LOCAL-STRUCTURE AND VIBRATIONAL SPECTROSCOPY OF DISORDERED CARBONS FOR LI BATTERIES - NEUTRON-SCATTERING STUDIES

Compositions, local atomic structures, porosity, and vibrational dynam ics of carbons obtained by pyrolyzing epoxy novolak resins at 650 and 1000 degrees C are investigated using several neutron scattering techn iques. The ultimate goal is to understand the origin of the very high capacity for Li uptake exhibited by these materials. Neutron radial di stribution function analysis and incoherent inelastic scattering show that the structural motif is a planar hexagonal graphene fragment simi lar to 10 Angstrom on a side, with edge carbons terminated by single h ydrogen atoms and random stacking between fragments. Small-angle neutr on scattering reveals substantial porosity on a length scale comparabl e to the size of the graphene fragments. Coupled with computer simulat ions, these results are consistent with two proposed mechanisms for un usually high Li capacity one analogous to conventional intercalation b ut with Li on both sides of isolated graphene fragments, the other inv olving bonding of Li to H-terminated edge carbons.