Speciation and dipole reorientation dynamics of glass-forming liquid electrolytes: Li[N(SO2CF3)2] mixtures of 1,3-propane sultone or tetrahydrothiophene-1,1-dioxide

Recently new ionic fluids such as super-concentrated electrolyte solutions, solvate ionic liquids and deep eutectic solvents have attracted much attention in the field of liquid electrolytes for next-generation electrochemical devices and processes. The basic composition of these new ionic fluids is similar among them; a solvent and a large/excess amount of salt mixtures, though the solvent is sometimes a solid at ambient temperatures. Here, we found and demonstrated that LiTFSA (TFSA = (CF3SO2)2N-) mixtures with 1,3-propane sultone (PS) or tetrahydrothiophene-1,1-dioxide (SL) yield a homogeneous liquid at room temperature within a wide range of compositions. In order to clarify the uniquely high Li+ transference number in these mixtures, speciation and dipole reorientation dynamics were studied to provide evidence of large-size aggregate formation in these mixtures.

Preparation of a High-Performance Asymmetric Supercapacitor by Recycling Aluminum Paper and Filter Components of Heated Tobacco

In this study, Al paper and cellulose acetate (CA) filters derived from heated tobacco waste were successfully converted into current collectors and active materials for a supercapacitor device. Typically, heated tobacco contains electrically discontinuous Al paper. First, Al was extracted from the tobacco waste using HCl to produce Lewis acid (AlCl3). This acid was then used in an Al electrodeposition process utilizing the chloroaluminate ionic liquid reaction between the acid and the base (RCl) at room temperature. To enhance the conductivity, a supplementary coating of Al metal was applied to the Al paper through electrodeposition, thus re-establishing the electrical continuity of the discontinuous parts and forming an Al-coated current collector. Moreover, the CA filters were carbonized under a nitrogen atmosphere, yielding carbon precursors (C-CA) for the supercapacitor electrodes. To further enhance the electrochemical performance, nickel oxide (NiO) was incorporated into C-CA, resulting in C-CA@NiO with pseudocapacitance. The specific surface area of CA increased with carbonization and the subsequent incorporation of NiO. The as-synthesized C-CA and C-CA@NiO materials were applied to an Al-coated current collector to obtain C-CA- and C-CA@NiO-based electrodes, exhibiting stable electrochemical behavior in the voltage range of -1.0 to 0 V and 0 to 1.0 V, respectively. An asymmetric supercapacitor (ASC) device was assembled with C-CA@NiO and C-CA as the positive and negative electrodes, respectively. This ASC device demonstrated a high specific capacitance of 40.8 F g-1, while widening the operating voltage window to 2.0 V. The high electrochemical performance of the device is attributed to the successful Al electrodeposition, which facilitates the electrical conductivity and increased porosity of the C-CA@NiO and C-CA materials. To the best of our knowledge, this is a pioneering study in regards to the conversion of biomass waste into current collectors and active materials to fabricate a practical ASC device. Our findings highlight the potential of reusing Al paper and CA filters from heated tobacco waste as essential components of energy storage devices.

Comparative Study of Guanidine-, Acetamidine- and Urea-Based Chloroaluminate Electrolytes for an Aluminum Battery

