Center for Functional Nanomaterials Seminar

Understanding electrochemical interfaces at the nanometer length scale can uncover the structure-dependent activity of reaction kinetics in energy conversion and storage systems. However, tracking transient species that influence the electrochemical reactions is challenging when they undergo compositional change without structural transformation. Such intricacy is further enhanced when the active materials undergo phase transformations during redox reactions, which is common in next-generation energy storage systems like lithium-sulfur (Li-S) and lithium-air batteries. Though lithium-sulfur (Li-S) is the most sought-after technology due to its high energy density (2600 Wh/kg) and low cost, its performance is guided by highly complex and non-equilibrium conversion reactions of several sulfur intermediates, known as lithium polysulfides (LiPS), along with solid-liquid-solid phase transformations at the cathode surface. Such Li-S batteries often face challenges like rapid capacity fade, sluggish reaction kinetics, short cycle life, and poor coulombic efficiency. Despite some success in mitigating these issues by employing a variety of cathode/electrolyte modifications and various in-situ/ex-situ techniques that have been deployed in the last decades, the full richness of Li-S transformations occurring at the electrode/electrolyte interfaces remains to be mapped. This presentation will leverage advanced techniques like Atomic force microscopy -Scanning Electrochemical Microscopy (AFM-SECM) coupled with Raman spectroscopy to study lithium-sulfur (Li-S) interfaces at nanoscale spatial resolution. Through systematic studies with suitable SECM modes, the probing of the Li-S interface reveals (i) explicitly the existence of most of the debated intermediate species, (ii) the detrimental influence of such intermediates on the reversibility, (iii) possible reaction mechanism leading to the evolution of intermediate species. The obtained results will explore how cathode nature, solvents, and electrolyte additives influence the sulfur redox mechanism across the electrode/electrolyte interface. The in situ advanced electrochemical techniques provide nanoscale-resolved information regarding the high-energy Li-S redox reactions related to electrode structure and its properties colocated and at a relevant length scale.