Kensuke Takechi

A Li–O2/CO2 battery

A new gas-utilizing battery using mixed gas of O(2) and CO(2) was developed and proved its very high discharge capacity. The capacity reached three times as much as that of a non-aqueous Li-air (O(2)) battery. The unique point of the battery is expected to be the rapid consumption of superoxide anion radical by CO(2) as well as the slow filling property of the Li(2)CO(3) in the cathode.

Catalytic Cycle Employing a TEMPO-Anion Complex to Obtain a Secondary Mg-O2 Battery.

Nonaqueous Mg-O2 batteries are suitable only as primary cells because MgO precipitates formed during discharging are not decomposed electrochemically at ambient temperatures. To address this problem, the present study examined the ability of the 2,2,6,6-tetramethylpiperidine-oxyl (TEMPO)-anion complex to catalyze the decomposition of MgO. It was determined that this complex was capable of chemically decomposing MgO at 60 °C. A catalytic cycle for the realization of a rechargeable Mg-O2 electrode was designed by combining the decomposition of MgO via the TEMPO-anion complex and the TEMPO-redox couple. This work also demonstrates that a nonaqueous Mg-O2 battery incorporating acrylate polymer having TEMPO side units in the cathode shows evidence of being rechargeable.

Avoiding short circuits from zinc metal dendrites in anode by backside-plating configuration.

Portable power sources and grid-scale storage both require batteries combining high energy density and low cost. Zinc metal battery systems are attractive due to the low cost of zinc and its high charge-storage capacity. However, under repeated plating and stripping, zinc metal anodes undergo a well-known problem, zinc dendrite formation, causing internal shorting. Here we show a backside-plating configuration that enables long-term cycling of zinc metal batteries without shorting. We demonstrate 800 stable cycles of nickel–zinc batteries with good power rate (20 mA cm−2, 20 C rate for our anodes). Such a backside-plating method can be applied to not only zinc metal systems but also other metal-based electrodes suffering from internal short circuits.

Solid-state solar cells consisting of polythiophene-porphyrin composite films

Sandwich-type solid-state solar cells using polythiophene-porphyrin composite films were fabricated. A spin-coated film of poly(3-dodecylthiophene) (P3DT) was fabricated on a gold electrode. Next, an electropolymerized polythiophene film was superimposed on the surface of the spin-coated P3DT film by electrochemical polymerization of bithiophene (BiTh) with repeated redox cycles in the 0–+2 V region. Then, tetrathienylporphyrin (TThP) was further assembled on the polythiophene-modified electrode by using the same electrochemical polymerization procedure (1 or 10 cycles), to obtain polythiophene-porphyrin-modified gold electrodes. Finally, an aluminum electrode was deposited on the polythiophene-porphyrin modified gold electrode by vacuum deposition, forming the sandwich-type solid-state solar cells. The morphological characterizations of the films were carried out by scanning electron microscopy. The thickness of the organic layer decreased from ~5 µm m to ~3 µm by performing TThP polymerization. The amount of porphyrin moiety in the composite film was larger for the modified electrode after 10 cycles of electrochemical TThP polymerization than for that after 1 cycle of TThP polymerization. The resultant photocurrent increased with scanning cycle of TThP polymerization in the 400–600 nm region. The combination of polythiophene and porphyrin in the electrochemically modified electrode is one of the useful systems for photocurrent generation.

A highly efficient Li2O2 oxidation system in Li–O2 batteries

A novel indirect charging system that uses a redox mediator was demonstrated for Li-O2 batteries. 4-Methoxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl (MeO-TEMPO) was applied as a mediator to enable the oxidation of Li2O2, even though Li2O2 is electrochemically isolated. This system promotes the oxidation of Li2O2 without parasitic reactions attributed to electrochemical charging and reduces the charging time.

