Conversion-type batteries, such as liquid-electrolyte lithium-sulfur (Li-S) systems, hold great promise for high-energy storage applications, due to the exceptional theoretical capacity and sustainability of active materials. The electrochemical phase transformation between solid sulfur (S) and solid lithium sulfide (Li₂S) largely defines the battery performance; it can occur through solid-liquid-solid, quasi-solid-state, and solid-state conversion, depending on the used electrolyte and cathode materials. While these pathways are widely discussed in literature, their precise distinctions and impacts on key performance metrics remain elusive due to the lack of techniques capturing the complex conversion pathways at the nanoscale.

This webinar focuses on operando small and wide angle X-ray scattering (SAXS/WAXS) and operando small angle neutron scattering (SANS) to track the growth and dissolution of solid deposits from atomic to sub-micron scales during operating Li-S battery cells with different conversion mechanisms. Machine-learning-assisted stochastic modelling based on the SANS (and SAXS) data allows quantification of the chemical phase evolution during discharge and charge. Combined with complementary data from cryo-transmission electron microscopy, we show that the deposit is comprised of nanocrystalline Li₂S and smaller, solid short-chain polysulfide particles. These insights offer a basis for influencing the reaction pathway and improving the performance of next-generation Li-S batteries.