Recent advances in in situ / operando characterization of lithium–sulfur batteries

The lithium–sulfur battery (LSB) is a next generation energy storage technology with potential to replace lithium-ion batteries, due to their larger specific capacity, cheaper and safer manufacturing materials, and superior energy density. LSBs are a rapidly progressing topic globally, with around 1800 publications each year and the market is expected to exceed 1.7 billion USD by 2028, as such many novel strategies are being explored to develop and commercialise devices. However, significant technical challenges must be solved to engineer LSBs with commercially viable cycle life, which requires a deeper understanding of the chemical mechanisms occurring within the battery structure. In recent years in situ/operando testing of LSBs has become a popular approach for deciphering the kinetics and mechanisms of their discharge process, which is notoriously complex, and visualising the effects of mass deposition onto the electrodes and how these factors affect the cell's performance. In this review, in situ and operando studies are discussed in the context of LSBs with particular focus on spectroscopic and morphological techniques in line with trends in the literature. Additionally, some techniques have been covered which have yet to be used widely in the literature but could prove to be invaluable tools for analysis in the future. These in situ/operando techniques are becoming more widely available, and a review is useful both for the research community and industry to help accelerate the commercialisation of this next-generation technology.