Enabling High‐Voltage “Superconcentrated Ionogel‐in‐Ceramic” Hybrid Electrolyte with Ultrahigh Ionic Conductivity and Single Li+‐Ion Transference Number

High room-temperature ionic conductivities, large Li+ -ion transference numbers, and good compatibility with both Li-metal anodes and high-voltage cathodes of the solid electrolytes are the essential requirements for practical solid-state lithium-metal batteries. Herein, a unique "superconcentrated ionogel-in-ceramic" (SIC) electrolyte prepared by an in situ thermally initiated radical polymerization is reported. Solid-state static 7 Li NMR and molecular dynamics simulation reveal the roles of ceramic in Li+ local environments and transport in the SIC electrolyte. The SIC electrolyte not only exhibits an ultrahigh ionic conductivity of 1.33 × 10-3 S cm-1 at 25 °C, but also a Li+ -ion transference number as high as 0.89, together with a low electronic conductivity of 3.14 × 10-10 S cm-1 and a wide electrochemical stability window of 5.5 V versus Li/Li+ . Applications of the SIC electrolyte in Li||LiNi0.5 Co0.2 Mn0.3 O2 and Li||LiFePO4 batteries further demonstrate the high rate and long cycle life. This study, therefore, provides a promising hybrid electrolyte for safe and high-energy lithium-metal batteries.