Molecular dynamics study on lithium‐ion transport in PEO branched nanopores with PYR14TFSI ionic liquid

Abstract

Abstract Lithium ion transport in a poly‐(ethylene oxide) (PEO) branched nanopore filled with a solution of [lithium][bis(trifluoromethanesulfonyl)imide]/[1‐butyl‐1‐methylpyrrolidinium][bis(trifluoromethanesulfonyl)imide] (LiTFSI/PYR14TFSI) was investigated by molecular dynamics using many‐body polarizable force field. The structural and dynamic properties of lithium ions in the nanopores with different sizes and ratios of ions to PEO chains were examined. The first coordination shell of the lithium ions had a lower intensity in the longitudinal direction than in the radial direction. Cluster analysis of [Lix(TFSI)n]−(n−x) showed the absence of large lithium clusters (x ≥ 2) as a result of the enhanced suppression of monodentate structures compared with binary electrolytes (i.e., LiTFSI/PYR14TFSI without PEO chains). The emergence of [Li(TFSI)2]− and its relatively small hydrodynamic radius facilitated rapid dynamics compared with binary electrolytes. The diffusion coefficients and ionic conductivities of the lithium ions in the longitudinal direction increased with an increase in the ratio of the ions to PEO chains and a decrease in the pore size. It was noted that the lithium‐ion transport was mainly governed by structural diffusion based on a shorter residual time for anions compared with binary electrolytes. In addition, single ion trajectory analysis was performed and more frequent anion exchanges were observed when PEO chains were introduced.

Keywords

• ionic liquid
• lithium‐ion transport mechanism
• many‐body polarizable force field
• molecular dynamics
• polyelectrolyte