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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

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

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

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