A High‐Performance Monolithic Solid‐State Sodium Battery with Ca²⁺ Doped Na₃Zr₂Si₂PO₁₂ Electrolyte

Abstract Solid‐state sodium batteries (SSSBs) are promising electrochemical energy storage devices due to their high energy density, high safety, and abundant resource of sodium. However, low conductivity of solid electrolyte as well as high interfacial resistance between electrolyte and electrodes are two main challenges for practical application. To address these issues, pure phase Na 3 Zr 2 Si 2 PO 12 (NZSP) materials with Ca 2+ substitution for Zr 4+ are synthesized by a sol‐gel method. It shows a high ionic conductivity of more than 10 −3 S cm −1 at 25 °C. Moreover, a robust SSSB is developed by integrating sodium metal anodes into NZSP‐type monolithic architecture, forming a 3D electronic and ionic conducting network. The interfacial resistance is remarkably reduced and the monolithic symmetric cell displays stable sodium platting/striping cycles with low polarization for over 600 h. Furthermore, by combining sodium metal anode with Na 3 V 2 (PO 4 ) 3 cathode, an SSSB is demonstrated with high rate capability and excellent cyclability. After 450 cycles, the capacity of the cell is still kept at 94.9 mAh g −1 at 1 C. This unique design of monolithic electrolyte architecture provides a promising strategy toward realizing high‐performance SSSBs.