Aluminum-based batteries are a promising alternative to lithium-ion as they are considered to be low-cost and more friendly to the environment. In addition, aluminum is abundant and evenly distributed across the globe. Many studies and Al battery prototypes use imidazolium chloroaluminate electrolytes because of their good rheological and electrochemical performance. However, these electrolytes are very expensive, and so cost is a barrier to industrial scale-up. A urea-based electrolyte, AlCl3:Urea, has been proposed as an alternative, but its performance is relatively poor because of its high viscosity and low conductivity. This type of electrolyte has become known as an ionic liquid analogue (ILA). In this contribution, we proposed two Lewis base salt precursors, namely, guanidine hydrochloride and acetamidine hydrochloride, as alternatives to the urea-based ILA. We present the study of three ILAs, AlCl3:Guanidine, AlCl3:Acetamidine, and AlCl3:Urea, examining their rheology, electrochemistry, NMR spectra, and coin-cell performance. The room temperature viscosities of both AlCl3:Guanidine (52.9 cP) and AlCl3:Acetamidine (76.0 cP) were significantly lower than those of the urea-based liquid (240.9 cP), and their conductivities were correspondingly higher. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) showed that all three electrolytes exhibit reversible deposition/dissolution of Al, but LSV indicated that AlCl3:Guanidine and AlCl3:Acetamidine ILAs have superior anodic stability compared to the AlCl3:Urea electrolyte, as evidenced by anodic potential limits of +2.23 V for both AlCl3:Guanidine and AlCl3:Acetamidine and +2.12 V for AlCl3:Urea. Coin-cell tests showed that both AlCl3:Guanidine and AlCl3:Acetamidine ILA exhibit a higher Coulombic efficiency (98 and 97%, respectively) than the AlCl3:Urea electrolyte system, which has an efficiency of 88% after 100 cycles at 60 mA g-1. Overall, we show that AlCl3:Guanidine and AlCl3:Acetamidine have superior performance when compared to AlCl3:Urea, while maintaining low economic cost. We consider these to be valuable alternative materials for Al-based battery systems, especially for commercial production.

Measuring and Enhancing the Ionic Conductivity of Chloroaluminate Electrolytes for Al-Ion Batteries

At the core of the aluminum (Al) ion battery is the liquid electrolyte, which governs the underlying chemistry. Optimizing the rheological properties of the electrolyte is critical to advance the state of the art. In the present work, the chloroaluminate electrolyte is made by reacting AlCl₃ with a recently reported acetamidinium chloride (Acet-Cl) salt in an effort to make a more performant liquid electrolyte. Using AlCl₃:Acet-Cl as a model electrolyte, we build on our previous work, which established a new method for extracting the ionic conductivity from fitting voltammetric data, and in this contribution, we validate the method across a range of measurement parameters in addition to highlighting the model electrolytes' conductivity relative to current chloroaluminate liquids. Specifically, our method allows the extraction of both the ionic conductivity and voltammetric data from a single, simple, and routine measurement. To bring these results in the context of current methods, we compare our results to two independent standard conductivity measurement techniques. Several different measurement parameters (potential scan rate, potential excursion, temperature, and composition) are examined. We find that our novel method can resolve similar trends in conductivity to conventional methods, but typically, the values are a factor of two higher. The values from our method, on the other hand, agree closely with literature values reported elsewhere. Importantly, having now established the approach for our new method, we discuss the conductivity of AlCl₃:Acet-Cl-based formulations. These electrolytes provide a significant improvement (5-10× higher) over electrolytes made from similar Lewis base salts (e.g., urea or acetamide). The Lewis base salt precursors have a low economic cost compared to state-of-the-art imidazolium-based salts and are non-toxic, which is advantageous for scale-up. Overall, this is a noteworthy step at designing cost-effective and performant liquid electrolytes for Al-ion battery applications.

Unraveling the multivalent aluminium-ion redox mechanism in 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)

Rechargeable Aluminium-organic batteries are an exciting emerging energy storage technology owing to their low cost and promising high performance, thanks to the ability to allow multiple-electron redox chemistry and multivalent Al-ion intercalation. In this work, we use a combination of Density Functional Theory (DFT) calculations and experimental methods to examine the mechanism behind the charge-discharge reaction of the organic dye 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) in the 1,3-ethylmethylimidazolium (EMIm⁺) chloroaluminate electrolyte. We conclude that, contrary to previous reports claiming the intercalation of trivalent Al³⁺, the actual ionic species involved in the redox reaction is the divalent AlCl²⁺. While a less-than-ideal scenario, this mechanism still allows a theoretical transfer of four electrons per formula unit, corresponding to a remarkable specific capacity of 273 mA h g^-1. However, the poor reversibility of the reaction and low cycle life of the PTCDA-based cathode, due to its solubility in the electrolyte, make it an unlikely candidate for a commercial application.

