Multimechanistic Electrical Transport in Macroscopic Graphene Assemblies: Bridging Theoretical and Practical Performance Limits.

Macroscopic graphene assemblies, such as fibers and films, offer high strength and thermal conductivity but achieve only about half the theoretical graphite limit in electrical conductivity, far below their stiffness and thermal performance. This gap underscores the need for theoretical guidance, complicated by atomic-scale chemistry and hierarchical microstructures, requiring multiscale, multimechanistic modeling. We present an integrated framework unifying quantum transport calculations, Monte Carlo simulations, and network modeling, accounting for band transport and hopping in the basal plane, alongside π-π coupling and tunneling across their interfaces. Anchored by experimental evidence, it quantitatively predicts in-plane and cross-plane conductivities as functions of sp2 fraction and sheet size. The results reveal a percolation transition in the basal plane near 60%, with stretched exponential and linear scaling in the highly-oxidized (hopping) and reduced (band conduction) limits, respectively, providing a measure of the requirement for chemical reduction and high-temperature graphitization. A sigmoidal ("S-shaped") size dependence reflects micrometer-scale constraints of flakes derived from graphite exfoliation and dispersion. In contrast to thermal transport, electrical conductivity is more tolerant of low-concentration defects and more strongly dependent on sheet size, indicating that preferentially selecting larger sheets from the dispersion is more essential for electrical performance. The orders-of-magnitude higher anisotropy of electrical versus thermal conductivity further indicates that thin films optimize thermal management by harnessing charge carriers as heat carriers. Our framework bridges the theoretical limits and practical performance of graphene assemblies, an advance not previously achieved, and is extensible to additional effects of structural fluctuations and chemical modifications. It also motivates targeted experimental characterization of key parameters at the level of basic structural units (closely packed laminates) and their interfaces, which contributes to a comprehensive composition-processing-microstructure-performance map.