Coordination Tuning of [VO 6 ] and [PO 4 ] Units Induced Solid-Solution Behavior in Na 3 V 2 (PO 4 ) 3 towards Aqueous Sodium-Ion Batteries

The widespread application of Na 3 V 2 (PO 4 ) 3 (NVP) in aqueous sodium-ion batteries is severely limited by irreversible capacity loss caused by vanadium dissolution and structural collapse due to the inherent instability of the V 3+ /V 4+ redox couple and sluggish Na + diffusion. Moving beyond conventional morphology and carbon-compositing strategies, we introduce a coordination engineering strategy through the simultaneous substitution of Zr 4+ at the V site ([VO 6 ] octahedron) and W 6+ at the P site ([PO 4 ] tetrahedron), aiming to synergistically stabilize the lattice and optimize the charge transfer. Theoretical and experimental results reveal that Zr/W pairs expand the lattice spacing, promoting rapid Na + /electron migration and, more importantly, shifting the Na + storage mechanism from a conventional two-phase reaction to a highly reversible solid-solution process. This transition effectively alleviates phase transition-induced strain and suppresses vanadium dissolution. Consequently, the optimized electrode delivers excellent cycling stability in full cells, retaining 62.6 mAh g –1 (71% retention) with activated carbon and 84.9 mAh g –1 (93.8% retention) with sodium titanium phosphate after 1000 cycles at 5.0 A g –1 . This work highlights the power of synergistic anion–cation coordination tuning to overcome fundamental material challenges, establishing a general design principle beyond the NASICON family.