Direct Observation of the Evolutionary Process in Room-Temperature Sodium-Sulfur/Selenium Batteries Using operando Light Microscopy.

Understanding the conversion mechanism of active materials in the electrode is essential to guide the design of room-temperature sodium-sulfur/selenium (RT Na-S/Se) batteries. However, there is still some confusion regarding the dissolution and formation of the insulating active particles. Conventional detection methods have difficulty in capturing and presenting the dynamic processes of these microscopic particles in the "black box" battery. In this study, a visualization technique was applied to track and monitor the internal evolution process of RT Na-S/Se batteries, visualizing the dissolution and formation details of insulating solid particles in real time. Supercooled liquid sulfur and spherulites were also observed for the first time in this system. The microstructural evolution mechanism is inferred based on the observation of the dynamic information on microscopic particles. This paper provides insights into the internal workings of RT Na-S and Na-Se batteries, allowing for a more comprehensive and in-depth understanding of their dynamics.