Radius Of Semicircle Research Articles

Effect of Electrode Pressing Process on the Electrode Characteristics of LiCoO2 Cathode.

Introduction Lithium-ion battery (LIB) has been used in a power source of mobile devices. Currently, LIB is demanded to be used for electric vehicles as a power source. Therefore, LIB with properties of high capacity, high power and long life have been requested. However, it is difficult to produce a LIB to meet all these requirements. In recent years, we have been selecting the condition to realize cathode sheets to perform for power usage or high energy storage to match the requirements for using the existing active material. In this study, we focused on the process of pressing cathode sheets. LiCoO2 cathodes were prepared by coating followed by pressing at varied pressures, as cause a change in packing density of active material and conducting carbon. Effect of the pressure on charge and discharge characteristics was investigated with various current loading rate. Furthermore, we tried to assess the effect of pressing cathode sheets using electrochemical impedance spectroscopy (EIS). Experiment LiCoO2 cathode was prepared in our laboratory by coating method. The thickness of the cathode before pressing is defined as thickness of 100 %. Then cathode sheet was pressed into the thickness upto 70 % with varying the pressure. Laminated cell was prepared with inserted reference electrode using a pressed LiCoO2 cathode. The anode sheets were prepared with graphite as the active material. The anode was pressed until the thickness of 90 %. 1.0 mol dm-3 LiPF6 in EC: DEC = 1:1 was used as electrolyte solution. Li-Al alloy reference electrode was used as the reference electrode. The inserted Al wire (f 25 mm ×4 mm) was alloying with Li by applying current of 5 mA for 60 minutes between Al wire and cathode. Initial charge-discharge of the laminate cells was carried out for 2 cycles at 7 mA. Rate performance was studied by 0.1 C, 0.5 C, 1 C, 5 C and 10 C for 2 cycles each. EIS was carried out at the SOC (state of charge) of 50 %, with frequency range 100 kHz - 10 mHz and amplitude 10 mV. The ac responses of the cathode and the anode were measured simultaneously by multi-potentiostat. Results and Discussion Discharge overvoltage was observed for the cathodes with thickness of 100 %, 90 %, 75 % in the charge and discharge curve. Discharge overvoltage that was observed in the charge and discharge curve at 0.5 C was 130 mV between the cathode thickness of 90 % and 75 %. In addition, overvoltage of between 100 % and 75 % was 370 mV. Discharge overvoltage that has been observed at 1.0 C was 220 mV between the film thickness of 90 % and 75 %. In addition, overvoltage of between the thickness of 100 % and 75 % was 520 mV. This result suggests that overvoltage decreases with an increasing of the pressing pressure. The results of the EIS are shown in Fig. 3. The radius of the semicircle in high-frequency region appeared in Nyquist plot becomes smaller in the order of 100 %, 90 %, and 75 % in thickness. From this result, the electric contact of cathode active material particles is considered likely to increase with increasing the pressing pressure. Also, the radius of the lower frequency side semicircle from Nyquist plot is found to becomes smaller in the order of 100 %, 90 %, and 75 % in thickness. This result suggests that charge transfer resistance decreases with increasing the pressure. A change in the charge transfer resistance as compared with the resistance value of the high-frequency side is small. These results suggest that resistance value of the high frequency sid has large influence on the charge and discharge characteristics. Conclusion Rate performance of the cathode sheet for LIB was investigated with varying the pressure for the press prior to the cell configuration after the cathode coating. The cathode sheets were pressed to be the thickness to 100 % (no press), 90 %, and 75 %. The overvoltage during the discharge of the cell decreased by the electrode pressing process. The EIS study suggests that both the electric resistance inside the cathode layer and the charge transfer of the cathode active material are reduced by the pressing of cathode sheet in the thickness range of 100 % and 75 %. Acknowledgements This work was partially aided by the MEXT-supported Program for the Strategic Research Foundation at Private Universities. Figure 1

Evaluation of HEV Batteries for Recycle ~Investigation for Estimating Battery Capacity By Electrochemical Impedance Spectroscopy~

