Probing the Solid-State Chemical Bonding of Energy-Storage-Relevant Na Materials at the Nanoscale using Low-Loss Electron Energy Loss Spectroscopy

Mapping the Na ion chemical bonding state in energy-related materials is one of the key challenges for understanding heterogeneity in interfacial regions, such as in solid–electrolyte interphases. Here, we use low-loss electron energy loss spectroscopy to study Na bonding in various energy-related materials. Both the plasmon region and Na L2,3 edge regions are measured using a direct electron detector in electron energy loss spectroscopy (EELS) and provide unique spectroscopic peaks and profiles for various compounds. The EELS spectra enable the identification of Na bonding at the nanoscale using electron doses that are considerably lower than when using the Na K edge region and therefore induce less damage to the sample and are more indicative of the intrinsic Na state. Finally, we show how EELS can be used to identify various Na bonding differences across regions of Na deposited by electrochemical methods using Na-TFSI electrolyte, which is a promising type of electrolyte for Na-ion batteries. These results provide insights into how EELS can be used for studying spatial heterogeneity in energy-storage-related Na materials.