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Title: Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries

Abstract

Electrolyte is the critical component of the Li-S battery. Past studies have shed light on the behavior of the Li-S cells when the electrolyte salt concentration is increased to the solvent-in-salt regime and demonstrated tremendously improved cycle life. However, there is no systematic study on the Li-S cell when the electrolyte salt concentration is reduced from the standard 1.0M condition. This work investigates the lower salt concentration regime by doing a systematic study with the standard LiTFSI in DME:DOL combination, using sulfur electrodes with relatively high loading (> 6 mg cm -2). Although reducing the electrolyte salt concentration lowers the ionic conductivity, it is found that the sulfur utilization and rate capability of the Li-S cells benefits from this process. Similar observations are also found when LiTFSI is replaced with LiI and LiBr, which form less conductive electrolytes than LiTFSI at the same concentration levels. Data correlation indicates a stronger correlation between the Li-S cell’s rate-capability and the electrolyte conductivity than electrolyte viscosity. It is proposed in this work that free Li + concentration, which is proportional to the electrolyte conductivity, is the real rate-capability determining parameter. Reducing the electrolyte salt concentration and replacing LiTFSI with less dissociable salts (LiI,more » LiBr) both will reduce the free Li + in the electrolyte, which will allow a higher saturation point of Li 2S 2/Li 2S. This probably will delay the insulating layer build-up on the cathode conductive network and improve the dissolved Li-polysulfide to Li 2S 2/Li 2S conversion efficiency. Both impedance and cathode morphology support this theorem.« less

Authors:
 [1];  [1];  [1]; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1495320
Report Number(s):
BNL-211287-2019-JAAM
Journal ID: ISSN 0013-4651
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 166; Journal Issue: 2; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Country of Publication:
United States
Language:
English
Subject:
29 ENERGY PLANNING, POLICY AND ECONOMY; Batteries Lithium; Electrolyte Concentration; Li-S Batteries; Sulfur Utilization

Citation Formats

Sun, Ke, Li, Na, Su, Dong, and Gan, Hong. Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries. United States: N. p., 2019. Web. doi:10.1149/2.0161902jes.
Sun, Ke, Li, Na, Su, Dong, & Gan, Hong. Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries. United States. doi:10.1149/2.0161902jes.
Sun, Ke, Li, Na, Su, Dong, and Gan, Hong. Fri . "Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries". United States. doi:10.1149/2.0161902jes.
@article{osti_1495320,
title = {Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries},
author = {Sun, Ke and Li, Na and Su, Dong and Gan, Hong},
abstractNote = {Electrolyte is the critical component of the Li-S battery. Past studies have shed light on the behavior of the Li-S cells when the electrolyte salt concentration is increased to the solvent-in-salt regime and demonstrated tremendously improved cycle life. However, there is no systematic study on the Li-S cell when the electrolyte salt concentration is reduced from the standard 1.0M condition. This work investigates the lower salt concentration regime by doing a systematic study with the standard LiTFSI in DME:DOL combination, using sulfur electrodes with relatively high loading (> 6 mg cm-2). Although reducing the electrolyte salt concentration lowers the ionic conductivity, it is found that the sulfur utilization and rate capability of the Li-S cells benefits from this process. Similar observations are also found when LiTFSI is replaced with LiI and LiBr, which form less conductive electrolytes than LiTFSI at the same concentration levels. Data correlation indicates a stronger correlation between the Li-S cell’s rate-capability and the electrolyte conductivity than electrolyte viscosity. It is proposed in this work that free Li+ concentration, which is proportional to the electrolyte conductivity, is the real rate-capability determining parameter. Reducing the electrolyte salt concentration and replacing LiTFSI with less dissociable salts (LiI, LiBr) both will reduce the free Li+ in the electrolyte, which will allow a higher saturation point of Li2S2/Li2S. This probably will delay the insulating layer build-up on the cathode conductive network and improve the dissolved Li-polysulfide to Li2S2/Li2S conversion efficiency. Both impedance and cathode morphology support this theorem.},
doi = {10.1149/2.0161902jes},
journal = {Journal of the Electrochemical Society},
number = 2,
volume = 166,
place = {United States},
year = {2019},
month = {1}
}

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Works referenced in this record:

Liquid electrolyte lithium/sulfur battery: Fundamental chemistry, problems, and solutions
journal, June 2013


Li�O2 and Li�S batteries with high energy storage
journal, January 2012

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