A model based approach to identifying performance limitations in lithium-sulfur batteries: from coin to pouch-cells
File(s)
Author(s)
Olisa, Elizabeth
Type
Thesis
Abstract
Lithium-sulfur (Li-S) batteries offer a promising alternative to current lithium-ion (Li-ion) batteries, with a high theoretical energy density, improved safety and high abundance of low cost materials. To be used commercially, it is essential to understand how the behaviour scales between cell formats. Physical differences contribute to the behavioural differences, in terms of achievable capacity, cyclability and potential degradation mechanisms.
To improve understanding of the causes of the observed behaviour changes, both experimental and modelling work is required. This work focuses on the steps required to capture and test coin-cell behaviour, building upon the existing pouch-cell models within the literature. The 0D model first tests the experimental hypotheses proposed, before implementing upgrades to improve the capability in terms of scaling and causality of predictions. The first upgrade to the model is the removal of the assumption of total active material utilisation, and the introduction of pore volume directly. This creates separate regions inside the cell which are later used in a simplified transport mechanism; the location of species within each region enables the 0D model to capture C-rate dependence. The following upgrade is to the porosity and area equations, creating separate dependencies on the influence of electrolyte volume and wetting, and precipitation leading to pore blocking. The model then separates the precipitation mechanism, accounting for both nucleation and particle growth, rather than assuming one mechanism occurs consistently throughout cycling.
The final model makes significant improvements to the capability and applicability of existing models; it captures many experimentally observed features that vary when scaling between cell formats, confirming the upgraded mechanisms are at least one explanation for the behaviour. Further work focusing on cell chemistry and degradation mechanisms is required for the model to be used alongside experimental testing to help determine the optimum conditions during cell manufacture.
To improve understanding of the causes of the observed behaviour changes, both experimental and modelling work is required. This work focuses on the steps required to capture and test coin-cell behaviour, building upon the existing pouch-cell models within the literature. The 0D model first tests the experimental hypotheses proposed, before implementing upgrades to improve the capability in terms of scaling and causality of predictions. The first upgrade to the model is the removal of the assumption of total active material utilisation, and the introduction of pore volume directly. This creates separate regions inside the cell which are later used in a simplified transport mechanism; the location of species within each region enables the 0D model to capture C-rate dependence. The following upgrade is to the porosity and area equations, creating separate dependencies on the influence of electrolyte volume and wetting, and precipitation leading to pore blocking. The model then separates the precipitation mechanism, accounting for both nucleation and particle growth, rather than assuming one mechanism occurs consistently throughout cycling.
The final model makes significant improvements to the capability and applicability of existing models; it captures many experimentally observed features that vary when scaling between cell formats, confirming the upgraded mechanisms are at least one explanation for the behaviour. Further work focusing on cell chemistry and degradation mechanisms is required for the model to be used alongside experimental testing to help determine the optimum conditions during cell manufacture.
Version
Open Access
Date Issued
2025-01-04
Date Awarded
01/09/2025
License URL
Advisor
Marinescu, Monica
Titirici, Magda
Wang, Huizhi
Cornish, Michael
Sponsor
The Faraday Institution
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)