Study and Development of Al-Air Battery Applying Room Temperature Ionic Liquid Electrolyte

Room-temperature ionic liquids (RTILs), i.e. organic molten salts with melting points below 100 ◦C, have been intensively developed for electrolytic media in various electrochemical systems due to the fact that RTILs have unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. Particularly, RTILs have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations; however, highly conductive and stable RTILs based on quaternary phosphonium cations2 have been rarely employed for this application. In this work, we report the electrooxidative polymerization of aniline in triethylpentylphosphonium bis(trifluoromethylsulfonly)amide (P2225-TFSA) and tributylmethylphosphonium bis(trifluoromethylsulfonly)amide (P4441-TFSA) in comparison with the other type of RTILs, characterizing the obtained polyaniline films. The preparation of the phosphonium RTILs was performed by aqueous ion exchange reaction of the precursor quaternary phosphonium halides with lithium TFSA. The electrooxidative polymerization of aniline in phosphonium RTILs containing 0.1 M H-TFSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a Pt disk working electrode. The electrochemical activity of the polyaniline films were evaluated by extended CV scanning technique.Figure 1 shows typical cyclic voltammograms for the electrooxidative pocesses of aniline. As shown in Fig. 1, it was found that relatively large voltammetric response was observed in P2225-TFSA when compared to that in P4441-TFSA. This seems to be attributed to the relatively low viscosity and high conductivity of P2225-TFSA. In addition, the voltammetric responses were enhanced by cycling, which indicates that ionic species could be efficiently doped into the polyaniline film. The surface morphology based on SEM images of the polyaniline films will be also discussed.References 1 K. Sekiguchi, et al, J. Electroanal. Chem. , 557, 1 (2003).2 K. Tsunashima, et al, Electrochem. Commun., 9, 2353 (2007). Figure 1

Plasma-engineered cobalt nanoparticle encapsulated N-doped graphene nanoplatelets as high-performance oxygen reduction reaction electrocatalysts for aluminum–air batteries

Anodic behavior of Al current collector in 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] amide ionic liquid electrolytes

Recently, the aluminum–air (Al–air) battery has spotlighted since its low cost, sustainable properties, and high theoretical potential. To improve battery performance, several approaches for Al anode modification have been introduced, such as alloy processes, metal oxide deposition, etc. However, such processes could induce critical side effects during battery operation for example, by-product creation by de-alloying, reduction of Al activity, and more. In this research, to overcome these problems, physically modified Al foils were used as Al anodes and an Al-air battery was fabricated. The Al anode was sandblasted by micro-sand blasting, employing around 10 μm beads, to increase surface area and reactivity. Indeed, an electrolyte solution was circulated between the battery structures to enhance cell stability and remove by-products from the anode reaction. The energy capacity of air battery with the sandblasted Al anode was 3.85 mWh and it was about 5 times improved than that of bare Al anode case. In addition, the energy capacity in the electrolyte circulation case was 4.5 mWh, which established that battery performance was increased about 6.5 times by the sandblasting and electrolyte circulation process. Therefore, this new type of Al-air battery has a great potential to be applied in various fields.

