation preserves the NASICON framework. Structural study reveals that Zn 2+ preferentially occupies the Na1 site, inducing subtle local lattice distortions and generating charge-compensating Na vacancies. Theoretical calculations demonstrate that Zn doping effectively smooths the Na + energy landscape and lowers the migration barrier along the dominant Na1–Na2–Na1 diffusion pathway, reaching a minimum of 0.354 eV at x = 0.04. The optimized Na 3-2x Zn x V 2 (PO 4 ) 3 /C (x = 0.04) cathode delivers superior rate capability and outstanding cycling stability, retaining 77.6% of its capacity after 1000 cycles at 10 C and maintaining high reversible capacity even at an ultrahigh rate of 50 C. This work elucidates the dual role of aliovalent Na-site doping in simultaneously tuning lattice topology and defect chemistry, thereby providing an effective strategy to enhance Na + transport kinetics.