A Dual‐Functional Artificial Interphase Design for High‐Efficient and Long‐Duration Anode‐Free Sodium All‐Solid‐State Battery

ABSTRACT Anode‐free solid‐state sodium batteries (AFSSBs) emerge as a highly promising next‐generation energy storage technology, offering exceptional energy density and significant cost advantages. However, their practical deployment remains challenging, primarily due to an insufficient understanding of Na dendrite formation and the absence of effective strategies to address the rigid multiphases interface, mitigate volume expansion, and reactivate inactive sodium. In this study, we systematically investigate the morphologies evolution of sodium at the interface between the Cu current collector and Na 5 SmSi 4 O 12 (NSSO) solid electrolyte. Building upon these findings, we design an iodinated polymeric elastic artificial interphase layer ( I ‐PIL) with dual functionality. This layer not only ensures conformal interfacial contact through photoinitiated polymerization and atomic bonding, but also reactivates dead sodium via spontaneous reaction with the incorporated I 3 − species. Consequently, Na|Cu half‐cells achieve remarkable cycling stability, remaining a Coulombic efficiency of 99.7% for over 1000 h at 1.5 mA cm −2 . When paired with Na 3 V 2 (PO 4 ) 3 cathode, the AFSSBs retain 85.8% capacity after 2000 cycles at 1.0 mA cm −2 and preserve 92.8% capacity over three months under high mass loading of 28 mg cm −2 . This work provides fundamental insights into sodium deposition and establishes a versatile and scalable interfacial design strategy for high‐performance, durable anode‐free solid‐state batteries.