Introduction Transparent and electrically conductive metal oxide nanoparticles (NPs) prepared by solution phase synthetic methods have attracted much attention due to their applicability to wet processing, such as ink-jet printing or spin coating, for fabrication of densely packed particulate films, which can be used to improve the performance of solar cells, transparent electrode, and sensors. Among various kinds of metal oxide particles, indium tin oxide (ITO) NPs are useful nanomaterials because of their high electronic conductivity, chemical stability, or unique optical properties induced by their surface plasmon resonance (LSPR) in the near-infrared region. So far, well-dispersed ITO NPs have been prepared by sol-gel technique or solvothermal method, though these conventional techniques required well-trained skills for obtaining particles with well-controlled size and shape. Recently a facile preparation method of colloidal metal particles in organic solvent has been reported with use of low-melting-point metals such as gallium, indium, and tin,[1] in which molten metals were mechanically dispersed in organic solvent containing surfactant molecules by ultrasonication and/or magnetic stirring, resulting in the formation of metal nanoparticles. On the other hand, room temperature ionic liquids (RTILs) with extremely low vapor pressure and thermal stability have been reported to be a useful medium for the preparation and stabilization of noble metal NPs. For example we have reported that the sputter deposition of noble metals such as Au, Ag, or Pt into RTILs produced corresponding ultrafine metal nanoparticles uniformly dispersed in the solution.[2]RTILs are also expected to act as a good medium not only for the preparation of low-melting-point metal NPs by mechanically dispersing but also for the oxidation of resulting metal particles with heat treatment due to high thermal stability of RTILs. However such attempt has not been carried out. In this study, we report a facile preparation of uniformly dispersed ITO NPs via direct oxidation of In-Sn alloy as a precursor in RTILs. Experimental Indium (0.5 g) was added in RTILs (2.0 cm3) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate (HyEMI-BF4), 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (HyEMI-TFSA), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA-TFSA), or 2-hydroxyethyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)amide (Ch-TFSA). The mixture was heated at 523 K for 10 h in air with vigorous stirring. Thus-obtained NPs dispersed in the solution were collected by a centrifugation and re-dispersed in acetonitrile for characterization. ITO NPs with different Sn content were prepared in the same method except for the use of an In-Sn alloy (Sn content; 3, 5, 10, 20, 30 wt%) as a precursor in the Ch-TFSA. Results and discussions The particles prepared by the oxidation of pure In metal as a precursor in RTILs of EMI-BF4, HyEMI-TFSA, TMPA-TFSA and Ch-TFSA, exhibited broad diffraction peaks in XRD pattern assignable to cubic In2O3. In contrast, the XRD pattern of particles prepared in HyEMI-BF4 was assignable to orthorhombic InOF. These results indicated that In metal was oxidized with oxygen molecule dissolved in TFSA-based RTILs to produce In2O3 or reacted with fluoride ion produced by the decomposition of BF4 - anion in HyEMI-BF during heat treatment, resulting in the formation of InOF. TEM observation revealed that uniformly dispersed spherical particles with average diameter of 27 and 39 nm were observed in hydroxyl-functionalized RTILs of HyEMI-TFSA and Ch-TFSA, respectively, while largely aggregated In2O3 particles appeared in EMI-BF4 and TMPA-TFSA. These indicated that hydroxyl group in cationic species of RTILs played an important role in the prevention of In2O3NPs in RTILs. To prepare ITO NPs, we carried out the similar preparation protocol, in which In-Sn alloy containing different Sn content (3-30 wt%) were oxidized in Ch-TFSA with vigorous stirring. Thus-obtained particles exhibited the XRD pattern assignable to ITO crystal structure. Figure 1 shows a TEM image of ITO NPs prepared with alloy containing 30 wt% Sn. Polygonal particles with average diameter ca. 40 nm were observed. With an increase in the Sn content from 3 to 30 wt% in alloy as a precursor, the amount of Sn doping in ITO NPs was enlarged from 0.67 to 10 wt%. ITO NPs exhibited a LSPR peak in the near-IR wavelength region in the extinction spectra, the peak wavelength being blue-shifted from 2860 to 2400 nm with an increase in the amount of Sn doping in NPs from 0.67 to 10 wt%.

