270 research outputs found
3D-Catenated [EMImCl/(TiCl4)1.4]/(δ-MgCl2)x Ionic Liquid Electrolyte for Mg Secondary Batteries
No full textThe rapid advance in the fields of portable electronics, load leveling and peak shaving for the power grid and zero-emission automotive applications require the development of new and improved electrical energy storage systems [1,2]. Since the 90’s major improvements have been achieved in magnesium battery technology [3-6]. In comparison to Li, Mg offers the following advantages: (i) a higher volumetric capacity (3832 vs. 2062 mAh•cm-3); (ii) far greater abundance in the Earth’s crust, lowering the costs; (iii) a safer operation and a better compatibility with the environment; and (iv) an acceptable standard reduction potential (-2.36 vs. -3.04 V) [7-9]. The main roadblock for these devices is the development of an efficient and stable electrolyte that is able to reversibly deposit and strip magnesium. Although Grignard and other organo-magnesium compounds exhibit good electrochemical performances [9], they do not exhibit an optimal stability due to their high vapor pressure and flammability. Ionic liquids dissolving a Mg salt with a high crystalline disorder were proposed as promising alternative electrolytes to organo-Mg systems owing to their good electrochemical performance and lack of flammability and thermal stability issues [10].
In the present work a new family of electrolytes is proposed, based on 1-ethyl-3-methylimidazolium chloride (EMImCl), titanium(IV) chloride (TiCl4) and increasing amounts of δ-MgCl2. Specifically, four EMImCl/(TiCl4)1.4/(δ-MgCl2)x electrolytes, with 0.00 ≤ x ≤ 0.23 are prepared and extensively characterized. The chemical composition was determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The thermal stability was gauged using High-Resolution Thermo Gravimetric Analysis (HR-TGA) and the phase transitions are highlighted with Modulated Differential Scanning Calorimetry (MDSC). Chemical interactions were studied through Fourier-Transform spectroscopy in the medium and far infrared (FT-MIR and FT-FIR) regions and confocal micro-Raman spectroscopy. The electrochemical performance was studied with: (i) Cyclic Voltammetry (CV), to probe Mg deposition and stripping (Fig. 1); (ii) Linear Sweep Voltammetry (LSV), to evaluate the electrochemical stability window; (iii) Chronopotentiometry (CP) experiments coupled with ICP-AES, to confirm and quantify the Mg deposition; and (iv) Broadband Electrical Spectroscopy (BES), to elucidate the long-range charge migration mechanisms of the electrolytes. High level density functional theory (DFT) based electronic structure calculations were undertaken to elucidate structures and vibrational frequency assignments.
References
1 M. Armand and J. M. Tarascon Nature 451, 652-657, (2008).
2 B. Dunn, H. Kamath and J. M. Tarascon Science 334, 928-935, (2011).
3 V. Di Noto and M. Fauri, Batterie Primarie (Non Ricaricabili) e Secondarie (Ricaricabili) a Base di Elettroliti Polimerici Basati su Ioni Magnesio, PD99A000179, (1999).
4 V. Di Noto and M. Fauri, Magnesium-based Primary (Non Rechargeable) and Secondary (Rechargeable) Batteries, PCT/EP00/07221, (2000).
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7 D. Aurbach, G. S. Suresh, E. Levi, A. Mitelman, O. Mizrahi, O. Chusid and M. Brunelli Adv. Mater. 19, 4260-4267, (2007).
8 T. D. Gregory, R. J. Hoffman and R. C. Winterton J. Electrochem. Soc. 137, 775-780, (1990).
9 J. Muldoon, C. B. Bucur, A. G. Oliver, T. Sugimoto, M. Matsui, H. S. Kim, G. D. Allred, J. Zajicek and Y. Kotani Energy and Environmental Science 5, 5941-5950, (2012).
