Homogeneous In Situ Interphase for Dendrite-Free Solid-State Sodium Metal Batteries under Extreme Working Conditions

Solid-state sodium metal batteries suffer from interfacial instability due to poor physical contact, uneven ion flux, and uncontrolled dendrite growth. Herein, a self-assembled homogeneous interphase composed of sodiophilic Na 15 Sn 4 and electronically insulating Na 2 S is proposed to homogenize Na + deposition, suppress dendrite growth, and ensure interfacial bonding stability. Ex situ SEM analysis after cycling reveals a crack-free and dendrite-free morphology, contrasting sharply with the catastrophic failure observed for bare Na. This composite anode endows the Na 15 Sn 4 /Na 2 S@Na//NFM full cell with ultrafast charging capability and outstanding wide-temperature performance (–30 °C ∼ 60 °C). The full cell retains 78.6% of its capacity after 500 cycles at 2 C. A pouch cell delivers 408 Wh kg –1 and passes destructive abuse tests (bending, nailing, shearing, and cutting), proving its practical viability. This work presents an interface engineering that balances ionic conductivity, mechanical strength, and chemical compatibility. It offers a versatile strategy for stabilizing reactive metal anodes beyond Na.