Additionally, maintaining effective connectivity between the electrode and electrolyte poses another significant challenge. The development of solid-fast ion conductors has witnessed notable progress in synthesizing new materials (Fig. ) and addressing these challenges. Researchers have explored a diverse range of mobile ionic species, including but not limited to Li + , Na + , H + , Ag + , Cu + , F -, O 2-, and H -, in their efforts to enhance the performance of solid fast ion conductors. Recent reviews have extensively documented and summarized this progress . In addition to materials that conduct monovalent ions, there is growing interest in the potential of divalent-cation-conducting materials, such as Mg 2+ , Ca 2+ , and Zn 2+ , for various energy-storage applications . These materials are garnering attention due to their significant promise in energy-storage devices, primarily attributed to their higher energy densities when compared to all-solid-state batteries (ASSBs) constructed using monovalent cations. Remarkably, ions such as O 2-and Mg 2+ have demonstrated notable mobility, with certain recently discovered Mg 2+ ion conductors achieving an impressive ionic conductivity of up to 0.1 mS cm -1 at room temperature (RT) . Among the various types of ionic conductors, particular emphasis has been placed on Li-ion and Na-ion conductors since the year 2000. These materials have been extensively studied due to their potential applications in energy storage and other technologies requiring efficient ion transport within solids.