Magaly Caillon-Caravanier

Aggregation behavior in water of new imidazolium and pyrrolidinium alkycarboxylates protic ionic liquids.

A novel class of anionic surfactants was prepared through the neutralization of pyrrolidine or imidazole by alkylcarboxylic acids. The compounds, namely the pyrrolidinium alkylcarboxylates ([Pyrr][C(n)H(2n+1)COO]) and imidazolium alkylcarboxylates ([Im][C(n)H(2n+1)COO]), were obtained as ionic liquids at room temperature. Their aggregation behavior has been examined as a function of the alkyl chain length (from n=5 to 8) by surface tensiometry and conductivity. Decreases in the critical micelle concentration (cmc) were obtained, for both studied PIL families, when increasing the anionic alkyl chain length (n). Surprisingly, a large effect of the alkyl chain length was observed on the minimum surface area per surfactant molecule (A(min)) and, hence the maximum surface excess concentration (Gamma(max)) when the counterion was the pyrrolidinium cation. This unusual comportment has been interpreted in term of a balance between van der Waals and coulombic interactions. Conductimetric measurements permit determination of the degree of ionization of the micelle (a) and the molar conductivity (Lambda(M)) of these surfactants as a function of n. The molar conductivities at infinite dilution in water (Lambda(infinity)) of the [Pyrr]+ and [Im]+ cations have been then determined by using the classical Kohlraush equation. Observed change in the physicochemical, surface, and micellar properties of these new protonic ionic liquid surfactants can be linked to the nature of the cation. By comparison with classical anionic surfactants having inorganic counterions, pyrrolidinium alkylcarboxylates and imidazolium alkylcarboxylates exhibit a higher ability to aggregate in aqueous solution, demonstrating their potential applicability as surfactant.

Alkylammonium-Based Protic Ionic Liquids Part I: Preparation and Physicochemical Characterization

Novel alkylammonium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reaction between an amine, such as diisopropylmethylamine, and diisopropylethylamine, and a Brønsted acid, HX, where X is HCOO-, CH 3COO-, or HF2-. The density, viscosity, acidic scale, electrochemical window, temperature dependency of ionic conductivity, and thermal properties of these PILs were measured and investigated in detail. Results show that protonated alkylammonium such as N-ethyldiisopropyl formate and N-methyldiisopropyl formate are liquid at room temperature and possess very low viscosities, that is, 18 and 24 cP, respectively, at 25 degrees C. An investigation of their thermal properties shows that they present a wide liquid range up to -100 degrees C and a heat thermal stability up to 350 degrees C. Alkylammonium-based PILs have a relatively low cost and low toxicity and show a high ionic conductivity (up a 8 mS cm(-1)) at room temperature. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media and catalysts as replacements of conventional inorganic acids.

Absorption ability and kinetics of a liquid electrolyte in PVDF–HFP copolymer containing or not SiO2

Abstract Gel polymer electrolytes have been prepared from PVDF–HFP copolymer with various silica contents incorporating Gamma valerolactone (VL) or VL/EC (80/20 in mole) (EC: ethylene carbonate) solutions of lithium bis(trifluoromethane sulfone) imide (LiTFSI). The influence of temperature, salt content and silica addition on the kinetics of absorption and wettability of the copolymer has been investigated. An empirical model, taking into account gel swelling during the absorption allows us to relate, at constant temperature, the wetting time and the volumetric fraction of trapped electrolyte, which is a critical factor for ionic conductivity of the gel. Increasing the silica content in the dry copolymer increases the porosity and consequently the rate of absorption and thus the amount of incorporated liquid phase at saturation. To a lower extent, an increase in the temperature of absorption has the same effects. The prepared gels have good mechanicals properties and conductivities. As an example, a gel of composition: PVDF – HFP / SiO 2 / VL / EC / LiTFSI of molar percentages 36/6.7/42/10.5/4.8 exhibits a conductivity of 2.9 mS cm − 1 at 293 K.

Conductive properties of polymer diacrylates incorporating solutions of lithium salts: Part I. Solvent–polymer and salt–solvent interactions

Abstract Gels were prepared by 1,3-butanediol diacrylate (BDD) or tetraethylene glycol diacrylate (TEG) polymerisation (UV irradiation with about 1 wt.% of benzoin methyl ether as initiator) in the presence of gamma butyrolactone (BL) or BL/LiN(CF 3 SO 2 ) 2 (LiTFSI) solutions which were incorporated in the polymer network. For the diacrylate/BL gels, the determination of molar polarisabilities and the Raman spectroscopic study allow to show that there is no specific interaction between the solvent and the polymer. The evolution of the ionic conductivity with the gel composition is related to the volumetric fraction of the liquid phase in the gel. The maximum absorption capacity of the diacrylate network towards the liquid phase is determined assuming a “cubic-like” structure. In order to compare, in the second part of this paper, the conductivities of the “free” and incorporated liquid phases, a simplified conductivity model is presented for the liquid electrolytes. In this article, the conductivity study is focused on the BDD/BL/LiTFSI electrolytes.