10 F. Bertasi, C. Hettige, F. Sepehr, X. Bogle, G. Pagot, K. Vezzù, E. Negro, S. J. Paddison, S. G. Greenbaum and M. Vittadello ChemSusChem 8, 3069-3076, (2015)
The Structure of Water-Methanol Mixtures Under an Electric Field: Ab Initio Molecular Dynamics Simulations
No full textLiquid methanol and water are examples of hydrogen-bonded systems which exhibit abnormal high proton conductivity. Their mixture is of fundamental interest due to the rich and complex structure and topology of the hydrogen-bonded network in the solution. Previous studies suggest that the water-methanol mixtures exist in form of ice-like water cages surrounding the hydrophobic groups of the methanol molecules. Recent experimental and theoretical studies proposed a new picture that, at low methanol concentrations, the mixture is consist of two separate percolating hydrogen-bonded networks.
Ab-Initio Molecular Dynamics (AIMD) simulations were performed using the VASP code to understand the local hydrophobic structures in water-methanol mixtures, especially under the influence of electric field. Simulations of the water-methanol mixtures were performed at five concentrations: pure water, X = 0.25 (20 HO and 7 CHOH molecules), X = 0.50 (13 H O and 14 CH OH), X = 0.75 (7 HO and 20 CHOH), and pure methanol in a supercell of length 12.22 Å. The finite electric field applied is between 0.25 and 0.75 V/Å.
The structure of pure methanol after applying electric field (E = 0.25 V/Å) along c-axis at 300 K is shown in Fig. 1 (a). It appears that most of the hydrogen-bonded network adopts motif structures, which is the predominant feature as predicted in the previous works. In the case of pure water (Fig. 1(b)), we see a different scenario. Under low electric field (E = 0.25 V/Å), the water molecules have evolved into separated cluster layers with hydrogen bond pointing outwards the empty space. With the electric field increased to E = 0.75 V/Å, a small amount of water molecules at the edges of two nearby cluster layers reach out to form a connecting cluster between the two layers. Also, there is no evidence of auto dissociation of the water molecules when subject to the electric fields being applied in this study.
Among the mixture structures, the mixture systems with concentration between X = 0.25 and X = 0.50 are of particular interest. The methanol and water are reported to form separate percolating hydrogen-bonded networks in the X range of [0.25, 0.50].5 Instead, our results of X = 0.25 mixture system shows that, before applying electric field, the structure of water in the mixture are still close to that of pure liquid water. There is evidence of the formation of water clusters, and the methanol molecules are randomly distributed in the water clusters. However, when a weak electric field (E = 0.25 V/Å) is applied, the methyl groups are aligned and form hollow channels inside the water clusters. (Fig. 1(c)) This local hydrophobic structure provides driving force for fast proton transport via structural or Grotthuss-type diffusion in the water-methanol mixtures.
In the X = 0.50 mixture, the resulted structures before and after applying the electric field show similar features of random mixing between the methanol and water molecules. (Fig. 1(d)) There is no evidence of separate hydrogen-bonded water and methanol networks.
In summary, from a molecular level, our AIMD simulations illustrate interesting features of a local hydrophobic structure in water-methanol mixtures when under an electric field. With the absence of ice-like water structure, the water molecules tend to present in the form of pure liquid water and form clusters. With a low electric field, the hydrophobic groups of the methanol molecules align themselves and form channels inside the water clusters. The abnormal high proton conductivity can be explained by this type of local structure based on a structural or Grotthuss-type diffusion mechanism
Haloaluminate Ionic Liquid Based Electrolytes for Secondary Magnesium Batteries: Ab-Initio and Experimental Vibrational Analysis.
No full textAb Initio Study and Vibrational Spectroscopy of Imidazolium Based Ionic Liquids with Dissolved δ-MgCl2
No full textIonic liquids (ILs) are liquid salts at room temperature having unusual properties as liquids. The most important properties of these electrolyte solutions are non-volatility and high ion conductivity which makes them a safe and advance choice for electrolyte solutions in energy devices. In general, ILs as the name implies, are comprised entirely of ions, usually organic cations and bulky anions. ILs are stable enough for ordinary use at temperatures of 200 to 300 ̊C. However, due to having organic cations their degradation begins at the weakest covalent bond. The chemical structure of ions can be tailored easily for the intended application. The structure and properties of these Coulomb systems are mainly determined by the type and strength of the intermolecular interactions between anions and cations. In particular, the subtle balance between Coulomb forces, hydrogen bonds (HBs) and dispersion forces is of great importance for understanding ILs.
