Recommended conditions for low kV ‘sweet spot’ imaging of battery materials

The characterisation of battery raw materials is imperative to understand the constituents that will eventually become manufactured cells, lately intensified because of the continuously evolving developments of new battery chemistries, formulations, and blends. Microscopy, also developing at a fast pace, offers an opportunity to characterise these materials, due to continuous advancements in optics, detectors, and resolution. When imaging battery raw materials, finding the optimal imaging conditions for multi-material samples is challenging; batteries are composed of hard (metallic foils, cathode and anode particles) and soft (carbon-based binder polymer) materials, as well as others, of differing chemical compositions, densities, and electron beam sensitivities. Therefore, inconsistent microscopic set ups are often required. A method to overcome these challenges is the 'sweet spot' imaging approach in a field emission scanning electron microscope (FE-SEM). Sweet spot imaging refers to the recommended conditions required to image different materials within the tested parameter space, by adjusting parameters such as the accelerating voltage (kV), the sample working distance, and the detector used. Here it is shown how adjusting these parameters optimises imaging conditions in a series of battery cathode foils, highlighting improvements in imaging particle surface features, foil structure, and binder properties, specifically at low kV and using the Inlens SE detector. Application of this approach leads to more successful segmentations for both academic and industrial research and development.