Novel electrolyte materials for rechargeable magnesium metal batteries
Novel electrolyte materials for rechargeable magnesium metal batteries
Rechargeable magnesium metal batteries (RMBs) are a potential candidate for the next generation of energy storage solutions due to the low cost, high theoretical volumetric capacity, and low reduction potentials (-2.37 V vs. SHE) of Mg. However, the development of RMBs is hindered by several pitfalls yet to be effectively addressed. One of these challenges is the development of an electrolyte that facilitates reversible Mg redox reactions without reducing on the Mg anode surface, forming an insulating passivation layer. Additionally, current electrolyte candidates for RMBs contain chloride ions which are corrosive to the current collectors and other cell parts. Hence, this work aims to develop chloride-free electrolytes which exhibit reversible plating/stripping of Mg and compatibility with current cathode materials.
Work is started on the standardisation of the electrochemical measurements, demonstrating the importance of the use of a distinct reference electrode within RMBs. Often, within the literature, the Mg counter electrode is also used as the reference electrode, which leads to changes on the Mg surface being attributed to the working electrode. Hence, by using a separate Mg reference electrode, the accuracy of electrochemical measurements is improved. However, further work is still required to identify an optimal reference electrode material. Additionally, the optimal formulation of a Chevrel phase, Mo6S8 cathode is explored to preserve comparability between electrochemical measurements on the electrolyte materials, this work aimed to investigate.
The development of electrolyte materials compatible with the Mg metal electrode is an important challenge in the realisation of the RMB. Fluorinated weakly coordinating anions have recently been utilised in Mg electrolytes with success noted with [Mg(DME)3][Al(HFIP)4]2 in glyme-based solvents. The novel complex, [Mg(THF)6][Al(HFIP)4]2, was successfully isolated and employed as an electrolyte in THF, showing favourable plating/stripping behaviour of Mg on an Au working electrode. Work was expanded to investigate the effects of complexation to macrocyclic ligands on electrochemical performance. It was found that by incorporating 18-crown-6 to form the complex, [Mg(18-crown-6)(THF)2][Al(HFIP)4]2, ionic conductivity, stripping efficiencies and solubility in non-ethereal solvent was improved.
Additionally, by adding a stoichiometric amount of 15-crown-5 to the electrolyte of 0.65 mol dm-3 [Mg(THF)6][Al(HFIP)4]2 / THF, both ionic conductivity and stripping efficiency are increased significantly. Finally, dual Mg salt electrolytes were investigated using a mixture of commercially sourced, and synthesised materials. The synthesis and characterisation of [Mg(THF)6][B(HFIP)4]2 was reported for the first time. Mg(TFSI)2, Mg(BH4)2, [Mg(THF)6][B(HFIP)4]2 Mg(BOB)2 and Mg(DFOB)2 were added to aliquots of 0.25 mol dm-3 [Mg(DME)3][Al(HFIP)4]2 in a 50 mmol dm-3 concentration. It was found that by adding Mg(TFSI)2, Mg(BOB)2 and Mg(DFOB)2 there was a significant hindrance in the plating/stripping of Mg on an Au working electrode, however, improvement was seen in the stripping efficiencies and ionic conductivities with the addition of Mg(BH4)2 and [Mg(THF)6][B(HFIP)4]2.
University of Southampton
Daw, Megan Rebecca
b1228283-4c69-432b-a5a1-8e4aef79e4df
2025
Daw, Megan Rebecca
b1228283-4c69-432b-a5a1-8e4aef79e4df
Hector, Andrew
f19a8f31-b37f-4474-b32a-b7cf05b9f0e5
Reid, Gill
37d35b11-40ce-48c5-a68e-f6ce04cd4037
Daw, Megan Rebecca
(2025)
Novel electrolyte materials for rechargeable magnesium metal batteries.
University of Southampton, Doctoral Thesis, 152pp.
Record type:
Thesis
(Doctoral)
Abstract
Rechargeable magnesium metal batteries (RMBs) are a potential candidate for the next generation of energy storage solutions due to the low cost, high theoretical volumetric capacity, and low reduction potentials (-2.37 V vs. SHE) of Mg. However, the development of RMBs is hindered by several pitfalls yet to be effectively addressed. One of these challenges is the development of an electrolyte that facilitates reversible Mg redox reactions without reducing on the Mg anode surface, forming an insulating passivation layer. Additionally, current electrolyte candidates for RMBs contain chloride ions which are corrosive to the current collectors and other cell parts. Hence, this work aims to develop chloride-free electrolytes which exhibit reversible plating/stripping of Mg and compatibility with current cathode materials.
Work is started on the standardisation of the electrochemical measurements, demonstrating the importance of the use of a distinct reference electrode within RMBs. Often, within the literature, the Mg counter electrode is also used as the reference electrode, which leads to changes on the Mg surface being attributed to the working electrode. Hence, by using a separate Mg reference electrode, the accuracy of electrochemical measurements is improved. However, further work is still required to identify an optimal reference electrode material. Additionally, the optimal formulation of a Chevrel phase, Mo6S8 cathode is explored to preserve comparability between electrochemical measurements on the electrolyte materials, this work aimed to investigate.
The development of electrolyte materials compatible with the Mg metal electrode is an important challenge in the realisation of the RMB. Fluorinated weakly coordinating anions have recently been utilised in Mg electrolytes with success noted with [Mg(DME)3][Al(HFIP)4]2 in glyme-based solvents. The novel complex, [Mg(THF)6][Al(HFIP)4]2, was successfully isolated and employed as an electrolyte in THF, showing favourable plating/stripping behaviour of Mg on an Au working electrode. Work was expanded to investigate the effects of complexation to macrocyclic ligands on electrochemical performance. It was found that by incorporating 18-crown-6 to form the complex, [Mg(18-crown-6)(THF)2][Al(HFIP)4]2, ionic conductivity, stripping efficiencies and solubility in non-ethereal solvent was improved.
Additionally, by adding a stoichiometric amount of 15-crown-5 to the electrolyte of 0.65 mol dm-3 [Mg(THF)6][Al(HFIP)4]2 / THF, both ionic conductivity and stripping efficiency are increased significantly. Finally, dual Mg salt electrolytes were investigated using a mixture of commercially sourced, and synthesised materials. The synthesis and characterisation of [Mg(THF)6][B(HFIP)4]2 was reported for the first time. Mg(TFSI)2, Mg(BH4)2, [Mg(THF)6][B(HFIP)4]2 Mg(BOB)2 and Mg(DFOB)2 were added to aliquots of 0.25 mol dm-3 [Mg(DME)3][Al(HFIP)4]2 in a 50 mmol dm-3 concentration. It was found that by adding Mg(TFSI)2, Mg(BOB)2 and Mg(DFOB)2 there was a significant hindrance in the plating/stripping of Mg on an Au working electrode, however, improvement was seen in the stripping efficiencies and ionic conductivities with the addition of Mg(BH4)2 and [Mg(THF)6][B(HFIP)4]2.
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Published date: 2025
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Local EPrints ID: 501216
URI: http://eprints.soton.ac.uk/id/eprint/501216
PURE UUID: 503499b4-e8d4-4d3e-9bc4-41686e7d96e7
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Date deposited: 27 May 2025 17:45
Last modified: 11 Sep 2025 03:24
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Megan Rebecca Daw
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