Visualisation and differentiation of binder components in hard carbon composite anodes by osmium tetroxide and uranyl acetate staining

Abstract In this study, we present a protocol to visualise, track and distinguish between two different binder components commonly used for batteries, styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), within a composite hard carbon electrode for sodium‐ion batteries using a two‐step staining method. The application of osmium tetroxide (OsO4) vapour followed by uranyl acetate (UA) solution enables the staining of different functional groups and the individual tracing of SBR and CMC by energy dispersive X‐ray spectroscopy (EDX) measurements using the osmium (Os) and uranium (U) content. This staining procedure and the filling of the pore space with conductive platinum carbon (PtC) composite via local electron‐beam‐induced deposition (EBID) results in an excellent contrast for all components of the electrode material. The tracking and visualisation of the binder components are demonstrated with secondary electron (SE) imaging and EDX mappings at focused ion beam (FIB) prepared facets as well as with focused ion beam/scanning electron microscopy (FIB/SEM) tomography. LAY DESCRIPTION: In this study, a sample preparation protocol for hard carbon (HC) composite electrode material is presented which allows to clearly distinguish between the HC particle and the two binder components, styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in focused ion beam/scanning electron microscopy (FIB/SEM) tomography and energy dispersive X‐ray spectroscopy (EDX) measurements. For that, the material was stained with osmium tetroxide (OsO4) and uranyl acetate (UA) and pore space was locally filled with electron‐beam‐induced deposition (EBID) of platinum carbon (PtC).