Superior fast-charging performance and prolonged lifespan of sodium vanadium phosphate via compositionally complex doping.

Abstract

The commercial viability of polyanionic Na3V2(PO4)3 (NVP) cathodes in sodium-ion batteries is critically hampered by its intrinsically low electronic conductivity and structural degradation upon prolonged cycling. Herein, we break the conventional equal-ratio multi-element doping paradigm and propose an asymmetric multi-element doping strategy at the vanadium site, yielding a composition of Na3V1.5Cr0.4(Ti,Al,Mg,Y,Zr)0.1(PO4)3 (HE-NVP). This design establishes a clear synergistic division of labor: Cr3+, with an ionic radius closely matched to V3+, serves as the primary electronic modulator to activate the reversible high-voltage V4+/V5+ redox pair, while the five co-dopants (Ti, Al, Mg, Y, Zr) collectively function as structural stabilizers and dynamic regulators, which effectively reduces the band gap, thereby enabling superior electronic conductivity and high-rate performance. Accordingly, HE-NVP delivers a high specific capacity of 116.2 mAh g-1 at 0.5C and demonstrates outstanding long-term stability, with 89.54% capacity retention after 3500 cycles at 20C. This work demonstrates that decoupling the functional roles of dopants offers a versatile and effective route for maximizing the electrochemical performance of NASICON-type cathodes for next-generation sodium-ion batteries.