Adiponitrile-Lithium Bis(trimethylsulfonyl)imide Solutions as Alkyl Carbonate-free Electrolytes for Li4 Ti5 O12 (LTO)/LiNi1/3 Co1/3 Mn1/3 O2 (NMC) Li-Ion Batteries.

Recently, dinitriles (NC(CH2 )n CN) and especially adiponitrile (ADN, n=4) have attracted attention as safe electrolyte solvents owing to their chemical stability, high boiling points, high flash points, and low vapor pressure. The good solvation properties of ADN toward lithium salts and its high electrochemical stability (≈6 V vs. Li/Li+ ) make it suitable for safer Li-ions cells without performance loss. In this study, ADN is used as a single electrolyte solvent with lithium bis(trimethylsulfonyl)imide (LiTFSI). This electrolyte allows the use of aluminium collectors as almost no corrosion occurs at voltages up to 4.2 V. The physicochemical properties of the ADN-LiTFSI electrolyte, such as salt dissolution, conductivity, and viscosity, were determined. The cycling performances of batteries using Li4 Ti5 O12 (LTO) as the anode and LiNi1/3 Co1/3 Mn1/3 O2 (NMC) as the cathode were determined. The results indicate that LTO/NMC batteries exhibit excellent rate capabilities with a columbic efficiency close to 100 %. As an example, cells were able to reach a capacity of 165 mAh g-1 at 0.1 C and a capacity retention of more than 98 % after 200 cycles at 0.5 C. In addition, electrodes analyses by SEM, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy after cycling confirming minimal surface changes of the electrodes in the studied battery system.

Dynamics of Li4Ti5O12/sulfone-based electrolyte interfaces in lithium-ion batteries.

Binary mixtures of cyclic (TMS) or acyclic sulfones (MIS, EIS and EMS) with EMC or DMC have been used in electrolytes containing LiPF6 (1 M) in both Li4Ti5O12/Li half-cells and Li4+xTi5O12/Li4Ti5O12 symmetric cells and compared with standard EC/EMC or EC/DMC mixtures. In half-cells, sulfone-based electrolytes cannot be satisfactorily cycled owing to the formation of a resistive layer at the lithium interface, which is not stable and generates species (RSO2(-) and RSO3(-)) able to migrate toward the titanate electrode interface. Potentiostatic and galvanostatic tests of Li4Ti5O12/Li half-cells show that charge transfer resistance increases drastically when sulfones are used in the electrolyte composition. Moreover, cyclability and coulombic efficiency are low. Conversely, when symmetric Li4+xTi5O12/Li4Ti5O12 cells are used, it is demonstrated that MIS-(methyl isopropyl sulfone) and TMS-(tetra methyl sulfone) based electrolytes exhibit reasonable electrochemical performances as compared to the EC/DMC or EC/EMC standard mixtures. Surface analysis by XPS of both the Li4+xTi5O12 (partially oxidized) and Li7Ti5O12 (reduced) electrodes taken from symmetric cells reveals that sulfones do not participate in the formation of surface layers. Alkylcarbonates (EMC or DMC), used as co-solvents in sulfone-based binary electrolytes, ensure the formation of surface layers at the titanate interfaces. Therefore, EMC reduction at the two Li4+xTi5O12/electrolyte interfaces in symmetric cells leads to the formation of carbonates, ethers and mineral compounds such as ROCO2Li and Li2CO3. Finally, huge amounts of LiF are detected at the titanate electrode surface, resulting in an increase in the resistivity of symmetric cells and capacity losses.

On the limited performances of sulfone electrolytes towards the LiNi0.4Mn1.6O4 spinel.

Cycling after storage of LiNi0.4Mn1.6O4/Li4Ti5O12 cells evidences lower total capacity losses for EMS-, TMS- and MIS-based electrolytes as compared to EC-based at 20 °C. The shuttle-type mechanism induced by the electrolyte oxidation is mainly present in the accumulators at this temperature, as compared to those due to the Mn(2+) and Ni(2+) dissolution. At 30 and 40 °C, EC is responsible for the polymer film formation on the LiNi0.4Mn1.6O4 surface, which limits the transition metal ion dissolution. This results in lower reversible capacity losses compared to sulfones, but are still important: 45% at 30 °C and 70-75% at 40 °C. XPS spectra reveal that EMS does not contribute to the surface film formation on the LiNi0.4Mn1.6O4 spinel, regardless of the cycling conditions and temperature. Only the EMC decomposition at high potential in sulfone/EMC electrolytes is responsible for an organic layer formation, which is composed of low passivating oligomers that comprise the C-O and C=O functional groups. Sulfones are promising compounds to be used in high voltage Li-ion batteries thanks to their non-reactivity towards the LiNi0.4Mn1.6O4 cathode. However, this does not allow the deposition of surface films that would have enabled stopping the Mn(2+) and Ni(2+) dissolution in the electrolyte. This is responsible for degraded performances of LiNi0.4Mn1.6O4/Li4Ti5O12 cells as compared to EC-based electrolytes over ambient temperatures, especially at 30 °C.

