Staging and defect-limited intercalation of FeCl₃ in graphite electrodes

The need for sustainable mobility and renewable energy systems has been a major driving force for battery research in recent years. While ion batteries are in widespread application, there remain unsolved questions regarding fundamental processes occurring within batteries during use that ultimately limit their performance. The most important of such processes is intercalation, which describes the reversible incorporation of a guest species into a host lattice. The early stages of this process, when only a limited amount of guest material is present, are still barely understood. In this work, we use advanced transmission electron microscopy to directly observe the structure and host/guest interactions in a partially intercalated graphite model system. We show the three-dimensional layer occupancy and demonstrate that the established staging laws break down in this regime. Finally, we elucidate the impact of host lattice defects on the intercalation process using 4D-STEM, moiré imaging and in situ heating.