Percolated Ionic Aggregate Morphologies and Decoupled Ion Transport in Precise Sulfonated Polymers Synthesized by Ring-Opening Metathesis Polymerization

Abstract

We describe a set of precise single-ion conducting polymers that form self-assembled percolated ionic aggregates in glassy polymer matrices and have decoupled transport of metal cations. These precise single-ion conductors (SICs), synthesized by a scalable ring-opening metathesis polymerization, consist of a polyethylene backbone with a sulfonated phenyl group pendant on every fifth carbon and are fully neutralized by a counterion X+ (Li+, Na+, or Cs+). Experimental X-ray scattering measurements and fully atomistic molecular dynamics (MD) simulations are in good agreement. The MD simulations show that the ionic groups nanophase separate from the polymer backbone to form percolating ionic aggregates. Using graph theory, we find that within the Li+- and Na+-neutralized polymers the percolated aggregates exhibit planar and ribbon-like configurations at intermediate length scales, while the percolated aggregates within the Cs+-neutralized polymers are more isotropic. Electrical impedance spectroscopy measurements show that the ionic conductivities exhibit Arrhenius behavior, with conductivities of 10–7 to 10–6 S/cm at 180 °C. In the MD simulations, the cations move between sulfonate groups in the percolated aggregates, larger ions travel further, and overall cations travel further than the polymer backbones, indicating a decoupled ion-transport mechanism. Thus, the percolated ionic aggregates in these polymers can serve as pathways to facilitate decoupled ion motion through a glassy polymer matrix.

Fluorine-Free Precise Polymer Electrolyte for Efficient Proton Transport: Experiments and Simulations

“…Temperature modulated differential scanning calorimetry (DSC) indicates a T g of 103 °C when dry. 17 The detailed synthesis and further characterization of the purity of these materials, including thermal gravimetric analysis, size exclusion chromatography, nuclear magnetic resonance (NMR) spectroscopy, and DSC, were reported previously. 13 Samples were prepared from 2 to 3 weight % of lyophilized p5PhSA polymer dissolved in deionized water.…”

“…[13][14][15][16] We recently investigated p5PhSA neutralized with a variety of metal cations, and found that in the dry state the ions and sulfonate groups strongly nanophase separate from the polymer backbone and self-assemble into percolated ionic aggregates. 17 We thus anticipated that p5PhSA would also nanophase separate into hydrophilic and hydrophobic domains. Accessing high proton conductivity with this polymer could lead to a new class of scalable materials for use as PEMs.…”

“…1,3,8,9,[18][19][20] The glass transition temperature (T g ) of p5PhSA is 103 °C, and the thermal degradation temperature (T d ) is 215 °C , both high enough that p5PhSA may have the thermal and mechanical stability necessary to operate as a PEM. 13,17 While this T g is lower than many other hydrocarbon-based PEMs, it may allow for easier processing of p5PhSA at lower temperatures compared to polymers with phenyl groups in the backbone.…”

Ionic Transport and Thermodynamic Interaction in Precision Polymer Blend Electrolytes for Lithium Batteries

“…In the bulk state, p 5PhS‐Li has been recently shown to nanophase separate into percolated ionic networks driven by the flexible yet non‐polar nature of the PE backbone/phenyl rings versus the precisely spaced polar regions of the neutralized sulfonate species. [ 39 ] These networks are persistent over a large temperature range. Combining this nanophase self‐assembly with another component (PEO) may be resulting in complex phase behavior of these blends at the varying compositions studied.…”

“…[ 49,50 ] Nonetheless, the experimental results indicate some degree of miscibility, which must be the case for the blends to exhibit higher ionic conductivity than that of neat p 5PhS‐Li due to the dissociation of lithium ions into PEO. Neat p 5PhS‐Li exhibits at least 2 orders lower ionic conductivity [ 39 ] at the same measured temperature as p 5PhS‐Li/PEO blends at all compositions.…”