1.Introduction After the end of life of hybrid electric vehicle (HEV), there is a possibility that some of the Nickel-metal hydride (Ni-MH) batteries for HEV remain capacity and we could reuse these batteries without any trouble. In order to utilize these reusable batteries, the capacity estimation method to reuse used batteries is essential. Ni-MH battery capacity decreases during the actual usage. Then we reported that the low capacity retention batteries caused by the negative electrode could be sorted out by the electrochemical impedance spectroscopy (EIS) in a charge state [1.2].On the other hand, it is well known that there are low capacity retention batteries caused by aging of NiOOH in the positive electrode. Among them, the most important thing to consider for reusing the Ni-MH batteries is low capacity retention batteries caused by “memory effect” [3]. When the memory effect occurs, the charging voltage at each SOC increased in accordance with history of the battery. The increase of charging voltage accelerates the side reaction. As a result, capacity decreases due to memory effect. Generally, the memory effect can be eliminated by low rate (0.3C-0.4C) charge and discharge refresh cycles. However, in order to completely eliminate the memory effect, it is necessary that charge and discharge cycles. As a result, it takes a long time to eliminate the memory effect. Thus, in order to determine quickly if the used battery could be reused, it is demanded that the easy method to detect the degree of capacity decrease due to the memory effect. In this study, we would like to report the quick and accurate method to detect the degree of capacity decrease due to the memory effect by EIS. 2.Experimental We used a Ni-MH battery for HEV (1.2 V - 6.5 Ah) as an experimental cell. In order to get the various degrees of capacity decrease due to the memory effect, the cells were charged and discharged for several cycles at constant current of 3 C rate at 35 oC in the range from SOC 0 % to SOC 20 %, SOC 40 %, SOC 60 %, and SOC 80 %. After the accumulated discharge capacity reached 2600 Ah, AC impedance measurements were carried out at SOC 60 %. The AC impedance spectra were obtained with 0.15 C of AC signal in the frequency range of 100 kHz to 0.01 Hz. All measurements were performed at 25 oC. We defined the degree of memory effect as the sum of difference of charging voltage (∫ΔVoltage) between the initial cell and the cycled cell. 3.Results and discussion Fig.1 (a) shows the charge curves of the cells which was obtained on test condition detailed before. We can see the charge curves difference by changing in the range of SOC. Fig.1 (b) shows the AC impedance spectra of these cells. Impedance spectrum of the Ni-MH battery shows semicircle which indicates the charge electron transfer reaction and linear part which indicates the diffusion process. The semicircle in impedance spectrum of the Ni-MH battery is mainly attributed to the negative electrode and the linear part is mainly attributed to the positive electrode. We found that the radius of semicircle in impedance spectrum decreased after cycled which indicate the resistance of electron transfer reaction of negative electrode decreased due to the activation of the negative electrode. On the other hand, in the linear part, we found that the imaginary value on each frequency get higher with the memory effect on the positive electrode. In order to confirm the relationship between the memory effect and impedance spectrum, we calculated (ΔZ"/Δ(ω-1))-1 [AsV-1] as the frequency response of the imaginary components of the linear part. Fig.1(c) shows the relationship between (ΔZ"/Δ(ω-1))-1 and the degree of memory effect (∫ΔVoltage). As shown in Fig.1 (c), (ΔZ"/Δ(ω-1))-1 correlates with the degree of memory effect. Thus, we can estimate the degree of memory effect by calculating (ΔZ"/Δ(ω-1))-1 from the linear part in impedance spectrum, suggesting that it is possible that the degree of capacity decrease due to memory effect can be detected by using (ΔZ"/Δ(ω-1))-1. Reference [1]H. Nishi, D. Koba, S. Ito, T. Yao, D. Mukoyama, H. Nara, S. Tsuda, T. Momma, T. Osaka, The 56rd Battery Symposium in Japan, 1M25 (2015)[2]D. Koba, H. Nishi S. Ito, T. Yao, D. Mukoyama, H. Nara, S. Tsuda, T. Momma, T. Osaka, The 56rd Battery Symposium in Japan, 1M26 (2015) [3] Y. Sato, S. Takeuchi, K.Kobayakawa, J. Power Sources 93 (2001) 20-24 Figure 1

