Effect of Organic Solvents on Li⁺ Ion Solvation and Transport in Ionic Liquid Electrolytes: A Molecular Dynamics Simulation Study

Molecular dynamics simulations of <i>N</i>-methyl-<i>N</i>-propylpyrrolidinium (pyr₁₃) bis­(trifluoromethanesulfonyl)­imide (Ntf₂) ionic liquid [pyr₁₃]­[Ntf₂] doped with [Li]­[Ntf₂] salt and mixed with acetonitrile (AN) and ethylene carbonate (EC) organic solvents were conducted using polarizable force field. Structural and transport properties of ionic liquid electrolytes (ILEs) with 20 and 40 mol % of organic solvents have been investigated and compared to properties of neat ILEs. Addition of AN and EC solvents to ILEs resulted in the partial displacement of the Ntf₂ anions from the Li⁺ first coordination shell by EC and AN and shifting the Li–Ntf₂ coordination from bidentate to monodentate. The presence of organic solvents in ILE has increased the ion mobility, with the largest effect observed for the Li⁺ cation. The Li⁺ conductivity has doubled with addition of 40 mol % of AN. The Li⁺–N^Ntf2 residence times were dramatically reduced with addition of solvents, indicating an increasing contribution from structural diffusion of the Li⁺ cations