Role of polymer architecture and interfacial mixing on ion transport in linear-brush polyether-based block copolymer electrolytes

Polyether-based block copolymers, in which two or more blocks self-assemble into phase-separated nanostructures, are of great interest for use as solid polymer electrolytes for lithium ion batteries as the constituent blocks can be independently tuned to impart multiple desirable, yet orthogonal thermal, mechanical, and electrochemical properties to the resulting material. Previous experimental and simulation work focused on linear-linear polyether-based block copolymer electrolytes, particularly PS-PEO/LiTFSI, found ionic conductivity to be highly dependent on segregation strength and that disruption of the solvation sites connectivity derived from interfacial mixing of PS with PEO is a more likely explanation for the lower conductivity typically observed near domains interface rather than just differences in glass transition temperature between blocks. [1] A clearer understanding on the relationship between polymer architecture and interfacial mixing with ion conduction, however, is still missing. In this work, we explore the role of polymer architecture and interfacial mixing on the ion transport in linear-brush block copolymer electrolytes as a function of side-chain length of the brush block. To this aim we prepared a series of lamella forming block copolymers with LiTFSI, specifically poly(trifluoroethyl methacrylate)-b-poly(ethylene glycol methyl ether methacrylate) (PTFEMA-b-POEM) to probe the effect of the branched architecture on the ionic conductivity, and further characterized them by impedance spectroscopy, vibrational spectroscopy, and soft X-ray reflectivity to determine and compare the ionic conductivity, degree of dissociation, polymer dynamics as well as the interface characteristics of such materials. In addition, we coupled molecular dynamic simulations to the experimental work to gain insights of the mechanisms and barriers to ion transport near the domain interface at the molecular level. Overall, we found polymer architecture and interface characteristics play a big role in determining conductivity in these systems.

[1] ACS Nano 2020, 14, 7, 8902–8914