1 A Geometry-Derived Structural Map of Graphite Intercalation Compounds across Chemically Diverse Intercalants

Abstract

The diversity of intercalants in graphite intercalation compounds (GICs) has prevented a unified understanding of their structure–composition relationships, leading predominantly to case-by-case interpretations. Here we present a geometry-derived structural map of GICs based solely on constraints of the graphitic host. We derive the local gallery volume Vlocal as defined by gallery height di, staging s, and carbon-tointercalant-ratio x. Analysis of 97 representative compounds—including metal cations, metal–Lewis base complexes, alkylammonium and heterocyclic cations, and a wide range of perfluoroanions—reveals three regimes. In Region I, the expanded di (7.4-14.5 Å) is just above a host-imposed residual separation. The vertical increase of Vlocal is controlled by lateral dilution. In Region II, increasing di up to 28 Å linearly grows the volume. This reflects gallery opening at a constant effective in-plane area Aeff depending on intercalant family. In Region III, intercalants enlarge di further (35 Å) but the volume decreases, ascribed to intercalant conformational flexibility and tight lateral packing. A critical gallery height di* is proposed dividing Region II and III. This host-controlled structural map unifies disparate GIC families without invoking electronic structure calculations or intercalant-specific bonding models. Our work provides a rational basis for comparing existing donor- and acceptor-type GICs and for navigating unexplored intercalation regimes.