In Situ Construction of a 3D Superionic Skeleton in Sodium Anode for Solid‐State Sodium Batteries with a 15 000‐Cycle Lifespan at 3C

Abstract Solid‐state sodium‐metal batteries (SSSMBs) have emerged as a promising candidate for next‐generation energy storage systems due to their natural abundance, cost‐effectiveness, and high safety. However, the intrinsically low ionic conductivity of sodium anode (SA) and poor wettability to solid‐state electrolyte (SSE) severely hinder the development of SSSMBs. In this study, a 3D superionic transport skeleton Na 3 P is in situ constructed within the sodium anode by simply melting inexpensive and low‐density red phosphorus with sodium, which successfully enhances the ion diffusion rate from 2.54 × 10 ‒8 to 1.33 × 10 ‒7 cm 2 s ‒1 . Moreover, Na 3 P in the composite sodium anode (CSA) effectively induces the uniform deposition of Na on the surface of SSE, significantly reducing the interface impedance of symmetric cells from the initial value of 749.15 to 14.97 Ω cm 2 . Enabled by the integrated 3D superionic transport skeleton, the symmetric cell achieves exceptional cycle stability of over 7000 h at 0.1 mA cm ‒2 and 4000 h at 0.3 mA cm ‒2 . Furthermore, SSSMBs incorporating CSA demonstrate an ultralong lifespan of over 15 000 cycles at 3C while maintaining a high‐loading operation capability, significantly outperforming previously reported studies. This study highlights the crucial role of cost‐effective CSA design with enhanced ion transport in advancing high‐performance SSSMBs.