Effect of Added Salt on Disordered Poly(ethylene oxide)-Block-Poly(methyl methacrylate) Copolymer Electrolytes

Abstract

We studied the effect of salt addition on a diblock copolymer system with a negative Flory-Huggins interaction parameter, χ, indicative of attractive interactions between the two blocks. The system studied is poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-PMMA) with added lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. We studied two asymmetric block copolymers, PEO-PMMA(10-33) and PEO-PMMA(10-64), where the numbers refer to the molar masses of the blocks in kg mol -1 . The small angle X-ray scattering (SAXS) profiles for PEO-PMMA(10-33) were featureless at all salt concentrations. In contrast, PEO-PMMA(10-64) exhibited SAXS peaks when the salt concentration was between 0.22 ≤ m (mol Li/kg polymer) ≤ 0.44. The appearance of SAXS peaks only in PEO-PMMA(10-64) is consistent with the predictions of ionic self-consistent field theory developed by de la Cruz and coworkers, which predicts that in systems with negative χ, ordered phases are only found when the volume fraction of the ionic block is about 10%.

Nanostructured Ionic Separator Formed by Block Copolymer Self-Assembly: A Gateway for Alleviating Concentration Polarization in Batteries

“…The morphology of this ionic separator was studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) using ruthenium tetroxide as the staining agent for the PSLiTFSI microphase (Figure ). − The bright stripes seen in Figure represent PSLiTFSI lamellae. The domain spacing, the center-to-center distance between adjacent PSLiTFSI lamellae, was measured to be around 18 nm by using the line scan across the box indicated in the figure.…”

The Unexpected Role of Cations in the Self-Assembly of Positively Charged Amphiphiles at Liquid/Liquid Interfaces

“…This result shows that Li + directly interacts with the tail, pinning it to the interface, in a manner that is analogous to previously reported H-bonding interactions at air/aqueous interfaces decorated with ODMS-MIM + . The binding of Li + to the tail parallels the interactions found in solutions, , polymers, battery materials, − and small molecules , where solvation and pairing interactions of the Li + cation by oxygen moieties were found. Similarly, recent work has shown how contact ion pairs are preferable in Li + binding to sulfate headgroups, yet they possess weak thermodynamic binding affinities relative to larger cations .…”

A Perspective on the Design of Ion-Containing Polymers for Polymer Electrolyte Applications

“…Charged diblock copolymers are multicomponent polymeric systems usually consisting of a charged block and a neutral block, they possess unique self-assembly behaviors where ion transport provided by the charged block and mechanical support from the neutral block are combined. This unique behavior gives rise to their potential as solid polymer electrolytes in energy storage and conversion devices, among other aforementioned applications. − Phase behavior of charged block copolymers has been investigated actively over the last several years. − Ionic correlations introduced by the charged species drive phase segregation in ion-containing polymers, even in those systems whose neutral counterparts have no immiscibility at all, i.e., χN = 0 (where χ is the Flory–Huggins parameter that describes the compatibility between different types of monomers and N is the degree of polymerization). , In these cases, the skewed phase boundaries caused by phase segregation due to electrostatic effects (the “chimney effect”) results from the Coulombic interaction between charged monomers and counterions. The phase diagram also includes an inverted cylinder phase, where the majority component, i.e., the neutral block, forms the cylinders, whereas the charged block, which is the minority component of the charged diblock copolymers, forms the matrix.…”

“…The synergy of theoretical and experimental studies can contribute to closing this design loop. Novel phase behaviors observed in experiments inspire theoretical studies; self-consistent field theory and molecular dynamics simulations, in turn, have been demonstrated to be helpful to experimental investigations. − …”