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Effect of TFSI/FSI Anion Composition on Ion Coordination and Transport in PEO-Based Electrolytes: A Molecular Dynamics Study

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Effect of TFSI/FSI Anion Composition on Ion Coordination and
Transport in PEO-Based Electrolytes: A Molecular Dynamics Study

Ehsan Hemmasi
Department of Chemical and Biomolecular Engineering, University of Tennessee

Molecular level understanding of polymer electrolytes is essential for the development of next-generation Li-ion batteries. In this work, molecular dynamics (MD) simulations are used to investigate ion coordination and diffusion in poly(ethylene oxide) (PEO) containing Li and mixed TFSI/FSI anions at salt concentration of 0.2 (r = [Li]/[EO] = 0.2). Three TFSI/FSI ratios are considered: 100/0 (%/%), 50/50, 0/100. Radial distribution function and coordination analyses reveal that Li is mainly coordinated with oxygens of PEO in all anion ratios and its primary solvation shell does not change. It is found that Li diffusivity is insensitive to anion type, and substituting TFSI with FSI improves the Li transport number not by speeding up Li, but by slowing down the anion.

This page shows an interactive animation extracted from the simulated 50/50 system containing lithium ions and mixed TFSI/FSI anions. The simplified trajectory contains Li+ ions, nitrogen atoms from TFSI-, and nitrogen atoms from FSI- across 100 frames. This reduced trajectory helps visualize the spatial distribution and motion of lithium ions relative to representative anion sites. The user can start, pause, rotate, zoom, change speed, and switch between Li+, TFSI, and FSI views. The PEO chains are excluded from the simulation box (free space between ions is filled with PEO).

Interactive Structures


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Drag inside the viewer to rotate the structure. Use the mouse wheel or trackpad to zoom.

Color Legend:

  • green spheres = Li+ ions
  • red spheres = nitrogen atoms from TFSI-
  • blue spheres = nitrogen atoms from FSI-
  • Note: in the XYZ file, FSI nitrogen atoms are encoded as a pseudo-element only so JSmol can color/select them separately from TFSI nitrogen atoms.

References

1. Kang, P.; Wu, L.; Chen, D.; Su, Y.; Zhu, Y.; Lan, J.; Yang, X.; Sui, G. Dynamical Ion Association and Transport Properties in PEO-LiTFSI Electrolytes: Effect of Salt Concentration. Journal of Physical Chemistry B 2022, 126 (24), 4531-4542.
2. Gullbrekken, Ø.; Schnell, S. K. Coupled Ion Transport in Concentrated PEO-LiTFSI Polymer Electrolytes. New J. Chem. 2023, 47, 20344.

posted: May 2026.
updated: May 2026.