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

Journal Article · · Journal of the Electrochemical Society
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  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
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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.

Research Organization:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0012704
OSTI ID:
1495320
Report Number(s):
BNL-211287-2019-JAAM
Journal Information:
Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 2 Vol. 166; ISSN 0013-4651
Publisher:
The Electrochemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Sulfur Speciation in Li–S Batteries Determined by Operando X-ray Absorption Spectroscopy journal September 2013
The Use of Redox Mediators for Enhancing Utilization of Li 2 S Cathodes for Advanced Li–S Battery Systems journal February 2014
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A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries journal February 2013
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Effect of Electrolyte on High Sulfur Loading Li-S Batteries journal January 2018
Electrochemical Impedance Spectroscopy Study of a Lithium/Sulfur Battery: Modeling and Analysis of Capacity Fading journal January 2013
Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries journal December 2014

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29 ENERGY PLANNING, POLICY, AND ECONOMY
Batteries Lithium
Electrolyte Concentration
Li-S Batteries
Sulfur Utilization