Investigation of Al(TfO)3-based deep eutectic solvent electrolytes for aluminium-ion batteries. Part I: understanding the positively charged Al complex formation

Aluminium-ion batteries (AIB) are very attractive energy storage systems due to the high availability and theoretical energy density of metallic aluminium. However, the practical performance of AIBs in AlCl₃-based electrolytes is limited by the low reversible capacity of the positive graphite electrode for large AlCl₄^- anions. Moreover, the use of high energy oxide-based electrodes such as MnO₂ requires the presence of positively charged aluminium complexes in the electrolyte. In this work, the coordination of Al complexes in deep eutectic solvents (DESs) composed of Al triflate Al(TfO)₃ as the conducting salt, urea and/or acetamide as the hydrogen bond donor and formamide and N-methylacetamide as the solvent was investigated. Both solvents were able to dissolve and dissociate Al(TfO)₃ principally to a single positively charged Al complex [Al(TfO)₂-solvent_n]⁺ which was confirmed by Raman and NMR spectroscopy analyses. Furthermore, the addition of urea led to further dissociation to the [AlTfO-solvent_n-urea₂]²⁺ complex that can be assigned to the bidentate hydrogen bonding of urea with TfO at a specific ratio of urea/Al(TfO)₃ of 4 : 1. Because of their partial miscibility with urea, other conventional solvents such as propylene carbonate and acetonitrile dissociate Al(TfO)₃ only once to form [AlTfO₂-solvent_n]⁺. The as-prepared formamide and N-methylacetamide-based DES electrolytes show good conductivity values of 9.65 and 2.45 mS cm^-1, respectively.

Amidine-based ionic liquid analogues with AlCl3: a credible new electrolyte for rechargeable Al batteries

Here we demonstrate the generation of novel ionic liquid analogue (ILA) electrolytes for aluminium (Al) electrodeposition that are based on salts of amidine Lewis bases. The electrolytes exhibit reversible voltammetric plating/stripping of Al, good ionic conductivities (10-14 mS cm^-1), and relatively low viscosities (50-80 cP). The rheological properties are an improvement on analogous amide-based ILAs and make these liquids credible alternatives to ILAs based on urea or acetamide, or conventional chloroaluminate ionic liquids (IL) for Al battery applications.

Ab initio Molecular Dynamics Investigations of the Speciation and Reactivity of Deep Eutectic Electrolytes in Aluminum Batteries

Deep eutectic solvents (DESs) have emerged as an alternative for conventional ionic liquids in aluminum batteries. Elucidating DESs composition is fundamental to understand aluminum electrodeposition in the battery anode. Despite numerous experimental efforts, the speciation of these DESs remains elusive. This work shows how ab initio molecular dynamics (AIMD) simulations can shed light on the molecular composition of DESs. For the particular example of AlCl₃ :urea, one of the most popular DESs, we carried out a systematic AIMD study, showing how an excess of AlCl₃ in the AlCl₃ :urea mixture promotes the stability of ionic species vs neutral ones and also favors the reactivity in the system. These two facts explain the experimentally observed enhanced electrochemical activity in salt-rich DESs. We also observe the transfer of simple [AlCl_x (urea)_y ] clusters between different species in the liquid, giving rise to free [AlCl₄ ]^- units. The small size of these [AlCl₄ ]^- units favors the transport of ionic species towards the anode, facilitating the electrodeposition of aluminum.

