Structural analysis of polyacenic semiconductor (PAS) materials with ¹²⁹xenon NMR measurements

Structural analysis of the polyacenic semiconductor (PAS) material prepared by the pyrolysis of phenol-formaldehyde resin at relatively low temperature (680°C) has been performed by applying ¹²⁹Xe nuclear magnetic resonance (NMR) measurements. One can obtain information on the microporous structure of the PAS material through adsorption of Xe atoms, since a ¹²⁹Xe nucleus is a very sensitive probe of its microscopic environment. All the introduced Xe atoms were adsorbed on the internal surface of the pure PAS sample, which indicated remarkably large surface area of the PAS material. The average pore size of the pure PAS sample has been determined to be 7.7± 1.6 Å from the pressure dependence of the Xe NMR chemical shift. In connection with the application of the PAS material to the electrode of the Li rechargeable battery, changes in the Xe NMR spectrum brought about by extrinsic additives such as binder, electrolyte solvent, and the doped Li have been investigated. In particular, it has been found that the Li-doping entirely prevents Xe atoms from entering into the micropores of the PAS material, probably due to adsorption of the solvent molecules on the internal surface of the micropores.