Is the Li-S battery an everlasting challenge for operando techniques?

The promise of high-energy density and the predicted role of the Li-S batteries in electrochemical energy storage applications are largely based on sulfur's high theoretical specific charge. Unfortunately, to date the commercialization of Li-S battery is still hindered due to the complexity of the reaction mechanism involving a sequence of dynamically changing liquid and solid equilibria. Operando techniques have been widely employed to study these performance-limiting phase transformations; however, they often fall short in tracking and resolving simultaneously the solid and liquid phases. Here, we present a review summarizing the last efforts in the field.