Energetics and Dynamics of Metal-Ion Coordination with Ionic Liquid Electrolytes: A Combined DFT and AIMD Investigation for Rechargeable Batteries

Abstract

In this work, we have employed density functional theory calculations and ab initio molecular dynamics (AIMD) simulations to identify suitable ionic liquids (ILs) as better electrolytes for rechargeable lithium (Li + ), sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), and aluminum (Al 3+ ) ion batteries. We have considered 12 different ILs which include imidazolium, pyridinium, pyrrolidinium, piperidinium cations, and [BF 4 ], [Cl], [DCA], [FSI], and [TFSI] anions for the calculations. Interaction studies were carried out between the ILs and Li + /Na + /K + /Mg 2+ /Al 3+ ions. In particular, we investigated the structural, electronic, and thermochemical properties to decode the binding and solvation properties of Li + /Na + /K + /Mg 2+ /Al 3+ solvated by [FSI]/[TFSI]/[DCA] anions. Lastly, AIMD simulations are carried out to investigate the structural and dynamical changes in the solvation shell surrounding Li + in the ILs and anions environments. In the Li + -ILs systems, the Li + ions are mostly coordinated by the atoms present in the anions. In Li + -[anion] systems, the oxygen atoms of [FSI] and [TFSI] are more coordinated around the Li + ions. The nitrogen atoms are coordinated to Li + to form the aggregates in the Li + -DCA system. The highest self-diffusion coefficient ( D s ) of Li + is calculated to be 5.61 × 10 –10 m 2 /s in [EMIM]-[FSI] when compared to [EMIM]-[DCA] and [EMIM]-[TFSI]. In an anion environment, Li + -[FSI] shows the highest D s value of 3.69 × 10 –10 m 2 /s. Therefore, it can be concluded that the Li + -ion solvation shell formation and diffusion in ILs are primarily influenced by the nature of the anions. In summary, our work reveals the solvation properties of ILs and their stability which offers new guidelines for designing more reliable electrolytes for rechargeable batteries.

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