Synchronized Stabilization and Multielectron Reactions in a Double‐Shelled Hollow Na 3 V 2 (PO 4 ) 2 F 3 /Na 3 V 2 (PO 4 ) 3 Heterostructure Toward High‐Energy‐Density Sodium‐Ion Batteries

ABSTRACT Unlocking stable multielectron redox reactions in sodium superionic conductor‐structured cathodes is pivotal for building high‐energy sodium‐ion batteries, yet remains a formidable challenge due to severe structural degradation and sluggish kinetics. In this work, a novel double‐shelled hollow Na 3 V 2 (PO 4 ) 2 F 3 /Na 3 V 2 (PO 4 ) 3 heterostructure is delicately devised, where the outer Na 3 V 2 (PO 4 ) 3 shell not only functions as a robust buffer layer to accommodate volume variations, but also effectively suppresses fluorine loss to ensure high phase purity of the inner Na 3 V 2 (PO 4 ) 2 F 3 . Meanwhile, the porous hollow architecture reduces Na + diffusion pathways and exposes a large number of active sites. Ultraviolet photoelectron spectroscopy (UPS) measurements combined with density functional theory (DFT) calculations reveal pronounced interfacial electron redistribution, which promotes charge‐transfer kinetics and facilitates the reversible V 4+ /V 5+ redox process. As a result, the optimized Na 3 V 2 (PO 4 ) 2 F 3 /Na 3 V 2 (PO 4 ) 3 cathode exhibits superior electrochemical performance compared to its individual counterparts, delivering a high specific capacity of 131.7 mAh g −1 at 20 mA g −1 (corresponding to 2.1‐electron transfer) with a high energy density of 471 Wh kg −1 and remarkable long‐term stability (78.8% capacity retention after 1000 cycles at 1 A g −1 ). This work provides a novel strategy for the development of high‐energy, long‐life sodium‐ion batteries.