Local Electric‐Field Homogenization via Ferroelectric Grain‐Boundary Engineering Enables Long‐Life, High‐Rate Solid‐State Sodium Metal Batteries

Achieving dendrite‐free and stable interfaces remains a critical challenge for solid‐state sodium metal batteries (SSMBs), especially under low‐temperature and high‐rate conditions. Here, we report a scalable grain boundary engineering strategy by integrating ferroelectric PbTiO 3 (PTO) into Na 3 Zr 2 Si 2 PO 12 (NZSP) electrolyte. Ferroelectric polarization induces local electric‐field homogenization at grain boundaries, suppressing sodium dendrite nucleation while improving densification and interfacial ion transport. The PTO‐NZSP delivers high ionic conductivities of 3.21 mS cm −1 at 25°C and 0.47 mS cm −1 at −20°C, along with markedly reduced interfacial resistance. The symmetric Na cells exhibit ultra‐stable plating/stripping for 8730 h at 25°C and 747 h at −20°C, with critical current densities up to 1.45 and 0.45 mA cm −2 , respectively. The full Na/PTO‐NZSP/Na 3 V 2 (PO 4 ) 3 cells achieve 81% capacity retention after 10 000 cycles at 20 C and 25°C, and 97% after 490 cycles at 3 C and −20°C, highlighting the local ferroelectric field regulation as an effective route toward durable, all‐climate SSMBs.