Yukinori Hato

Characteristics of deeply Li-doped polyacenic semiconductor material and fabrication of a Li secondary battery

Abstract Electrochemical properties of deeply Li-doped polyacenic semiconductor (PAS) material have been investigated. It has been found that a PAS electrode can be doped up to the C 2 Li stage without any Li-metal electrolysis and that it has a reversible capacity of 850 mAh/g. Fabrication of the secondary PAS battery of the cylindrical type has also been attempted. The energy density of this battery has turned out to be 450 Wh/l, which is about twice as large as that of conventional Li-ion batteries.

Polymer battery employing polyacenic semiconductor

Abstract Recently, we have succeeded to prepare a new type of polyacenic semiconductor (PAS) which is made in the form of sheet or plate with a bulk density of about 0.4g/cm 3 from phenol-formaldehyde resin through pyrolytic process. A typical PAS has a H/C molar ratio of 0.25 and an electrical conductivity of 10 −5 S/cm. The specific surface area is above 2000m 2 /g and the bending strength is 100–150kg/cm 2 . We constructed two types of storage batteries using a disk formed PAS as electrode and solution of lM LiClO 4 in SL + γ-BL (1:1 in volume) as electrolyte. These batteries displayed excellent reversibility for electrochemical doping-undoping process and very small self-discharge. We believe PAS battery is one of the first application of conductive polymers for practical use.

Studies of porous polyacenic semiconductors toward application I. Preparation and structural analysis

Abstract A detailed description of the preparation of porous polyacenic semiconductor (PAS) materials is reported. The structural analyses of these materials by the combination of mercury porosimetry and adsorption isotherm measurements have revealed that there are two kinds of pores distinguished by their radii therein. The smaller pore (micropore) size of the porous PAS sample prepared by specific pyrolysis temperature is estimated as about 5 A being much larger than those of active carbons and, hence, rationalizes the ‘dopability’ of the present sample with bulky dopants already reported.

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

Abstract 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 A 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.

Studies of porous polyacenic semiconductors toward application II. Fundamental electrochemical properties

Abstract Fundamental electrochemical measurements on the porous polyacenic semiconductor (PAS) materials reported in our preceding paper I ( Synth. Met., 38 (1990) 169–175) have been performed. It has been found that the charge-storing capacity becomes maximum in the porous PAS sample with a [H]/[C] molar ratio in the range 0.15–0.3. Detailed examination of the electrochemical doping-undoping processes in this sample has revealed a reversibility during these processes utilizing both the p-type and n-type regions.

ESR study of Li-doped polyacenic semiconductor (PAS) materials

Abstract The polyacenic semiconductor (PAS) material prepared from phenol resin at relatively low temperature (680 °C) can be doped by a much larger amount of lithium atoms up to the C 2 Li state compared with graphite (C 6 Li state). To understand the Li storage mechanism as well as the electronic structure, 7 Li nuclear magnetic resonance (NMR) measurements have been performed for the Li-doped PAS materials. In the initial doping stage a broad signal was observed at 0 ppm, while the successive doping causes a Knight shift to 9 ppm. It is suggested from this Knight shift that the Li nucleus slightly undergoes the Fermi contact interaction with conduction electrons delocalizing through carbon π -atomic orbitals. From the spin-lattice relaxation rate ( 1/ T 1 ), it is found that the Li nucleus in the PAS material loses its mobility by the surrounding Li nuclei with the proceeding doping and that the Li nucleus is more loosely trapped than that in the C 6 Li state of graphite.

Fractal dimension analysis of polyacenic semiconductive (PAS) materials

Abstract The fractal dimensions D of the pristine and the Li-doped polyacenic semiconductive (PAS) materials have been analyzed by small-angle X-ray scattering (SAXS) and compared with that of graphite. It has become clear that the Li doping generally makes D smaller, which suggests fixation effect of the nanopores on the surface of the material by the doped Li atoms. It is pointed out that the fractal dimension analysis affords an alternative picture to the conventional N 2 adsorption and rather new technique using 129 Xe nuclear magnetic resonance method in discussion of the surface structures for general amorphous carbon particularly when it is doped or mixed with binders.

Preparation of polyperinaphthalenic organic semiconductive nanoparticles by excimer laser ablation and their application to optic and electronic devices

Polyperinaphthalene (PPN) nanoparticles are prepared by excimer laser ablation (ELA) of a 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) target or a mixture target of PTCDA with Co or TiO2 powder (PTCDA/X: X=Co, TiO2) using XeCl excimer laser beams. Enhancement of elimination reaction of side groups of PTCDA is observed by ELA of PTCDA/Co and PTCDA/TiO2. In particular, for PTCDA/TiO2, the reaction occurs at a fluence of 0.25 J cm−2 pulse−1 much lower than the case of PTCDA/Co at room temperature. Heterojunctions between the PPN nanoparticle layer and Si wafers are formed. Well rectifier property is demonstrated for the junction with n-Si substrates. Current versus voltage curve of the heterojunction with a n-Si substrate in the dark and under illumination shows the possibility of the junction as a photovoltaic cell. Furthermore, PPN nanoparticles are applied to anode electrodes for ultrathin rechargeable Li ion batteries. In situ Raman spectroscopy under lithium ion doping is performed to elucida...

Correlation of Li ion and the environmental elements in the surface nano-reaction field of polyacenic semiconductive material as the battery electrode

Abstract The correlation of lithium ion and other elements at the surface of the battery electrode made of polyacenic semiconductive (PAS) material film is discussed focusing on the passivation-layer formation. Behavior of these elements in the passivation layer of the Li-doped PAS films at several stages of doping were examined by the depth-profiling technique of X-ray photoelectron spectroscopy (XPS) together with the Li-doped graphite film sample for the reference. A certain different nature of the doped Li ion (Li δ+ ) and carbanion (C δ− ) between the PAS and graphite films has been revealed. It was concluded that the PAS material film possesses certain surface nanopores or nano-reaction fields to accommodate the passivation species near its surface, being completely different from the graphite film.

Preparation of carbonous nanoparticles for anode electrodes of ultrathin lithium ion rechargeable batteries by laser ablation

Carbonous nano-particles basically consisting of PPN, one of the low dimensional conducting polymers, are prepared on substrates at various temperatures by excimer laser ablation of 3, 4, 9, 10-perylenetetracarboxylic dianydride using a 308nm pulsed excimer laser beam. Particles deposited on the substrates are applied to anode electrodes for ultra thin rechargeable Li ion batteries. Substrate temperature dependence of effective capacitance of lithium ions at first cycle are investigated. In addition, in-situ Raman spectroscopy of the particles under lithium ion doping and undoping is performed to elucidate the storage mechanisms of lithium ion at cis-polyacetylene-type edge of PPN structure. Reversible change of the spectrum in the region related C-H bending of PPN structure in lithium doping and undoping process supports a lithium insertion mechanism proposed by Zheng et al where lithium atoms bind on the hydrogene- terminated edged of hexagonal carbon fragments.