Lithium-sulfur (Li-S) batteries are considered a promising next-generation battery technology. Sulfur is an abundant, low-cost material with minimal environmental impact and offers large theoretical capacities. Li-S batteries are composed of a sulfur infiltrated, highly porous carbon cathode soaked with a non-aqueous electrolyte and paired with a Li-metal anode. Widespread adoption of Li-S batteries is, however, hindered by factors such as poor S/Li2S mass loadings, slow rate capabilities and a continuous loss of active material. The latter stems from the dissolution of polysulfides (PS) that are formed during discharge and shuttle towards the anode. There, the PS irreversibly react with the Li-metal. All of these issues find a common cause in the lacking understanding of the underlying S-to-Li2S conversion mechanism. 

In this work, we investigate how the multiphase cathode structure changes during galvanostatic cycling using operando small angle neutron scattering (operando SANS) and cryogenic transmission electron microscopy (cryo-TEM). By studying the structure-property relationship in the cathode, the previously elusive conversion mechanism can be uncovered. We interpret the operando SANS data using Plurigaussian Random Fields (PGRF) models, from which we obtain statistically representative 3D structures spanning several hundred nanometers. Solving this inverse design problem via PGRF is computationally intensive. Therefore, we train a generative adversarial model to speed up the simulation process. Complementary cryo-TEM measurements reveal model-free structural and chemical information with atomic resolution. Combining the time-resolved structural changes obtained from operando SANS and ex situ TEM micrographs reveals the local compositional information on discharged cathodes. Our results give evidence for a solid discharge product consisting of more than one phase; solid nanocrystalline Li2S, embedded in smaller solid Li2Sx particles.