Interface Stable Kinetics Triggered by Interfacial Built‐In Electric Field in Solid‐State Sodium‐Metal Battery

Solid‐state sodium‐metal batteries (SSSBs) have emerged as a potential next‐generation energy storage technology due to their abundant resource, high energy density, and safety. However, the uncontrolled Na dendrite growth and low charging/discharging rate pose a severe constraint on their practical applications. Herein, high interfacial sodium‐ion diffusion performance and interface stability of Na anode are achieved in SSSBs by designing an interfacial built‐in electric field (IBEF) driven by a laminated hybrid solid electrolyte with a mixed‐ion/electron‐conducting layer. The electrochemical characterizations and density functional theory (DFT) calculations reveal that IBEF effectively improves interfacial sodium‐ion diffusion by reinforcing electron delocalization and decreasing Na + transfer energy barrier. Furthermore, finite element simulation and experiments indicate that the IBEF endows a uniform interfacial charge distribution and Na deposition during plating/stripping. The IBEF boosts the cyclability of solid‐state symmetric cells, enabling ultralong cycle life over 26 400 cycles at 0.1 mA cm −2 , the Na/Na 3 V 2 (PO 4 ) 3 (NVP) full cells display a remarkable capacity retention of 97.4% after 1500 cycles at 2.0 C and stable charging/discharging even at −20 °C. Na/NVP pouch cells exhibit a capacity of 65.7 mAh g −1 after 50 cycles under 0.19 mA g −1 .