The effect of acetonitrile as an additive on the ionic conductivity of imidazolium-based ionic liquid electrolyte and charge-discharge capacity of its Li-ion battery

In this paper, we report the effect of a small quantity of acetonitrile (ACN) addition to an ionic liquid-based electrolyte for lithium-ion (Li-ion) batteries, which is comprised of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt dissolved in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI). The addition of a small amount of ACN results in the increase of ionic conductivity, and at a proper molal fraction, it may significantly improve the charge-discharge capacity of its half-cell battery. A large amount of ACN addition, however, reduces the specific capacity because ACN molecules are more susceptible to irreversible redox reactions at the battery electrodes. The experimental results are also compared with the X-ray diffraction (XRD pattern) of the solutions, which may lead to a suggestion in the formation of coordination complexes between the Li+ cations with ACN molecules, which effectively hinders the formation of strong Li+-TFSI- ionic bonding and therefore increases the Li+ cation mobility. Different from other reports, the role of this small quantity of ACN is considered not only as a co-solvent, but also as an additive to this LiTFSI/BMIMTFSI electrolyte.