Experimental Study of Flow Field of Large Air-Cooled Turbine Generator for Multi-Ventilation Ducts of Stator

To study rotational air flow field of rotor and complicated flow distinction owing to multi-ventilation ducts of stator in a large air-cooled turbine generator, considering axial symmetry of air supply, an experiment setup of ventilation system of semi-machine configuration was built in this paper. At condition of rotating, ventilation is measured by hot-wire anemometer. Firstly, ventilation in 16 different semi-circle radius is got. Measurement shows that ventilation in different radius varies much. Then ventilation of outlet of stator ducts is measured. The result shows that ventilation which is affected by flow back and jet less is higher. The conclusion will provide theoretical references for ventilation cooling of rotor ducts in large air-cooled turbine generators.

Augmentation Method of Triple Phase Boundary in Thin Film Solid Oxide Fuel Cell via Physical Vapor Deposition

Triple phase boundaries (TPBs) where electrode, electrolyte, and reactant meet altogether were augmented in thin film solid oxide fuel cell when Pt cathode was deposited on yttrium-doped barium zirconate electrolyte (BZY) via sputter. The augmented TPBs were observed to exist as three-dimensional structures, which is different from what are known to exist as two-dimensional planes or interfaces, by using energy dispersive spectroscopy (EDS). The permeating phenomenon of sputtered Pt into BZY was found to depend on dc sputtering power. Polarization curves showed increasing tendency of maximum powers in accordance with increasing thickness of Pt cathode and spectra of ac impedances showed decreasing tendency of faradaic resistances. If TPBs were located as an interfacial structure between electrode and electrolyte, oxygen could not diffuse well into TPBs, causing radius of semicircle in impedance spectra to decrease. The results are violating this expectation. As a result, as long as charge transfer resistance is a function of temperature, reactant concentration, activation barrier and TPB length, TPB must be only a factor to affect the results in this experiment.

Full Simulation Study of UV Photodetectors Based on Pn Junctions in Silicon Carbide

This paper deals with optical and electrical simulations of 4H-SiC UV-Photodetectors based on pn junctions. The simulations are performed under the UV light, with wavelengths varying between 200 nm and 300 nm. Under reverse bias, the simulation results point out the influence of surface patterns on the current density. The studied structures of the patterns consist in a semicircle with or without a flat surface. The patterned surfaces are parametrized according to the semicircle radius R and the flat surface length L. We show that the optical absorption strongly depends on these parameters, giving a maximum value whatever the wavelength with R = 100 nm and L = 0 nm (no flat surface). However, to optimise the carrier harvest, it is important for the space charge region to be situated in a zone where the optical generation is high. This study shows that the photodetector current density increases within three orders of magnitude (from 9x10-14 A.cm-2 to 3x10-10 A.cm-2), by using the specific surface pattern given above.

Preparation of long-chain branching polypropylene and investigation on its foamability

In this work, zinc N,N-dimethyldithiocarbamate (ZDMC) was used to mediate the melt modification of polypropylene (PP) with 1,6-hexanediol diacrylate (HDDA) in an internal mixer in the presence of dicumyl peroxide (DCP). Fourier transformed infrared spectroscopy analysis revealed that HDDA was directly grafted onto PP backbone. The dependence of torque on processing time indicated that the presence of ZDMC restrained the degradation of PP, and the end-torque value increased with the addition of ZDMC. Dynamic rheological measurement indicated that the modified PP possessed higher G′ and lower tan δ at low frequency, displaying an increase in η* and disappearance of Newtonian plateau in η*–ω plot, as well as larger radius of semicircle in Cole–Cole plot. All the rheological characterizations, together with the decreased gel content with the increase of ZDMC, confirmed the formation of long-chain branching. Subsequently, the foamability of the modified samples was investigated by one-step compression–molding process. The cellular structure and morphology of the obtained foams were observed by scanning electron microscopy, and the results showed that the addition of ZDMC decreased the cell size, increased the cell density, and brought about well-defined closed cell structure. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Transient and asymptotic dispersion in confined sphere packings with cylindrical and non-cylindrical conduit geometries

