Modelling structure and ionic diffusion in a class of ionic liquid crystal-based solid electrolytes.

Next-generation high-efficiency Li-ion batteries require an electrolyte that is both safe and thermally stable. A possible choice for high performance all-solid-state Li-ion batteries is a liquid crystal, which possesses properties in-between crystalline solids and isotropic liquids. By employing molecular dynamics simulations together with various experimental techniques, we have designed and analyzed a novel liquid crystal electrolyte composed of rigid naphthalene-based moieties as mesogenic units, grafted to flexible alkyl chains of different lengths. We have synthesized novel highly ordered lamellar phase liquid crystal electrolytes at 99% purity and have evaluated the effect of alkyl chain length variation on ionic conduction. We find that the conductivity of the liquid crystal electrolytes is directly dependent on the extent of the nanochannels formed by molecule self-organization, which itself depends non-monotonously on the size of the alkyl chains. In addition, we show that the ion pair interaction between the anionic center of the liquid crystal molecules and the Li+ ions plays a crucial role in the overall conductivity. Based on our results, we suggest that further improvement of the ionic conductivity performance is possible, making this novel family of liquid crystal electrolytes a promising option for the design of entirely solid-state Li+ ion batteries.

Phenylacetonitrile (C6H5CH2CN) Ionic Liquid Blends as Alternative Electrolytes for Safe and High-Performance Supercapacitors.

The increasing need in the development of storage devices is calling for the formulation of alternative electrolytes, electrochemically stable and safe over a wide range of conditions. To achieve this goal, electrolyte chemistry must be explored to propose alternative solvents and salts to the current acetonitrile (ACN) and tetraethylammonium tetrafluoroborate (Et4NBF4) benchmarks, respectively. Herein, phenylacetonitrile (Ph-ACN) has been proposed as a novel alternative solvent to ACN in supercapacitors. To establish the main advantages and drawbacks of such a substitution, Ph-ACN + Et4NBF4 blends were formulated and characterized prior to being compared with the benchmark electrolyte and another alternative electrolyte based on adiponitrile (ADN). While promising results were obtained, the low Et4NBF4 solubility in Ph-ACN seems to be the main limiting factor. To solve such an issue, an ionic liquid (IL), namely 1-ethyl-3-methylimidazolium bis [(trifluoromethyl)sulfonyl] imide (EmimTFSI), was proposed to replace Et4NBF4. Unsurprisingly, the Ph-ACN + EmimTFSI blend was found to be fully miscible over the whole range of composition giving thus the flexibility to optimize the electrolyte formulation over a large range of IL concentrations up to 4.0 M. The electrolyte containing 2.7 M of EmimTFSI in Ph-ACN was identified as the optimized blend thanks to its interesting transport properties. Furthermore, this blend possesses also the prerequisites of a safe electrolyte, with an operating liquid range from at least -60 °C to +130 °C, and operating window of 3.0 V and more importantly, a flash point of 125 °C. Finally, excellent electrochemical performances were observed by using this electrolyte in a symmetric supercapacitor configuration, showing another advantage of mixing an ionic liquid with Ph-ACN. We also supported key structural descriptors by density functional theory (DFT) and COnductor-like Screening Model for Real Solvents (COSMO-RS) calculations, which can be associated to physical and electrochemical properties of the resultant electrolytes.

Acyclic and Cyclic Alkyl and Ether-Functionalised Sulfonium Ionic Liquids Based on the [TFSI]- and [FSI]- Anions as Potential Electrolytes for Electrochemical Applications.

This work provides a study based on acyclic and cyclic sulfonium ionic liquids (ILs) with alkyl and ether-functionality on the cation paired with the bis{(trifluoromethyl)sulfonyl}imide, [TFSI]- , or the bis(fluorosulfonyl)imide, [FSI]- , as the counter anion. Herein, thermophysical characterisation of nine sulfonium-based ILs concerning the density, viscosity and conductivity and thermal properties including phase transition behaviour and decomposition temperature is reported. The electrochemical stability of the ILs was also measured by cyclic voltammetry at a glassy carbon macro-disk electrode. All of the ILs showed low melting point, low viscosity and good conductivity and could serve as potential electrolytes for energy storage devices.