Dual thermal-stimulated self-adhesive mixed-phase interface to enable ultra-long cycle life of solid-state sodium metal batteries

The pursuit of low-cost and intrinsically safe high-energy storage has significantly triggered the development of solid-state sodium–metal batteries. The solid–solid interface between the sodium anode and rigid electrolytes plays a critical role in the stable cycling of solid-state batteries. Undesirable interfacial contact during sodium deposition and stripping tends to induce the generation of voids and dendrites, leading to interface deterioration and cell failure. Herein, we constructed a self-adhesive and mixed-phase interface via a dual thermal stimulation strategy to enable an ultra-long cycling life of over 17 000 h (close to 2 years). A dense and robust SnF₂ interface layer was constructed on the surface of the solid electrolyte via a melting and self-adhesive effect induced by a physical thermal stimulation treatment. A secondary thermal activation was performed to trigger the in situ transformation of the interface layer into an ion/electron mixed ionic/electric conductor. Due to the robust contact and high conductivity of this self-adhesive mixed-phase interfacial layer, the cycling life of the sodium symmetric cell was dramatically increased from 50 h to 17 000 h with stable charging/discharging curves. Additionally, full cells coupled with the Na₃V₂(PO₄)₃ cathode provided a capacity of 102.2 mA h g⁻¹ with a coulombic efficiency of 99.72% in the first cycle. The capacity maintained was 91.3 mA h g⁻¹ after 2000 cycles, with a capacity retention rate above 89.3%. This work provides a new strategy for constructing a robust and long-lasting stable interface in solid-state sodium–metal batteries.