Li-7 NMR and ESR analysis of lithium storage in hard carbon materials

Microstructures of hard carbon (non-graphitizable carbon) materials heat-tr eated at various temperatures were characterized by the pore distribution a nd X-ray diffraction (XRD) methods. Lithium storage was discussed on the ba sis of XRD, Li-7 nuclear magnetic resonance (NMR), and electron spin resona nce (ESR) data of lithiated hard carbons. Hard carbons could be divided int o three types according to the difference of lithium insertion mechanism an d preparation temperatures. The hard carbons heat-treated below 700 degrees C showed NMR and ESR profiles similar to those for soft-carbon heat-treate d below 700 degrees C. Two or three different signals were observed in Li-7 NMR and ESR profiles of lithiated hard carbons heat-treated at 700-1600 de grees C. These signals are considered to be related to the irreversible lit hium storage in an unorganized carbon, the reversible lithium intercalation into disordered stacking layers, and lithium insertion into nano-pores. Th e carbons heat-treated above 1600 degrees C showed the same behavior as tur bostratic disordered carbon. Lithium is considered to be intercalated into disordered carbon stacking layers.