Multi-Reaction Numerical Modeling of Lithium-Sulfur Cells
Authors: Korff Daniel M. , DeCaluwe Steven C. , Colclasure Andrew M. , Smith Kandler 
Published: December 2020

Lithium-sulfur batteries present a promising alternative to current, widely commercialized lithium-ion
battery technology. Lithium-sulfur batteries take advantage of the high specific capacity (~1675 Ah/kgsulfur)
and abundance of sulfur in an attempt to produce lighter, cheaper batteries for portable applications.
Despite promising theoretical capacity, commercialization of lithium-sulfur batteries is limited by low
conductivity of cathode end products and low battery cyclability. The first issue requires an electrically
conductive cathode host network, typically carbon, which reduces the specific capacity. The second issue
is due to polysulfide shuttling, which can lead to precipitation of insoluble intermediates and loss of active
material.
Current research is largely focused on either preventing the dissolution of intermediate products into the
electrolyte or preventing their migration to the anode where they can be reduced to insoluble species [1-3].
Concurrent efforts to reduce the electroltyte/sulfur ratio will maximize the battery’s gravimetric energy
density. For any of these strategies, it is critical to understand and control the impact on the intermediate
species concentrations in the electrolyte, both to optimize performance and to minimize capacity fade due
to precipitation of species which exceed their solubility limits.
The proposed presentation will demonstrate a physico-chemical model of a lithium-sulfur battery with
detailed intermediate chemistry, thermodynamic consistency, and physically derived parameters. At
present, most models trade off one or more of these model components for others [4-6]. Model results are
validated against operando measurements of dissolved polysulfide concentrations in the electrolyte [7,8].
Results will demonstrate how C-rate, electrolyte/sulfur ratio, sulfur loading, and cation-selective
membranes impact cell performance and battery lifetime.
Figures 1 and 2 show preliminary model results for varying C-rates. The discharge profiles in Figure 1
indicate only moderate losses in potential with increasing C-rate. However, these are associated with a
shift toward lower-order, less-soluble polysulfides, as shown in Figure 2, the irreversible precipitation of
which leads to capacity fade over multiple cycles. In this manner, the model serves as a quantitative guide
to the rational design and operation of next-generation Li-S batteries. In this presentation, we will discuss
implications from the model results regarding the battery design and operating strategies to mitigate Li-S
battery degradation while improving metrics such as gravimetric energy and power density.
References
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Phases in Batteries and Fuel Cells. J. Electrochem. Soc., 2012, 159 (8), A1528-A1542
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Figure 1