Role of Electronic Conductivities Toward Practical All-Solid-State Lithium-Metal/Sulfur Batteries

Inorganic solid-state electrolytes (ISSEs) are recognized as promising candidates for safer and higher energy-density all-solid-state lithium-metal/sulfur batteries (ASSLM/SBs). Significant efforts have been directed at designing ISSEs with better chemical/electrochemical stability, superior lithium-ion conductivity, and extensive working voltage windows. However, it has been investigated that Li-dendrites produced within bulk ISSEs during the charge-discharge process short-circuit ASSLM/SBs. Notably, non-negligble electronic conductivity (σ_e) ≈10⁻⁸ S cm⁻¹ can trigger nucleation of Li-dendrites at intrinsic defects, e.g., grain boundaries, pores, and cracks of ISSEs, leading to a significant self-discharge phenomenon in ASSLM/SBs. Furthermore, the reasons behind the insufficient utilization of cathode active materials (CAMs) in ASSLM/SBs at practical current densities or C-rate remained overlooked. Herein, first, the strategies to reduce the σ_e of sulfide-based SSEs to prevent the Li-dendrite formation at intrinsic defects are discussed. Second, strategies to enhance sulfur-based cathodes' ionic and electronic conductivity (CAMs: Li₂S and S₈) are addressed. How a balanced ionic and electronic conductivity in the positive cathode layer realizes fast kinetics and maximizes the utilization of CAMs and reversibility for high-performance ASSLM/SBs is also discussed. Finally, an extensive conclusion and innovative perspectives are presented to give readers a clearer insight into ASSLM/SBs.