Electrostatically Tuned Microdomain Morphology and Phase-Dependent Ion Transport Anisotropy in Single-Ion Conducting Block Copolyelectrolytes

Abstract

Block copolyelectrolytes are solid-state singleion conductors which phase separate into ubiquitous microdomains to enable both high ion transference number and structural integrity. Ion transport in these charged block copolymers highly depends on the nanoscale microdomain morphology; however, the influence of electrostatic interactions on morphology and ion diffusion pathways in block copolyelectrolytes remains an obscure feature. In this paper, we systematically predict the phase diagram and morphology of diblock copolyelectrolytes using a modified dissipative particle dynamics simulation framework, considering both explicit electrostatic interactions and ion diffusion dynamics. Various experimentally controllable conditions are considered here, including block volume fraction, Flory−Huggins parameter, block charge fraction or ion concentration, and dielectric constant. Boundaries for microphase transitions are identified based on the computed structure factors, mimicking small-angle X-ray scattering patterns. Furthermore, we develop a novel "diffusivity tensor" approach to predict the degree of anisotropy in ion diffusivity along the principal microdomain orientations, which leads to highthroughput mapping of phase-dependent ion transport properties. Inclusion of ions leads to a significant leftward and upward shift of the phase diagram due to ion-induced excluded volume, increased entropy of mixing, and reduced interfacial tension between dissimilar blocks. Interestingly, we discover that the inverse topology gyroid and cylindrical phases are ideal candidates for solid-state electrolytes in metal-ion batteries. These inverse phases exhibit an optimal combination of high ion conductivity, well-percolated diffusion pathways, and mechanical robustness. Finally, we find that higher dielectric constants can lead to higher ion diffusivity by reducing electrostatic cohesions between the charged block and counterions to facilitate ion diffusion across block microdomain interfaces. This work significantly expands the design space for emerging block copolyelectrolytes and motivates future efforts to explore inverse phases to avoid engineering hurdles of aligning microdomains or removing grain boundaries.

Triblock Copolymer/Polyoxometalate Nanocomposite Electrolytes with Inverse Hexagonal Cylindrical Nanostructures

“…[ 3–5 ] Theoretical simulations and experimental results demonstrated that ion conductivity of nanostructured block copolymer electrolytes highly depends on ionic domain continuity and orientations across grain boundaries. [ 6–10 ] Among diverse morphologies, the double gyroid phases and inverse hexagonal cylinders with ion‐conductive domains as the matrix (HEX′) have attracted more interest. Owing to the interconnected three‐dimensional ion‐conductive domains, these morphologies can promote more efficient ion transport while retaining a percolated mechanical phase.…”

“…Owing to the interconnected three‐dimensional ion‐conductive domains, these morphologies can promote more efficient ion transport while retaining a percolated mechanical phase. [ 7,9,11 ] Considering the double gyroid phases occupy a narrow phase window in the phase diagram and their formation usually requires rigorously controlled conditions, the attention paid to the HEX′ phase has gradually increased. [ 12 ]…”

“…[3][4][5] Theoretical simulations and experimental results demonstrated that ion conductivity of nanostructured block copolymer electrolytes highly depends on ionic domain continuity and orientations across grain boundaries. [6][7][8][9][10] Among diverse morphologies, the double gyroid phases and inverse hexagonal cylinders with ion-conductive domains as the matrix as proton-conducting channels. [41] Our group utilized POMs as electrostatic crosslinkers to access bicontinuous nanocomposites with enhanced proton conductivity and modulus from lamellar poly(styrene-block-2-vinylpyridine) (PS-b-P2VP).…”

“…Owing to the interconnected three-dimensional ion-conductive domains, these morphologies can promote more efficient ion transport while retaining a percolated mechanical phase. [7,9,11] Considering the double gyroid phases occupy a narrow phase window in the phase diagram and their formation usually requires rigorously controlled conditions, the attention paid to the HEX′ phase has gradually increased. [12] Changing the block volume fraction and the incompatibility between blocks via covalent or non-covalent modification of traditional linear block copolymers usually results in the variation of intrinsic self-assembled morphologies and the appearance of intriguing new morphologies.…”

Tailored morphology and highly enhanced phonon transport in polymer fibers: a multiscale computational framework

“…A scalable modeling framework, enabled by coarse-grained (CG) MD simulations, could greatly extend the length and time scales of conventional AA-MD simulations by two orders of magnitude. [32][33][34][35] However, to the best of our knowledge, the application of CG-MD simulations to precisely model heat conduction in thermally drawn bulk polymer fibers has not been reported yet.…”