The electrodeposition of Zn from trimethyl propylammonium bis(trifluoromethylsulfonyl)imide (TMPATFSI) was investigated. Powdery zinc electrodeposits were obtained from the TMPATFSI-Zn (TFSI)2 (80:20 mol%) bath at the constant potential of −1.7 V vs. Pt/I−, I3− and at the constant current density of 50–200 A m−2. By the addition of ethylene glycol, however, the cathodic current density and the cathodic current efficiency for the Zn electrodeposition were increased; moreover, the metallic-colored zinc electrodeposits were obtained.
Coated graphite electrodes are widely used as the anode in Li-ion batteries, in which an electrically conductive additive is mixed with the active material for keeping good electric contact between the active material and current collector. We examined the state of mixing of the conductive additive in the coated electrode in detail. The electrode coated with a homogeneous distribution of conductive additive over the electrode prolonged the cycle performance with high discharge capacity, while the electrode with inhomogeneously distributed conductive additive exhibited remarkable degradation of cycleability even though the same materials were used in the same ratio. The SEM images of the well-mixed electrode showed no appreciable change after many cycles, while the poorly mixed electrode showed a number of solid deposits over the surface after cycling. The deposit was identified to be electrically nonconductive Li2CO3, which is presumed to be the cause of the suppressed cycleability. Such an inhomogeneous electrical contact also enlarged the initial charging capacity loss. The results of the analysis of impedance spectra for both electrode types during cycling agreed with the results obtained through electrochemical evaluation.
Nanofabrication processes of Si substrates based on localized anodization and subsequent chemical etching were investigated. The anodization procedure of aluminum sputtered on a Si substrate was monitored by measuring the current transient at a constant voltage. The porous alumina with a self-ordered configuration acted as a mask for the localized anodization of the underlying Si substrate and controlled the position of the silicon oxide pattern, which was produced only in the Al2O3/Si interface. The transfer of the geometric pattern of anodic porous alumina into a Si substrate could be achieved by two independent processes: i) the hole array structure can be obtained by the selective removal of silicon oxide from the Si substrate using wet etching in HF solution; and ii) the column array structure can be obtained by the selective etching of Si substrate in KOH solution using silicon oxide as a mask. Based on this approach, the different nanostructures could be obtained arbitrarily by the selection of appropriate local anodization stages and etching conditions.
For improving the cycle performance of the positive electrode of Ni-MH battery using Ni-coated three-dimensional sheet with lower cost than a conventional Ni-foam, the effect of decreasing the amount of binder was examined by mechanical strength and electrochemical measurements. The results indicated that the electrode using the mixture of 1 wt% styrene maleic acid (SMA) and 1 wt% polytetrafluoroethylene (PTFE) had the same peeling strength as the electrode using 2 wt% SMA only, and made it possible to decrease the omission of active material to 0 in the bending test. Furthermore, by changing the thickener from CMC to xanthan gum (XG) with a three-dimensional structure and good stability in alkaline solution, the total amount of the binder in the positive electrode could be decreased from 2.2 wt% to 1.3 wt%. And the battery using this electrode showed higher discharge rate and better low temperature performance than that using the electrode with CMC. By using this new composition of binder, the power density of the battery was improved from 480 W/kg to 980 W/kg. In the HEV-mode cycle test at 45°C, the capacity of the cell remained at more than 80% of the initial value even after 50000 cycles (corresponding to a mileage of 200,000 km).
Polymer electrolyte fuel cell having capacitor property was prepared by compositing polyaniline (PAn) with Pt-deposited carbon (Pt–C) in catalyst layer. Two types of cathodes were prepared; one has a layer structure consisting of Pt–C and polyaniline (PAn) layer, and the other has a separate structure where the Pt–C and PAn layers are put separately. Fuel cell with latter electrode exhibits higher performance. Membrane-electrode assembly (MEA) fabricated with no PAn showed abrupt voltage drop when output current was changed. On the other hand, in the case of MEA including PAn, rate of voltage drop was alleviated due to discharge of PAn in catalyst layer.