Synthesis, characterization, and structural modeling of graphite intercalation compounds with fluoroanions

New synthetic strategies have been investigated for nano-dimensioned graphite particles or even isolated graphene sheets. One approach is to prepare graphite intercalation compounds (GICs) with low layer charge density and appropriate gallery height, followed by the colloidal dispersion or exfoliation of the resulting GICs. A series of anions has been designed and synthesized to lower the charge density in intercalate galleries. New GICs containing chelatoborates and perfluoroalkylsulfonates are prepared and characterized.; Three chelatoborate anions, including bis(perfluoropinacolato)borate(B[OC(CF 3)2C(CF3)2O]2- ), bis(hexafluorohydroxyisobutyrato)borate (B[OC(CF3) 2C(O)O]2-), and bis(oxalato)borate (B[OC(O)C(O)O] 2-), have been studied. GICs up to stage n = 1 containing B[OC(CF3)2C(CF3)2O] 2- have been prepared, but only GICs with stage n = 2--4 in the B[OC(CF3)2C(O)O]2 - electrolyte. PXRD data and the structural refinement of these GICs indicate that the intercalate anions "stand up" in the gallery with the longer anion dimension oriented perpendicular to the graphene sheets, leading to a relatively large gallery height of 13.3--14.5 A. The electrochemical data show that GICs containing B[OC(CF3)2 C(CF3)2O]2- and B[OC(CF3)2C(O)O]2- have lower sheet charge densities than most acceptor-type GICs.; On the other hand, the intercalation of B[OC(O)C(O)O]2 - fails due to the prevailing decomposition of the electrolytes. The relative anion oxidative stabilities of B[OC(CF3)2C(CF 3)2O]2- > B[OC(CF3) 2C(O)O]2- > B[OC(O)C(O)O]2 - are determined experimentally and compared with HOMO energy level calculations. The linear relation of intercalation potential to reciprocal of gallery height and the steric effects of large anion intercalates are also described. The stability requirement for electrolytes is thereby extrapolated for highly separated graphene layers or single-sheet graphene layer colloids.; Three new GICs containing the perfluoroalkylsulfonate anions, C 10F21SO3-, C2F 5OC2F4SO3- and C2F5(C6F10)SO3 - are prepared chemically. The intercalate bilayers are oriented with anion sulfonate headgroups towards graphene sheets. The details on anion concentrations, orientations, and conformations are provided by structure models refined from one-dimensional electron density maps. Due to the more efficient packing of anions in the gallery, the intercalated anion conformations show changes in dihedral angles, involving rotations about C-C or C-O bonds.