Toshiyuki Momma

Electrodeposited Sn-Ni Alloy Film as a High Capacity Anode Material for Lithium-Ion Secondary Batteries

Thin Sn-Ni alloy films containing various Sn/Ni ratios were prepared by electrodeposition and characterized as lithium-ion secondary battery anodes. The initial drop in discharge capacity varied with the Sn content of thesample; i.e., for samples with 54 atom % Sn and 62 atom % Sn, the drop was less than 100 mAh/g, whereas for those with 84 atom % Sn and 92 atom % Sn, the drop exceeded 500 mAh/g. Among these thin films, the 62 atom % Sn film showed the highest reversible capacity of ca. 650 mAh/g at about the 70th cycle, whereas the other samples (54 atom % Sn, 84 atom % Sn. 92 atom %. Sn) showed a capacity of 300 mAh/g.

An Electrochemical Double Layer Capacitor Using an Activated Carbon Electrode with Gel Electrolyte Binder

An electric double layer capacitor (EDLC) was prepared with an activated carbon powder electrode with poly(vinylidene fluoridehexafluoropropylene) (PVdF-HFP) based gel electrolyte. Ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizer and tetraethylammonium tetrafluoroborate (TEABF4) was used as the supporting electrolyte. An optimized gel electrolyte of PVdF-HFP/PC/EC/TEABF4 5 23/31/35/11 mass ratio exhibited high ionic conductivity of 5 3 10 23 S cm 21 , high electrode capacitance, and good mechanical strength. An electrode consisting of activated carbon (AC) with the gel electrolyte as the bind er (AC/PVdF-HFP based gel, 7/3 mass ratio) showed a higher specific capacitance and a lower ion diffusion resistance within the electrode than a carbon electrode, prepared with PVdF-HFP binder without plasticizer. This suggests that an electrode mixed with the gel electrolyte has a lower ion diffusion resistance inside the electrode. The highest specific capacitance of 123 F g 21 was achieved with an electrode containing AC with a specific surface area of 2500 m 2 g 21 . A coin-type EDLC cell with optimized components showed excellent cycleability exceeding 10 4 cycles with ca. 100% coulombic efficiency achieved when charging and discharging was repeated between 1.0 and 2.5 V at 1.66 mA cm 22 .

Electrochemical modification of active carbon fiber electrode and its application to double-layer capacitor

Abstract Electrochemical oxidation of an active carbon fiber (ACF) electrode showed an enhancement effect of the electrode capacitance. The modification of ACF, however, increased the electrode inner resistance with an increase in the capacitance. Au deposition, the deaeration and the electrochemical reduction (discharge) after the modification showed a decrease in the inner resistance. Thus, the capacitor using the modified ACF electrodes with deaeration. Au deposition and/or discharge treatment showed an enhancement of capacitance with decreasing inner resistance.

Application of Solid Polymer Electrolyte to Lithium/Polypyrrole Secondary Battery System

An all solid-state lithium/polypyrrole (PPy) battery using polyethylene oxide (PEO)-LiClO[sub 4] as a solid polymer electrolyte was assembled, and the effects of the morphology of the PPy film and the concentration of LiClO[sub 4] on battery performance were investigated. Optimum conditions for the redox properties of PPy films in PEO-LiClO[sub 4] at 80 C were obtained with an LiClO[sub 4] concentration of n = 8 [approximately] 20 (n=[EO]/[Li]) when using rough PPy film. A Li/PPy battery using PEO-LiClO[sub 4] with optimized conditions exhibited high coulombic efficiency, above 90% at 0.1 mA cm [sup [minus]2] at 80 C. Cyclability of 1,400 cycles with high coulombic efficiency was attained.

