A zero dimensional model of lithium–sulfur batteries during charge and discharge

Abstract

Lithium-sulfur cells present an attractive alternative to Li-ion batteries due to their large energy density, safety, and possible low cost. Their successful commercialisation is dependent on improving their performance, but also on acquiring sufficient understanding of the underlying mechanisms to allow for the development of predictive models for operational cells. To address the latter, we present a zero dimensional model that predicts many of the features observed in the behaviour of a lithium-sulfur cell during charge and discharge. The model accounts for two electrochemical reactions via the Nernst formulation, power limitations through Butler-Volmer kinetics, and precipitation/dissolution of one species, including nucleation. It is shown that the flat shape of the low voltage plateau typical of the lithium-sulfur cell discharge is caused by precipitation. During charge, it is predicted that the dissolution can act as a bottleneck, because for large enough currents the amount that dissolves becomes limited. This results in reduced charge capacity and an earlier onset of the high plateau reaction, such that the two voltage plateaus merge. By including these effects, the model improves on the existing zero dimensional models, while requiring considerably fewer input parameters and computational resources than one dimensional models. The model also predicts that, due to precipitation, the customary way of experimentally obtaining the open circuit voltage from a low rate discharge might not be suitable for lithium-sulfur. This model can provide the basis for mechanistic studies, identification of dominant effects in a real cell, predictions of operational behaviour under realistic loads, and control algorithms for applications.

Electrodeposition Kinetics in Li-S Batteries: Effects of Low Electrolyte/Sulfur Ratios and Deposition Surface Composition

“…The increase in polarization is especially dramatic for the feature associated with nucleation and growth, where the minimum voltage now reaches 1.81 V as opposed to 2.08 V for E/S ratio of 7.9 mL/g S. Taken relative to the equilibrium voltage for the Li 2 S plateau of 2.19 V, these voltage minima correspond to overpotentials of 380 mV and 110 mV for E/S of 4.2 and 7.0 mL/g S, respectively. 11,[23][24][25] The nucleation and growth process clearly become much more sluggish as electrolyte volume decreases and maximum polysulfide concentration increases, as is further quantified below.…”

The Effect of Current Inhomogeneity on the Performance and Degradation of Li-S Batteries

“…• C cell is the incomplete dissolution of precipitated Li 2 S, 23 as it is charged with a higher average current. The degradation of the 40…”

Solvent Effects on Polysulfide Redox Kinetics and Ionic Conductivity in Lithium-Sulfur Batteries

“…[10][11][12] Previously, several of the present authors published an experimental study of the kinetics of Li 2 S deposition from polysulfide solutions. 13 Here we extend our investigation to the important rate limiting processes in the soluble regime, where x in Li 2 S x is between 4 and 8, which have not been extensively reported.…”