Mixed Ionic-Electronic Conductive Interfacial Design for All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium–sulfur (Li–S) batteries, offering high energy density, improved safety, and potential low cost, are promising candidates for next-generation energy storage technology. However, interfacial challenges, such as poor solid-solid contact, limited reaction area, and interfacial chemical/electrochemical degradation, fundamentally threaten the battery's energy density and cycle life. In the cathode, sulfur conversion reactions are confined to the limited triple-phase boundary among carbon, active material, and solid-state electrolyte (SSE), resulting in low sulfur utilization. At the anode, the (electro)chemical instability and mechanical incompatibility give rise to impedance growth, unfavorable Li stripping/plating, and dendritic penetration, ultimately causing rapid cell failure. Here, we introduce mixed ionic-electronic conductive interfacial designs for both sulfur cathodes and Li anodes to address these challenges. In the cathode, replacing conventional SSE with mixed ionic–electronic conductors extends the sulfur conversion reaction beyond triple-phase boundaries to binary interfaces, unlocking the potential of sulfur conversion reactions. A conductive interfacial layer is formed between sulfur and the mixed conductor, enabling efficient interfacial electron/ion transport and accelerating lithiation kinetics. As a result, the discharge capacity of sulfur cathodes (50 wt% active material) increases from below 1000 mAh/g to over 1450 mAh/g at 0.1 C and 60 °C. At the anode, inserting a self-lithiated mixed ion-electronic conductive Sn-C interlayer between Li metal and SSE enables seamless interfacial contact, uniform Li ion flux, and dendrite-free deposition. Stable cycling of Li||Li symmetric cells is achieved for over 7000 hours. Combining these cathode and anode strategies yields all-solid-state Li–S cells with stable cycling for over 300 cycles and high discharge capacities exceeding 1000 mAh/g under low stacking pressure (8 MPa) at 1.0 C/0.3 C discharge/charge rate and 60 °C. The mixed ionic-electronic conductive interfacial designs highlight a general strategy for overcoming interfacial limitations, advancing the practical application of all-solid-state Li–S batteries.