Ionic liquids are a class of compounds having a liquid phase below 100°C (an arbitrary value) in which the constituents are only ions. Due to this feature, stronger interactions exist between the molecules of ionic liquids vs. those in non-ionic liquids, resulting in a very low volatility in the former. A wide selection of stable cations and anions are now available and can be used to obtain ionic liquids with a very high thermal and electrochemical stability. And since they are exclusively constituted of ions they are intrinsic ionic conductors and they don’t require any support electrolyte to be added for their use in electrochemical cells. The number of cation-anion combinations possible that can form an ionic liquid is estimated to be 10^18, and research is currently oriented toward the understanding how the chemical structure of the ions affects the property and the microscopic structure of the ionic liquid. Our research involves ionic liquids for a potential use as electrolyte in energy storage devices.
Electroactive ionic liquids
Electroactive ionic liquids (or redox ionic liquids, RIL) are obtained through the modification of the cation or anion from an ionic with a redox moiety that can be either based on an organic or a transition metal complex structure. Some redox ionic liquids prepared in our group are listed below. These RIL allow studying electrochemical reactions directly on the solvent which is at high concentration, rather than in traditional solute-solvent systems. The relationship between the RIL structure and their properties are currently studied to module their viscosity, melting point and redox potential.
Ionic liquids in batteries
The electroactive ionic liquids presented above are studied as electrolyte and redox additives (redox shuttles) in lithium-ion batteries. Redox shuttles are solubilized in battery electrolyte to protect the cathode against overcharging and degradation. The development of electroactive ionic liquids as battery electrolyte allows combining the thermal stability and low volatility of ionic liquid with the cathode protection properties offered by the redox shuttle principle.
Pseudocapacitive systems are mainly under study in our group to develop novel electrolytes based on ionic liquids. Pseudocapacitors rely on faradaic (redox) reactions on the surface and in the bulk of the electrode material to store and release electric energy. The electrochemistry of materials such as ruthenium dioxide are studied in protic ionic liquids (ionic liquids obtained from the proton transfer between a Bronsted acid and a base) allows us to learn on how heterogeneous proton transfer at electrodes are affected by the nature of the ionic liquid. More information available in this document.
Rare earth ions extraction
Ionic liquids are used to extract earth metal ions from acidic aqueous solutions. The ionic liquid is used either as the water immiscible solvent in which the extractant is dissolved to perform the extraction or is modified to bear a functional group for the extraction on its structure. The effect of the nature of the ions in the ionic liquid on the rare earth extraction efficiency and selectivity is studied.