Aluminum-air (Al-air) batteries are promising candidates for use in electric vehicles due to their high pack-level energy densities and to the abundance, recyclability, lightweight, low cost, and three-electron-redox properties of aluminum. Severe capacity fade during open-circuit conditions, however, has limited Al-air commercialization for over 50 years. Open-circuit capacity fade is caused by corrosion wherein the aluminum anode reacts with water from the aqueous electrolyte. Existing strategies to mitigate open-circuit corrosion, however, generally lead to reduced powers and energy densities. Optimized aqueous systems that use anode alloying and or electrolyte additives achieve high powers (500 mW cm-2) and energy densities (4 kWh kg-Al-1) but suffer from unacceptably high open-circuit corrosion currents (10 mA cm-2). In contrast, gel electrolyte systems yield low powers (91.1 mW cm-2) and energy densities (1.2 kWh kg-Al-1) but achieve no long-term open-circuit corrosion. Here we present a high-power (433 mW cm-2), energy-dense (3.9 kWh kg-Al-1) Al-air battery that experiences no long-term open-circuit corrosion. Open-circuit corrosion can be stopped with no discernible effect to closed-circuit performance by displacing the aqueous electrolyte with a non-conducting liquid oil. When the battery is in closed-circuit conditions, the aqueous electrolyte can effectively displace the oil due to the natural and designed underwater oleophobic properties of the anode and cathode—the oil beads up and is flushed out by the electrolyte. The figure shows measured anode corrosion via hydrogen collection before and after the electrolyte has been displaced by oil and suggests that long-term open-circuit corrosion is completely stopped. We estimate that an Al-air vehicle battery pack with the proposed corrosion mitigation system could achieve energy densities of 222 Wh-kg-1 (2x that of Li-ion vehicle packs) and 183 Wh-L-1 (comparable to Li-ion vehicle packs) at costs as low as 18 US$-kWh-1 (33x less than Li-ion packs). We anticipate that our findings will further enable the use of aluminum as a critical element for energy storage. Figure 1

The development of nonprecious metal‐based electrocatalysts for the oxygen reduction reaction holds the decisive key to many energy conversion devices. Among several potential candidates, transition metal and nitrogen co‐doped carbonaceous materials are the most promising, yet their activity and stability are still insufficient to meet the needs of practical applications. In this study, a core–shell hybrid electrocatalyst is developed via the self‐polymerization of dopamine and cobalt on carbon nanotubes (CNTs), followed by high‐temperature pyrolysis. The polymer‐derived carbonaceous shell contains abundant structural defects and facilitates the formation of CoN/C active sites, whereas the graphitic carbon nanotube core provides high electrical conductivity and corrosion resistance. These two components separately fulfill different functionalities, and jointly afford the catalyst with excellent electrochemical performance. In 1 m KOH, CoN/CNT exhibits a positive half‐wave potential of ≈0.91 V, low peroxide yield of <7%, as well as great stability. When used as the air catalyst of primary Zn–air and Al–air batteries, this hybrid electrocatalyst enables large discharge current density, high peak power density, and prolonged operation stability.

Characterization of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide-based polymer electrolytes for high safety lithium batteries

