Katsuhiko Naoi

Quartz Crystal Microbalance Study: Ionic Motion Across Conducting Polymers

In situ monitoring of mass change was performed during electrochemical growth and redox cycling of a conducting polymer(polypyrrole) on a quartz crystal microbalance. For the polypyrrole films grown with large polymeric anions(poly(4-styrenesulfonate) and polyvinylsulfonate), mostly cations and solvent molecules were inserted and removed to compensate charge in polypyrrole. The films formed with medium-sized anions (tosylate) showed both apparent anion and cation motion during the redox process. The films prepared in the presence of small anions (ClO 4 − and BF 4 − ) showed mostly anion motion, but apparent cation motion also became significant for higher oxidation and/or reduction state

Dependence of Film Thickness on Electrochemical Kinetics of Polypyrrole and on Properties of Lithium/Polypyrrole Battery

The charging-discharging behavior of lithium/LiClO/sub 4//polypyrrole battery was found to show a different dependence on the thickness of a polypyrrole film cathode prepared at various polymerization potentials. Lithium batteries constructed with a polypyrrole cathode formed at a higher potential show better charging-discharging performance characteristics than those with a film prepared at a lower potential. The electrode kinetics of electrochemically prepared polypyrrole were investigated in an attempt to clarify the interesting dependence of the behavior of Li/polypyrrole battery on the thickness of polypyrrole cathode as a function of formation potential. A potential step chronoamperometry, together with an ac impedance measurement, has evidenced that there is a strong relationship between the doping charges and the apparent diffusion coefficients of polypyrrole electrodes. In practice, the battery performance of Li/LiClO/sub 4//polypyrrole cells was examined by varying the current density. The upper limit of the current density at which the coulombic yield in the charging-discharging curves remains at 100% was found for both thin and thick films of 1 and 5 C cm/sup -2/ film formation charges.

Quartz crystal microbalance analysis. Part I. Evidence of anion or cation insertion into electropolymerized conducting polymers

Abstract : The mass change during electropolymerization and redox process was monitored for polypyrrole films using Quartz Crystal Microbalance Gravimetry. During reduction process the polypyrrole films which had incorporated large poly(4-styrene-sulfonate) anions showed a mass increase instead of decrease (cation doping). On the other hand, the polypyrrole film formed with a small ClO4 anion showed a mass decrease (anion doping). Quartz crystal microbalance, Conducting polymer, Battery, Polypyrrole.

Impedance Analysis of Ionic Transport in Polypyrrole‐Polyazulene Copolymer and Its Charge‐Discharge Characteristics

Ionic-transport behavior across an electropolymerized polypyrrole/polyazulene composite film was investigated by using ac impedance analysis, and its charge-discharge characteristics were also studied. Co-electropolymerization of pyrrole and azulene was well defined and fairly stoichiometric in propylene carbonate solution. The charge capacity for the composite films showed a remarkable increase for films around 50 to 75% of azulene monomer content, and the behavior was correlated with morphological and diffusivity changes. The charge-discharge characteristics were examined for cells with a lithium anode and various polypyrrole/polyazulene composite cathodes. Pure polypyrrole cathodes behaved exactly like a capacitor at low frequency, while pure polyazulene cathodes showed excellent rechargeable behavior with very flat discharge curves. Composite cathodes showed intermediate behavior.

Application of electrochemically formed polypyrrole in lithium secondary batteries: Analysis of anion diffusion process

Abstract A long cycle-life has been obtained with an Li/LiClO 4 -propylene carbonate (PC)/polypyrrole (PPy) battery when a PPy film formed in LiPF 6 /PC by electro-oxidative polymerization is used in an LiClO 4 /PC electrolyte after undoping PF 6 − anions. The apparent diffusion coefficients of anions within the PPy film and the impedance spectra for PPy film electrodes are strongly dependent upon the film formation conditions. Electrolyte anions used in the film formation, which influence the morphology of the polymer film, have been found to play an important role in determining the electrochemical process and the cycle life of the Li/PPy battery.

Electrochemical Study on Charge‐Discharge Performance of Lithium/Polyazulene Battery

Electrodeposited polyazulene (PAz) films show high electoactivity and fast redox switching behavior when polymerized under suitable conditions. Such PAz films are more electroactive than electrodeposited polypyrrole or polyaniline and were successfully applied in a rechargeable lithium battery. The authors determine suitable polymerization conditions so as to obtain an electroactive PAz film possessing the highest charge-storing ability and fastest electrode processes. Specifically, the electrochemical kinetics (anion doping-undoping process) of PAz films was investigated by varying the pplymerizing current density and formation charge. Charge capacity showed a maximum value when polymerized at 1.4 mAcm{sup {minus} 2} by passage of 5C cm{sup {minus} 2}. Cyclic voltammograms coupled with scanning electrons microscope observation of PAz films evidenced that a highly electroactive PAz film can be prepared at 1.4 mA cm{sup {minus} 2}. The charge-discharge property and cylability of Li/LiCIO{sub 4}/PAz batteries were studied. Li/LiCIO{sub 4}/PAz batteries were studied. Li/LiCIO{sub 4}/PAz batteries showed fairly high and flat discharge voltage (ca.3.2V), while maintaining 100% coulombic efficiency when charging by ca.45% of doping level(per unit cathode weight). The Li/LiCIO{sub 4}/PAz battery performed best when PAz film was formed at 1.4 mA cm{sup {minus} 2} by passage of 5C cm{sup {minus} 2}.