Lithium-ion batteries (LIB) are undoubtedly the most popular and mature electrochemical storage devices and, for future use, a higher degree of safety, a longer cycle life, and a higher specific energy are desirable. In order to achieve this goal, numerous publications have been devoted to new active materials and new electrolytes [1] but far less to interfaces. As a matter of fact the solid-electrolyte interphase (SEI) formed through the reductive decomposition of solvent molecules plays a crucial role in the performances of LIB. The robustness and efficiency of the SEI [2] therefore significantly affect the power capability, stability, safety and cycle life of a LIB. In this study, we investigate the impact of several lithium salts, already present in the SEI like LiF, Li 2 O, LiOH, Li 2 CO 3 , LiOCH 3 and LiOC 2 H 5 , on the cycling ability of a graphite or LiNiMnCoO 2 electrodes [3] in Li half cells containing the standard (EC/PC/3DMC + 1 M LiPF 6 ) electrolyte. These lithium salts are soluble (LiF), slightly soluble (LiOCH 3 and LiOC 2 H 5 ) or almost insoluble (Li 2 O, LiOH, Li 2 CO 3 ) but present in solution as a colloidal suspension at saturation. Results show that these lithium salts, dissolved or in suspension in the electrolyte have a non-negligible impact on the electrode capacity during cycling, depending on the type of electrode and nature of the salt. Mineral salts like LiOH, Li 2 O and LiF (at high concentration) degrade battery performances by forming a resistive film at the electrode surface. On the contrary, LiOCH 3 and Li 2 CO 3 are beneficial to cycling performances owing to the formation of a Li conductive coating. In order to avoid the negative impact of dissolved LiF, glymes like diglyme (G2), triglyme (G3) and tetraglyme (G4) have been added as these compounds are known to complex strongly Li + ions. A complementary approach has been the use of fluorinated surfactant additives able to modify the interfacial material/electrolyte free energy. Electrochemical characterization by galvanostatic cycling and cyclic voltammetry, combined with XPS and SEM surface characterization have been performed to evaluate the impact of each additive and to clarify its mechanism of action. Results show that the addition of glymes limits the negative effect of SEI lithium salts, while the surfactant improves the wettability of the electrodes leading to better cycling performances. [1] J.B. Goodenough, Y. Kim, Chemistry of Materials, 22 (2010) 587-603. [2] P. Verma, P. Maire, P. Novák, Electrochimica Acta, 55 (2010) 6332-6341. [3] Fabien Chrétien, Jennifer Jones, Christine Damas, Daniel Lemordant, Patrick Willmann, M. Anouti, Journal of Power Sources, 248 (2014) 969-977.

The Solid Electrolyte Interphase (SEI), formed during the first cycles of life in lithium-ion batteries, contains a variety of lithium salts, with direct effect on the aging performance of the battery. In this work, we investigate the impact of addition of SEI lithium salts (LiF, Li2CO3, LiOH, Li2O, LiOCH3 and LiOC2H5) in the electrolyte on the cycling ability of graphite and LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes. Results show that NMC is more sensitive to salt addition than graphite material. Furthermore, results demonstrate that both LiOH and Li2O have a negative effect on the SEI formation. Conversely, Li2CO3, LiOCH3 and LiOC2H5 are beneficial and promote the formation of a polymeric coating on the SEI. Finally, the impact of the presence of LiF on the SEI depends mainly on its concentration. The effect of the presence of additives capable of complexing lithium salts such as the glyme series, CH3O[CH2CH2O]nCH3 (Gn, with n = 2, 3 or 4), is investigated by cyclic voltammetry, galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). Results show that the glymes chain length is a determining factor in their complexation mechanism, which depends on both the nature and the concentration of the lithium salt.

Li-ion batteries are undoubtedly the most popular and mature electrochemical storage devices. Numerous studies deal with the development of new materials and electrolytes for such systems [1-3]. However, there are several factors that limit the development of this technology, and one of the key questions is the limitation the life time. Efficient cycling of lithium-ion batteries is associated with the formation of a passivation layer at the electrodes surface, referred to as the SEI (Solid Electrolyte Interphase) [4]. The quality of this film is decisive for battery performance: it must prevent solvent intercalation in the electrode, limit electrolyte degradation upon cycling, but still allow an optimal transport of Li ions between the electrode and the electrolyte.