[Introduction] Rechargeable batteries for the storage of electrical energy are required for the introduction of renewable energy and compact electronic devices for the sustainable society.[1] Although lithium-ion batteries currently dominate the market, rechargeable metal–air batteries with very high energy densities have been attracting attention due to increasing power consumption and demand for low environmental burden. They are composed of oxygen from air as the cathode-active material, metal as the anode-active material and a strong alkaline solution as the electrolyte. They have the advantage of high energy density and low environmental burden due to the use of oxygen as the cathode-active material. While primary Zn–air batteries are commercialized, rechargeable metal–air batteries are under investigation due to their low cycle performance caused by dendrites and metal oxides formed on the metal anode, which leads to disposal of anode-active materials. In addition, strong basic electrolytes are used due to their high ionic conductivity, and the carbonate clogging by carbon dioxide in the air is also a problem. Therefore, rechargeable air batteries, which consist of acid or neutral electrolyte and anode-active materials which is recyclable and do not form dendrites or metal oxides, are required. Organic redox molecules, which are reversibly redox-active organic compounds, are composed of earth-abundant and relatively available building blocks (C, H, N, O, and S), and their functions can be tuned by molecular design, which has attracted attention as new electrode-active materials. We have previously reported that rechargeable polymer–air batteries using an organic redox polymer with organic redox molecules in the side chain of polymer as the anode-active material and acidic aqueous solution as the electrolyte charged and discharged without the formation of dendrites or carbonates.[2] However, organic materials suffer from low durability, and organic redox materials with structural stability in the electrolyte have been required. In the current work, we focused on UiO-66, a metal-organic framework with structural stability in acid and base electrolyte, and synthesized UiO-66-(OH2) with 1,4-dihydroxybenzene, an organic redox molecule as a linker, which undergoes a reversible redox reaction even in acid electrolytes. An anode-active material composed of UiO-66-(OH2) did not form dendrites or metal oxides in H2SO4 aqueous electrolyte (pH 1) and exhibited charge storage with high cycle stability. A rechargeable acidic MOF–air battery was demonstrated for the first time. After use, UiO-66-(OH2) electrode was facilely decomposed and separated to the original raw chemicals by NH4HCO3 aqueous solution.[Results and Discussion] We synthesized UiO-66-(OH2) from zirconium(IV) chloride and 2,5-dihydroxyterephthalic acid by microwave irradiation. UiO-66-(OH2) was coated on a glassy carbon plate in the presence of single-walled carbon nanotube as the conductive additive. The UiO-66-(OH2) electrode exhibited charging-discharging curves of a plateau voltage at 0.2 V, and the ratio of discharging vs. charging capacity (i.e. coulombic efficiency) were nearly 96%. The high capacity of the UiO-66-(OH2) electrode suggested that almost all of the -OH moieties contributed to charge storage. Even after 300 cycles, UiO-66-(OH2) electrode exhibited high cycle performance, which was relatively robust compared to other n-type redox materials for rechargeable aqueous air batteries. These results demonstrated that UiO-66-(OH2) has high cycle stability as an anode-active material for rechargeable acidic MOF-air batteries. A rechargeable acidic MOF-air battery was fabricated with a UiO-66-(OH2), Pt/C, and H2SO4 aqueous electrolyte (pH 1) as the anode material, cathode material, and electrolyte, respectively. The coulombic efficiencies of the battery were nearly 97%, demonstrating the reversible charge storage property of the cell. The high capacity for the anode suggested that almost all of the -OH moieties contributed to charge storage. Even after 100 charging-discharging cycles, the battery kept the high discharging capacity even at a rapid discharging. These results demonstrated the long-life ability of the rechargeable acidic MOF-air battery. UiO-66-(OH2) electrode in the battery was facilely decomposed and separated to the original raw chemicals by NH4HCO3 aqueous solution after charging and discharging.[Conclusions] We synthesized UiO-66-(OH2), which is stable in aqueous electrolyte, and applied it to an anode-active material. The rechargeable acidic MOF-air battery exhibited high cycle performance without the formation of dendrites or carbonates. In addition, we successfully recycled UiO-66-(OH2) electrode after charging and discharging. The current work presented a first step for developing electrode materials for the future energy storage.[References][1] J. Kim, Y. Kim, J. Yoo, G. Kwon, K. Kang et al., Nat. Rev. Mater. , 8, 54–70, 2023.[2] K. Oka, S. Furukawa, S. Murao, H. Nishide, K. Oyaizu et al., Chem. Commun. , 56, 4055–4058, 2020. Figure 1

Metal–Air Batteries In article number 2105594, Miao Yu, Jie Zhang, and co-workers report the development of iron phthalocyanine (FePc) anchored onto N,S–doped hollow carbon spheres (HNSCs) to form FePc@HNSC. The charge distribution and d–band center of Fe atoms can be efficiently optimized. The material is applied as an efficient oxygen reduction electrocatalyst for aluminum–air batteries.

