Tracking Dynamic Sulfur Electrochemistry by Operando Techniques in Alkali Metal‐Sulfur Batteries

ABSTRACT Alkali metal‐sulfur batteries (AMSBs) offer high energy densities, elemental abundance, and conversion‐type electrochemistry, positioning them as promising candidates for next‐generation energy storage beyond conventional intercalation batteries. However, their practical application is severely hindered by polysulfide dissolution and shuttling, sluggish sulfur redox kinetics, and dynamically evolving electrode‐electrolyte interfaces. Conventional ex situ characterization captures only end‐state products and often obscures transient intermediates, interfacial reconstruction, and pathway reaction dynamics that ultimately govern reversibility and degradation. In situ and operando characterization has therefore become indispensable for directly probing sulfur redox chemistry, solvation structures, phase evolution, and interfacial processes in working cells. This Review summarizes recent advances in in situ and operando studies of AMSBs, with emphasis on how real‐time spectroscopic, scattering, and imaging methods have reshaped mechanistic understanding across electrodes, electrolytes, and interphases. In particular, we place Li‐S, Na‐S, and K‐S batteries within a unified mechanistic perspective, enabling direct comparison of reaction pathways, polysulfide behaviors, and kinetic limitations. We further highlight the emerging integration of operando experiments with theoretical modelling and machine learning, which is transforming qualitative observation into quantitative and predictive insight. Remaining methodological challenges and opportunities for correlative operando approaches are critically assessed, providing guidance for the rational design of advanced AMSBs.