The SEI (Solid Electrolyte Interphase) at the surface of electrodes in lithium-ion batteries is composed of various lithium compounds, organic or mineral, which have a direct impact on cycling performance. The main lithium species constituting the SEI and selected in this study are lithium fluoride LiF, lithium carbonate Li2CO3, lithium hydroxide LiOH, lithium oxide Li2O, lithium methoxide LiOCH3 and lithium ethoxide LiOC2H5. Their solubilities were determined in ethylene, propylene, dimethyl, diethyl and vinylene carbonates (EC, PC, DMC, DEC and VC) and in one of their mixtures commonly used in lithium-ion batteries (EC/PC/3DMC) by mean of atomic absorption spectroscopy (AAS). These solutions were also investigated by EIS (Electrochemical Impedance Spectroscopy) and conductimetry measurements. Results show that while solubilization properties differ between LiF and other lithium compounds considered, their association pattern in solution is identical and solutions are mainly constituted of quadrupolar aggregates. (C) 2011 Elsevier B.V. All rights reserved.

The solubility of lithium fluoride in ethylene carbonate (EC), propylene carbonate (PC) and water is studied by conductimetry and by electrochemical impedance spectroscopy to explain the nature of species in solution in these solvents. The observed molar conductivity Λ values of LiF in alkylcarbonates are explained by the presence of free ions Li+ and F−, ion pairs LiF and higher ionic aggregates, “symmetrical” triple ions (Li2F+ and LiF2−), and quadrupoles (Li2F2). The experimental Λ values could be fitted taking into account higher ion aggregations. Results indicate that for PC and EC, the formation of quadrupoles predominates with increasing salt concentration, whereas for aqueous solutions free ion formation predominates at low concentration, then dipole formation becomes favourable. In all solvents studied, triple ions formation is negligible. The tendency of LiF to form quadrupoles is essentially due to particular properties of the F− ion, which is a critical member of the halides. Results of this study indicate that LiF is structured in symmetrical aggregates whose dipole moment is null and with Li2F2 as a basic unit.

The solubility of lithium fluoride has so far never been studied in alkylcarbonate solvents. These data is essential to understand the behavior of this salt in solution, in particular in the field of lithium-ion batteries. The solubility of lithium fluoride (LiF) was measured at various temperatures in propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC) by atomic absorption spectroscopy. The LiF free enthalpy, enthalpy and entropy of dissolution in these solvents were deduced from the results. The solubility of LiF differs significantly with the nature of the solvent, EC being by far the most solubilizing media. The high solubilizing power of EC towards LiF cannot be explain by any of the physico-chemical properties of the solvent, but by an entropy-driven phenomenon. The solubilities of LiF in water–alkylcarbonates mixtures were determined by conductimetry at several temperatures leading to the corresponding LiF thermodynamic properties in these media. Results are discussed and compared to those obtained by atomic absorption measurements. Finally, a scheme representing the different stages for the dissolution of LiF in alkylcarbonates is proposed.

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][CnH2n+1COO]) and imidazolium alkylcarboxylates ([Im][CnH2n+1COO]), 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. (C) 2009 Elsevier Inc. All rights reserved.

Lithium-ion batteries for space applications, such as satellites, are subjected to cosmic radiations, in particular, γ-irradiation. In this study, the effects of this radiation on electrolytes and their components used in the lithium-ion batteries are investigated. The conductivity and viscosity of the samples have been measured before and after the irradiation. The modifications are evaluated by spectral analyses such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H and 13C NMR), solid phase microextraction-gas chromatography (SPME-GC) and gas chromatography–mass spectroscopy (GC–MS). The experimental results show that only the samples containing vinylene carbonate and/or the lithium salt LiPF6 are degraded by γ-radiation.