Site-Selective Cation–Anion Cosubstitution Rewires Na+ Transport in NASICON-Type Na3V2(PO4)2F3 Cathodes

Abstract NASICON-type Na3V2(PO4)2F3 is a promising cathode for sodium-ion batteries owing to its robust three-dimensional framework and high operating voltage. However, the strong Coulombic attraction imposed by the highly electronegative F– ions suspended above and below the diffusion channels, together with the ordered arrangement of Na+ ions, severely restricts the mobility of Na+. Herein, we propose a trace cation–anion cosubstitution strategy by introducing Li+ into Na+ sites and substituting Cl– for F– to synergistically regulate the local diffusion environment. The large-radius Cl– doping expands the lattice and widens the diffusion channel, while the Li+ ions act as a “pillar” to reinforce the framework. Meanwhile, such cosubstitution reduces the electrostatic attraction between pendant F– and Na+ and disrupts the ordered Na+ arrangement, thereby constructing favorable pathways for Na+. The optimized cathode exhibits reduced polarization and improved kinetics, delivering a high reversible capacity of 125.1 mAh g–1 at 0.1C, an excellent rate capability of 97.1 mAh g–1 at 15C, and 90.1% capacity retention after 1000 cycles. Density functional theory (DFT) calculations confirm the reconstructed electrostatic environment and favorable Na+ transport pathways. This work offers a new paradigm for enhancing the reaction kinetics of polyanionic cathodes.