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Concentrated electrolytes have been found to play host to stellar phenomena previously unachievable in solutions at diluted or moderate concentrations. In an attempt to explore the possible utility of concentrated electrolytes in electroplating, this study reports the electrodeposition of Cr metal using a concentrated aqueous solution of Cr(II) (4.0 mol kg⁻¹) without additives. Target aqueous CrCl₂ solutions are characterized by UV–visible spectroscopic and ionic conductivity measurements. The influence of concentration, current density, and agitation on Cr metal deposition is discussed on the basis of cyclic voltammetry, galvanostatic electrolysis, X-ray diffraction, and scanning electron microscopy. Here, electrolysis of the concentrated electrolyte at medium current densities (20 mA cm⁻²) under agitation is found to engender dense metallic α-Cr deposits with high adhesivity to the substrate. The results further show that increasing the current density to expedite the deposition process promotes the involvement of an impurity phase and deposition of the δ-Cr phase.

Ionic liquid (IL) electrolytes have been applied to lithium ion capacitors (LICs) composed of porous three-dimensional (3D) current collector. LIC cells containing IL electrolytes showed reversible charge-discharge potential profiles and their capacity degradation was hardly observed during 3000 cycles. In particular, a cell with 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMImFSI) containing lithium FSI (LiFSI) as Li salt kept over 90% of its initial capacity even after 3000 cycles. The EMImFSI-based IL electrolyte system (LiFSI/EMImFSI) also provided better rate performance than that of a conventional LiPF6-based organic electrolyte system. Considering high-temperature (60 °C) characteristics in the IL system and LiPF6-based system, charge-discharge operation in LiFSI/EMImFSI was stable compared to that in the LiPF6-based solvent system. Moreover, the LIC cell with LiFSI/EMImFSI was stably cycled even at 0 °C and its discharge capacity was superior to that of the LiPF6-based solvent electrolyte at 0 °C.

Ni–Sn porous metals with different concentrations of Sn were prepared as potential current collectors for solid oxide fuel cells (SOFCs). The weight increase of these species was evaluated after heat-treatment under elevated temperatures in air for thousands of hours to evaluate the long-term oxidation resistance. Ni–Sn porous metals with 5–14 wt% of Sn exhibited excellent oxidation resistance at 600 °C, although oxidation became significant above 700 °C. Intermetallic Ni3Sn was formed at 600 °C due to phase transformation of the initially solid solutions of Sn in Ni in the porous metals. For the porous metal with 10 wt% of Sn, the oxidation rate constant at 600 °C in air was estimated to be 8.5 × 10−14 g2 cm−4 s−1 and the electrical resistivity at 600 °C was almost constant at approximately 0.02 Ω cm2 up to an elapsed time of 1000 h. In addition, the gas diffusibility and the power-collecting ability of the porous metal were equivalent to those of a platinum mesh when applied in the cathode current collector of a SOFC operated at 600 °C. Ni–Sn porous metals with adequate contents of Sn are believed to be promising cathode current collector materials for SOFCs for operation at temperatures below 600 °C.

