Magnetochemical and Molecular Orbital Analyses on Lithium Electrochemically Doped Non-Graphitizable Carbon Electrode of Lithium Ion Rechargeable Batteries

The electronic characteristics of electrochemically doped lithium in non-graphitizable carbon, which was obtained by heat-treating polyfurfuryl alcohol (PFA-C) and was used as the negative electrode of lithium ion rechargeable batteries, were examined with the aid of 7Li solid-state nuclear magnetic resonance (NMR) and electron spin resonance (ESR). In order to clarify how lithium is incorporated in the carbon electrode, discrete variational-Xα (DV-Xα) molecular-orbital calculations were also performed on a model system. These experimental and theoretical results suggest that the lithium doped in the carbon exists in a non-metallic state with low electron density as compared to the ionic crystal, and that the unpaired electrons in the lithium doped carbon are delocalized at the peripheral carbon domains of the system. This was theoretically supported by the fact that the singly occupied molecular orbital (SOMO) of the lithium doped carbon is lower by 5.388 eV than the orbital localized predominantly on li...