In situ TEM studies of electrochemistry of high temperature lithium-selenium all-solid-state batteries

Lithium sulfur (Li-S) battery has very high theoretical specific capacity, which is a potential "beyond lithium" energy storage technology for electrical vehicle and grid energy storage applications. However, the poor electronic conductivity of sulfur has plagued the performance of Li-S battery. This prompts the research in lithium selenium (Li-Se) battery, in which the electronic conductivity of Se is more than 25 orders of magnitude higher than that of S. Herein, we have investigated the electrochemistry of Li-Se all-solid-state batteries (ASSBs) at different temperatures using in situ transmission electron microscopy (TEM) technique equipped with a microelectromechanical systems (MEMS) heating device. We found that different from liquid electrolyte, polyselenides were absent during discharge and charge of Li-Se ASSBs. Moreover, we revealed that the discharge products of Li2Se cannot be decomposed at room temperature. However, Li2Se was decomposed easily at high temperatures because of increased Li+ ion conduction, indicating conclusively that it is the Li+ ion conductivity rather than the electronic conductivity that dictates the performance of Li-Se ASSB. Our studies provide not only new understanding to the Li2Se electrochemistry, but also an important strategy to boost the performance of Li-Se ASSBs for energy storage applications.