All-solid-state batteries (ASSBs) are considered as an alternative to current Li-ion batteries for next generation electrified transportation, owing to their good safety property and higher energy density. Solid electrolyte (SE) is the key component of ASSBs and is the major barrier for the commercialization of this technology. A good SE must possess many essential properties, including high ionic conductivity, low electrolyte conductivity, wide electrochemical window, good mechanical compatibility and low cost, etc. To date, no known electrolyte simultaneously meets all these requirements. Here we report our recent progresses in developing high-performance SEs, including the design, synthesis, in situ structural characterizations and processing of a number of novel solid state ionic conductors. Ultrahigh ionic conductivity of >10 mS/cm was achieved at room temperature. Their structure-property relationship was investigated with multiple complementary characterizations. ASSBs with using these new compounds as electrolyte were successfully fabricated to offer outstanding cycling performances.