Abstract
Ionic liquids (ILs) have attractive unique properties for safer batteries, including important thermal stability and negligible volatility. In addition, they have a high ionic conductivity (10-3 to 10-2 S/cm at room temperature) and a wide electrochemical stability window (up to 6 V in the case of piperidinium and pyrrolidinium salts). However, the dissolution of a [Li+][X-] salt in the ionic liquid [A+][X-] leads to an ionic liquid electrolyte (ILE) with increased viscosity, lower conductivity, and as a result, hinders its use as an electrolyte.This manuscript describes the development of hybrid organic–inorganic materials based on ionic liquids immobilized on the surface of metal oxide nanoparticles. A solid electrolyte thus obtained (solvent-free) reduces the risk of batteries ignition as well as electrolyte leakage. In addition, the reached conductivities are comparable to those of the polymer systems reported in the literature. We focused our research on a panel of ionic liquids derived from imidazolium salts and their grafting on silica and zirconium(IV) oxide nanoparticles. We report herein a new electrolyte prepared from the coordination of carboxylic acid functionalized imidazolium salt. After optimization of the lithium salt content, a stable ionic conductivity is obtained between 80 °C and 25 °C (respectively from 0,6 x 10-4 S/cm to 0,15 x 10-4 S/cm). Furthermore, the impact of the chemical structure of the ionic liquid on the lithium ions transport is discussed. Among others, the influence of the carbon chains length, the anchoring function, the nature, and the structure of the support was studied. This research has involved electrolytes analysis by electrochemical impedance spectroscopy and solid-state NMR. Finally, integration tests in half-cell models conclude this manuscript