Conductivity study of diacrylate-based gels. Part III. Influence of the nature of the constituents and improvement of a theoretical model of ionic transport

Abstract Several gel electrolytes were prepared by incorporation of a liquid electrolyte in a polymer diacrylate network. The liquid electrolytes were solutions of lithium trifluoromethane sulfonate (LiTF) or lithium bis(trifluoromethane sulfone) imide (LiTFSI) in gamma butyrolactone (BL), gamma valerolactone (VL) and an optimized mixture of ethylene carbonate (EC) and 2-methoxyethyl ether (DG: diglyme) of molar percentage: EC/DG (45:55). The monomer diacrylates were: 1,3-butanediol diacrylate (BDD), 1,3-butanediol dimethacrylate (BDDM), ethylene glycol dimethacrylate (EGDM) and tetraethylene glycol diacrylate (TEG). The variation of conductivity with the polymer, solvent and lithium salt contents and with temperature was studied. The volumetric weight of these gels were also determined at room temperature. The experimental results were related to the competitive salt solvent and salt polymer interactions, quantified through a theoretical model of ionic conductivity. The ionic transport in the gel electrolytes was assumed to be of the liquid type. The decrease in ionic conductivity of the liquid electrolyte, enclosed in the polymer network, relative to the “free” liquid solution, is due to the fixation of some fraction of the salt on the polymer, to increase of the viscosity of the media and to a tortuous path for the ion migration. From the proposed model, the conductivity variations with the gel composition as well as with the nature of the constituents are explained.

Intermolecular Interactions in Lactone-Based Electrolytes

The viscosities (η), conductivities (σ), and enthalpies of dissolution (ΔH 0 sln ) of LiCF 3 SO 3 (LiTF) and LiN(CF 3 SO 2 ) 2 (LiTFSI) are measured in γ-butyrolactone (BL), γ-valerolactone (VL), and mixtures of ethylene carbonate (EC) with tetrahydrofuran (THF) and diglyme (DG): EC:THF (20:80, in moles) and EC: DG (45:55, in moles). From the variations of η with the salt concentration, the B and D coefficients in the extended Jones-Dole equation are determined at different temperatures. The concentration dependence of the conductivity is analyzed on the basis of a a model involving (i) a chemical equilibrium between free ions and ion pails (ii) the use of the Walden product to correct molar conductivities for viscosity variations, and (iii) the calculation of ion activity coefficients by the cube root law derived from the quasi-lattice model. According to this model, the limiting molar conductivities (Λ c ) and ion pair dissociation constants (K D ) are inferred. The solvation enthalpies of the salts arc deduced from the heat of dissolution of LiTF and LiTFSI in BL, VL, and the EC:DG mixture. The formation of solvent-separated ion pairs in lactones and contact ion pairs in the EC mixture is deduced from the analysis of the experimental data as the result of a competition between ion-ion and ion-solvent interactions. The dissociation coefficient of ion pairs determined by Raman spectroscopy agrees well with those deduced from conductivity measurements. From the variation of the area of the band at 676 cm -1 with salt concentration, a coordination number of 4 molecules is found for the solvation of the Li + ion by BL molecules.

LiNi0.4Mn1.6O4 / Electrolyte and Carbon Black / Electrolyte High Voltage Interfaces: To Evidence the Chemical and Electronic Contributions of the Solvent on the Cathode- Electrolyte Interface Formation

Solvent and lithium salt decomposition products on LiNixMnyO4-type electrodes are known to be ROM, ROCO2M (M= Li, Ni, Mn), LiF, LixPFyOz, polycarbonates and polyethers. These compounds are chemically formed due to the high nucleophilic character of spinel oxide and LiPF6 decomposition. The high potentials (> 4.7 V vs. Li/Li+) may cause EC and PC polymerization, while DMC forms oligomers. The use of carbon black-based electrodes highlights electronic and, surprisingly, chemical contributions to the cathode-electrolyte interface. A comparison between EC/DMC (1:1 in weight) 1 M LiPF6 and PC/DMC (1:1 in weight) 1 M LiPF6 electrolytes for Li/carbon black-PVdF cells demonstrated a superior ability of the EC/DMC solution to form a well-covering passivation film via faradaic reactions thanks to a higher stability toward oxidation. Electrochemical cycling in Li/LiNi0.4Mn1.6O4 cells confirms this EC/DMC superiority when it comes to forming passivation films, in turn leading to reduced capacity losses and a higher Columbic efficiency.

Conductive properties of polymer diacrylates incorporating solutions of lithium salts: Part II. Model of ionic transport in the gel in relation with the polymer network structure

Abstract Gamma butyrolactone (BL) or BL/LiN(CF 3 SO 2 ) 2 (LiTFSI) solutions were incorporated in the polymer network of 1,3-butanediol diacrylate (BDD) or tetraethylene glycol diacrylate (TEG) polymerized under UV irradiation with about 1 wt.% of benzoin methyl ether as initiator. The evolution of the ionic conductivity, determined by ac impedance technique, with both gel composition and temperature, is related to the ions–solvent and ions–polymer interactions, assuming a cubic lattice structure for the polymer network. The decrease in conductivity from the “free” liquid phase to the incorporated liquid phase is due to both a dynamic equilibrium of solvation of ions between the solvent and the polymer, and, for the “free” ions, a drastic decrease in their mobility because of long-range interactions with the polymer. These interactions are quantified in terms of a “fixation equilibrium constant” and a “microscopic viscosity” relative to ion mobility in the gel. In addition, the moving of ions is not straight in the gel and a tortuosity coefficient in relation with the gel composition is defined.