Triethylammonium bis(tetrafluoromethylsulfonyl)amide protic ionic liquid as an electrolyte for electrical double-layer capacitors.

This study describes the preparation, characterization and application of [Et(3)NH][TFSA], either neat or mixed with acetonitrile, as an electrolyte for supercapacitors. Thermal and transport properties were evaluated for the neat [Et(3)NH][TFSA], and the temperature dependence of viscosity and conductivity can be described by the VTF equation. The evolution of conductivity with the addition of acetonitrile rendered it possible to determine the optimal mixture at 25 °C, with a weight fraction of acetonitrile of 0.5. This mixture was also evaluated for transport properties, and showed a Newtonian behavior, as the neat PIL. An electrochemical study demonstrated, at first, a passivation on Al after the second cyclic voltammogram. Subsequently, the electrochemical window was estimated using a three-electrode cell to 4 V on a platinum electrode, and to 2.5 V on activated carbon. Finally, the neat PIL was found to exhibit good performances as promising electrolyte for supercapacitor applications.

Morphology engineering of silicon nanoparticles for better performance in Li-ion battery anodes.

Amorphous silicon nanoparticles were synthesized through pyrolysis of silane gas at temperatures ranging from 575 to 675 °C. According to the used temperature and silane concentration, two distinct types of particles can be obtained: at 625 °C, spherical particles with smooth surface and a low degree of aggregation, but at a higher temperature (650 °C) and lower silane concentration, particles with extremely rough surfaces and high degree of aggregation are found. This demonstrates the importance of the synthesis temperature on the morphology of silicon particles. The two types of silicon nanoparticles were subsequently used as active materials in a lithium half cell configuration, using LiPF6 in an alkylcarbonate-based electrolyte, in order to investigate the impact of the particles morphology on the cycling performances of silicon anode material. The difference in morphology of the particles resulted in different volume expansions, which impacts the solid electrolyte interface (SEI) formation and, as a consequence, the lifetime of the electrode. Half-cells fabricated from spherical particles demonstrated almost 70% capacity retention for over 300 cycles, while the cells made from the rough, aggregated particles showed a sharp decrease in capacity after the 20th cycle. The cycling results underline the importance of Si particle engineering and its influence on the lifetime of Si-based materials.

Ionic association analysis of LiTDI, LiFSI and LiPF6 in EC/DMC for better Li-ion battery performances.

New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF6), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and 7Li self-diffusion coefficient have been deeply investigated. Moreover, as these properties are directly linked to the nature of the interionic interactions and ion solvation, a better understanding of the structural properties of electrolytes can be obtained. The Li salt concentration has been varied over the range of 0.1 mol L-1 to 2 mol L-1 at 25 °C and the working temperature from 20 °C to 80 °C at the fixed concentration of 1 mol L-1. Experimental results were used to investigate the temperature dependence of the salt ion-pair (IP) dissociation coefficient (α D) with the help of the Walden rule and the Nernst-Einstein equation. The lithium cation effective solute radius (r Li) has been determined using the Jones-Dole-Kaminsky equation coupled to the Einstein relation for the viscosity of hard spheres in solution and the Stokes-Einstein equation. From the variations of α D and rLi with the temperature, it is inferred that in EC/DMC LiFSI forms solvent-shared ion-pairs (SIP) and that, LiTDI and LiPF6 are likely to form solvent separated ion-pairs (S2IP) or a mixture of SIP and S2IP. From the temperature dependence of α D, thermodynamic parameters such as the standard Gibbs free energy, enthalpy and entropy for the ion-pair formation are obtained. Besides being in agreement with the information provided by the variations of α D and rLi, it is concluded that the ion-pair formation process is exergonic and endothermic for the three salts in EC/DMC.

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.

Alkylammonium-based protic ionic liquids. II. Ionic transport and heat-transfer properties: fragility and ionicity rule.

