Pore-Filling Induced Solid Electrolyte Failure of Ti-Doped Na₃Zr₂Si₂PO₁₂ Characterized by Operando Synchrotron X-Ray Tomography**

Solid-state batteries (SSBs), particularly those utilizing sodium metal, are emerging as a promising technology due to their potential for enhanced safety, higher energy density, and longer cycle life. NASICON (Na superionic conductor) materials, known for their robust crystalline structure and high ionic conductivity, are pivotal in the development of efficient sodium all-solid-state batteries. These materials exhibit high room-temperature ionic conductivity and electrochemical stability, making them ideal for various applications. Research has focused on improving NASICON's ionic conductivity and stability through doping, interface regulation, and composite anode design. Recent advancements include Ti-doped Na₃Zr₂Si₂PO₁₂ (Ti-NZSP), which demonstrates improved surface stability, higher ionic conductivity, and increased critical current density. However, challenges such as Na dendrite formation and mechanical integrity under operational conditions persist. Advanced imaging techniques like operando synchrotron X-ray tomography have provided insights into failure mechanisms, revealing that pore-filling and dendrite growth are significant issues. Understanding these processes is essential for enhancing the performance and safety of Na-based SSBs. This study underscores the need for continued research to address these challenges and develop reliable, high-performance solid-state electrolytes for future energy storage solutions.