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Design and Validation of a Computational Model of the Lithium/Sulfur Cell

Fronczek, David Norman and Latz, Arnulf and Cairns, Elton J. and Bessler, Wolfgang G. (2014) Design and Validation of a Computational Model of the Lithium/Sulfur Cell. 17th International Meeting on Lithium Batteries, 10.-14. Jun. 2014, Como, Italien.

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The lithium-sulfur (Li/S) battery is among the most promising next-generation systems for electrochemical energy storage. Its key benefits are improved specific energy and volumetric energy density as well as cheap, safe, and environmentally benign raw materials. Recent advancements in rate capability and cycle life bring the system even closer to practical applications. However, the complex redox chemistry of sulfur, the large number of soluble intermediates and the dissolution and precipitation of solid phases, still present a major challenge to understanding and mastering Li/S electrochemistry. The goal of this work is to contribute to the understanding and design of future Li/S batteries by investigating the internal states of a battery via simulations with a physically-based electrochemical model of the cell. The computational model used for this work is based on our previously published model of the Li/S cell including a multi-step reaction mechanism, a detailed model of the evolution of solid phases as well as multi-component mass and charge transport in the liquid electrolyte. To parameterize and refine the model, experimental data were obtained from Li/S coin cells operated under various conditions. The cells used for this study are composed of Li metal anodes, an ionic liquid based electrolyte and positive electrodes made from a carbon/binder/lithium sulfide composite. The techniques used for analysis include electrochemical methods, i.e., short and long term cycling at different charge/discharge rates, cyclic voltammetry, impedance spectroscopy (also during cycling) as well as ex situ methods, e.g. SEM imaging at various states of charge and states of health. Along with prior knowledge about the materials used and the geometrical properties of the cells, these data were used to determine most parameters required by the model. Using the refined model, experimental results can be reproduced with good agreement. Validated in such a way, the model is used to simulate properties of the Li/S cell that are not easily accessible by experiments, e.g., lithium and polysulfide concentration gradients within the electrolyte and electrode volume expansion during cycling. Results include simulations of charge/discharge profiles and electrochemical impedance spectra as well as distribution of solids and concentration profiles. The results confirm that the discharge behavior for the most common type of Li/S cell is governed by the presence of solid reactant and product phases in exchange with the dissolved sulfur poly-anions. The first and second discharge stages are characterized by the presence of solid S8 and Li2S, respectively, while all sulfur compounds are dissolved in the electrolyte during an intermediate stage. Simulated electrochemical impedance spectra indicate that the contributions of various processes to the cell's overpotential are significantly different for different stages of charge. These findings help to understand what is happening in the cell during operation, which in turn allows for the identification of optimized operating conditions as well as the improvement of cell design on the electrode and material level.

Item URL in elib:https://elib.dlr.de/88861/
Document Type:Conference or Workshop Item (Poster)
Title:Design and Validation of a Computational Model of the Lithium/Sulfur Cell
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Fronczek, David Normandavid.fronczek (at) dlr.deUNSPECIFIED
Latz, Arnulfarnulf.latz (at) dlr.deUNSPECIFIED
Cairns, Elton J.Lawrence Berkeley National LaboratoryUNSPECIFIED
Bessler, Wolfgang G.Hochschule OffenburgUNSPECIFIED
Date:13 June 2014
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:Modellierung; modeling; lithium-sulfur battery; Lithium-Schwefel Batterie; DENIS; validation; Modellvalidierung
Event Title:17th International Meeting on Lithium Batteries
Event Location:Como, Italien
Event Type:international Conference
Event Dates:10.-14. Jun. 2014
Organizer:The Electrochemical Society
HGF - Research field:Energy
HGF - Program:Efficient Energy Conversion and Use (old)
HGF - Program Themes:Fuel Cells (old)
DLR - Research area:Energy
DLR - Program:E EV - Energy process technology
DLR - Research theme (Project):E - Elektrochemische Prozesse (old)
Location: Stuttgart , other
Institutes and Institutions:Institute of Engineering Thermodynamics > Computational Electrochemistry
Deposited By: Fronczek, David N.
Deposited On:22 Apr 2014 14:32
Last Modified:31 Jul 2019 19:46

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