Unraveling Multiphase Conversion Pathways in Lithium-Sulfur Batteries through Cryo Transmission Electron Microscopy and Machine Learning-Assisted Operando Neutron Scattering.

Understanding the complex physicochemical processes in conversion-type batteries requires investigations across multiple length scales. Here, we present a methodological approach to examine Li-S batteries on the nanoscale by combining cryogenic transmission electron microscopy (cryoTEM) with operando small-angle neutron scattering (SANS). CryoTEM revealed discharge products with a biphasic structure consisting of nanocrystalline LiS within an amorphous LiS matrix. Data analysis of complementary operando SANS measurements was accelerated by a convolutional neural network trained to predict scattering curves based on plurigaussian random fields, enabling comprehensive parameter space exploration for model fitting. Our findings are in line with disproportionation-driven deposition of LiS particles that agglomerate and partially reduce to LiS via solid-state conversion. This challenges the conventional view of direct, stepwise electroreduction of polysulfides at the electrode-electrolyte interface. Overall, our multitechnique approach demonstrates the value of combining localized high-resolution imaging with time-resolved operando scattering measurements to understand complex electrochemical conversion pathways in next-generation energy storage systems.