Ferroelectric Interlayer Regulating Uniform Sodium Plating for Solid-State Sodium Metal Batteries

Solid-state sodium metal batteries hold promise for next-generation energy storage but face interfacial challenges at the anode/solid electrolyte, including poor contact, polarization fluctuations, and dendrite formation. Herein, we demonstrate a ferroelectric interlayer strategy by coating Na 3 Zr 2 Si 2 PO 12 solid electrolyte with Bi 4 Ti 3 O 12 nanoplates rendering ferroelectric features to homogenize interfacial charge distribution and suppress dendrite-like Na propagation. Homogeneous Na + flux distribution induced by the ferroelectric interlayer is confirmed by finite element analysis, and flat sodium plating around the Bi 4 Ti 3 O 12 nanoplates is observed by focus-ion-beam scanning electron microscopy. Besides, distribution of relaxation time analysis on the electrochemical impedance reveals a small interfacial resistance of 6.5 Ω·cm 2 for the symmetrical Na|Bi 4 Ti 3 O 12 -Na 3 Zr 2 Si 2 PO 12 |Na cells at 30 °C. Long-term Na plating/stripping cycles are achieved for 8,770 h at 0.2 mA/cm 2 , further indicating the excellence of the ferroelectric interlayer design. Additionally, full cells using Na 3 V 2 (PO 4 ) 3 cathodes with an active mass loading around 15 mg/cm 2 demonstrate a reversible capacity of 1.42 mAh/cm 2 with 96.49% retention after the 90th cycle at a 1 C rate and 30 °C. This work provides fundamental insights into ferroelectric-electrochemical interactions and will promote the development of high-capacity solid-state sodium metal batteries working at ambient temperature.