Electrical, electrochemical and thermal properties of the ionic liquid + lactone binary mixtures as the potential electrolytes for lithium-ion batteries

Electrical conductivity of four binary mixtures containing 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid, [bmim][NTf2], with selected lactones, namely: β-butyrolactone (BBL), γ-valerolactone (GVL), δ-valerolactone (DVL) and ε-caprolactone (ECL) was measured at temperatures from (293.15 to 323.15) K at atmospheric pressure (p = 0.1 MPa) over the whole composition range. The effects of the temperature and ionic liquid (IL) concentration on the electrical conductivity were correlated using Casteel-Amis and Arrhenius equations. It was found that addition of lactone does not reduce electrochemical stability of investigated solution. In order to determine the flammability of the mixtures, the electrolyte self-extinguishing time (SET) was measured and evaluated. DSC was used to determine thermophysical properties of pure compounds and mixtures such as phase transition temperatures and changes in heat capacities. Different heating rates were used to evaluate the kinetic events. Determination of these properties for investigated systems is relevant for their possible applications in the field of electrochemistry.