Quantifying Intrinsic Interfacial Transport Properties in Block Copolymer Electrolytes

Nanostructure-forming block copolymer electrolytes are of great interest related to their application towards a variety of electrochemical devices. However, questions remain about the nature of ion transport through these nanostructured materials. Specifically, decoupling extrinsic structural effects of tortuosity and grain boundaries from intrinsic phenomena occurring near the block copolymer domain interface has been challenging. This is due to the difficulty in precisely controlling or quantifying the film structure. Here, we present a new platform to probe defect-free single grains of any block copolymer electrolyte. We specifically focus on a model system of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) with LiTFSI to quantitatively demonstrate that interfacial mixing is the predominant factor in reducing ionic mobility near the interface. Using SCFT calculations we directly correlate the interfacial width to reduced ionic conductivity as a function of lithium salt concentration. These findings are supported by atomistic simulations, which give further insight into the exact mechanisms by which this mixing layer restricts ion motion.