Introduction Some perovskite oxides, such as doped BaCeO3 and BaZrO3 electrolyte-based protonic ceramic fuel cell (PCFC) have received increasing attention as electrolytes of reduced temperature to operate [1,2]. Furthermore, PCFC leads to the production of water vapor at the cathode side, which helps to improve the conversion efficiency of SOFC system. And it is possible to reduce the cost of the stack because inexpensive metal materials can be used for interconnectors in stacks. However most of the previous researches on PCFC are small-sized cell and it is necessary to further improve the power density. In this work, we reported that a cell stack of a new structure was designed and made with large-sized PCFC and porous alloys for anode and cathode current collector to improve power density, and the characteristics were evaluated. Experimental 2.1 Preparation of large-sized PCFC BaCe0.8Y0.2O3-δ(BCY20) and BaZr0.8Y0.2O3-δ(BZY20) were prepared by solid state reaction method and were mixed with NiO by a ball-mill to prepare an anode powder. The powder was pressed uniaxially under 40 MPa into anode pellet. On anode pellet BCY20 and BZY20 electrolyte layer were deposited by a screen printing and co-sintered at 1450 ºC for 10 hours. LSCF cathode powder was also deposited and sintered at 1000 ºC. Figure 1(A) shows an optical image of a large-sized PCFC. 2.2 Preparation of Ni and Ni-Sn porous metals A polyurethane foam with interconnected cells was treated to become electrically conductive. This was followed by the application of a predetermined amount of nickel via electrodeposition. The base material, or plastic foam, was removed through heat treatment at 800 ºC. The remaining nickel was reduced in a reducing gas at approximately 1000 ºC to become a nickel porous metal. Next, the Ni porous metal was coated with a predetermined amount of Sn by electrodeposition. Additionally, this was heat-treated in a reducing gas at approximately 1000 ºC to become a Ni-Sn porous alloy by means of Sn diffusion into Ni. Figure 1(B) shows an SEM image of the surface of the Ni-Sn porous alloy [3]. Result The power generating characteristics of a single-PCFC in which Ni-Sn porous alloy and Ni porous metal were applied as a cathode and anode collector was evaluated at the operating temperature of 600 ºC. Peak power densities of 500 mW/cm2 and 333 mW/cm2 were achieved, respectively, at 600 ºC and 500 ºC operating on hydrogen fuel. [1] H. Iwahara, et al., Solid State Ionics, 61, 65 (1993) [2] J. Dailly, et al., Journal of Power Sources, 240, 323 (2013) [3] C. Hiraiwa, et al., International Journal of Hydrogen Energy, 42, 12567 (2017) Figure 1

To improve the cycle-life performance of LiFePO 4 /Cu-Sn lithium ion battery, a new methodology using a foam-type three-dimensional current collector was investigated. By applying the three-dimensional nickel substrate for the negative electrode, instead of conventional copper foil, the cycle performance of the Cu-Sn electrode was improved. In addition, a heat treatment of the electrode was revealed to suppress the capacity decline drastically: the heat treated electrode showed the capacity above 400 mAh g −1 even after 50 cycles. A full-cell which combined the developed negative electrode and a positive electrode based on LiFePO 4 also showed a favorable cycle performance. Furthermore, a full-cell using aqueous slurry was prepared, and the cell exhibited an excellent cycle-life performance in which it maintained above 90% of the maximum capacity even at the 200th cycle.

In order to improve the power performance of the lithium ion battery based on lithium iron phosphate (LiFePO 4 ), a new methodology using a three-dimensional micro-porous current collector was described. The three-dimensional current collector was manufactured based on foamed polyurethane and nickel–chromium alloy. The cell using the three-dimensional current collector exhibited a superior high-rate discharge capability as compared to a conventional-type cell using the aluminum foil current collector. Furthermore, impedance analysis revealed the size reduction of a semicircle for the charge-transfer resistance by applying the three-dimensional current collector, which indicates a superior current collecting ability for the developed substrate.

A new positive substrate for high-power nickel/metal-hydride (Ni/MH) battery was designed and prepared based on a nonwoven cloth technique. For the substrate, the amount of plated nickel was reduced to less than half compared with the conventional foam-type substrate, and the manufacturing process was simplified, which lowers the manufacturing cost of the substrate. The sub-C size cylindrical sealed cell using the developed substrate exhibited superior high-rate discharging capability to the cell using the foam-type one in spite of the reduction in the amount of plated nickel due to the characteristic three-dimensional micronetwork structure of the developed substrate. In addition, the prepared cell exhibited a long cycle-life of more than 2000 cycles at 25 °C. A hybrid electric vehicle (HEV) mode cycle test consisting of multiple pulse patterns was also performed on the cell at 45 °C, and the cell remained more than 85% power of the initial value even after 100,000 cycles (driving distance: ca. 300,000 km). The developed micronetwork substrate was revealed to satisfy both high-power output and long cycle-life.

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh–Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti–Goncharov procedure with a one-dimensional...

The lithium-ion capacitor (LIC) is a new storage device that combines an electric double-layer capacitor (EDLC) with a lithium-ion battery (LIB). Although LIC features an excellent power density like EDLC, the energy density of LIC is lower than that of LIB. Therefore, improvement of energy density is required for LIC. In the present study, to achieve high energy density of LIC, a porous 3-dimensinal (3-D) current collector is applied to LIC electrodes. This 3-D current collector can increase the packing density of active material. It is, however, expected that diffusion of ionic carriers is limited when we use a conventional organic electrolyte because an electrode based on a 3-D current collector should be massive and hence too long ionic diffusion pathways. As a result, LIC using a 3-D current collector may deliver limited power. Here ionic liquids (ILs) that have a high carrier density would be useful as an electrolyte for LIC to maintain power. The purpose of this study is applying IL-based electrolytes to LICs with the porous 3-D current collector. We assembled a three-electrode cell. A positive electrode using an aluminum 3-D current collector was composed of activated carbon, acetylene black (AB) and polyvinylidene di-fruoride (PVdF). A negative electrode using a copper 3-D current collector was composed of hard carbon, AB and PVdF. A lithium foil was used as a counter electrode as well as reference electrode. We used lithium bis(fluorosulfonyl)imide/1-ethyl-3-methylimidazorium bis(fluorosulfonyl)imide (LiFSI/EMImFSI) as an IL-based electrolyte. The cell was charged and discharged for 3000 cycles at 1.0 C-rate in a voltage range of 2.0 – 3.8 V. We also evaluated rate performance of the LIC cells by rapid charging and discharging test up to 30 C-rate. When we observed the potential profiles of the positive and negative electrodes during charge and discharge at the 2nd, 1000th and 3000th cycles, it was found that the LIC cell containing our FSI-based IL electrolyte can be charged and discharged reversibly as well as stably. Even though we applied long-term cycling such as 3000 cycles to the LIC cell, the capacity has not significantly degraded. We compared rate performance among the IL electrolyte and conventional organic electrolytes. Although the IL has a relatively high viscosity, it was shown that the FSI-based IL electrolyte has high rate performance comparable to that of a LiPF6-based organic electrolyte. This may be due to a high carrier density of the IL. These results suggest that application of the FSI-based IL electrolyte to LIC electrodes with the porous 3-D current collector is promising to keep or enhance energy and power capability.

Introduction A Nickel (Ni) porous metal is used for anode current collector in solid oxide fuel cells (SOFCs)[1]. However, it is difficult to be applied as cathode current collector due to its large oxidation resistance at high temperature. In this work, we investigated characteristics and applicability of a new Ni-Sn porous alloy as the cathode current collector for SOFCs. Experimental The Ni porous alloy was prepared by electroplating process. Sn was deposited continuously by electroplating onto the surface of the Ni porous metal. Then, heat treatment was performed under hydrogen atmosphere to obtain the Ni-Sn porous alloy [2]. Figure 1(A) shows a SEM image of three-dimensional structure of the as-prepared sample. Oxidation resistances were evaluated by measuring weight increase due to the heat treatment, and the area-specific resistance at high temperature. The crystalline phases of the specimens before and after heat treatment were identified by XRD. Mechanically polished cross-sections of the specimens were observed via SEM-EPMA. Finally, the prototype SOFCs were fabricated using the Ni-Sn porous alloy as the cathode current collector. Results and Discussion For Ni-Sn porous alloys with various Sn contents, figure 1(B) shows the weight increase due to the heat treatments in air at 800 °C for 1,000 hours and at 600 °C for 3,000 hours. In the case of the heat treatment at 800 °C for 1,000 hours, the weight of Ni-Sn porous alloys increased regardless of the Sn content. And the weight increased more than 1.7 mg/cm2, revealing a noticeable level of oxidation. In contrast, for Ni-Sn porous alloy with Sn content of 5 wt% or more, the oxidation was noticeably retarded in spite of a long-term heat treatment at 600 °C for 3,000 hours. Figure 1(C) shows the distribution of oxygen by using EPMA-EDS to analyze the cross-section area of the Ni-10wt%Sn porous alloy before and after heat treatment at 600 °C in air for 1,000 hours. After heat treatment, one can see a clear existence of oxygen in the depth about 1 μm from the surface, indicating the oxidation of this region. The IV relationship and the power output characteristics of SOFCs with the cathode current collectors made of Pt mesh or the Ni-10wt%Sn porous alloy. Both the behavior of the IV relationship and the output power of the SOFC with the Ni-10wt%Sn porous alloy were almost equivalent to that using the Pt mesh. Conclusions The Ni-Sn porous alloy has relatively low electrical resistance after the heat-treatment in oxygen, and also high electric conductivity at 600 °C. Thus, this new Ni porous alloy has promising perspective to be applied as the cathode current collector for SOFCs operating in an intermediate temperature range. And such demand is expected to grow in near future. [1] W. Guan, et al., Fuel Cells, 12(2012), 1085-1094 [2] K. Okuno, et al., SEI Technical Review, 75(2012), 137-140 Figure 1

We have successfully applied rice husk activated carbon (RHAC) as an active material for the electric double layer capacitor using a three-dimensional (3D) porous current collector. The capacity and cycle stability were evaluated in a 1.0 mol dm−3 tetraethylammonium tetrafluoroborate/propylene carbonate solution in the range of 0–2.5 V. The specific capacity of the RHAC was about 14 mAh g−1 at the 50 mA g−1 discharge rate, corresponding to 19 F g−1 under the present conditions. The RHAC cell using the 3D porous current collector possessed a lower internal resistance and better high-rate discharge properties than the RHAC cell using a conventional aluminum (Al) foil collector. After 5000 cycles of charging and discharging, the RHAC cell with the 3D current collector maintained 95% of its initial capacity, while the capacity of the one with the Al foil collector dropped to only 30%.

A lithium ion capacitor (LIC) is a new storage device which combines an electric double-layer capacitor (EDLC) with a lithium ion battery (LIB). Namely, LIC consists of an activated carbon as positive electrode and lithium-ion-intercalating carbon material such as hard carbon as negative electrode. LIC also contains functionalities derived from both EDLC and LIB. During charge and discharge of LIC, ion adsorption/desorption occurs on the surface of the positive electrode, while lithium ion intercalation/de-intercalation occurs at the negative electrode. Although LIC features an excellent power density like EDLC, the energy density of LIC is lower than that of LIB. Therefore, improvement of energy density is required for LIC. In the present study, to achieve high energy density of LIC, porous 3-dimensinal (3D) current collector is applied to LIC electrodes. It is possible to increase the packing density of active material and make a LIC cell lighter. It is, however, expected that diffusion of carriers is limited with conventional organic electrolytes because electrodes using porous 3D current collector become massive; the typical thickness is ca. 1 mm. As a result, LIC using porous 3D current collector may deliver limited power. Thus, ionic liquids which have high carrier density would be useful as electrolyte of LIC to maintain power. The purpose of this study is applying an ionic liquid electrolyte to LICs with porous 3D current collector and investigating the basic operating characteristics. We assembled a three-electrode cell. A positive electrode using aluminum porous 3D current collector was made from activated carbon (AC, 87 wt.%), acetylene black (AB, 3 wt.%) and polyvinylidene di-fruoride (PVdF, 10 wt.%). A negative electrode using copper porous 3D current collector was made from hard carbon (HC, 87 wt.%), AB (8 wt.%) and PVdF (5 wt.%). A lithium foil was used as a counter electrode and reference electrode. The electrolyte was 1.5 mol dm−3 LiFSI/EMImFSI. The cell was galvanostatically charged and discharged for 3000 cycles at 1.0 C-rate in a voltage range of 2.0 – 3.8 V after a pre-doping process under predetermined conditions. We also evaluated rate performances of LIC cells with various electrolytes by rapid charging and discharging test. 1.5 mol dm−3 LiFSI/EMImFSI was used as standard ionic liquid electrolyte. 1.0 mol dm−3 LiPF6 / EC : DMC = 1 : 1 (v/v) and 1.0 mol dm−3 LiBF4 / EC : DMC = 1 : 1 (v/v) were used as organic electrolytes for comparison. C-rates for the power performance test were varied from 0.1 C to 30 C every 5 cycles after 100 pre-cycles. Fig. 1 shows potential profiles of positive and negative electrodes during charge and discharge at 2, 1000, 3000 cycles. It turns out that the LIC cell containing ionic liquid electrolytes is possible to charge and discharge reversibly as well as stably. Even though it was long-term cycling such as 3000 cycles, its capacity has not significantly decreased. Therefore, long-term cycle stability is high. Fig. 2 compares rete performances with the ionic liquid electrolyte and two organic electrolytes. Although ionic liquids have high viscosity [1], it is shown that FSI-based ionic liquid electrolyte has high rete performances comparable to a LiPF6-based organic electrolyte. This may be ascribed to high carrier density of ionic liquids. Rate performances of the FSI-based ionic liquid electrolyte and LiPF6-based organic electrolyte are superior to that of the LiBF4-based organic electrolyte. This is attributed to lower ionic conductivity of LiBF4. These results suggest that applying the ionic liquid electrolyte to a LIC electrode with porous 3D current collector is promising. FSI-based ionic liquid electrolytes may replace conventional organic electrolytes as electrolyte of LIC because of their resulting high cycle stability and high energy density without power loss. References [1] M. Ishikawa, T. Sugimoto, M. Kikuta, E. Ishiko, and M. Kono, J. Power Sources, 162, 658 (2006). Figure 1

