Molecular dynamics calculation on three lithium atoms in planar cluster model C150H30 for glassy carbon Original Research Article

As the preliminary step to elucidate the charge-discharge mechanism in the glassy carbon cathode of lithium (Li) secondary battery, the molecular dynamics (MD) calculation was applied at molecular mechanics 2 (MM2) level for three Li atoms stabilized in the form of regular triangle in the central area of the hydrogen terminated planar cluster, C150H30. The stabilized Li sites are given on the basis of the structural optimization. Up to 10 K, the triangular Li aggregate kept at almost the same figure as that formed by three stabilization sites, rotating parallel to the cluster plane, goes around the central area of it, whereupon interatomic vibrational stretching is observed. Below 75 K, the aggregate of three Li atoms separates to a pair of two atoms and one Li atom arbitrarily, however, reformation of the pair occurs periodically among three atoms with the lapse of simulation time. Then, three Li atoms move correlatively irrespective of the long interatomic distance of 18 Å at maximum. However, at 100 K one Li atom goes out of the cluster model directly and the rest of two atoms continues the revolutional movement with the rotation as a pair in the central area of the cluster model. Thus, three Li atoms show the appreciably stable movements in the glassy carbon by forming the aggregate or the atomic pair, which will be responsible for the hysteresis in the charge–discharge cycle of lithium secondary battery.