Lithium-Ion Dynamics in Sulfolane-Based Highly Concentrated Electrolytes

Abstract

Here, we report the use of molecular dynamics simulations with a polarizable force field to investigate Li-ion dynamics in sulfolane (SL)-based electrolytes. In SL-based highly concentrated electrolytes (HCEs) (e.g., SL/Li = 2:1), Li displays faster translational motion than other components, which should be related to the structural and dynamical properties of SL. In HCEs, a transient conduction network that penetrated the simulation system was always observed. Rapid (<1 ns) Li-ion hopping between adjacent coordination sites was observed throughout the network. Additionally, SLs rotated in the same timeframe without disrupting the conduction network. This rotation is believed to promote the hopping diffusion in the network. This was followed by a rotational relaxation of the SL dipole axis around the non-polar cyclohydrocarbon segment of SL (∼3.3 ns), which involves a reorganization of the network structure and an enhancement of the translational motion of the coordinating Li ions. The observed lifetime of Li−SL coordination was longer (>11 ns). Hence, it was concluded that the faster Li translational motion was obtained due to the faster rotational relaxation time of SL rather than the lifetime of Li−SL binding. The faster rotation of SL is related to its amphiphilic molecular structure with compact non-polar segments. Transport properties, such as the Onsager transport coefficients, ionic conductivity, and transference number under anion-blocking conditions, were also analyzed to characterize the features of the SLbased electrolyte.

Li-Ion Transport and Solution Structure in Sulfolane-Based Localized High-Concentration Electrolytes

“…30 Previously reported OPLS-AAbased force-field parameters for SL and LiTFSA were used to model the polarizable force fields. 31 New parameters were developed for HFE based on ab initio molecular orbital calculations. The details for the polarizable force fields are provided in Figure S2 and Tables S3−S7.…”

Molecular Level Origin of Ion Dynamics in Highly Concentrated Electrolytes

“…In addition, the RDF peaks of the Li + –O (anion) species were observed at distances similar to those obtained for the Li + –O (solvent) species. The radii of the first solvation and coordination shells for each electrolyte were defined as 3.0 Å, which corresponds to the first minimum distance in the RDFs of the Li + –O (solvent/anion) species. , …”

“…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 …”

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

“…Molecular volumes (volumes within contours of 0.001 electron bohr –3 density) were calculated at the MP2/6-311G** level. MPDynPFF program , was used for molecular dynamics simulations using a polarizable force field . Details of the polarizable force field are shown in Supporting Information.…”