Physicochemical properties of three ionic liquids containing a tetracyanoborate anion and their lithium salt mixtures

Given their relevant physicochemical properties, ionic liquids (ILs) are attracting great attention as electrolytes for use in different electrochemical devices, such as capacitors, sensors, and lithium ion batteries. In addition to the advantages of using ILs containing lithium cations as electrolytes in lithium ion batteries, the Li⁺ transport in ILs containing the most common anion, bis(trifluoromethanesulfonyl) imide anion ([Tf₂N]), is reportedly small; therefore, its contribution to the overall conductivity is also low. In this work, we describe the preparation and characterization of two new and one known IL containing the tetracyanoborate anion ([B(CN)₄]) as the anionic species. These ILs have high thermal and chemical stabilities, with almost twice the ionic conductivity of the [Tf₂N] ILs and, most importantly, provide a greater role for the Li⁺ ion throughout the conductivity process. The experimental ionic conductivity and self-diffusion coefficient data show that the [B(CN)₄]-based ILs and their Li ⁺ mixtures have a higher number of charge carriers. Molecular dynamics simulations showed a weaker interaction between Li⁺ and [B(CN)₄] than that with [Tf₂N]. These results may stimulate new applications for ILs that have good Li⁺ transport properties.