Molecular Dynamics Simulations of High-Concentration Li[TFSA] Sulfone Solution: Effect of Easy Conformation Change of Sulfolane on Fast Diffusion of Li Ion

Abstract

The parameters of the polarizable force field used for molecular dynamics simulations of Li diffusion in high-concentration lithium bis­(trifluoro­methanesulfonyl)­amide (Li­[TFSA]) sulfone (sulfolane, dimethylsulfone, ethylmethylsulfone, and ethyl-i-propylsulfone) solutions were refined. The densities of the solutions obtained by molecular dynamics simulations reproduced well the experimental values. The calculated concentration, temperature, and solvent dependencies of self-diffusion coefficients of ions and solvents in the mixtures well reproduce the experimentally observed dependencies. Ab initio calculations show that the intermolecular interactions between Li ions and four sulfones are not largely different. Conformational analyses show that sulfolane can change the conformation more easily owing to lower barrier height for pseudorotation compared to the rotational barrier heights of diethylsulfone and ethylmethylsulfone. Molecular dynamics simulations indicate that the easy conformation change of solvent affects the rotational relaxation of the solvent and the diffusion of Li ion in the mixture. The easy conformation change of sulfolane is one of the causes of faster diffusion of Li ion in the mixture of Li­[TFSA] and sulfolane compared to the mixtures of smaller dimethylsulfone and ethylmethylsulfone.

Exploring lithium salt solution in sulfone and ethyl acetate-based electrolytes for Li-ion battery applications: a molecular dynamics simulation study

“…This finding is in accordance with the observations in Li[TFSI]–EMS binary systems. 81 Similarly, in the first solvation shell of Li–F (as shown in Fig. 3(b)), the number of fluorine atoms around the Li + ion is approximately 1.53 and 0.01 in the EA and EMS solvents, respectively.…”

“…This observation is consistent with the trends observed in other Li salt–sulfone binary systems. 81,85,86 The barrier height for changing the conformation of the solvent can also influence the diffusion of Li ions, along with the factors of ion size and shape, as well as cation–anion attraction. Notably, a study by Tsuzuki et al found that the lower barrier height associated with TMS's conformation change is a key factor contributing to its fast Li-ion diffusion.…”

Evolving better solvate electrolytes for lithium secondary batteries

“…The obtained activation energy and Vogel–Fulcher–Tammann parameters are similar to those reported from diffusion data in the literature. 67 The relaxation time parameter τ 0 is in the order of 10 ns, which indicates large relaxing units or diffusive motion. These observations are consistent with strong coupling between cation, anion, and sulfolane.…”

Molecular Level Origin of Ion Dynamics in Highly Concentrated Electrolytes

“…For the purpose of these simulations, the OPLS-AA-based polarizable force field was employed, as described in our previous report , and in the Supporting Information (see Tables S7–S10 and Figures S11 and S12). For structural analysis, visualization of the structures was carried out using VMD software …”