Ordered–Disordered Ionic Cocrystalline Solid-State Electrolytes for Rapid Ion Migration in Sodium Metal Batteries

Solid-state electrolytes for sodium–metal batteries are restricted by intrinsically low ion mobility and stability. Herein, we report an ionic cocrystalline solid-state electrolyte featuring a unique ordered–disordered hybrid lattice by integrating sodium perchlorate with succinonitrile, namely, NaClO4(SN)3. It has a single phase with an ordered Na+-coordination backbone, while orientationally disordered SN molecules reside in interstitial sites and serve as ionic pathways. This eutectic hybrid architecture establishes an ordered 3D continuous Na+ single-ion conduction network associated with immobilized ClO4– anions, while supplemented by interconnected ionic flowpaths through disordered regions. This design principle enables rapid Na+ hopping transport and maintains mechanical compliance for intimate electrode contact, thereby mitigating polarization and promoting uniform sodium deposition. The NaClO4(SN)3 electrolyte exhibits a low activation energy of 0.26 eV, an ionic conductivity of 0.94 mS cm–1 at 25 °C, and an electrochemical stability window beyond 4.6 V (vs Na/Na+). It also features a melting point of 36.2 °C and a glass-transition temperature of −37.9 °C, allowing convenient in situ melting infiltration into electrodes followed by solidification to form conformal, low-impedance interfaces with enhanced dendrite resistance. These combined attributes exemplify an order–disorder hybrid cocrystal engineering strategy to develop solid-state electrolytes with rapid ionic conductivity, long cycling durability, and cost-effective scalability, providing a promising solution for rechargeable solid-state alkali metal batteries.