Abstract: | Highly Li‐ion conductive Li4(BH4)3I@SBA‐15 is synthesized by confining the LiI doped LiBH4 into mesoporous silica SBA‐15. Uniform nanoconfinement of P63 mc phase Li4(BH4)3I in SBA‐15 mesopores leads to a significantly enhanced conductivity of 2.5 × 10?4 S cm?1 with a Li‐ion transference number of 0.97 at 35 °C. The super Li‐ion mobility in the interface layer with a thickness of 1.2 nm between Li4(BH4)3I and SBA‐15 is believed to be responsible for the fast Li‐ion conduction in Li4(BH4)3I@SBA‐15. Additionally, Li4(BH4)3I@SBA‐15 also exhibits a wide apparent electrochemical stability window (0 to 5 V vs Li/Li+) and a superior Li dendrite suppression capability (critical current density 2.6 mA cm?2 at 55 °C) due to the formation of stable interphases. More importantly, Li4(BH4)3I@SBA‐15‐based Li batteries using either high‐capacity sulfur cathode or high‐voltage oxide cathode show excellent electrochemical performances, making Li4(BH4)3I@SBA‐15 a very attractive electrolyte for next‐generation all‐solid‐state Li batteries. |