Sulfur cathode design for high-energy-density metal–sulfur batteries: from liquid to solid electrolyte cells

Metal-sulfur batteries are attracting broad interest as next-generation energy-storage systems because sulfur offers a high theoretical capacity, low cost, and natural abundance. Among them, lithium-sulfur (Li-S) batteries remain the most extensively studied, while room-temperature sodium-sulfur (Na-S) batteries are emerging as attractive alternatives for low-cost and large-scale storage. However, their practical implementation remains limited by inefficient sulfur utilization, sluggish redox kinetics, severe interfacial and chemo-mechanical degradation, and the distinct challenges imposed by different electrolyte environments. In this review, sulfur cathode design is examined as the central enabling factor for translating the theoretical advantages of metal-sulfur chemistry into practical high-energy-density batteries. We first discuss the key cell-level parameters that govern practical energy density and the fundamental reaction and degradation processes in liquid and solid electrolyte systems. We then analyze how sulfur cathode design has evolved from simple sulfur confinement toward multiscale architectures that regulate sulfur chemistry, transport, and structural stability, spanning both liquid electrolyte and all-solid-state configurations. By comparing these two regimes within a unified framework, this review highlights which design principles are broadly transferable, which must be redefined, and how sulfur cathodes should be coupled with electrolytes and realistic cell constraints. Finally, we outline the major challenges and future opportunities for advancing metal-sulfur batteries toward practical implementation.