Having these superior properties, ILs can be used as a good carrier for ion transport in batteries. Recently, imidazolium based ILs with δ-MgCl ions have been under investigations as new electrolytes for Mg-based batteries. These batteries show advantages over other competing types owing to the abundant source of Mg in the earth’s crust, better disposal and waste management. In addition, they have wide operation temperature range and their capacity loss over time is little.
The aim of this work is to use the results of first principles electronic structure calculations to study the structure of the new imidazolium based ILs with dissolved δ-MgCl . Although, there have been many studies on the imidazolium based ILs, but there is still a debate on whether the hydrogen bonding is responsible for the red shifted C–H stretching frequencies and downfield shifted C–H proton chemical shifts or not. Therefore, further studies on the structure and interactions of imidazolium based ILs especially in presence of δ-(MgCl ) are essential and helpful in optimal design of this new genre of electrolytes.
Differential scanning calorimetry on electrolytes composed of different amount of δ-MgCl dissolved in a homogeneous mixture of aluminum tri-chloride and 1-ethyl-3-methylimidazolium chloride (EMImCl) ionic liquid has been done. The results show that by varying δ-MgCl concentration at least two types of Mg complex depending on δ-MgCl concentration are formed. The IR spectrums show new peaks in the far infrared region by increasing the concentration of δ-MgCl indicating the formation of new bimetallic complexes. Also, Experimental IR investigations on EMImBF /[δ-(MgCl ) ] indicate that by increasing f which is the concentration of δ-(MgCl ), the Clˉ interaction band at 3050 cm , typical of the hydrogen bonding network in EMImCl appears in the difference spectra. The comparison between the profiles of pristine IL and EMImBF /[δ-(MgCl ) ] show that Mg forms different complexes with BF ˉ anion. However, these new complexes are not known.
Electronic structure calculations were undertaken on the ethyl-methyl imidazolium cation in proximity to a number of different anions (Clˉ, AlCl ˉ, BF ˉ) using Hatree-Fock (HF), post HF, DFT, and Hybrid methods with different basis sets. The calculations were performed using Gaussian 09 suite of program.
Geometry optimizations were followed by frequency calculations to confirm the presence of each local minimum. Different initial structures have been searched for each system to determine the global minimum. Then the calculated IR spectrums are compared to the experimental spectrums and the least expensive method which is capable of describing the experimental spectrum is chosen for further calculations. Next calculations are performed on larger clusters of cations and anions which contains MgCl . The IR spectrums are compared to experimental spectrums and the assignments of vibrational modes are done by visualizing the vibrational frequencies of the calculated structures
Interplay Between Vibrational Modes and Relaxations in Electrolytes for Secondary Magnesium Batteries Based on Haloaluminate Ionic Liquids
No full texthe search for electrolytes with enhanced performance is a crucial point for the development of efficient secondary Mg batteries. Early work on Mg deposition and stripping from Grignard-based non-aqueous solution were proposed in 1990 by Gregory et al., while the first example of polymer electrolytes comprising PEG400 and δ-MgCl2 was proposed in 1998. In the following years, electrolytes based on EthylMgBr and PEO, Grignard, and other organo-Mg7compounds were explored.
Among all proposed materials, Grignard and organo-Mg compounds, suffer from several drawbacks associated with their chemical stability in ethereal-based solvents, which are characterized by a high vapor pressure and flammability. On the contrary, Ionic Liquids (ILs) seem a very appealing class of materials for applications in Mg secondary batteries due to their: a) very low volatility, high thermal stability and non-flammability; b) high ion density and high conductivity; c) wide electrochemical stability window; and d) easiness of synthesis by evaluating the best cation and the anion for each application.
There are still several aspects that are not fully understood regarding the use of ILs in electrochemical devices. Indeed, the conductivity mechanisms, the formation of the solid-electrolyte interface (SEI) and long-term performance of these systems are still open questions. Nevertheless, from a fundamental point of view, understanding the interplay between the ILs relaxations and the charge carrier migration is crucial in order to clarify the effect of the ILs matrix on the conductivity mechanism of Mg2+ions.
