Core‐Shell Structured Composite Solid Electrolyte Enables High‐Rate All‐Solid‐State Sodium Batteries

All-solid-state sodium batteries (ASSSBs) have emerged as the promising candidates for large-scale energy storage; however, they still face challenges related to ionic transport across multi-scale interfaces, which leads to suboptimal battery performances. In this study, we propose a core-shell structured composite electrolyte with Na₃PS₄ sulfide solid electrolyte (SE) as the core and Na_2.25Y_0.25Zr_0.75Cl₆ halide SE as the shell. This design strategy boosts high SE's oxidative stability (4.0 V), ionic conductivity (0.44 mS cm^-1) and mechanical strength (Young's modulus of 9.19 GPa). These properties enable the composite SE to effectively mitigate the chemo-mechanically-induced multi-interfacial contact losses at the cathode side. Additionally, the homogeneous full-cell configuration, utilizing the core-shell structured composite electrolyte as both catholyte and SE layer, demonstrates superior rate capability, achieving a discharge capacity of 76.4 mAh g⁻¹ at 2.0 C, significantly outperforming the conventional sandwich-like designs. This work not only provides a novel design strategy for functional SE but also offers valuable insights into the chemo-mechanical failure mechanism at multiscale interfaces of ASSSBs.