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Title: Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes

Abstract

The optimization of ionic conductivity and lithium-ion battery stability can be achieved by independently tuning the ion transport and mechanical robustness of block polymer (BP) electrolytes. However, the ionic conductivity of BP electrolytes is inherently limited by the covalent attachment of the ionically conductive block to the mechanically robust block, among other factors. Herein, the BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights. The incorporation of a higher molecular weight homopolymer additive (α > 1 state) promoted a “dry brush-like” homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the “wet brush-like” (α < 1 state) and unblended composites, where α is the molecular weight ratio between the POEM homopolymer and the POEM block in the copolymer. Here, neutron and X-ray reflectometry (NR and XRR, respectively) provided additional details on the lithium salt and polymer distributions. From XRR, the α > 1 blends showed increased interfacial widths in comparison to their BP (unblended) or α < 1 counterparts because of the more central distribution of the homopolymer. This result, paired with NR data that suggested even salt concentrationsmore » across the POEM domains, implied that there was a higher salt concentration in the homopolymer POEM-rich regions in the dry brush blend than in the wet brush blend. Furthermore, using 7Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (TLi mobility) that was a function of blend type. TLi mobility was found to be 39 °C above Tg in all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the α > 1 composites, even though these composites had higher Tgs than the α < 1 composites, demonstrating that homopolymer-rich conducting pathways formed in the α > 1 assemblies had a larger influence on conductivity than the greater lithium ion mobility in the α < 1 blends.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [2];  [2]; ORCiD logo [1]
  1. University of Delaware, Newark, DE (United States)
  2. National Institute of Standards and Technology (NIST), Gaithersburg, MD (United States)
Publication Date:
Research Org.:
Univ. of Delaware, Newark, DE (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
OSTI Identifier:
1658235
Grant/Contract Number:  
SC0014458; DMR-1610134
Resource Type:
Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 52; Journal Issue: 24; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; Salts; Homopolymers; Electrolytes; Lithium; Polymers

Citation Formats

Morris, Melody A., Sung, Seung Hyun, Ketkar, Priyanka M., Dura, Joseph A., Nieuwendaal, Ryan C., and Epps, III, Thomas H.. Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes. United States: N. p., 2019. Web. https://doi.org/10.1021/acs.macromol.9b01879.
Morris, Melody A., Sung, Seung Hyun, Ketkar, Priyanka M., Dura, Joseph A., Nieuwendaal, Ryan C., & Epps, III, Thomas H.. Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes. United States. https://doi.org/10.1021/acs.macromol.9b01879
Morris, Melody A., Sung, Seung Hyun, Ketkar, Priyanka M., Dura, Joseph A., Nieuwendaal, Ryan C., and Epps, III, Thomas H.. Thu . "Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes". United States. https://doi.org/10.1021/acs.macromol.9b01879. https://www.osti.gov/servlets/purl/1658235.
@article{osti_1658235,
title = {Enhanced Conductivity via Homopolymer-Rich Pathways in Block Polymer-Blended Electrolytes},
author = {Morris, Melody A. and Sung, Seung Hyun and Ketkar, Priyanka M. and Dura, Joseph A. and Nieuwendaal, Ryan C. and Epps, III, Thomas H.},
abstractNote = {The optimization of ionic conductivity and lithium-ion battery stability can be achieved by independently tuning the ion transport and mechanical robustness of block polymer (BP) electrolytes. However, the ionic conductivity of BP electrolytes is inherently limited by the covalent attachment of the ionically conductive block to the mechanically robust block, among other factors. Herein, the BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights. The incorporation of a higher molecular weight homopolymer additive (α > 1 state) promoted a “dry brush-like” homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the “wet brush-like” (α < 1 state) and unblended composites, where α is the molecular weight ratio between the POEM homopolymer and the POEM block in the copolymer. Here, neutron and X-ray reflectometry (NR and XRR, respectively) provided additional details on the lithium salt and polymer distributions. From XRR, the α > 1 blends showed increased interfacial widths in comparison to their BP (unblended) or α < 1 counterparts because of the more central distribution of the homopolymer. This result, paired with NR data that suggested even salt concentrations across the POEM domains, implied that there was a higher salt concentration in the homopolymer POEM-rich regions in the dry brush blend than in the wet brush blend. Furthermore, using 7Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (TLi mobility) that was a function of blend type. TLi mobility was found to be 39 °C above Tg in all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the α > 1 composites, even though these composites had higher Tgs than the α < 1 composites, demonstrating that homopolymer-rich conducting pathways formed in the α > 1 assemblies had a larger influence on conductivity than the greater lithium ion mobility in the α < 1 blends.},
doi = {10.1021/acs.macromol.9b01879},
journal = {Macromolecules},
number = 24,
volume = 52,
place = {United States},
year = {2019},
month = {12}
}

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