Hydrodynamic instabilities are key issues of the physics of inertial confinement fusion (ICF) targets. Among the instabilities, Rayleigh-Taylor (RT) instability is the most important because it gives the largest growth factor in the ICF targets. Perturbations on the laser irradiated surface grow exponentially, but the growth rate is reduced by ablation flow. The growth rate γ is written as Takabe-Betti formula: γ = [kg/(1+kL)]1/2–βkm/pa, where k is wave number of the perturbation, g is acceleration, L is density scale-length, β is a coefficient, m is mass ablation rate per unit surface, and ρa is density at the ablation front. We experimentally measured all the parameters in the formula for polystyrene (CH) targets. Experiments were done on the HIPER laser facility at Institute of Laser Engineering, Osaka University. We found that the β value in the formula is ~ 1.7, which is in good agreements with the theoretical prediction, whereas the β for certain perturbation wavelengths are larger than the prediction. This disagreement between the experiment and the theory is mainly due to the deformation of the cutoff surface, which is created by non-uniform ablation flow from the ablation surface. We also found that high-Z doped plastic targets have multiablation structure, which can reduce the RT growth rate. When a low-Z target with high-Z dopant is irradiated by laser, radiation due to the high-Z dopant creates secondary ablation front deep inside the target. Since, the secondary ablation front is ablated by x-rays, the mass ablation rate is larger than the laser-irradiated ablation surface, that is, further reduction of the RT growth is expected. We measured the RT growth rate of Br-doped polystyrene targets. The experimental results indicate that of the CHBr targets show significantly small growth rate, which is very good news for the design of the ICF targets.

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A low-cost substrate for the positive electrode of nickel/metal-hydride battery was developed by using a nonwoven cloth with a three-dimensional micronetwork structure, in which the amount of plated nickel was less than half compared with the conventional foam-type substrate. The substrate was designed to have a finer structure than the foam-type substrate. The cylindrical sealed cell using the substrate exhibited superior high-rate discharging capability to the cell using the foam-type substrate, despite the reduction of plated nickel. The characteristic microporous structure of the substrate presumably contributes to the improvement of high-rate discharge performance.

A three-dimensional porous current collector made of a nickel-chromium alloy was developed based on foamed polyurethane. The foam-type substrate exhibited a high tolerance at high voltages in nonaqueous electrochemical systems. The electric double layer capacitor (EDLC) using the foam-type substrate exhibited stable charge/discharge behavior and showed a superior high-rate discharge capability as compared to an EDLC using the conventional aluminum foil. Furthermore, impedance analysis revealed an improved current collecting ability for the foam-type substrate. To improve the performance of EDLCs, a methodology that uses a three-dimensional current collector was described.

The influence of nickel foam pore structure on the high-rate capability of nickel/metal-hydride (Ni/MH) batteries was studied to develop a substrate suitable for high-power use. Three types of nickel foam substrates with different pore structures were used for preparing the sealed cells. Among the three prepared sealed cells, the cell using the substrate with a smallest pore diameter and largest surface area exhibited the best high-rate discharging performance. The electrochemical impedance measurement also showed a close relationship between the charge-transfer resistance and the pore structure of the substrate. The contact area between the current collector and the active material is considered to significantly affect the contact resistance and the charge-transfer resistance. The pore-size reduction and the enlargement of the surface area of the substrate were revealed to be effective in improving the high-rate performance of Ni/MH batteries.

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