On-Chip Fuel Cell: Micro Direct Methanol Fuel Cell of an Air-Breathing, Membraneless, and Monolithic Design

This paper proposes a novel design for a microfuel cell as an on-chip power source and demonstrates its fabrication and operation to prove the concept. Its simple design is important from the viewpoints of fabrication (e.g., replication), integration, and compatibility with other microdevices. In testing, the prototype cell was able to generate electric power (maximum: ca. 1.4 microW) on methanol without pumps under both neutral and acidic conditions. As for the size, the electrode part of the cell (two cathodes and one anode) is 400 microns in width and 6 mm in length. The evaluation demonstrated that the proposed design is a promising on-chip power source for miniature devices.

Enhancement of lithium anode cyclability in propylene carbonate electrolyte by CO{sub 2} addition and its protective effect against H{sub 2}O impurity

The charge-discharge behavior of a lithium metal anode in propylene carbonate (PC) electrolyte containing added CO{sub 2} was investigated using in situ ac impedance measurements during galvanostatic cycling. In PC electrolyte with CO{sub 2}, the anode`s cycle life was twice as long and its charge transfer resistance was smaller than in the same electrolyte without CO{sub 2}. These enhancements are observed only when lithium is electrodeposited in the presence of CO{sub 2} on nickel substrate; the enhancement does not occur when lithium is deposited without CO{sub 2} and is cycled with CO{sub 2}. Even large amounts of H{sub 2}O in the electrolyte during cycling do not adversely affect the cycle life enhancement by CO{sub 2}. The CO{sub 2} enhancement seems to be due to products formed by reaction of lithium with CO{sub 2} on the electrodeposited lithium surface.

Surface characterization of electrodeposited lithium anode with enhanced cycleability obtained by CO{sub 2} addition

Electrodeposited lithium produced with and without CO{sub 2} in LiClO{sub 4}/propylene carbonate electrolytes was investigated for charge-discharge cycleability, surface morphology, and composition of the surface layer. The addition of CO{sub 2} in the electrolyte enhances the cycleability, produces smoother surface morphology, and forms Li{sub 2}CO{sub 3} in the inner region of the surface film. This paper describes experimental results showing those three different effects of CO{sub 2} addition, and discusses the interrelation among them.

Potentiometric biosensor for urea based on electropolymerized electroinactive polypyrrole

Abstract A urea biosensor was developed by immobilizing urease into an electropolymerized electroinactive polypyrrole (PPy) on a platinum electrode. This enzyme-immobilized PPy electrode showed a stable potential response to urea based on the pH response of the electroinactive PPy film electrode. The electropolymerization conditions were optimized, and thus the biosensor showed a Nernstian response with a slope of 31.8 mV decade −1 over concentration range of 1 × 10 −4 − 0.3 mol dm −3 urea.

Ambient-temperature, rechargeable, all-solid lithium/polypyrrole polymer battery

An ambient-temperature, all-solid lithium battery was fabricated by combining a poly(acrylonitrile), PAN-based polymer electrolyte with a lithium metal anode and a polypyrrole, PPy, film cathode. The influence of the morphology of the PPy film cathode on the battery performance was investigated. The results show that the electrode morphology does not considerably influence the charge-discharge cycling response and that the solid-state, Li/PPy battery exhibits high coulombic efficiency, approaching 90%. However, at the present time, the battery has a poor shelf life, and work is in progress for overcoming this drawback.

A Lithium-Ion Sulfur Battery Based on a Carbon-Coated Lithium- Sulfide Cathode and an Electrodeposited Silicon-Based Anode

In this paper, we report a lithium-ion battery employing a lithium sulfide cathode and a silicon-based anode. The high capacity of the silicon anode and the high efficiency and cycling rate of the lithium sulfide cathode allowed optimal full cell balance. We show in fact that the battery operates with a very stable capacity of about 280 mAh g(-1) at an average voltage of 1.4 V. To the best of our knowledge, this battery is one of the rare examples of lithium-metal-free sulfur battery. Considering the high theoretical capacity of the employed electrodes, we believe that the battery here reported may be of potential interest as high-energy, safe, and low-cost power source for electric vehicles.