Intrinsic Ion Transport Properties of Block Copolymer Electrolytes

Daniel Sharon; Peter Bennington; Moshe Dolejsi; Michael A Webb; Ban Xuan Dong; Juan J de Pablo; Paul F Nealey; Shrayesh N Patel

doi:10.1021/acsnano.0c03713

Intrinsic Ion Transport Properties of Block Copolymer Electrolytes

ACS Nano. 2020 Jul 28;14(7):8902-8914. doi: 10.1021/acsnano.0c03713. Epub 2020 Jun 16.

Authors

Daniel Sharon^{1

2

3}, Peter Bennington¹, Moshe Dolejsi¹, Michael A Webb⁴, Ban Xuan Dong¹, Juan J de Pablo^{1

2

3}, Paul F Nealey^{1

2

3}, Shrayesh N Patel^{1

2}

Affiliations

¹ Pritzker School of Molecular Engineering, University of Chicago, 5640 S. Ellis Avenue, Chicago, Illinois 60637, United States.
² Center for Molecular Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
³ Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
⁴ Department of Chemical and Biological Engineering, Princeton University, 50-70 Olden Street, Princeton, New Jersey 08540, United States.

PMID: 32496776
DOI: 10.1021/acsnano.0c03713

Abstract

Knowledge of intrinsic properties is of central importance for materials design and assessing suitability for specific applications. Self-assembling block copolymer electrolytes (BCEs) are of great interest for applications in solid-state energy storage devices. A fundamental understanding of ion transport properties, however, is hindered by the difficulty in deconvoluting extrinsic factors, such as defects, from intrinsic factors, such as the presence of interfaces between the domains. Here, we quantify the intrinsic ion transport properties of a model BCE system consisting of poly(styrene-block-ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt using a generalizable strategy of depositing thin films on interdigitated electrodes and self-assembling fully connected parallel lamellar structures throughout the films. Comparison between conductivity in homopolymer poly(ethylene oxide) (PEO)-LiTFSI electrolytes and the analogous conducting material in SEO over a range of salt concentrations (r, molar ratio of lithium ion to ethylene oxide repeat units) and temperatures reveals that between 20% and 50% of the PEO in SEO is inactive. Using mean-field theory calculations of the domain structure and monomer concentration profiles at domain interfaces-both of which vary substantially with salt concentration-the fraction of inactive PEO in the SEO, as derived from conductivity measurements, can be quantitatively reconciled with the fraction of PEO that is mixed with greater than a few volume percent of polystyrene. Despite the detrimental interfacial effects for ion transport in BCEs, the intrinsic conductivity of the SEO studied here (ca. 10^-3 S/cm at 90 °C, r = 0.085) is an order of magnitude higher than reported values from bulk samples of similar molecular weight SEO (ca. 10^-4 S/cm at 90 °C, r = 0.085). Overall, this work provides motivation and methods for pursuing improved BCE chemical design, interfacial engineering, and processing.

Keywords: block copolymer; ionic conductivity; lithium ion battery; nanomaterials; polymer electrolyte.