Adaptive Piezoelectric Grain Boundaries Enabling Dendrite‐Free Solid‐State Sodium Metal Batteries

Solid‐state sodium batteries are a key direction for energy storage due to their cost‐effectiveness and high safety. NASICON‐based ceramic electrolytes, particularly Na 3 Zr 2 Si 2 PO 12 (NZSP), hold great promise because of their high ionic conductivity. However, severe dendrite growth and interfacial instability hinder the application of NASICON‐based electrolytes in solid‐state sodium batteries. In this work, we propose an adaptive grain boundary engineering strategy by introducing a ferroelectric NaNbO 3 (NN) second phase into the NZSP matrix. This approach not only densifies the microstructure but also regulates interfacial ion transport dynamics. Specifically, the spontaneous polarization of the ferroelectric NN phase establishes a localized space charge layer, effectively enhancing grain boundary conductivity and reducing the activation energy. Furthermore, a unique dynamic piezoelectric self‐regulation mechanism modulates Na + flux, transforming disordered deposition into a uniform coating. Consequently, the symmetric sodium cell achieves a high critical current density of 2.00 mA cm −2 and stable cycling for over 3370 h at 0.1 mA cm −2 . Moreover, quasi‐solid‐state sodium batteries with an NVP cathode demonstrate exceptional cycling stability and rate performance, realizing 90.75% capacity retention after 848 cycles at 2 C. This research provides novel insights into electrolyte design for high‐performance quasi‐solid‐state sodium metal batteries.