Development of Cryogenic Techniques for Characterizing Energy Storage Materials in Electrochemical Process

Lithium-ion batteries (LIBs) commercially dominate portable energy storage and have been extended to hybrid/electric vehicles by utilizing electrode materials with enhanced energy density. The energy density and cycling life of LIBs must extend beyond the current reach of commercial electrodes to meet the performance requirements for transportation applications. Recently, researchers proposed to use Li metal as the anode to achieve higher energy density. However, the dendritic growth of Li metal during cycling will result in low coulombic efficiency as well as safety issue which is detrimental for practical applications. It is proposed solid state electrolytes (SSE) are compatible with lithium metal because of lithium penetration resistance, which can be the ultimate choice to achieve the energy density of 500 Wh/kg. The performance of existing all-solid-state batteries is still not optimal, which is mainly attributed to the poor interfacial stability. Further improvements and developments of these energy storage materials rely on a fundamental understanding of their electrochemical cycling mechanisms at atomic level. Characterization of Li anodes and SSE/Li-metal interfaces remains difficult due to their sensitivity to beam damage, the nano-scale of interfacial decomposition products, and their buried nature. Our group has demonstrated the importance of cryogenic techniques for preparation (cryogenic focused ion beam, cryo-FIB) and characterization (cryogenic transmission electron microscopy, cryo-TEM), to preserve the morphology and structure of lithium metal. These breakthroughs enabled unprecedented characterization of plated Li metal and are currently being extended to all-solid-state batteries.<br/><br/>The first demonstration of the functionality of the cryo-TEM will focus on characterizing the morphology and crystallinity of electrochemically cycled lithium metal with different electrolytes. This work will also cover recent advances on cryo-EM development for Li/LiPON/LNMO interfaces. The combination of cryo-FIB and cryo-EM is necessary for quantitative structural and chemical analysis due to extreme susceptibility of both lithium metal and LiPON to air and beam damage. The obtained results provide new insights of decomposition, diffusion of chemical species, and chemical evolution along the interface, which leads to a better understanding of the cycling stability for Li metal batteries.