Install the Patch to Unlock Novel Na ⁺ Storage Sites for Achieving Ultrahigh‐capacity Na ₃ V ₂ (PO ₄ ) ₃ Cathodes

ABSTRACT The energy density of sodium‐ion batteries is constrained by cathodes with low‐voltage plateau and limited capacity. Herein, we report a novel patch repair strategy that in situ embeds highly conductive VN patches into the Na 3 V 2 (PO 4 ) 3 matrix, generating dual‐functional Na + storage pathways. The VN phase serves as a dynamic reservoir that unlocks interface adsorption/desorption storage, while its strong electronic coupling with the NVP host enhances bulk diffusion, facilitating fast Na + kinetics in both plateau and slope regions. The optimal electrode delivers a specific capacity of 145.4 mAh g −1 at 0.1 C, exceeding the theoretical capacity of Na 3 V 2 (PO 4 ) 3 by 123.6%, while maintaining over 95% capacity retention after 5000 cycles at 20 C. A pouch cell achieves an energy density of 423.05 Wh kg −1 and 98.56% capacity retention over 500 cycles at 2 C, along with reliable low‐temperature performance. More significantly, in situ XRD analysis corroborates a reduced diffusion barrier in the plateau region induced by VN, and unveils for the first time a continuous solid‐solution reaction in the slope region, offering direct visualization of the non‐diffusion‐controlled storage mechanism. This work establishes a promising paradigm for enhancing interfacial storage in NASICON‐type phosphates.