Effect of Clusters on [Li] Solvation and Transport in Mixed Organic Compound/Ionic Liquid Electrolytes under External Electric Fields

The utilization of ionic liquids (ILs) as electrolytes in lithium-ion batteries is of great academic and industrial significance. Previous studies have shown that clusters can be formed in IL electrolytes. However, the influence of clusters on [Li] solvation and transport is still ambiguous, especially under external electric fields. The structural, dynamical, and transport properties of mixed organic compound/IL electrolytes, consisting of lithium salts ([Li] [TFSI], [Li][BF4], and [Li][PF6]), organic solvents (ethylene carbonate (EC) and dimethyl carbonate (DMC)), and ILs ([EMIM] [TFSI], [EMIM][BF4], [EMIM] [PF6], and [PYR14][TFSI]) under external electric fields were investigated using molecular dynamics (MD) simulations. The results suggest a strong relationship between the cluster structures and the applied external electric fields. Under low electric fields, no obvious change of cluster structures was observed, but due to the electrophoretic effect, [Li] diffusion was weakened. Under high electric fields, the anions around [Li] could be partially substituted by DMC molecules, and it was found that [Li] diffusion could be increased significantly. The physical insights provided in the study demonstrate that the original larger ion clusters tend to be smaller on increasing the strength of the external electric fields, thereby enhancing the transport of [Li].