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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an ab initio density functional study. J. Mater. Chem. A, 2018, 6, 2984-2994

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[4] Jonathan P. Neidhardt et al. A Flexible Framework for Modeling Multiple Solid, Liquid and Gaseous

Phases in Batteries and Fuel Cells. J. Electrochem. Soc., 2012, 159 (8), A1528-A1542

[5] Andreas F. Hofmann et al., Mechanistic modeling of polysulfide shuttle and capacity loss in lithiumsulfur

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Figure 1