(594g) Non-Invasive in Operando Imaging of Lithium-Sulfur Battery Using Light Microscopy

Lithium-sulfur battery could increase the energy density of current Li-ion batteries by 300-500%, but their overall performance (cycle life, Coulombic efficiency, areal capacity, reproducibility) is still not ready for large-scale application. Mechanistic understanding of Li-S battery could provide guidance to overcome the intrinsic materials challenges, but are limited mainly due to the instability of sulfur species under electron or X-ray irradiation, and when removed from their native environment. A non-invasive in operando techniques is ideal for studying Li-S batteries. Light microscopy has been heavily used in biological science but has been paid little attention in materials science, mainly due to its lower resolution than electron microscopy. However, because of its ambient working condition, low sample damage, and different contrast mechanism, optical microscopy is ideal for studying complex and delicate materials system under real time, real environment, without radiation damage. Using optical techniques and specifically designed transparent cells, we have discovered new metastable species in operating Li-S batteries, and provided direct evidence on the debated reaction mechanism. The newly elucidated mechanism is correlated to the performance of the battery as well. This light microscopy technique could also be powerful in studying other high-energy batteries with delicate/complex electrochemistry.