For the purpose of comparison, Fig. provides an overview of the ionic conductivities (low to high conductivity range in (b)) and the activation energy of key ionic conductors along with their structures. The chronological order of their discovery is also displayed in Fig. . Notably, Yttria (Y 2 O 3 ) stabilized zirconia (ZrO 2 ) and AgI have been recognized as fast ion conductors since the early twentieth century . In more recent times, the breakthrough discoveries of M Ag 4 I 5 (where M = Rb, K, and NH 4 ) , and Na β-alumina have significantly contributed to the field. Hong and Goodenough et al. conducted a comprehensive study in 1976, reporting high alkali ion conduction in a series of skeleton structural solids such as KSbO 3 , RbMgAlF 6 , NaAlSiO 4 , and Na 1+x Zr 2 P 3-x Si x O 12 (0 ≤ x ≤ 3). Inorganic solid electrolytes can be further classified into oxide, sulfide, halide, and hydride-based categories . Among oxide-based materials, Lithium Super Ionic Conductors (LISICONs), Na superionic conductors (NASICONs), garnets, perovskites, and anti-perovskites are the most widely studied . Sulfide-based electrolytes are thio-LISICONs, Li 10 GeP 2 S 12 (LGPS) and its analogs, argyrodites (Li 6 PS 5 X , where X = Cl, Br, or I). In halide class, Li 3 M X 6 (M = Y, Er; X = Cl, Br, I) find attractive, owing to the high ionic conductivity (≈ 1 mS cm -1 ) and a higher electrochemical stability comparable to known oxides . Complex metal hydrides fall under the hydride category. Each group of materials has distinct advantages: oxide-based electrolytes generally exhibit lower ionic conductivity and high hardness but superior stability in atmospheric and electrode environments. Sulfide and hydride-based electrolytes, on the other hand, tend to demonstrate higher ionic conductivity, though they are quite sensitive to ambient conditions. Notably, the mixture of two different complex hydrides (NaCB 9 H 10 and NaCB 11 H 12 ) has achieved the highest known ionic conductivity thus far, based on our current knowledge .