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

Abstract

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][BF 4 ], and [Li][PF 6 ]), organic solvents (ethylene carbonate (EC) and dimethyl carbonate (DMC)), and ILs ([EMIM][TFSI], [EMIM][BF 4 ], [EMIM][PF 6 ], and [PYR 14 ][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].

Multicomponent Phase Separation in Ternary Mixture Ionic Liquid Electrolytes

“…The calculated diffusion rates of Li + at room temperature are approximately 1 order of magnitude smaller than the diffusion coefficients of Li + in neat IL measured experimentally (∼6–20 × 10 –12 ) − and are comparable to diffusion of Li + in IL based on nonpolarizable forcefields (∼0.2–3 × 10 –12 ). − On the other hand, polarizable forcefields are shown to improve dynamic properties of ILs and have predicted Li + diffusion rates in better agreement with experiments. ,,, Even though the inclusion of polarizability enhances the system dynamics, nonpolarizable forcefields are proven to reproduce structural features of various ILs more accurately. − Moreover, when compared to nonpolarizable forcefields, the polarizable models fail to predict the trend of ion concentration dependency of the diffusion and viscosity measurements . Even though, nonpolarizable forcefields may not accurately predict the concentration cut-off below which phase separation occurs, they are expected to reproduce the general trend and concentration dependency of phase separation in ternary IL mixtures.…”

Insights into Ionic Liquids: From Z-Bonds to Quasi-Liquids

“…Furthermore, the ionic cluster can catalyze conversion of CO 2 and ethylene oxide to dimethyl carbonate, 44 which exhibits a relatively lower energy barrier in comparison to that in the single IL pair. In general, ionic clusters are present in mixed systems of ILs and other liquids 109 (such as water, dimethyl sulfoxide, Brønsted acids, and organic electrolytes). In such a cluster system, the basic interactions include not only the Z-bond but also conventional or ionic HBs.…”

Understanding Electric Field‐Dependent Structure Variation of Functional Ionic Liquids at the Electrode Interface

“…To maintain the stable interfacial structure, E < 0.4 V/Å is considered for all imidazole ILs in the present work, which agree with the strength of electric field used in the previous works. [54][55][56] When E is beyond the critical electrical field, the pistol will be pulled out by the separated cations and leading to the destroy of the ILs-solid interfaces.…”