“Synergia Armor” Hierarchical Configuration Enables Interface Engineering Optimization Boosting Protective Effects and Kinetic Characteristics of Na ₃ V ₂ (PO ₄ ) ₃

Abstract The continuous dissolution of vanadium and inferior effects from reaction with electrolyte lead to poor performance of Na ₃ V ₂ (PO ₄ ) ₃ (NVP). Herein, a “synergia armor” hierarchical configuration featuring heterojunction‐structured NaPO ₃ interfaces and encapsulated within S/N co‐doped carbon coating is proposed for NVP system. The S/N co‐doping engineered carbon matrix generates abundant defects and electrochemically active sites, which is investigated by DFT calculations. The NaPO ₃ phase behaves dual significant effects, including constructing heterogeneous interfaces with NVP to establish built‐in electric filed (BIEF) and functioning as protective layer to suppress parasitic reactions and inhibit vanadium dissolution. DFT and UV/UPS measurements clearly expound the formation mechanism of BIEF and detailed promoting principle to accelerate the ionic migration. XPS valence band further indicates the BIEF upshift the vanadium D‐band center toward Fermi level, effectively optimizing the electronic structure. Furthermore, DFT verifies the nearly metallic DOS state and much lower adsorption energy of Na ⁺ for the NVP/NaPO ₃ dual heterostructure. Depth‐profiled XPS reveals that the NaPO ₃ interface yields beneficial effects on anchoring V and resisting F. Ex situ XPS/XRD/SEM collectively demonstrate the advanced charge compensation mechanism and near‐zero strain characteristic. In situ EIS and DRT validate the optimal charge transfer property. NVP@S,N0.01 exhibits exceptional rate capability and cyclic performance.