Embedded 3D Superionic Network Enables Pressure-Free Solid-State Sodium Batteries with Ultrafast Na ⁺ Diffusivity over a Wide Temperature Range

Rechargeable solid-state sodium-metal batteries (SSSMBs) are promising for next-generation energy storage, yet their performance severely deteriorates at ultralow temperatures due to interfacial degradation and sluggish bulk Na⁺ transport. The core issue lies in the low Na⁺ diffusivity within the anode, which induces interfacial void formation and nonuniform Na plating, triggering dendrite growth and rapid capacity fading. To fundamentally address this challenge, we designed an innovative composite anode by constructing an in situ 3D continuous superionic Na₃P network within the sodium anode. The engineered 3D superionic network can facilitate uniform Na⁺ stripping/plating along the ion-conducting backbone, which effectively stabilizes the solid-state interface against cyclic degradation and dramatically enhances the Na⁺ diffusivity to 8 × 10^-7 cm² s^-1. Consequently, symmetric solid-state cells achieve an areal capacity of 14 mAh cm^-2 without stacking pressure; fascinatingly, full solid-state cells with this composite anode also demonstrate cyclic stability across a wide temperature range (-25 to 60 °C) and sustain over 540 cycles under a mass loading of 10 mg cm^-2. This work highlights the superionic network integration as a practical strategy toward high-performance and extreme-temperature SSSMBs without stacking pressure, emphasizing the critical role of high atomic diffusivity in enabling durable, pressure-free solid-state batteries.