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 Concentrated AlCl3-Diglyme Electrolyte for Hard and Corrosion-Resistant Aluminum Electrodeposits

A concentrated aluminum chloride (AlCl₃)-diglyme (G2) electrolyte is used to prepare hard and corrosion-resistant aluminum (Al) electrodeposited films. The Al electrodeposits obtained from the electrolyte with an AlCl₃/G2 molar ratio x = 0.4 showed a void-free microstructure composed of spherical particles, in stark contrast to flake-like morphologies with micro-voids for lower x. Neutral complexes rarely exist in the x = 0.4 electrolyte, resulting in a relatively high conductivity despite the high concentration and high viscosity. Nanoindentation measurements for the Al deposits with >99% purity revealed that the nanohardness was 2.86 GPa, three times higher than that for Al materials produced through electrodeposition from a well-known ionic liquid bath or through severe plastic deformation. Additionally, the void-free Al deposits had a <100> preferential crystal orientation, which accounted for better resistance to free corrosion and pitting corrosion. Discussions about the compact microstructure and <100> crystal orientation of deposits obtained only from the x = 0.4 concentrated electrolyte are also presented.

Aluminum electrolytes for Al dual-ion batteries

In the search for sustainable energy storage systems, aluminum dual-ion batteries have recently attracted considerable attention due to their low cost, safety, high energy density (up to 70 kWh kg^-1), energy efficiency (80-90%) and long cycling life (thousands of cycles and potentially more), which are needed attributes for grid-level stationary energy storage. Overall, such batteries are composed of aluminum foil as the anode and various types of carbonaceous and organic substances as the cathode, which are immersed in an aluminum electrolyte that supports efficient and dendrite-free aluminum electroplating/stripping upon cycling. Here, we review current research pursuits and present the limitations of aluminum electrolytes for aluminum dual-ion batteries. Particular emphasis is given to the aluminum plating/stripping mechanism in aluminum electrolytes, and its contribution to the total charge storage electrolyte capacity. To this end, we survey the prospects of these stationary storage systems, emphasizing the practical hurdles of aluminum electrolytes that remain to be addressed.

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.

High-Performance Rechargeable Aluminum-Selenium Battery with a New Deep Eutectic Solvent Electrolyte: Thiourea-AlCl3

Aluminum-sulfur batteries (ASBs) have attracted substantial interest due to their high theoretical specific energy density, low cost, and environmental friendliness, while the traditional sulfur cathode and ionic liquid have very fast capacity decay, limiting cycling performance because of the sluggishly electrochemical reaction and side reactions with the electrolyte. Herein, we demonstrate, for the first time, excellent rechargeable aluminum-selenium batteries (ASeBs) using a new deep eutectic solvent, thiourea-AlCl₃, as an electrolyte and Se nanowires grown directly on a flexible carbon cloth substrate (Se NWs@CC) by a low-temperature selenization process as a cathode. Selenium (Se) is a chemical analogue of sulfur with higher electronic conductivity and lower ionization potential that can improve the battery kinetics on the sluggishly electrochemical reaction and the reduction of the polarization where the thiourea-AlCl₃ electrolyte can stabilize the side reaction during the reversible conversion reaction of Al-Se alloying processes during the charge-discharge process, yielding a high specific capacity of 260 mAh g^-1 at 50 mA g^-1 and a long cycling life of 100 times with a high Coulombic efficiency of nearly 93% at 100 mA g^-1. The working mechanism based on the reversible conversion reaction of the Al-Se alloying processes, confirmed by the ex situ Raman, XRD, and XPS measurements, was proposed. This work provides new insights into the development of rechargeable aluminum-chalcogenide (S, Se, and Te) batteries.

Tough Polymer Gel Electrolytes for Aluminum Secondary Batteries Based on Urea: AlCl3, Prepared by a New Solvent-Free and Scalable Procedure

