Recent advances in electron microscopical techniques now enable valuable insights into chemical and crystallographic processes of battery materials. Influences on battery performance due to cycling rates or cycling iterations are now directly observable utilizing High-Resolution Scanning Transmission Electron Microscopy (HR-STEM), integrated Differential Phase Contrast Imaging (iDPC), a variety of electron diffraction approaches, as well as Electron Energy Loss Spectroscopy (EELS). Here, we demonstrate novel approaches to utilize and optimize these techniques for quantifying local Li content to better understand ion transport and charging mechanisms within battery electrodes and solid-state electrolytes.
Using LiFePO4 (LFP) as an example, we observe the distribution of residual lithium within electrochemically delithiated LFP crystallites for the first time at the atomic level. Additionally, selected area electron diffraction (SAED) is employed for precise measurements of local crystal lattice parameters to identify and quantify local variations in cathode lithiation. We show that our methodology can be applied to other Li-based material systems, such as LiVPO4 or sulfur-based solid-state electrolytes. Furthermore, by applying 4D-Scanning Confocal Electron Diffraction in tandem with conventional methods, we establish a new scheme for analyzing beam-sensitive battery materials at nanometer resolution, providing a more holistic view of battery cycling behavior.