All-solid-state lithium–sulfur batteries through a reaction engineering lens

All-solid-state lithium–sulfur (Li–S) batteries have emerged as a promising energy storage solution due to their potential high energy density, cost effectiveness and safe operation. Gaining a deeper understanding of sulfur redox in the solid state is critical for advancing all-solid-state Li–S battery technology. In particular, the key electrochemical reactions of solid-state sulfur are distinct from those in the liquid state, yet discussion of such aspects remains lacking thus far. This Perspective provides a fundamental overview of all-solid-state Li–S batteries by delving into the underlying redox mechanisms of solid-state sulfur, placing a specific emphasis on key reaction engineering principles, such as mass transport, electrochemical kinetics and thermodynamics. The dimensionless Damköhler number is underscored to elucidate transport and kinetics limitations in solid-state sulfur. Furthermore, advanced characterization techniques, such as cryogenic electron microscopy, are highlighted as powerful tools to bridge the current gaps in understanding that limit the deployment of all-solid-state Li–S batteries. All-solid-state lithium–sulfur batteries have been recognized for their high energy density and safety. This Perspective explores sulfur redox in the solid state, emphasizing the critical roles of electrochemical kinetics, thermodynamics, mass transport and advanced techniques such as cryogenic electron microscopy to help bridge gaps in current understanding.