In recent years, research scholars have conducted in-depth research on the efficient and stable electrocatalysts for oxygen reduction reaction (ORR) and analyzed how to reduce the polymer binders in the cathode of metal–air batteries. Although some research progress has been made, there are still many challenges. On the basis of full consideration of factors such as good electrical conductivity, unique porous structure, improved performance, surface area, and synergistic effects, composite materials (m-Co3O4/3DG) of three-dimensional graphene and mesoporous Co3O4 nanowires are prepared on a Ni foam substrate. Here, a facile solution (NaBH4) reduction method is introduced, resulting in an increase in the oxygen vacancies on the surface of the mesoporous Co3O4 nanowires, thereby improving the electrocatalytic activity of m-Co3O4/3DG ORR. The reduced m-Co3O4/3DG composite exhibits a much positive half-wave potential of 0.84 V (vs. RHE) and onset potential of 0.93 V (vs. RHE), and much higher mass activity of 0.109 A mg−1 at 0.766 V (vs. RHE) compared with m-Co3O4/3DG, m-Co3O4, and 3D graphene electrocatalysts, or even superior to the Pt/C catalyst. In addition, when reduced m-Co3O4/3DG is used as the binder-free cathode of the aluminum–air battery, showing a 422.74 mAh g−1 specific capacity and a 1.53 V open-circuit voltage under the discharge current density of 1.0 mA cm−2, which are more excellent compared with the traditional Pt/C, m-Co3O4, and m-Co3O4/3DG electrodes. The 1D and 3D morphology hierarchically porous feature leads to high-efficiency surface reduction and charge and mass transportation. This research provides a solution reduction method with a simple operation to generate more defect states on electrocatalysts and supplies valuable view into the development of reduced Co3O4/3DG with excellent ORR electrocatalytic performance as binder-free cathodes in aluminum–air battery.

La1−xSrxMnO3 (LSM) has been proposed as one of the best oxygen reduction reaction catalysts (ORRCs) to substitute noble metals. It is well known that an improvement of the oxygen‐adsorption capacity is beneficial to the catalytic activity of LSM perovskites. Herein, the composite material La0.7Sr0.3MnO3@Ce0.75Zr0.25O2 (LSM@CZ) has been synthesized by a facile electrostatic self‐assembly method in a two‐step strategy. The CZ nanoparticles are well distributed on the surface of the LSM material. The LSM‐4CZ composite catalyst exhibits a good catalytic activity in alkaline solution. The onset potential, half‐wave potential, and electron transfer number of the LSM‐4CZ composite catalyst are 0.898 V, 0.695 V, and 4, respectively. The LSM‐4CZ composite catalyst has a good durability with current retention of 93.9 % after 80 000 s and it exhibits a much better stability than Pt/C, the retention of which is 83.5 %. If we used LSM‐CZ as the ORRC, the maximum power density of the Al–air battery reached 242.9 mW cm−2, which is approximately 40 % higher than that of the battery with LSM (177.3 mW cm−2). This indicates that the LSM@CZ composite material is a promising cathodic electrocatalyst for metal–air batteries.

Liquid-liquid extraction techniques are one of the major tools in chemical engineering, analytical chemistry, and biology, especially in a system where two immiscible liquids have an interface solutes exchange between the two liquid phases along the interface up to a point where the concentration ratios in the two liquids reach their equilibrium values [1]. Solutes including nucleic acids and proteins of interests can be extracted from one liquid phase to the other immiscible liquid phase as a preparation step for many analytical processes. There are several advantages in miniaturizing the liquid-liquid extraction methods to on-chip level extraction. Usual advantages of miniaturization are the reduction in the sample size and portability. In addition, transport phenomena is faster in Micro-systems than in ordinary size systems, and therefore, one may expect that liquid-liquid extraction takes less time to achieve in miniaturized devices. It is due to shorter diffusion time in micro scale as well as high surface to volume ratio of Microsystems. Electrowetting on dielectric (EWOD) digital microfluidics is an efficient platform to process droplet based analytical processes [2]. Nanoliter (nL) or smaller volume of aqueous liquid droplets can be generated and transported on a chip by EWOD process. In addition to the high surface to volume ratio, high chemical potential can be expected in droplet based extraction when the droplets are in motion. In this paper, we propose to use room temperature ionic liquid (RTIL) as a second liquid phase for extraction, which forms immiscible interface with aqueous solutions. Properties of RTIL can be tailored by choice of cation, anion and substituents. RTIL has been investigated as replacements for the organic solvents and various “task-specific” ionic liquid are being developed which exhibit many attractive properties such as very low vapor pressure, high thermal stability [3]. We recently published EWOD properties of various RTILs toward microfluidic applications [4]. To demonstrate liquid-liquid micro extraction on chip, we fabricated and tested EWOD digital microfluidic devices. Fig. 1 shows (a) top and (b) cross sectional views of EWOD device. Two model extraction systems were tested. One is organic dye extracted from RTIL (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide or BMIMNTf2) to water and the other is iodine (I2) extracted from water to BMIMNTf2. The later model experiment is demonstrated in Fig. 2. Droplets of aqueous solution and BMIMNTf2 solution were generated on chip reservoir then transported for extraction and separated by EWOD actuation. When an aqueous solution and BMIMNTf2 solution join together, they created an interface, since water and BMIMNTf2 are immiscible. Extraction of I2 was done along the interface. After successful extraction, two immiscible liquid phases were separated by EWOD actuation and formed two separate droplets. From the result shown in Fig 2 (g), it is expected that extraction performance at the interface of moving droplet would be enhanced compared to the stationary droplet, because a moving interface prevent the chemical equilibrium, thus more chemical extraction potential can be provided with a moving interface than at a stationary interface. This demonstration is the first step toward total analysis system. The presented result opens the way to on-chip micro extraction, which will be readily integrated with other sample preparation microfluidic components and detection components. Currently, micro extraction systems for larger molecules such as nucleic acids, proteins and biological cells are being developed for further analytical applications.

Aluminum–air batteries are promising electronic power sources because of their low cost and high energy density. However, traditional aluminum–air batteries are greatly restricted from being used in the field of flexible electronics due to the rigid battery structure, and the irreversible corrosion of the anode by the alkaline electrolyte, which greatly reduces the battery life. To address these issues, a three-dimensional dual-network interpenetrating structure PVA/LiCl/PEO composite gel polymer electrolyte (GPE) is proposed. The gel polymer electrolyte exhibits good flexibility and high ionic conductivity (σ = 6.51 × 10−3 S cm−1) at room temperature. Meanwhile, benefiting from the high-performance GPE, an assembled aluminum–air coin cell shows a highest discharge voltage of 0.73 V and a peak power density (Pmax) of 3.31 mW cm−2. The Al specific capacity is as high as 735.2 mA h g−1. A flexible aluminum–air battery assembled using the GPE also performed stably in flat, bent, and folded states. This paper provides a cost-effective and feasible way to fabricate a composite gel polymer electrolyte with high performance for use in flexible aluminum–air batteries, suitable for a variety of energy-related devices.

Ionic liquids based on the imide salts of the dialkyl azepanium cation, AZ (R1, R2) were synthesized, characterized, and evaluated as electrolytes in lithium batteries. Nine salts were synthesized with variation in the length of the two alkyl groups [R1, R2 = methyl (1), ethyl (2), propyl (3) and butyl (4)]. It was found that the asymmetric ones with R2-R1 ≥ 2 are liquids at ambient temperature. The three room-temperature ionic liquids (AZ13-TFSI, AZ14-TFSI, AZ24-TFSI) showed, in the neat form, ionic conductivities in the range of 0.1–0.6 mS/cm, viscosities of 260–350 cP and an electrochemical window of 5.5–6 V. It was found that mixing the ionic liquids with ethylene carbonate gave electrolytes with lower viscosities, increased conductivities and improved electrochemical cathodic stability. Electrolytes based on the ILs were evaluated in lithium half cells with different chemistries; Li/LiFePO4, Li/Li4Ti5O12, Li/LiCoO2; and in the case of AZ14-TFSI a Li/LiFePO4 cell, gave discharge capacities reaching 125 mAh.g−1 over 100 cycles with 98% coulombic efficiencies.