Polymer gel electrolytes have been prepared with polyethylene oxide (PEO) and the deep eutectic mixture of AlCl₃: urea (uralumina), a liquid electrolyte which has proved to be an excellent medium for the electrodeposition of aluminum. The polymer gel electrolytes are prepared by mixing PEO in the liquid electrolyte at T > 65 °C, which is the melting point of PEO. This procedure takes a few minutes and requires no subsequent evaporation steps, being a solvent-free, and hence more sustainable procedure as compared to solvent-mediated ones. The absence of auxiliary solvents and evaporation steps makes their preparation highly reproducible and easy to scale up. PEO of increasing molecular weight (Mw = 1 × 10⁵, 9 × 10⁵, 50 × 10⁵ and 80 × 10⁵ g mol^-1), including an ultra-high molecular weight (UHMW) polymer, has been used. Because of the strong interactions between the UHMW PEO and uralumina, self-standing gels can be produced with as little as 2.5 wt% PEO. These self-standing polymer gels maintain the ability to electrodeposit and strip aluminum, and are seen to retain a significant fraction of the current provided by the liquid electrolyte. Their gels' rheology and electrochemistry are stable for months, if kept under inert atmosphere, and their sensitivity to humidity is significantly lower than that of liquid uralumina, improving their stability in the event of accidental exposure to air, and hence, their safety. These polymer gels are tough and thermoplastic, which enable their processing and molding into different shapes, and their recyclability and reprocessability. Their thermoplasticity also allows the preparation of concentrated batches (masterbatch) for a posteriori dilution or additive addition. They are elastomeric (rubbery) and very sticky, which make them very robust, easy to manipulate and self-healing.

Room-Temperature Electrodeposition of Aluminum via Manipulating Coordination Structure in AlCl3 Solutions

The coordination mechanism of chloroaluminate species in aluminum chloride (AlCl₃) solutions in γ-butyrolactone (GBL) is investigated using electrochemical, spectroscopic, and computational methods. The liquid-state ²⁷Al NMR spectroscopy shows a sequence of new species generated in the AlCl₃-GBL solutions with increasing AlCl₃/GBL ratio. Ab initio molecular dynamics simulation reveals the dynamic coordination process between GBL and AlCl₃, and the resultant chloroaluminate species are identified as [AlCl₂·(GBL)₂]⁺, AlCl₄^-, AlCl₃·GBL, and Al₃Cl₁₀^-. The species are further confirmed by surface enhanced Raman spectroscopy combined with calculated Raman spectra from methods based on density functional theory. Electrochemical deposition of Al is achieved from the AlCl₃-GBL solution containing Al₃Cl₁₀^-, which is one of the few noneutectic electrolytes for room-temperature Al deposition reported to date.

Paving the Path toward Reliable Cathode Materials for Aluminum-Ion Batteries

Aluminum metal is a high-energy-density carrier with low cost, and thus endows rechargeable aluminum batteries (RABs) with the potential to act as an inexpensive and efficient electrochemical device, so as to supplement the increasing demand for energy storage and conversion. Despite the enticing aspects regarding cost and energy density, the poor reversibility of electrodes has limited the pursuit of RABs for a long time. Fortunately, ionic-liquid electrolytes enable reversible aluminum plating/stripping at room temperature, and they lay the very foundation of RABs. In order to integrate with the aluminum-metal anode, the selection of the cathode is pivotal, but is limited at present. The scant option of a reliable cathode can be accounted for by the intrinsic high charge density of Al³⁺ ions, which results in sluggish diffusion. Hence, reliable cathode materials are a key challenge of burgeoning RABs. Herein, the main focus is on the insertion cathodes for RABs also termed aluminum-ion batteries, and the recent progress and optimization methods are summarized. Finally, an outlook is presented to navigate the possible future work.

Fast Microwave-Assisted Hydrothermal Synthesis of Pure Layered δ-MnO₂ for Multivalent Ion Intercalation

