Several classes of Li-ion SEs have been developed in the past decades, including oxides, sulfides, polymer, and oxide-polymer composites (Table , Supporting Information). Among them, oxides are especially attractive because they have a good balance between high Li-ion conductivity and wide electrochemical stability window . However, their Li-ion conductivity (10 -3 ~10 -8 S cm -1 ) is still much lower than that of liquid electrolytes (~10 -2 S cm -1 ). To address this challenge, various strategies have been proposed to increase the ionic conductivity of oxide SEs. The most common one is structural engineering by elemental substitution, including both cation substitution and anion substitution . For example, many researchers try to substitute La 3+ and/or Ti 4+ in Li3xLa2/3-x □ 1/3-2xTiO3 (LLTO) . However, most substitution shows minimal enhancement of Li-ion conductivity except for the substitution of Ti 4+ with Al 3+ , Ge 4+ . In contrast, replacing O with larger and more polarizable anions (e.g., S) has been proven to be more effective because the high polarizability of anion weakens interactions of Li + with the anionic sub-lattice . For example, Kanno first reported the enhancement of Li-ion conductivity for LiSICONs SEs by replacing O with S . This discovery triggers an intensive study of sulfides-based SEs , resulting in a Li-ion conductivity comparable to that of liquid electrolytes (up to 10 -2 S cm -1 ) . However, the intrinsically low electrochemical stability window (0.3~0.6 V) of sulfide SEs constrains their application in LIBs . Therefore, the research efforts in modifying existing oxide SEs have shown limited progress. Designing new oxide SE materials is highly essential to the success of solid-state LIBs.