Facile Fabrication and Photocurrent Generation Properties of Electrochemically Polymerized Fullerene–Poly(ethylene dioxythiophene) Composite Films

Fullerene–poly(ethylene dioxythiophene) (polyEDOT) composite films consisting of 3,4-ethyeledioxythiophene (EDOT) and a thiophene derivative of C60 fullerene (ThC60) or C60 fullerene were fabricated on a transparent indium–tin-oxide (ITO) electrode by electrochemical polymerization of the electrolyte solution of ThC60 (or C60) and EDOT. Incorporation of the C60 fullerene moiety in the polythiophene film was strongly suggested from absorption spectra of the composite film. We have found a higher degree of incorporation of the C60 fullerene moiety into the ThC60–polyEDOT film, as compared with the C60–polyEDOT film. In the presence of methylviologen as an electron acceptor, the as-prepared C60–polyEDOT and ThC60–polyEDOT composite films generated stable cathodic photocurrents in the 400–700 nm region with broad peaks. The photocurrent intensity and the internal photon-to-current quantum efficiency of the ThC60–polyEDOT composite film were considerably larger than those of C60–polyEDOT and polyEDOT films. The thiophene unit of ThC60 was confirmed to be quite effective for a stable incorporation of the C60 fullerene moiety in the film and a higher photocurrent generation.

Effects of Hole Transport Layer on Photoelectrochemical Responses from Polythiophene–Porphyrin Composite Polymer Electrode

The effect of a hole transport layer on the photoelectrochemical responses from an organic solar cell consisting of a composite polymer film of 5,10,15,20-tetra(3-thienyl)-21H,23H-porphyrin and polythiophene was investigated. The polyalkylthiophene layer that was inserted between the above-described photoactive polymer film and a transparent electrode acted as the hole transport layer. This layer remarkably suppressed the recombination of separated charge carriers generated in the composite polymer film and substantially improved both photocurrent and conversion efficiencies.

Non-Aqueous Primary Li–Air Flow Battery and Optimization of its Cathode through Experiment and Modeling

A primary Li-air battery has been developed with a flowing Li-ion free ionic liquid as the recyclable electrolyte, boosting power capability by promoting superoxide diffusion and enhancing discharge capacity through separately stored discharge products. Experimental and computational tools are used to analyze the cathode properties, leading to a set of parameters that improve the discharge current density of the non-aqueous Li-air flow battery. The structure and configuration of the cathode gas diffusion layers (GDLs) are systematically modified by using different levels of hot pressing and the presence or absence of a microporous layer (MPL). These experiments reveal that the use of thinner but denser MPLs is key for performance optimization; indeed, this leads to an improvement in discharge current density. Also, computational results indicate that the extent of electrolyte immersion and porosity of the cathode can be optimized to achieve higher current density.

An Influence of Monomeric Porphyrin Structure on the Electropolymerized Photoactive Electrode for Polymer Solar Cells

We have fabricated and compared photocurrent generation properties of electropolymerized films consisting of 2,2′-bithiophene and a porphyrin derivative, 5,10,15,20-tetra(3-thienyl)-21H,23H-porphyrin or 5,10,15,20-tetra(2-thienyl)-21H,23H-porphyrin. It was found that the location and the concentration of porphyrin moieties in the films were different between the two porphyrin monomers, and the polymer film with the former porphyrin gave larger photocurrent than the latter. The result indicates that the molecular design of the polymer electrode is very important for effective photocurrent generation.

Fabrication and Photocurrent Properties of Fullerene-Polyethylenedioxythiophene Composite Films

Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Department of Applied Chemistry, Faculty of Engineering, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Phone: +81-92-802-2816 E-mail: t-akitcm@mbox.nc.kyushu-u.ac.jp Center for Future Chemistry, Kyushu University, 744, Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan Battery & Cells Div., Secondary Battery Lab. III, Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan Motohiro Special Research Lab., Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan Hybrid Vehicle Material Engineering Div., Toyota Motor Corporation, Shizuoka, 410-1193, Japan Material Engineering Div. III, Toyota Motor Corporation, Shizuoka, 410-1193, Japan