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Lithium-sulfur batteries: an investigation into the electrolyte and the polysulfide species within

Lithium-sulfur batteries: an investigation into the electrolyte and the polysulfide species within
Lithium-sulfur batteries: an investigation into the electrolyte and the polysulfide species within
The lithium-sulfur (Li-S) battery is one of the most promising candidates in next generation energy storage, offering high theoretical specific capacities through the use of inexpensive and environmentally benign positive electrode materials. However, full commercialisation has been prevented by several technical challenges, most notably polysulfide shuttling. Despite significant scientific interest in recent years, the mechanism of the discharge and charge processes is still poorly understood. Whilst it is known that a variety of different processes occur between electrochemically active species during cycling, the identity of the polysulfides species remains unknown. Additionally, the polysulfide concentrations at different stages of discharge and charge, as well as their thermodynamic and kinetic properties are still poorly understood.

In this project, the significance of cell design on the cycling performance of a Li-S battery is highlighted. The reproducibility of a selected cell design and the effect of lithium nitrate as an electrolyte additive is investigated. To obtain a thorough understanding of the electrolyte system used throughout this report (LiTFSI in DOL), various electrolytes containing different concentrations of the electrolyte salt are prepared and analysed. Using a Walden plot, it is revealed that at high salt concentrations, this electrolyte system begins to exhibit properties similar to that of an ionic liquid. Additionally, employing high salt concentrations improves the cycling performance of the Li-S battery. Two methods have been developed to quantitatively determine the total ‘sulfur’ content of an electrolyte containing polysulfides, as well as its average oxidation state. These techniques have enabled production of the first experimental ternary phase diagram for the Li-S battery. Finally, the galvanostatic intermittent titration technique (GITT) method is quantitatively analysed using a model redox system to assess its ability to determine the diffusion coefficient of the redox system. This study offers a unique assessment of the ability to use GITT to study the mass transport of polysulfide intermediates within a Li-S battery.
University of Southampton
Dibden, James William
0a189dfc-bdec-48fa-ba0f-c1d8dcaddcc2
Dibden, James William
0a189dfc-bdec-48fa-ba0f-c1d8dcaddcc2
Garcia-Araez, Nuria
9358a0f9-309c-495e-b6bf-da985ad81c37

Dibden, James William (2017) Lithium-sulfur batteries: an investigation into the electrolyte and the polysulfide species within. University of Southampton, Doctoral Thesis, 267pp.

Record type: Thesis (Doctoral)

Abstract

The lithium-sulfur (Li-S) battery is one of the most promising candidates in next generation energy storage, offering high theoretical specific capacities through the use of inexpensive and environmentally benign positive electrode materials. However, full commercialisation has been prevented by several technical challenges, most notably polysulfide shuttling. Despite significant scientific interest in recent years, the mechanism of the discharge and charge processes is still poorly understood. Whilst it is known that a variety of different processes occur between electrochemically active species during cycling, the identity of the polysulfides species remains unknown. Additionally, the polysulfide concentrations at different stages of discharge and charge, as well as their thermodynamic and kinetic properties are still poorly understood.

In this project, the significance of cell design on the cycling performance of a Li-S battery is highlighted. The reproducibility of a selected cell design and the effect of lithium nitrate as an electrolyte additive is investigated. To obtain a thorough understanding of the electrolyte system used throughout this report (LiTFSI in DOL), various electrolytes containing different concentrations of the electrolyte salt are prepared and analysed. Using a Walden plot, it is revealed that at high salt concentrations, this electrolyte system begins to exhibit properties similar to that of an ionic liquid. Additionally, employing high salt concentrations improves the cycling performance of the Li-S battery. Two methods have been developed to quantitatively determine the total ‘sulfur’ content of an electrolyte containing polysulfides, as well as its average oxidation state. These techniques have enabled production of the first experimental ternary phase diagram for the Li-S battery. Finally, the galvanostatic intermittent titration technique (GITT) method is quantitatively analysed using a model redox system to assess its ability to determine the diffusion coefficient of the redox system. This study offers a unique assessment of the ability to use GITT to study the mass transport of polysulfide intermediates within a Li-S battery.

Text
James Dibden - Thesis (with corrections) - Version of Record
Restricted to Repository staff only until 22 February 2021.
Available under License University of Southampton Thesis Licence.

More information

Published date: August 2017

Identifiers

Local EPrints ID: 419056
URI: http://eprints.soton.ac.uk/id/eprint/419056
PURE UUID: 34dc798b-694e-4093-9e6a-3ff0de7dbd97
ORCID for Nuria Garcia-Araez: ORCID iD orcid.org/0000-0001-9095-2379

Catalogue record

Date deposited: 28 Mar 2018 16:30
Last modified: 14 Mar 2019 01:35

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