In this paper we report on the investigation of ionic liquid-based electrolytes with enhanced characteristics. In particular, we have studied ternary mixtures based on the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and two ionic liquids sharing the same cation (N-methyl-N-propyl pyrrolidinium, PYR 13 ), but different anions, bis(trifluoromethanesulfonyl)imide (TFSI) and bis(fluorosulfonyl)imide (FSI). The LiTFSI-PYR 13 TFSI-PYR 13 FSI mixtures, found to be ionically dissociated, exhibit better ion transport properties (about 10 −3 S cm −1 at −20 • C) with respect to similar ionic liquid electrolytes till reported in literature. An electrochemical stability window of 5 V is observed in carbon working electrodes. Preliminary battery tests confirm the good performance of these ternary electrolytes with high-voltage NMC cathodes and graphite anodes. Ionic liquids (ILs) are being investigated as substitutes of volatile and flammable organic electrolyte solvents in rechargeable lithiumion battery systems 1,2 to enhance safety of the electrochemical device. ILs are considered, in fact, strong flame retardants, displaying negligible vapor pressure in combination with relatively fast ion transport properties and wide chemical/electrochemical/thermal stability.3,4 So far, single ILs did not generally fully satisfy the requirements and/or operative conditions of practical devices, although their properties can be finely tuned by properly modifying their architecture.3,4 A promising approach, however, is represented by suitably combining different ionic liquids, leading to beneficial synergic effects on the physicochemical properties of the resulting mixtures. [5][6][7] In previous work, 8,9 we have demonstrated the possibility of favorably combining two ionic liquids, sharing the N-methyl-Npropyl pyrrolidinium cation (PYR 13 + ) and bis (trifluoromethanesulfonyl)imide (TFSI − ) and bis(fluorosulfonyl)imide (FSI − ) anions. The TFSI ion was proved to be stable toward oxidation and thermally robust 2 while FSI-based ILs exhibit good ion conduction even at low temperature and protective film-forming capability onto electrodes. 2,10,11 In particular, proper PYR 13 TFSI-PYR 13 FSI formulations 8,9 were found to display ionic conductivities largely overcoming 10 −4 S cm −1 at −20 • C whereas the pure IL materials, still in solid state, exhibit conduction values about four orders of magnitude lower. This behavior is likely due to the different hindrance of the anions, resulting in worse ion packing and, therefore, inhibiting the crystallization process of the IL blend. [5][6][7] In addition, average, even if moderate, variation of the linear density vs mole composition behavior of the PYR 13 TFSI-PYR 13 FSI mixtures was observed at intermediate FSI mole fraction. 9 This issue suggests rearrangement of the ion structural organization within the IL blend, which may positively reflect on the transport properties. On the basis of the obtained results, the TFSI:FSI mole ratio of 2:3 was selected. 9 * Electrochemical Soci...

No abstract

No abstract

No abstract

Abstract:In this work a purification route of precursors for ionic liquids tailored to electrochemical energy storage systems is reported and described. The study was carried out on the N-butyl-N-methylpyrrolidinium bromide (PYR 14 Br) precursor, which represents the intermediate product of the synthesis process of the N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14 TFSI) hydrophobic ionic liquid. The target is to develop an easy and cost-effective approach for efficiently purifying several kinds of ionic liquid precursors and determining their purity content. The PYR 14 Br precursor was synthesized through an eco-friendly preparation procedure, which requires water as the only processing solvent, and purified through sorbent materials, such as activated charcoal and alumina. The effect of the treatment/nature/content of sorbents and processing temperature/time was investigated. The impurity content was detected by UV-VIS spectrophotometry measurements. Additionally, a correlation between the measured absorbance and the content of impurities within the precursor was obtained. The purity level of the precursor was seen to play a key role in the electrochemical performance of the ionic liquids.