Structure–Property Relationships in Single-Ion Conducting Multiblock Copolymers: A Phase Diagram and Ionic Conductivities

Abstract

We investigated the nanoscale morphologies and ionic conductivities of polyethylene-based multiblock copolymers as single-ion conducting polymer electrolytes. These polymers contain short polar blocks with a single sodium sulfonate group separated by polyethylene blocks of fixed length (PESxNa, x = 10, 12, and 18). At room temperature, these multiblock copolymers exhibit layered ionic aggregates with semicrystalline polyethylene backbones. For PES12Na and PES18Na, the layered ionic aggregate morphologies transition into Ia3̅d gyroid morphologies upon melting the polyethylene blocks and further transition into hexagonal morphologies at higher temperatures. With a shorter polyethylene block, PES10Na exhibits a layered to hexagonal transition at the melting temperature, without an intermediate gyroid morphology. The phase diagram of these PESxNa polymers is reminiscent of conventional diblock copolymers and identifies the presence of gyroid morphologies at a polar block volume fraction of ∼0.27 to 0.41, which is broad compared to typical diblock copolymers. Temperature-dependent ionic conductivities reveal faster ion transport through bicontinuous gyroids than hexagonal ionic aggregate morphologies and a relationship between conductivity and the characteristic distance between ionic aggregates. This study presents material design strategies for single-ion conducting polymers with a bicontinuous ionic aggregate and toward efficient ion transport.

Sub-3-Nanometer Domain Spacings of Ultrahigh-χ Multiblock Copolymers with Pendant Ionic Groups

“…The absence of recrystallization in these polymers is attributed mainly to the strong polar interactions that slow the crystallization kinetics. Similar behavior was previously observed with the sodium sulfonate multiblock copolymers (PES x Na) in our previous studies . The morphological transitions characterized by X-ray scattering experiments are consistent with the thermal transitions observed in the DSC (Figures S4 and S5).…”

“…Similar behavior was previously observed with the sodium sulfonate multiblock copolymers (PESxNa) in our previous studies. 45 The morphological transitions characterized by X-ray scattering experiments are consistent with the thermal transitions observed in the DSC (Figures S4 and S5).…”

“…Ion-containing polymer systems are a promising strategy for preparing high-χ multiblock copolymers, because the presence of ionic groups effectively increases the segregation strength between the blocks. ,− For example, our previous studies examined the phase behaviors of polyethylene-based sodium sulfosuccinate (PES x Na) multiblock copolymers, which contain short polar blocks with pendant Na + SO 3 – groups and nonpolar polyethylene blocks of x carbons ( x = 10–48). − Notably, these ion-containing multiblock copolymers microphase separate into ordered morphologies such as lamellar, gyroid, and hexagonally packed cylinder morphologies, and the smallest domain spacing is ∼2.2 nm in the lamellar and hexagonal morphologies of PES10Na. These results suggest that the nonpolar polyethylene blocks are highly incompatible with the polar ionic blocks, indicating a high χ in these PES x Na polymers.…”

Dry Polymer Electrolyte Concepts for Solid‐State Batteries

“…[45,46] The issues related with the determination of the initial current may be circumvented by a galvanostatic or low-frequency EIS approach. [46][47][48][49] Sometimes, the ratio of the measured self-diffusion coefficient of the alkali metal atom (e.g., 7 Li, 23 Na) to the sum of the self-diffusion coefficient of the alkali metal atom and the atom found in the anion (e.g., 19 F) from a pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is given as an additional t +,eff value. These values are less insightful than the ones observed from the electrochemical measurements, as the average of all species containing the atom are being measured, regardless of their charge and moving direction.…”

“…The repulsion of the two blocks induces structural microphase separation (e.g., local segregation) often leading to formation of periodical, nanoscale domains such as lamellar or gyroid phases. [16][17][18][19] For extracting maximal benefit from the two polymer blocks, one block is tuned to be a stiff high-T g polymer such as polystyrene (PS) or poly(methyl acrylate) (PMMA), while the other is a more ionically conductive low-T g polymer, such as PEO. [20][21][22] Polymerized ionic liquids prepared by ion exchange reactions or direct copolymerization of the two ionic liquid monomers are another interesting type of polymer electrolytes, where targeted molecular design could potentially lead to a number of useful materials.…”