Role of Intra-Domain Heterogeneity on Ion and Polymer Dynamics in Block Polymer Electrolytes: An Approach for Spatially Resolving Dynamics and Ion Transport

The design of safe and high-performance, nanostructured block polymer (BP) electrolytes for lithium-ion batteries requires a thorough understanding of the key parameters that govern local structure and dynamics. Yet, the interfaces between microphase-separated domains can introduce complexities in this local behavior that can be challenging to quantify. Herein, the local polymer, cation (Li+), and anion dynamics were described in salt-doped polystyrene-block-poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) through a quantitative framework that considered the effects of polymer architecture, segmental mixing, chain stretching, and confinement on polymer mobility and ion transport. This framework was validated through nuclear magnetic resonance (NMR) spectroscopy measurements on solid (dry) polymer electrolyte samples. Notably, a mobility transition temperature (T-mobility) was identified through NMR spectroscopy that captured the local dynamics more accurately than the thermal glass transition temperature. Additionally, the approach quantitatively described the mobility gradient across a domain when segmental mixing effects were combined with chain stretching and confinement information, especially at higher segregation strengths, facilitating the assessment of local ion diffusion and conductivity. Spatially averaged local ion diffusion predictions quantitatively matched NMR-measured ion diffusivities in the BP samples, while spatially summed ionic conductivity predictions across a domain qualitatively captured trends in the measured ionic conductivities.

Automated summary

This study presents a quantitative framework to describe the local polymer and ion dynamics in nanostructured block polymer electrolytes, which is validated through nuclear magnetic resonance spectroscopy measurements. The framework considers various factors such as polymer architecture, segmental mixing, chain stretching, and confinement to accurately capture the local dynamics. It provides insights into ion diffusion and conductivity at the local level and shows good agreement with experimental results.