Secondary Electron Hyperspectral Imaging of Carbons: New Insights and Good Practice Guide

Energy storage technologies such as lithium-ion batteries (LIBs) incorporate carbon components key to their function. Graphite and carbon binder components in LIB electrodes are engineered to deliver critical electrical and mechanical properties, as are the surface chemistry and morphology of carbon blacks (CBs) in LIBs and catalysts. The challenge of relating surface chemistry to morphology is complicated by the numerous forms of carbon bonding and potential for surface functional groups. Furthermore, materials processing can influence bonding and structure of carbon at multiple length scales, as seen in mechanochemical functionalization of CBs. To understand the nature of carbon surfaces, secondary electron hyperspectral imaging (SEHI) is introduced as a spatially resolved analysis bridging the nano to microscale. The ability to provide novel insights is demonstrated three example applications: observation of nanoscale "satellite" particles of amorphous hydrogenated carbon on graphitic CB particles, differentiation between graphitic and amorphous hydrogenated nano-thickness carbon coatings on particles of lithium iron phosphate, and differentiation between graphitic carbon active material and carbon binder domain in a LIB anode material. SEHI analysis using peak fitting models for graphitic and disordered carbons is developed based on reference materials and standard spectroscopic methods: Raman spectroscopy and X-ray photoelectron spectroscopy.