Electrochemical insertion of lithium into polyacrylonitrile-based disordered carbons

Electrochemical lithium insertion into polyacrylonitrile (PAN)-based disordered carbons was studied using the techniques of discharge/charge tests, cyclic voltammetry, and {sup 7}Li nuclear magnetic resonance (NMR) spectroscopy. The PAN-based carbons were prepared by vacuum pyrolysis of PAN at 500, 800, and 1,000 C. They showed charge capacities between 254 and 380 mAh/g in the first cycle. {sup 7}Li NMR spectra showed two kinds of lithium insertion sites in the PAN-based carbons: a reversible site where lithium is removed in the subsequent charge process and an irreversible site where lithium remains intact. The NMR results suggest that lithium in fully Li-inserted PAN-based carbons has an ionic character, and reversible site lithium resides between negatively charged carbon layers.