High-Power and Long-Lifetime Na-Ion Batteries Enabled by High-Loading Vanadium-Based Phosphate Heterostructure Cathodes

High-loading electrodes are particularly crucial for the practical application of Na-ion batteries (NIBs) in large-scale energy storage systems. To enable high-power long-lifetime NIBs, cathode materials with rapid Na-ion diffusion and structural stability must be developed. In this study, a novel vanadium-based phosphate heterostructure cathode material of Na₈V₅(P₂O₇)_2.925(PO₄)_3.75 (N₈VPP) was synthesized by the spray-drying method with a unique dual-phase heterostructure comprising Na₇V₄(P₂O₇)₄(PO₄) and Na₃V₂(PO₄)₃ in a molar ratio of 0.725:1. The P₂O₇^4-/PO₄^3- polyanionic hybrid heterostructure shows a pronounced increase in the number of electronic states near the Fermi level. This resulting electronic feature lowers the Na⁺ migration energy barrier and promotes charge transfer, as confirmed by density functional theory (DFT) calculations. Under high-loading conditions (10 mg cm^-2), the N₈VPP cathode delivers remarkable capacities of 90.51 mAh g^-1 and 41.88 mAh g^-1 at 0.1 A g^-1 and 10 A g^-1, respectively. Additionally, the capacity retention ratio is 71.8% with 64.3 mAh g^-1 after 1000 cycles at 2 A g^-1, demonstrating excellent cycling stability and power capability. Furthermore, a Na-ion full battery of N₈VPP//NaTi₂(PO₄)₃ achieves an excellent capacity and outstanding cycling life of 73 mAh g^-1 at 5 A g^-1 and 3000 cycles at 2 A g^-1, respectively. This study offers key design insights for high-performance N₈VPP cathodes toward practical sodium-ion energy storage.