The application of in situ liquid cell TEM in advanced battery research

The fast development of modern battery research highly relies on advanced characterisation methods to unveil the fundamental mechanisms of their electrochemical processes. The continued development of in situ characterisation techniques allows the study of dynamic changes during battery cycling rather than just the initial and the final phase. Among these, in situ transmission electron microscopy (TEM) is able to provide direct observation of the structural and morphological evolution in batteries at the nanoscale. Using a compact liquid cell configuration, which allows a fluid to be safely imaged in the high vacuum of the TEM, permits the study of a wide range of candidate liquid electrolytes. In this review, the experimental setup is outlined and the important points for reliable operation are summarised, which are critical to the safety and reproducibility of experiments. Furthermore, the application of in situ liquid cell TEM in understanding various aspects, including dendrite growth, the solid electrolyte interface (SEI) formation, and the electrode structural evolution in different battery systems, is systematically presented. Finally, challenges in the current application and perspectives of the future development of the in situ liquid cell TEM technique are briefly addressed.