Exploring the current engineering challenges of solid-state lithium-sulfur batteries with fundamental materials science: A review

Abstract Lithium sulfur batteries offer high theoretical energy density and low material cost, but their practical use depends on electrolyte systems that satisfy several fundamental criteria. Solid state electrolytes provide a promising route by removing the liquid phase and improving safety. This review outlines the reaction pathways in lithium sulfur cells and the mechanisms of ion transport in solid electrolytes, followed by a generational comparison of major electrolyte classes, including polymers, oxides, sulfides, halides, garnets and composite systems. Four key criteria for solid state electrolyte use in lithium sulfur batteries are then examined: stability with electrodes, polysulfide behaviour, sulfur utilization and mechanical versatility. Existing strategies are evaluated in terms of how effectively they satisfy each requirement. Finally, two solid state cell designs that meet all identified criteria are proposed, together with quantitative considerations for electrolyte and cathode design. These insights provide a framework for guiding the development of practical solid state lithium sulfur batteries. Highlights This work identifies the key requirements that solid electrolytes must meet to enable high-energy lithium–sulfur batteries. It also highlights two practical cell designs that satisfy these requirements and point toward viable solid-state lithium–sulfur technology. Discussions The lack of quantitative data on polysulfide solubility in solid polymers remains a major barrier to rational design of solid-state lithium–sulfur batteries, raising the question of whether industry should invest heavily in this chemistry before these fundamentals are resolved. Although solid electrolytes are widely promoted as a safer alternative to liquid systems, their real-world reliability against lithium dendrites remains unsettled, especially under manufacturing imperfections and high-power operating conditions. The practical energy and sustainability benefits of solid-state lithium–sulfur batteries depend not only on materials breakthroughs but also on whether new manufacturing lines—potentially requiring ceramic processing and polymer casting hybrids—can be deployed at commercial scale without prohibitive cost or environmental burden. Graphical Abstract