Essential Geometric and Electronic Properties in Stage-n FeCl3-Graphite Intercalation Compounds

Abstract

Recently, the well battery capacity was obtained with ferric chloride–graphite intercalation compounds (FeCl3-GICs) as electrode materials for lithium-ion batteries. It has attracted more attention for energy storage and conversion devices because of their chemical stability and electrical properties. For further investigation, the full-fledged and delicate calculations are indispensable. We present a theoretical analysis of the physical and chemical properties based on first-principles calculations, stage-n FeCl3-graphite intercalation compounds where n = 1, 2, 3, and 4. The calculated results cover the optimized structures, spatial charge distributions, charge variations, band structures, and density of states. The orbital hybridizations including the intralayer and interlayer chemical bonds are thoroughly clarified from the highly non-uniform chemical environments of Moiré superlattices, the atom-dominated band structures at specific energy ranges, the spatial charge densities/charge variations after intercalations, and van Hove singularities at the various energies in the density of states. The important chemical bondings could contain the intralayer/interlayer C-C bonds, the interlayer C-intercalant bonds, and the intra-molecule/inter-molecule bonds. The observable multi-/single-orbital hybridizations of C-C/C-Cl/Fe-Cl/Cl-Cl chemical bonds cover [2s, 2px, 2py]-[2s, 2px, 2py] &2pz-2pz/2pz-[3px, 3py, 3pz]/[3dxy, 3dyz, 3dz2, 3dxz, 3dx2]-[3s, 3px, 3py, 3pz]/[3s, 3px, 3py, 3pz]-[3s, 3px, 3py, 3pz]. However, the evidence almost disappears for the C-Fe and Fe-Fe bonds. Moreover, the strong charge transfers between graphitic layers and molecular intercalants, the zone-folding effects due to the intercalant stackings and arrangements, and the van der Waals interactions are responsible for the featured quasiparticle behaviors.