We study the time and length scales of hydrodynamic dispersion in confined monodisperse sphere packings as a function of the conduit geometry. By a modified Jodrey-Tory algorithm, we generated packings at a bed porosity (interstitial void fraction) of ε=0.40 in conduits with circular, rectangular, or semicircular cross section of area 100πd(p)(2) (where d(p) is the sphere diameter) and dimensions of about 20d(p) (cylinder diameter) by 6553.6d(p) (length), 25d(p) by 12.5d(p) (rectangle sides) by 8192d(p) or 14.1d(p) (radius of semicircle) by 8192d(p), respectively. The fluid-flow velocity field in the generated packings was calculated by the lattice Boltzmann method for Péclet numbers of up to 500, and convective-diffusive mass transport of 4×10(6) inert tracers was modelled with a random-walk particle-tracking technique. We present lateral porosity and velocity distributions for all packings and monitor the time evolution of longitudinal dispersion up to the asymptotic (long-time) limit. The characteristic length scales for asymptotic behaviour are explained from the symmetry of each conduit's velocity field. Finally, we quantify the influence of the confinement and of a specific conduit geometry on the velocity dependence of the asymptotic dispersion coefficients.

Sensing mechanism of hydrogen gas sensor based on RF-sputtered ZnO thin films

The mechanism of hydrogen (H 2) gas sensing in the range of 200–1000 ppm of RF-sputtered ZnO films was studied. The I–V characteristics as a function of operating temperature proved the ohmic behaviour of the contacts to the sensor. The complex impedance spectrum (IS) of the ZnO films showed a single semicircle with shrinkage in the diameter as the temperature increased. The best fitting of these data proved that the device structure can be modelled as a single resistance-capacitance equivalent circuit. It was suggested that the conductivity mechanism in the ZnO sensor is controlled by surface reaction. The impedance spectrum also exhibited a decreased in semicircle radius as the hydrogen concentration was increased in the range from 200 ppm to 1000 ppm.

Hydrogen effects on pitting corrosion and semiconducting properties of nitrogen-containing type 316L stainless steel

Abstract The effects of hydrogen pre-charging on pitting corrosion resistance and semiconducting nature of passive film formed on two different nitrogen-containing type 316L stainless steel (0.076 and 0.086 wt% N) have been studied. Auger electron spectroscopy (AES) analysis of the alloys after passivation indicated weak nitrogen peak, but the presence of nitrogen and NH3/NH4+ was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis. The results of pitting corrosion in 0.5 M NaCl (pH ≈ 5.7) solution revealed that hydrogen increased the passive current density and significantly reduced the pitting resistance. In 0.3 M H3BO3 + 0.075 M Na2B4O7·10H2O (pH ≈ 8.45) solution, increase in passive current density without affecting the breakdown or transpassive potential was observed for both the alloys. Electrochemical impedance spectroscopy (EIS) measurement after hydrogen pre-charging showed decrease in semi-circle radius of Nyquist plot, and the polarization resistance, RP associated with the resistance of the passive film. The decrease was significant with increasing hydrogen-charging current density (−50 to −100 mA/cm2). The results of the capacitance measurement and Mott–Schottky plots revealed that passive films exhibit n-type and p-type semiconductivity films for both the uncharged and hydrogen charged specimens of the investigated alloys. Doping densities obtained from Mott–Schottky plots increased with hydrogen pre-charging. The overall results indicated that hydrogen pre-charging deteriorated the passive film stability and lowered pitting corrosion resistance. The effects of hydrogen pre-charging on pitting corrosion, passive film and semiconducting properties are discussed in light of the above results.

Electrochemical characterization of ion selectivity in electrodeposited nickel hexacyanoferrate thin films

The ion selectivity of electrodeposited nickel hexacyanoferrate (NiHCF) thin films was investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). NiHCF thin films were prepared by cathodic deposition on Pt and Al substrates. EIS and CV curves were determined in 1 mol/L (KN0 3+CsNO 3) and 1 mol/L (NaNO 3+CsNO 3) mixture solutions, which were sensitive to the concentration of Cs + in the electrolytes. Experimental results show that all Nyquist impedance plots show depressed semicircles in the high-frequency range changing over into straight lines at lower frequencies. With increasing amounts of Cs +, the redox potentials in CV curves shift toward more positive values and the redox peaks broaden: the semicircle radius in corresponding EIS curves and the charge transfer resistance also increase. EIS combining CV is able to provide valuable insights into the ion selectivity of NiHCF thin films.

