高出力・長寿命ナトリウムイオン電池を実現する高負荷型バナジウム系リン酸塩ヘテロ構造カソード

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.