Inside lithium–sulfur batteries: Real-time multimodal insights into structure and polysulfide dynamics

Lithium–sulfur (Li–S) batteries are increasingly designated as a viable choice for future energy storage systems, owing to their substantial theoretical energy density, economic viability, and the abundant availability of sulfur. However, despite their significant potential, widespread commercialization has been limited by major obstacles, encompassing the polysulfide shuttle effect, slow sulfur redox reaction dynamics, and substantial structural degradation during cycling. To overcome these limitations and fully realize the optimal strength of Li–S batteries, a comprehensive comprehension of the fundamental electrochemical processes and real-time morphological changes during operation is crucial. This study offers a wide-ranging evaluation of recent progress in in situ and operando methods that enable direct observations of the dynamic behavior of Li–S systems under real-world conditions. Techniques including neutron scattering, X-ray tomography, X-ray reflectometry (XRR), Raman spectroscopy, small-angle neutron scattering (SANS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are examined in detail for their ability to monitor key processes like polysulfide dissolution, phase transitions, and electrochemical reactions. This review emphasizes a comparative and integrative perspective, highlighting how different diagnostic techniques collectively address critical challenges such as polysulfide migration, sluggish Li₂S conversion, and electrode degradation. Furthermore, the review highlights future research avenues aimed at enhancing these experimental techniques and integrating computational models to deepen our understanding of battery degradation mechanisms. The role of machine learning in predicting battery behavior and optimizing performance is also discussed as a key area for future exploration. This review emphasizes the transformative potential of real-time monitoring in overcoming the challenges encountered by Li–S batteries, accelerating their development toward widespread adoption and large-scale application.