Role of Molecular Architecture on Ion Transport in Ethylene oxide-Based Polymer Electrolytes

Abstract

This work aims to develop a detailed mechanistic understanding of the role of a graft polymer architecture on lithium ion (Li+) transport in poly­(ethylene oxide)-based polymer electrolytes. Specifically, we compare Li+ transport in poly­(ethylene oxide) (PEO) versus poly­(oligo oxyethylene methacrylate) (POEM) polymers doped with lithium bis­(trifluoromethanesulfonyl) (LiTFSI) salts, using both experimental electrochemical characterization and molecular dynamics (MD) simulations. Our results indicate that POEM exhibits a range of relaxation processes that cannot be interpreted solely in terms of glass-transition temperature (T g) effects. Due to its side-chain architecture, the segmental relaxation of POEM is nonuniform across ether oxygens (EOs) and shows a more pronounced sensitivity to temperature above T g compared to PEO. Moreover, POEM also exhibits a nonuniform Li+ coordination behavior, in which Li+ is primarily solvated by two different chains in POEM, compared to a single chain in PEO. Li+ transport in POEM occurs via two events with distinct characteristic times: a fast intrachain hopping along side chains and a slow interchain hopping between side chains. Taken together, the relaxation processes and ion transport mechanisms identified in POEM provide useful insights into design of more effective solid polymer electrolytes.

Enhancing the Ionic Conductivity of Poly(3,4-propylenedioxythiophenes) with Oligoether Side Chains for Use as Conductive Cathode Binders in Lithium-Ion Batteries

“…On the other hand, OE side chains are well known to be Li +ion conductors in disordered form. 81,82 Because doping is not able to induce significant crystallinity in the high OE fraction samples, we find that the ionic conductivity shows an opposite trend compared to the electronic conductivity. Higher OE fraction samples are the most disordered and thus show higher ionic conductivity.…”

Lithium ion transport in solid polymer electrolyte filled with alumina nanoparticles

“…PEO has a flexible macromolecular chain, which benefits Li + transport [17]. Several Li + transport pathways have been observed in simulation studies, such as Li + moving along the PEO chains, Li + complexing and decomplexing with anions, and Li + occasionally hopping between the adjacent PEO chains [18], [19], [20]. Borodin et al [15] showed that Li cations moving along the PEO chains generally show stronger mobility than those that jump between the PEO chains, suggesting that enhancing the movement along the PEO chains can significantly promote Li + diffusion.…”

Crosslinked Polymer‐Brush Electrolytes: An Approach to Safe All‐Solid‐State Lithium Metal Batteries at Room Temperature

“…[42,43] With regard to brush polymers, simulation studies found that the middle of the side chains offer more permutations to form the contiguous six or three EO solvating segments to complex Li + , whereas the positions near the backbone and side chain tails share the less solvation probability. [44,45] As a result, the polymer brush with shorter side chain length, especially with 350 Da or less that holds only a few EO units, has lower fraction of effective solvation sites, leading to a decrease of c. Synergistically, the enhancement of μ and c results in the increased ionic conductivity with the side chain length.…”