St Andrews Research Repository

St Andrews University Home
View Item 
  •   St Andrews Research Repository
  • Chemistry (School of)
  • Chemistry
  • Chemistry Theses
  • View Item
  •   St Andrews Research Repository
  • Chemistry (School of)
  • Chemistry
  • Chemistry Theses
  • View Item
  •   St Andrews Research Repository
  • Chemistry (School of)
  • Chemistry
  • Chemistry Theses
  • View Item
  • Login
JavaScript is disabled for your browser. Some features of this site may not work without it.

Multivalent thermal batteries : concept, development and advances

Date
29/07/2020
Author
Dickson, Stewart Alan Mackenzie
Supervisor
Irvine, John T. S.
Funder
Engineering and Physical Sciences Research Council (EPSRC)
AWE plc
Keywords
Thermal battery
Multivalent
Magnesium
Calcium
Sulfides
Phosphates
Operando neutron diffraction
Metadata
Show full item record
Altmetrics Handle Statistics
Altmetrics DOI Statistics
Abstract
Thermal batteries are single-use energy devices designed to deliver a one-time source of power. They can be adapted to fit the application, such as high currents and pulse loads, making them important in military and space applications where reliable power generation is required. This work has sought to understand and analyse the possibility of producing a thermal battery which does not rely upon traditional lithium chemistry, by finding suitable magnesium and calcium eutectic electrolytes and cell compositions to challenge the traditional thoughts surrounding thermal battery chemistries. All-magnesium thermal batteries were firstly studied by selection of magnesium-containing halide eutectics, which were analysed in depth through a variety of techniques including PXRD, SEM, wetting and conductivity. Cells were constructed using the well-characterised FeS₂ cathode material to find the optimal chemistries, of which the cells containing eutectic in the anode and eutectic and carbon in the cathode exhibited the best performance with capacities exceeding 400 mA h g⁻¹. The discharge mechanism of the cells was deemed to be unclear, with multiple possibilities examined. An operando neutron powder diffraction experiment was carried out to elucidate a mechanism, and found that MgS, FeS and iron were formed, indicating dissolution and reaction in the eutectic melt as KCl crystallised out. Also, a change in the unit cell of FeS₂ was observed, indicating some solid solution formation. Experience of the magnesium cell chemistry was transferred over to the calcium analogues. A similar approach was undertaken using the CaCl₂-NaCl eutectic salt, with a wide variety of experiments to explore the properties of the eutectic. The cells constructed for these tests were found to perform most optimally with a pure calcium anode and cathode of FeS₂ mixed with the eutectic with voltages in excess of 2 V and capacities of ~ 200 mA h g⁻¹. As the cells were not able to be optimised to reach their full discharge potential, a mechanism was derived from the PXRD analysis, which found that the conversion of the material proceeded to form CaS, but only reached around ¼ of the total theoretical discharge capacity of FeS₂, which is due to a number of factors. The operando neutron diffraction experiment proved to be less successful but did identify the presence of CaS and FeS during operation, suggesting a similar mechanism as the magnesium derivative. Finally, several new cathode materials were tested against for these cell chemistries. CoS₂ is an alternative sulfide cathode material with greater temperature resistance, and obtained similar performances to the FeS₂ material, though the discharge mechanisms observed were also affected by the conversion of CoS₂ to CoCl₂ by dissolution in the electrolyte, in both the magnesium and calcium eutectics. ZrS₃ was also synthesised and analysed as a potential cathode material in both the optimised magnesium and calcium systems, which showed some appreciable performance. Cells were then analysed in a mixed-phase by using LiCl-KCl in the magnesium cathode material. The cells performed well and demonstrated a very long discharge plateau of over 300 mA h g⁻¹ capacity, but the discharge mechanism was different to what has been observed in literature. Instead, the formation of other phases was observed instead of the Li₂ZrS₄ spinel structure shown in literature, which is explained in greater detail. Two phosphate-based materials were synthesised and characterised, Cu₃(PO₄)₂ (CP) and Na₃V₂(PO₄)₂F₃ (NVPF). Both materials were firstly studied against the lithium silicon alloy to understand their discharge mechanisms. The Cu₃(PO₄)₂ material exhibited a large sloping discharge plateau from 2.6 V, with a long discharge plateau at around 1.4 V. The discharge mechanism was deemed to follow literature procedure, converting into Li₃PO₄ and copper with a capacity of > 400 mA h g⁻¹. Substitution of copper for vanadium was found to increase the voltage of the material slightly but was not able to be substituted in significant levels due to the coordination of the copper sites in the material. At higher current densities, most of the capacity was retained and a higher initial voltage, closer to literature, was observed at the start of the discharges when the material was processed by ball milling. Multivalent cells were also explored and deemed to show some, but not ideal performance in terms of capacity and voltage. Na₃V₂(PO₄)₂F₃ was also synthesised by two separate methods. Both powders showed a pure phase and then one tested against the lithium silicon alloy. The discharge plot identified a plateau at 1.6 V which corresponded to the insertion of 1 lithium into the material. The discharge mechanism of the material was not able to be identified, due to the amorphization of the material during discharge, but it was assumed from the electrochemical data that an insertion mechanism occurred to produce the reduced Na₃LiV₂(PO₄)₂F₃ material. The rate capability of the material was also analysed and was found to perform extremely well at high current densities. A magnesium-based cell showed an expected lower voltage with lower capacity, whilst the calcium cell exhibited similar voltage plateau to the lithium derivative, however with even lower capacity than the magnesium cell. This proved that the multivalent ions were unlikely to favourably react with the material.
DOI
https://doi.org/10.17630/10023-20255
Type
Thesis, PhD Doctor of Philosophy
Rights
Embargo Date: 2022-04-16
Embargo Reason: Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 16th April 2022
Collections
  • Chemistry Theses
URI
http://hdl.handle.net/10023/20255

Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.

Advanced Search

Browse

All of RepositoryCommunities & CollectionsBy Issue DateNamesTitlesSubjectsClassificationTypeFunderThis CollectionBy Issue DateNamesTitlesSubjectsClassificationTypeFunder

My Account

Login

Open Access

To find out how you can benefit from open access to research, see our library web pages and Open Access blog. For open access help contact: openaccess@st-andrews.ac.uk.

Accessibility

Read our Accessibility statement.

How to submit research papers

The full text of research papers can be submitted to the repository via Pure, the University's research information system. For help see our guide: How to deposit in Pure.

Electronic thesis deposit

Help with deposit.

Repository help

For repository help contact: Digital-Repository@st-andrews.ac.uk.

Give Feedback

Cookie policy

This site may use cookies. Please see Terms and Conditions.

Usage statistics

COUNTER-compliant statistics on downloads from the repository are available from the IRUS-UK Service. Contact us for information.

© University of St Andrews Library

University of St Andrews is a charity registered in Scotland, No SC013532.

  • Facebook
  • Twitter