The physicochemical characterization of six alkylammonium-based protic ionic liquids (PILs) is presented. These compounds were prepared through a simple and atom-economic neutralization reaction between a tertiary amine and a Brønsted acid, HX, where X- is HCOO-, CH3COO-, HF2-. The temperature dependency and the effect of added water on properties such as density, viscosity, ionic conductivity, and the thermal comportment of these PILs were measured and investigated. The results allowed us to classify them according to a classical Walden diagram and to appreciate their great "fragility". PILs have applicable perspectives in replacements of conventional inorganic acids for fuel cell devices and thermal transfer fluids.

Synthesis and characterization of new pyrrolidinium based protic ionic liquids. Good and superionic liquids.

New pyrrolidinium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reactions between pyrrolidine and Brønsted acids, HX, where X is NO 3 (-), HSO 4 (-), HCOO (-), CH 3COO (-) or CF 3COO (-) and CH 3(CH 2) 6COO (-). The thermal properties, densities, electrochemical windows, temperature dependency of dynamic viscosity and ionic conductivity were measured for these PILs. All protonated pyrrolidinium salts studied here were liquid at room temperature and possess a high ionic conductivity (up to 56 mS cm (-1)) at room temperature. Pyrrolidinium based PILs have a relatively low cost, a low toxicity and exhibit a large electrochemical window as compared to other protic ionic liquids (up 3 V). Obtained results allow us to classify them according to a classical Walden diagram and to determinate their "Fragility". Pyrrolidinium based PILs are good or superionic liquids and shows extremely fragility. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional inorganic acids.

Physicochemical characterization of morpholinium cation based protic ionic liquids used as electrolytes.

New protic ionic liquids (PILs) based on the morpholinium, N-methylmorpholinium, and N-ethyl morpholinium cations have been synthesized through a simple and atom-economic neutralization reaction between N-alkyl morpholine and formic acid. Their densities, refractive indices, thermal properties, and electrochemical windows have been measured. The temperature dependence of their dynamic viscosity and ionic conductivity have also been determined. The results allow us to classify them according to a classical Walden diagram and to evaluate their "fragility". In addition, morpholinium based PILs exhibit a large electrochemical window as compared to other protic ionic liquids (up 2.91 V) and possess relatively high ionic conductivities of 10-16.8 mS x cm(-1) at 25 degrees C and 21-29 mS x cm(-1) at 100 degrees C, and a residual conductivity close to 1.0 mS x cm(-1) at -15 degrees C. PIL-water mixtures exhibit high ionic conductivities up to 65 mS x cm(-1) at 25 degrees C and 120 mS x cm(-1) at 100 degrees C for morpholinium formate with water weight fraction w(w) = 0.6. Morpholinium based PILs studied in this work have a low cost and low toxicity, are good ionic liquids, and prove extremely fragile. They have wide applicable perspectives as electrolytes for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional solvents.

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.

X-ray powder diffraction structure determination of gamma-butyrolactone at 180 K: phase-problem solution from the lattice energy minimization with two independent molecules.

The crystal structure of the solid phase of the dipolar aprotic solvent gamma-butyrolactone (BL1), C(4)H(6)O(2), has been solved using the atom-atom potential method and Rietveld-refined against powder diffraction data collected at T = 180 K with a curved position-sensitive detector (INEL CPS120) using Debye-Scherrer diffraction geometry with monochromatic X-rays. It was first deduced from the X-ray experiment that the lattice parameters are a = 10.1282 (4), b = 10.2303 (5), c = 8.3133 (4) A, beta = 93.291 (2) degrees and that the space group is P2(1)/a, with Z = 8 and two independent molecules in the asymmetric unit. The structure was then solved by global energy minimization of the crystal-lattice atom-atom potentials. The subsequent GSAS-based Rietveld refinement converged to the final crystal-structure model indicator R(F(2)) = 0.0684, profile factors R(p) = 0.0517 and R(wp) = 0.0694, and a reduced chi(2) = 1.671. After further cycles of heating and cooling, a powder diffraction pattern markedly different from the first pattern was obtained, again at T = 180 K, which we tentatively assign to a second polymorph (BL2). All the observed diffraction peaks are well indexed by a triclinic unit cell essentially featuring a doubling of the a axis. An excellent Le Bail fit is obtained, for which R(p) = 0.0312 and R(wp) = 0.0511.

Ion-dipole interactions in concentrated organic electrolytes.

An algorithm is proposed for calculating the energy of ion-dipole interactions in concentrated organic electrolytes. The ion-dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion-dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion-ion interactions. The ion-dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton-Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of epsilon = 3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of gamma-butyrolactone (BL) as solvent and lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts.