Visualization of battery materials and their interfaces/interphases using cryogenic electron microscopy

Future innovations and developments in advanced rechargeable batteries require atomic-scale observation and understanding of the failure mechanisms of secondary batteries. Unfortunately, battery chemistry is highly sensitive to air or moisture and cannot stand electron beam radiation at high dose rates essential for atomic-scale resolution, hence limiting the use of conventional electron or optical microscopes. Recently, cryogenic electron microscopy (cryo-EM) has shown that battery-sensitive materials and interface/interphases can be protected, stabilized, and imaged under cryogenic conditions, facilitating novel insights into key components and phenomena that have a substantial impact on the cell operation. Herein, we highlight the significance and essential role of cryo-EM in characterizing sensitive battery materials (such as Li/Na/K metal anodes, sulfur, lithiated silicon, etc.), key components and interfaces, and summarize the recent contributions and discoveries enabled by cryo-EM. The chemistries and evolving nanostructures at electrode/electrolyte interphase in various electrolytes (both solid and liquid), hosts, artificial interphases, and temperature ranges for lithium-based batteries, and beyond are discussed in detail. Finally, the conclusions and the perspectives on the future direction of cryo-EM in analyzing the battery materials and interfaces are briefly discussed. We believe that the insights and discoveries obtained from this characterizing tool will provide guidelines for developing energy materials with improved electrochemical performance.