Title: Molecular Level Differences in Ionic Solvation and Transport Behavior in Ethylene Oxide-Based Homopolymer and Block Copolymer Electrolytes

Abstract

Block copolymer electrolytes (BCE) such as polystyrene-block-poly(ethylene oxide) (SEO) blended with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and composed of mechanically robust insulating and rubbery conducting nanodomains are promising solid-state electrolytes for Li batteries. Here, we compare ionic solvation, association, distribution, and conductivity in SEO-LiTFSI BCEs and their homopolymer PEO-LiTFSI analogs toward a fundamental understanding of the maximum in conductivity and transport mechanisms as a function of salt concentration. Ionic conductivity measurements reveal that SEO-LiTFSI and PEO-LiTFSI exhibit similar behaviors up to a Li/EO ratio of 1/12, where roughly half of the available solvation sites in the system are filled, and conductivity is maximized. As the Li/EO ratios increase to 1/5 the conductivity, of the PEO-LiTFSI drops nearly 3-fold, while the conductivity of SEO-LiTFSI remains constant. FTIR spectroscopy reveals that additional Li cations in the homopolymer electrolyte are complexed by additional EO units when the Li/EO ratio exceeds 1/12, while in the BCE, the proportion of complexed and uncomplexed EO units remains constant; Raman spectroscopy data at the same concentrations show that Li cations in the SEO-LiTFSI samples tend to coordinate more to their counteranions. Atomistic-scale molecular dynamics simulations corroborate these results and further show that associated ions tend to segregate to themore » SEO-LiTFSI domain interfaces. The opportunity for "excess" salt to be sequestered at BCE interfaces results in the retention of an optimum ratio of uncompleted and complexed PEO solvation sites in the middle of the conductive nanodomains of the BCE and maximized conductivity over a broad range of salt concentrations.« less

Authors:

Sharon, Daniel  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3385-1536"

Bennington, Peter  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-0501-1441"

Webb, Michael A.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-7420-4474"

Deng, Chuting  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-0416-178X"

de Pablo, Juan J.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3526-516X"

Patel, Shrayesh N.  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-3657-827X"

Nealey, Paul F.  ^[1]

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• Search DOE PAGES for ORCID "0000-0003-3889-142X"

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+ Show Author Affiliations

1. Univ. of Chicago, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)
2. Univ. of Chicago, IL (United States)
3. Princeton Univ., NJ (United States)

Publication Date:

Mon Feb 22 00:00:00 EST 2021

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; National Science Foundation (NSF)

OSTI Identifier:

1821198

Grant/Contract Number:  

AC02-06CH11357; ECCS-1542205; DMR-1420709; DMR-1928629

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Volume: 143; Journal Issue: 8; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Block copolymers; Phase separation; Ion transport; Vibrational spectroscopy; Ion association; Salts; Ions; Ionic conductivity; Homopolymers; Electrolytes