Unraveling the lithium iodide-mediated interfacial process in lithium-sulfur batteries: An in situ AFM study

Among various energy storage devices, lithium–sulfur batteries have attracted widespread attention due to their high theoretical energy density and specific capacity. To improve the performance and realize practical applications of lithium–sulfur batteries, it is crucial to unravel the dynamic evolution and reaction mechanism at the electrode/electrolyte interfaces during cycling. Nevertheless, the details are still not well known despite generous efforts, which need more in situ and non-destructive imaging characterizations. Herein, we have combined AFM with an electrochemical workstation to dynamically visualize the morphological evolution and structural changes of the lithium iodide–mediated interfacial process and how they affect the interfacial reactions in lithium–sulfur batteries. Without the addition of lithium iodide, insoluble sulfides were only partially oxidized after 10 cycles of cycling, which reduced the capacity of lithium–sulfur batteries. In situ measurements showed that the electrode surface was coated with a reticular layer that contained elemental iodine and polyether during charging. These findings shed new light on the interfacial mechanism and establish design ideas for the future development of better electrolytes for lithium–sulfur batteries.