Hydrogen effects on the passive film formation and pitting susceptibility of nitrogen containing type 316L stainless steels

The effects of hydrogen on the passivity and pitting susceptibility of type 316L stainless steels have been investigated with alloys containing different nitrogen contents (0.015, 0.198 and 0.556 wt.% N). The study revealed that electrochemically pre-charged hydrogen significantly reduced the pitting resistance of alloys conatining 0.015 and 0.198 wt.% nitrogen contents. In alloy with highest nitrogen content (0.556 wt.% N), an increase in the passive film current density with hydrogen was observed without affecting breakdown potential. Auger electron spectroscopy (AES) analysis of the passive film indicated the presence of nitrogen in the passive film. On other hand, for hydrogen charged samples, nitrogen was found to be significantly less in the passive film. In Electrochemical impedance spectroscopy (EIS) measurement, the decrease in semi-circle radius of Nyquist plot, and the polarization resistance, R P associated with the resistance of the passive film was observed with hydrogen, indicating that hydrogen decreased the stability of the passive film. The present investigation indicated that precharged hydrogen deteriorated the passive film stability and pitting corrosion resistance in these alloys, and the increase in nitrogen content of the alloy offsets the deleterious effect of precharged hydrogen.

Role of buffer layer on the performances of amorphous silicon solar cells with incorporated nanoparticles produced by plasma enhanced chemical vapor deposition at 27.12 MHz

The aim of this paper is to present results concerning the role of the buffer layer on pin devices, deposited in a single chamber for plasma enhanced chemical vapor deposition, using high hydrogen dilution and pressures at 27.12 MHz. By doing so, we allow the incorporation of nanoparticles into the i-layer, during plasma process. The results show solar cells with 8.8% efficiency with a collection efficiency of 95% in the blue region of the spectra. Apart from that, the results from impedance spectroscopy, imaginary impedance vs. real impedance, show difference of a semicircle radius as function of sample temperatures, which could be explained by total device series resistance variation.

On the Stress Concentration in a Slotted Curved Beam

In this study, the stress concentration factors of a slotted curved beam subjected to uniform bending are reported.The experiment was carried out by the photoelastic method. Epoxy resin plates with thickness of 6mm were used as specimens, and a uniform bending moment was applied. The width of the curved beam and the length of the slot were maintained as constant. The radius of the curvature was varied in four steps (including the case of a straight beam) and the radius of semi-circle at both ends of the slot, and also the eccentricity of the slot from the center line of the beam were changed in three ways, respectively.The stress concentrations along the upper and lower edges, through the minimum cross section and around the slot were examined, and the stress concentration factors at four main points were measured for several cases of the test conditions mentioned above. Moreover, the ratio of stress of the curved beam to that of the straight beam at each corresponding point was also investigated.From the experimental results, the following conclusion has been made.(1) The s.c.f. at the upper or lower edge of the beam decreases or increases, respectively, with the increase of curvature. But the s.c.f. at the upper or lower end of the slot shows an inverse tendency to that at the edge. As to the effect of eccentricity, the approach of the slot to each edge raises the s.c.f. at the edge. This trend is identical for the s.c.f. at the upper or lower end of the slot, when the slot approaches the upper or lower edge, respectively. The maximum values of s.c.f. obtained in this experiment are 1.4 and 1.8, respectively, for the lower edge of the beam and for the upper end of the slot.(2) The ratio of stress of the curved beam to that of the straight beam is more than unity at the lower edge of the beam as well as at the upper end of the slot in all cases. This fact confines our attention to these points.(3) In order to secure that none of the stresses at several main points of the slotted curved beam become specially large, it is desirable to locate the slot on the centre line of the beam, avoiding the eccentricity of the slot.