Here we present a family of electrolytes based on 1-ethyl-3-methylimidazolium iodide, aluminium iodide, and δ-MgI28 with general formula [EMImI/(AlI3)m]/(δ-MgI2)n. The short-range structural features and the interactions in the electrolytes are elucidated by coupling Raman and Infrared (both in the medium and in the far infrared) spectroscopy with DFT calculations.
The detailed electrical response of the [EMImI/(AlI3)m]/(δ-MgI2)n materials in terms of polarization and relaxation events at temperatures higher and lower than the melting of EMImI/(AlI3)m are investigated by using Broadband Electrical Spectroscopy (BES). The results allow us to correlate the dielectric relaxation of the imidazolium cations with the overall long-range charge migrations, thus elucidating the interplay existing between conductivity and nanostructure of this new class of IL
Magnesium Batteries: Toward a Magnesium-Iodine Battery
No full textCover: On page 4860, V. Di Noto and co-workers show the first iodoaluminate ionic liquid for the development of future Mg/I2 secondary batteries. Reversible magnesium deposition/stripping with low overvoltage and high (99.94%) coulombic efficiency is achieved and a detailed investigation of the Mg interaction scenario is reported
Toward a Magnesium-Iodine Battery
No full textThe quest for new electrolyte and cathode materials is a crucial point for beyond-lithium-ion energy storage systems. Following this, an electrolyte for secondary magnesium batteries based on a new iodoaluminate ionic liquid and δ-MgI 2 is reported. Promising electrochemical performance in terms of Mg plating-stripping, coulombic efficiency, and conductivity, demonstrates the potential of this iodine-based system for future Mg secondary batteries
The influence of the cationic form and degree of hydration on the structure of NafionTM
No full textFT-IR ATR spectroscopy has been undertaken to elucidate how the structure of NafionTM membranes is affected by the cationic form (i.e., H+, D+, and Na+) and water content. Three distinct hydration levels were considered: (a) completely dry (λ ≡ Η2Ο/ - SO3 - ≅ 0); (b) minimal hydration (λ ≅ 2); and (c) fully hydrated (λ ≅ 22). The measured spectra reveal that the associated cation and degree of hydration have a significant effect on the vibrational modes of the perfluoroether side chains of the ionomer. Two peaks ascribed to the {single bond}SO3X terminal groups and the features attributed to the COC linkages were clearly identified. The latter were studied in detail, and are shown to be diagnostic of the conformation of the side chains. A comprehensive framework of interpretation of the experimental results is proposed, with emphasis on: (a) the role played by the interactions between the {single bond}SO3X terminal groups of the different side chains; and (b) how the latter interactions are affected by the amount of H2O or D2O in the samples. In particular, reference is made to the formation and spatial distribution of the positively-charged species characterized by significantly different structural features
Neighbourhood effects and social mobility: a longitudinal analysis
No full textWhat impact do neighbourhoods have on social mobility? For years, thisquestion has received widespread international attention in scholarly debates and withinsociety at large. This paper seeks to contribute to this discussion by presenting theresults of an investigation into the relationship between household social mobility andthe composition of the residential environment. The analyses are based on an extensiveempirical longitudinal study conducted in the Netherlands. The most remarkableconclusion is that, in the Dutch context, the environment has only a modest influenceon the social mobility of households with a weak economic position. It was found thatthe chance of a household living purely on welfare benefits at the beginning of the studyperiod to escape the ‘welfare trap’ was barely dependent on the number of similarlychallenged households in the immediate vicinity. Interestingly, the environment provedto have a more powerful effect on the social mobility of households with a strongereconomic position. The probability that households with at least one paid job at thebeginning of the research would still have a job at the end clearly decreases as the shareof benefit-dependent households in the neighbourhood rises. A possible explanation forthis is that for the first category (weak starting position) the negative effect of their ownwelfare situation is far more determinative for their future prospects than the compositionof their environment. Because these negative individualistic conditions are absentfor the second category (stronger starting position), environmental factors may play arelatively larger role. Another interpretation is that area-based policies are not justtargeting the areas with bigger problems more intensively, but especially the long-termunemployed in these areas, and not so much the short-term unemployed (those who hada job at the start of the research period and lost the job afterwards)
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