Laure Timperman

Role of propane sultone as an additive to improve the performance of a lithium-rich cathode material at a high potential

This study presents the use of 1,3-propane sultone (PS) in the [EC–DMC + 1 mol L−1 LiPF6] electrolyte as a protective additive for the Li-rich-NMC xLi2MnO3–(1 − x)LiMO2 (x ≫ 1; M = Ni, Co, Mn) cathode–electrolyte interface during cathode material activation and cycling at a high potential (5 V vs. Li). The results showed that the presence of 1% PS (w/w) ensured complete and better electrode activation during the first cycle than EC–DMC + 1 mol L−1 LiPF6. Thus, Li//Li-rich-NMC half-cell and Gr//Li-rich-NMC full-cell provided capacities as high as C = 330 mA h g−1 during charge and C = 275 mA h g−1 during discharge with a higher cut-off voltage of 5 V. Measurements by cyclic voltammetry demonstrated that activating at such a voltage enhanced the redox activity from Li2MnO3 activation. At same time, the contribution of nickel and cobalt electroactivity is decreased at their regular voltage. This feature was attributed to structural modifications occurring on the surface to the bulk of the material. Long-cycling tests of Li//Li-rich-NMC half-cells with PS provided a higher reversible capacity and superior capacity retention (245 mA h g−1 after 240 cycles) with good coulombic efficiency (99 ± 1%) and better high-discharge rate capability (above 180 mA h g−1 at 1 C regime) than those obtained using conventional electrolytes without additive.

Synthesis and Thermophysical Properties of Ether Functionalized Sulfonium Ionic Liquids as Potential Electrolytes for Electrochemical Applications

Abstract During this work, a novel series of hydrophobic room temperature ionic liquids (ILs) based on five ether functionalized sulfonium cations bearing the bis{(trifluoromethyl)sulfonyl}imide, [NTf2]− anion were synthesized and characterized. Their physicochemical properties, such as density, viscosity and ionic conductivity, electrochemical window, along with thermal properties including phase transition behavior and decomposition temperature, have been measured. All of these ILs showed large liquid range temperature, low viscosity, and good conductivity. Additionally, by combining DFT calculations along with electrochemical characterization it appears that these novel ILs show good electrochemical stability windows, suitable for the potential application as electrolyte materials in electrochemical energy storage devices.

Physicochemical and electrochemical properties of a new series of protic ionic liquids with N-chloroalkyl functionalized cations

Six new protic ionic liquids (PILs) based on N-chloroalkyl functionalized morpholinium, piperidinium, pyrrolidinium and alkylammonium cations, with bis[(trifluoromethyl)sulfonyl]imide as counter-ion, were synthesized by a metathesis reaction. To understand the differences of structure, charge distribution and volume between the various investigated N-chloroalkyl functionalized cations, as well as between their non-chloro analogues, computational methods were used to generate the COSMO volume and the sigma profile of each ion. Physicochemical investigations showed lowered melting point of these PILs (−8.5 °C < Tm < 34.1 °C) as compared to their non-functionalized analogues and a high thermal stability with T5%onset in the range 280–337 °C. The alkylammonium and pyrrolidinium-based PILs display reasonable conductivity (1.23 mS cm−1 < σ < 1.71 mS cm−1), although their viscosity values are relatively high (0.0665 Pa s < η < 0.1093 Pa s). The effect of temperature on the transport properties of each PIL has then investigated by fitting the experimental data with the Arrhenius law and the Vogel–Tamman–Fulcher (VTF) equations, revealing the convergence of viscosity with the former model and conductivity with the latter one. The electrochemical stability of cations towards reduction is discussed in light of the frontier orbital theory. All N-chloroalkyl functionalized PILs display a wide electrochemical stability window (4.1–5.1 V), in the same range as the representative of non-chloro functionalized analogues, [HN222][TFSI], (4.3 V).

Tunable gold nanoparticles shape and size in reductive and structuring media containing protic ionic liquids

Herein, a facile method was developed for preparing high concentration of monodispersed gold nanoparticles (NPs) at room temperature from gold(III) chloride by using different media based on N,N-dimethylformamide or water solutions containing a protic ionic liquid (PIL), namely, the octylammonium formate or the bis(2-ethyl-hexyl)ammonium formate, based on which both PILs were used as redox-active structuring media. The formation of gold NPs in these systems was then characterized using UV–visible spectroscopy, transmission electron microscopy, and dynamic light scattering. From these investigations, it appears that the structure and aggregation pathway of PILs in selected solvents affect strongly the formation, growth, the shape, and the size of gold NPs. In fact, by using this approach, the shape-/ size-controlled gold NPs (branched and spherical) can be generated under mild condition. This approach suggests also a wealth of potential for these designer nanomaterials within the biomedical, materials, and catalysis communities by using designer and safer media based on PILs.

Deep eutectic solvent based on sodium cations as an electrolyte for supercapacitor application

This study proposes a new deep eutectic solvent based on sodium nitrate and N-methylacetamide as an electrolyte for carbon-based supercapacitors at 80°C. The reversible intercalation of ions into the graphitized ultra-micropores of activated carbon, separately detected at negative and positive electrodes, permits high pseudo-capacitance (up to 302 F g−1). The SEM/EDX mapping and XRD profile show homogeneous distribution of Na in negative polarized electrodes indicating that sodium is well incorporated in the ultra-micropores of the carbon structure. The good capacitance obtained at 80 °C in two-electrode cells at an operating voltage up to 2.0 V remained stable after 1000 charge–discharge cycles. Based on its physicochemical properties, as well as its electrochemical performances and stabilities, the sodium based DES can be considered a promising electrolyte for supercapacitor applications.