Understanding the Molecular Structure of the Elastic and Thermoreversible AlCl3 : Urea/Polyethylene Oxide Gel Electrolyte

It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of ultra-high molecular weight polyethylene oxide (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl₃ and urea at a molar ratio of 1.5 : 1 (AlCl₃ /urea). The experimental vibrational spectra (FTIR and Raman) provide valuable information on the structure and composition of the gel electrolyte. However, the complexity of this system requires computational simulations to help interpretation of the experimental results. This combined approach allows us to elucidate the speciation of the DES liquid electrolyte in the gel and how it interacts with the polymer chains to give rise to an elastic network that retains the electroactivity of the liquid electrolyte to a very great extent. The observed reactions occur between the ether in the polymer and both the amine groups in urea and the aluminum species. Thus, similar elastomeric gels may likely be prepared with other aluminum liquid electrolytes, making this procedure an effective way to produce families of gel aluminum electrolytes with tunable rheology and electroactivity.

A Critical Evaluation of the Effect of Electrode Thickness and Side Reactions on Electrolytes for Aluminum-Sulfur Batteries

The high abundance and low cost of aluminum and sulfur make the Al-S battery an attractive combination. However, significant improvements in performance are required, and increasing the thickness and sulfur content of the sulfur electrodes is critical for the development of batteries with competitive specific energies. This work concerns the development of sulfur electrodes with the highest sulfur content (60 wt %) reported to date for an Al-S battery system and a systematic study of the effect of the sulfur electrode thickness on battery performance. If low-cost electrolytes made from acetamide or urea are used, slow mass transport of the electrolyte species is identified as the main cause of the poor sulfur utilization when the electrode thickness is decreased, whereas complete sulfur utilization is achieved with a less viscous ionic liquid. In addition, the analysis of very thin electrodes reveals the occurrence of degradation reactions in the low-cost electrolytes. The new analysis method is ideal for evaluating the stability and mass transport limitations of novel electrolytes for Al-S batteries.

How a Transition-Metal(II) Chloride Interacts with a Eutectic AlCl3 -Based Ionic Liquid: Insights into the Speciation of the Electrolyte and Electrodeposition of Magnetic Materials

Electrostatic interactions are characteristic of ionic liquids (ILs) and play a pivotal role in determining the formation of species when solutes are dissolved in them. The formation of new species/complexes has been investigated for certain ILs. However, such investigations have not yet focused on eutectic liquids, which are a promising class of ILs. These liquids (or liquid coordination complexes, LCCs) are rather new and are composed of cationic and anionic chloro complexes of metals. To date, these liquids have been employed as electrolytes to deposit metals and as solvents for catalysis. The present study deals with a liquid that is prepared by mixing a 1.2:1 mol ratio of AlCl₃ and 1-butylpyrrolidine. An attempt has been made to understand the interactions of FeCl₂ with the organic molecule using spectroscopy. It was found that dissolved Fe(II) species interact mainly with the IL anion and such interactions can lead to changes in the cation of the electrolyte. Furthermore, the viability of depositing thick magnetic films of Fe and Fe-Al has been explored.

Suppressing the dendritic growth of zinc in an ionic liquid containing cationic and anionic zinc complexes for battery applications

Metallic zinc is a promising negative electrode for high energy rechargeable batteries due to its abundance, low-cost and non-toxic nature. However, the formation of dendritic zinc and low Columbic efficiency in aqueous alkaline solutions during charge/discharge processes remain a great challenge. Here we demonstrate that the dendritic growth of zinc can be effectively suppressed in an ionic liquid electrolyte containing highly concentrated cationic and anionic zinc complexes obtained by dissolving zinc oxide and zinc trifluoromethylsulfonate in a protic ionic liquid, 1-ethylimidazolium trifluoromethylsulfonate. The presence of both cationic and anionic zinc complexes alters the interfacial structure at the electrode/electrolyte interface and influences the nucleation and growth of zinc, leading to compact, homogeneous and dendrite-free zinc coatings. This study also provides insights into the development of highly concentrated metal salts in ionic liquids as electrolytes to deposit dendrite-free zinc as an anode material for energy storage applications.

An Investigation of the Symmetric and Asymmetric Cleavage Products in the System Aluminum Trihalide/1-Butylimidazole

Mixtures of AlX₃ (X=Cl, Br) with 1-butylimidazole (BuIm) in various ratios were investigated. The mixtures were characterized by multinuclear (¹ H, ²⁷ Al, ¹³ C, and ¹⁵ N) NMR, IR, and Raman spectroscopy and in part by single-crystal X-ray diffraction. Depending on the molar fraction x(AlBr₃ ) of the AlBr₃ -based mixtures, the cationic aluminum complexes [Al(BuIm)₆ ]³⁺ and [AlBr₂ (BuIm)₄ ]⁺ , the neutral adduct [AlBr₃ (BuIm)], as well as the anions Br^- , [AlBr₄ ]^- , and [Al₂ Br₇ ]^- could be identified as the products of the symmetric and asymmetric cleavage of dimeric Al₂ Br₆ . Furthermore, there are hints at the formation of [AlBr₂ (BuIm)₂ ]⁺ or related cations. Comparison of the AlBr₃ /BuIm system with AlCl₃ -based mixtures revealed the influence of the halide: In contrast to AlBr₃ , the trication [Al(BuIm)₆ ]³⁺ could not be detected as main product in a 1:6 mixture of AlCl₃ and BuIm. Additionally, [AlCl₃ (BuIm)] crystallizes from a mixture with x(AlCl₃ )=0.60 at room temperature, whereas the corresponding AlBr₃ -based mixture remains liquid even at +6 °C. Three AlBr₃ -based mixtures are liquid at room temperature, whereas all other mixtures are solids with melting points between 46 and 184 °C. The three liquid mixtures exhibit medium to high viscosities (117 to >1440 mPa s), low conductivities (0.03-0.20 mS cm^-1 ), but high densities (1.80-2.21 g cm^-3 ). Aluminum could be successfully deposited from one of the neat Lewis acidic mixtures of the AlBr₃ -based system.