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.