Recent advances and challenges in the design of Li–air batteries oriented solid-state electrolytes

Solid-state Li–air batteries with ultrahigh energy density and safety are promising for long-range electric vehicles and special electronics. However, the challenging issues of developing Li–air battery-oriented solid-state electrolytes (SSEs) with high ionic conductivity, interfacial compatibility, and stability to boost reversibility, increase stable triple-phase boundaries, and protect the Li anode in an open system substantially impede their applications. Herein, we systematically summarize the recent progress achieved in terms of SSEs for Li–air batteries, and describe in detail the basic characteristics of SSE|air cathode interfaces and SSE|Li anode interfaces. First, the major characteristics of SSEs in Li–air batteries in terms of ionic/electronic conductivity, chemical/electrochemical/thermal stability, mechanical strength, and interfacial compatibility are briefly introduced according to three types of SSEs: inorganic, organic, and hybrid SSEs. Second, key strategies of integrating catalytic sites, porous structures, and electronic conductors with SSEs to enhance triple-phase boundaries at the SSE|air cathode for improving Coulombic efficiency are described in detail. Moreover, the protection of Li metal from H₂O, CO₂, O₂, and redox mediators at the SSE|Li anode to ensure safety is elaborately overviewed. Finally, future opportunities and perspectives on three important topics of three-dimensional structural integration, external field assistance, and operando characterizations are proposed for advanced solid-state Li–air batteries.