Synergistic Electronic and Ionic Modulation of Na3V2(PO4)3 Cathode: Sn4+/Cu2+ Heterovalent Co-Doping for High-Rate and Long-Life Sodium-Ion Batteries

Abstract Na3V2(PO4)3 is a promising cathode for sodium-ion batteries but suffers from poor electronic conductivity. In this work, a heterovalent Sn4+/Cu2+ codoping strategy is proposed, and comprehensive structural analyses, electrochemical tests, and density functional theory calculations are employed to elucidate the synergistic modification mechanism. The results show that Sn4+ and Cu2+ are uniformly incorporated into the V-sites, which introduces emerging hybrid orbitals near the Fermi level, narrowing the band gap from 1.36 to 1.11 eV, thereby enhancing intrinsic electronic conductivity. Besides, Sn4+/Cu2+ codoping also modifies its Na+ migration channels, which significantly lower the Na+ migration energy barriers. More importantly, the robust Sn–O and Cu–O bonds reinforce lattice rigidity and suppress structural distortion. Benefiting from these synergistic effects, the optimized Sn0.05Cu0.05-NVP@C cathode delivers high capacities of 115.97 mAh g–1 at 0.1 C and 96.22 mAh g–1 at 40 C, with excellent cycling stability (93.59% retention over 3000 cycles at 10 C). In situ XRD confirms highly reversible two-phase transition reaction between Na3V1.9Sn0.05Cu0.05(PO4)3 and NaV1.9Sn0.05Cu0.05(PO4)3. This work establishes a general heterovalent codoping approach for optimizing NASICON-type cathodes, offering mechanistic insights into structure–property correlations for advanced sodium-ion batteries.