This work reports on the synthesis of layered manganese oxides (δ-MnO₂) and their possible application as cathode intercalation materials in Al-ion and Zn-ion batteries. By using a one-pot microwave-assisted synthesis route in 1.6 M KOH (Mn_VII:Mn_II = 0.33), a pure layered δ-MnO₂birnessite phase without any hausmannite traces was obtained after only a 14 h reaction time period at 110 °C. Attempts to enhance crystallinity level of as-prepared birnessite through increasing of reaction time up to 96 h in 1.6 M KOH failed and led to decreases in crystallinity and the emergence of an additional hausmannite phase. The influence of Mn_II:OH⁻ ratio (1:2 to 1:10) on phase crystallinity and hausmannite phase formation for 96 h reaction time was investigated as well. By increasing alkalinity of the reaction mixture up to 2.5 M KOH, a slight increase in crystallinity of birnessite phase was achieved, but hausmannite formation couldn’t be inhibited as hoped. The as-prepared layered δ-MnO₂ powder material was spray-coated on a carbon paper and tested in laboratory cells with Al or Zn as active materials. The Al-ion tests were carried out in EMIMCl/AlCl₃ while the Zn-Ion experiments were performed in water containing choline acetate (ChAcO) or a ZnSO₄ solution. Best performance in terms of capacity was yielded in the Zn-ion cell (200 mWh g⁻¹ for 20 cycles) compared to about 3 mAh g⁻¹ for the Al-ion cell. The poor activity of the latter system was attributed to low dissociation rate of tetrachloroaluminate ions (AlCl₄⁻) in the EMIMCl/AlCl₃ mixture into positive Al complexes which are needed for charge compensation of the oxide-based cathode during the discharge step.

A rechargeable Al-ion battery: Al/molten AlCl3-urea/graphite

A new Al-ion battery based on an affordable and nontoxic liquid electrolyte made from molten AlCl₃/urea was assembled. As the cathode material, natural graphite shows two well-defined discharge voltage plateaus at about 1.9 and 1.5 V with a high specific capacity of 93 mA h g^-1 and excellent coulombic efficiency (>99%). The attractive capacity (about 78 mA h g^-1) is retained even at a high current density of 1000 mA g^-1. Moreover, no faster fading in capacity is observed after 500 cycles. This electrolyte could provide a new system for Al ion batteries, which can be used for large scale energy storage, owing to its cost advantages, high-rate capability and durability.

Determination of the Lewis acidity of amide–AlCl3 based ionic liquid analogues by combined in situ IR titration and NMR methods

A combinatorial method to determine both acidic strength and acidic amount of each Lewis acid site in amide–AlCl₃ based ionic liquid (IL) analogues was developed by the combination of in situ IR titration and NMR analysis. ³¹P NMR was used to distinguish effectively the acidic strength of each Lewis acid site in the amide–AlCl₃ based IL analogues. Nitrobenzene was used as a molecular probe to measure the total Lewis acidic amount of the amide–AlCl₃ based IL analogues by in situ IR titration. The acidic amount of each Lewis acid site in the amide–AlCl₃ based IL analogues was calculated with the assistance of ²⁷Al NMR analysis.

The Lewis acidic strength and amount of amide–AlCl₃ IL analogues are determined by the combination of in situ IR titration and NMR analysis.

Acetamide: a low-cost alternative to alkyl imidazolium chlorides for aluminium-ion batteries

Acetamide forms a room temperature liquid eutectic with AlCl₃, which can be used as a low-cost electrolyte for aluminium-ion 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.

Kish Graphite Flakes as a Cathode Material for an Aluminum Chloride-Graphite Battery

Nonaqueous, ionic liquid-based aluminum chloride-graphite batteries (AlCl₃-GBs) are a highly promising post-Li-ion technology for low-cost and large-scale storage of electricity because these batteries feature exclusively highly abundant chemical elements and simple fabrication methods. In this work, we demonstrate that synthetic kish graphite, which is a byproduct of steelmaking, can be used as a cathode in AlCl₃-GB and exhibits high capacities of ≤142 mAh g^-1. The comprehensive characterization of kish graphite flakes and other forms of graphite by X-ray diffraction, Raman spectroscopy, and Brunauer-Emmett-Teller surface area analysis provides solid evidence that the exceptional electrochemical behavior of kish graphite flakes is mainly determined by the high structural order of carbon atoms, a low level of defects, and a unique "crater morphology". In view of the nonrocking chair operation mechanism of AlCl₃-GB, we have tested the achievable energy densities as a function of the composition of chloroaluminate ionic liquid (AlCl₃ content) and have obtained energy densities of up to 65 Wh kg^-1. In addition, the kish graphite flakes can rapidly charge and discharge, offering high power densities of up to 4363 W kg^-1.

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.