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 Na₃Zr₂Si₂PO₁₂ (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 NaNbO₃ (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.