Cryo-TEM for Atomic Imaging of Solid Electrolytes in Li-Ion Batteries

Transmission electron microscopy (TEM) is an indispensable method to characterize materials structure and composition at the atomic scale, which is particularly important for battery research to investigate crystal lattices, defects, as well as microstructural and chemical heterogeneities within materials used in battery electrodes, electrolytes, and other components. Despite the rapid advancement of in situ TEM that has enabled the real-time observation of various dynamical phenomena and chemical processes during battery cycling and phase transformations, there are still pressing challenges that need to be addressed in order to obtain accurate and reliable findings relevant to real-world applications. For example, the radiation damage by the high-energy electron beam, as well as the side reactions between lithium compounds and moisture and oxygen in the air, are required to be avoided or mitigated. Therefore, it is desired to develop reliable electron microscopy and microanalysis strategies for the characterization, analysis, and diagnosis of real-world battery materials, for which cryo-TEM is of unique powerfulness.<br/><br/>Here, we report the technical development of effective methodologies and instrumentation to tackle the critical issues described above. Specifically, we developed a seamless workflow to integrate the cryo-TEM techniques with low-kV and low-dose settings to minimize the impact of electron beam radiation and sustain the original material structures from radiolysis and knock-on damage. We also built a dedicated air-free transfer system to present unwanted by-products of sensitive Li-containing species caused by side reactions with oxygen and moisture during sample preparation and transfer. With careful control of imaging conditions through a series of control experiments, we provided benchmarks for damage-free atomic-scale microscopy and microanalysis using cryo-TEM. These results were demonstrated in the atomic imaging of garnet-type solid electrolyte Li₇La₃Zr₂O₁₂ (LLZO), a promising superionic conductor for next-generation solid-state Li-ion batteries. It is expected that this approach can be generalizable to implement in the reliable characterization of a large variety of sensitive materials for energy storage relevant to real-world technologies.