Entropy-driven structure and dynamics in carbon nanocrystallites
New carbon composite materials are being developed that contain carbon nanocrystallites in the range of 5–17 Å in radius dispersed within an amorphous carbon matrix. Evaluating the applicability of these materials for use in battery electrodes requires a molecular-level understanding of the thermodynamic, structural, and dynamic properties of the nanocrystallites. Herein, molecular dynamics simulations reveal the molecular-level mechanisms for such experimental observations as the increased spacing between carbon planes in nanocrystallites as a function of decreasing crystallite size. As the width of this spacing impacts Li-ion capacity, an explanation of the origin of this distance is relevant to understanding anode performance. It is thus shown that the structural configuration of these crystallites is a function of entropy. The magnitude of out-of-plane ripples, binding energy between layers, and frequency of characteristic planar modes are reported over a range of nanocrystallite sizes and temperatures. This fundamental information for layered carbon nanocrystallites may be used to explain enhanced lithium ion diffusion within the carbon composites.
KeywordsNanocrystallite Carbon Entropy Graphene Nanoparticle Composite Modeling and simulation Energy applications
Q.W. was supported by the Joint Directed Research and Development program (JDRD) of the University of Tennessee Science Alliance. N.M. was supported by a grant from the Oak Ridge Associated Universities High Performance Computing Program and by a grant from the Sustainable Energy Education and Research Center of the University of Tennessee. This research project used resources of the National Institute for Computational Sciences (NICS) supported by NSF under agreement number: OCI 07-11134.5. This research was also sponsored in part by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy. We thank Dr. Don Nicholson for invaluable advice during the preparation of this manuscript.
- Press WH, Teukolsky SA, Vetterling WT, Flannery BP (1992) Numerical recipes in FORTRAN: the art of scientific computing, vol 1, 2nd edn. Cambridge University Press, CambridgeGoogle Scholar