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Lithium-oxygen batteries: the significance of the electrolyte and the use of soluble catalysts

Lithium-oxygen batteries: the significance of the electrolyte and the use of soluble catalysts
Lithium-oxygen batteries: the significance of the electrolyte and the use of soluble catalysts
Research has been carried out into lithium-oxygen cells over the last 20 years in an effort to develop the next generation of energy storage devices. Due to the high theoretical specific capacity of lithium peroxide, 1165 mAh . g-1Li2O2, lithium-oxygen cells promise to deliver high specific energy devices. However, their development has been hampered by several issues, including degradation reactions primarily initiated by the reactive superoxide radical, an intermediate reduction product of oxygen. Another issue is the slow kinetics of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this work the use of in situ SERS spectroscopy as a method for monitoring the degradation of electrolytes has been investigated. It was demonstrated that it was possible to monitor the formation of superoxide in two ionic liquids. As the experiment progressed it was possible to monitor the formation of breakdown products resulting from degradation reactions in one ionic liquid, while in the second ionic liquid it was possible to observe the formation of lithium peroxide, the desired discharge product.

The use of soluble redox catalyst for both the ORR and OER offers many advantages in lithium-oxygen cells. This is primarily a result of the nature of the lithium peroxide discharge product. As it is both insoluble and insulating, it forms a deposit on the electrode surface that limits the cell performance. In this work we have demonstrated techniques that can be used to assess the performance of potential soluble redox catalysts. Based on their standard potentials and their Gibbs free energy of reaction ethyl viologen was identified as being a suitable redox catalyst of the ORR, while cobalt terpyridine (CoTerpy) was identified as being a suitable catalyst of both the ORR and the OER. However, experimental results showed that while ethyl viologen was an efficient mediator of the ORR CoTerpy was not able to mediate the ORR or the OER.
Frith, James
349b19de-36a7-4136-9f2d-af8160311d38
Frith, James
349b19de-36a7-4136-9f2d-af8160311d38
Owen, John
067986ea-f3f3-4a83-bc87-7387cc5ac85d

(2016) Lithium-oxygen batteries: the significance of the electrolyte and the use of soluble catalysts. University of Southampton, Department of Chemsitry, Doctoral Thesis, 233pp.

Record type: Thesis (Doctoral)

Abstract

Research has been carried out into lithium-oxygen cells over the last 20 years in an effort to develop the next generation of energy storage devices. Due to the high theoretical specific capacity of lithium peroxide, 1165 mAh . g-1Li2O2, lithium-oxygen cells promise to deliver high specific energy devices. However, their development has been hampered by several issues, including degradation reactions primarily initiated by the reactive superoxide radical, an intermediate reduction product of oxygen. Another issue is the slow kinetics of both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this work the use of in situ SERS spectroscopy as a method for monitoring the degradation of electrolytes has been investigated. It was demonstrated that it was possible to monitor the formation of superoxide in two ionic liquids. As the experiment progressed it was possible to monitor the formation of breakdown products resulting from degradation reactions in one ionic liquid, while in the second ionic liquid it was possible to observe the formation of lithium peroxide, the desired discharge product.

The use of soluble redox catalyst for both the ORR and OER offers many advantages in lithium-oxygen cells. This is primarily a result of the nature of the lithium peroxide discharge product. As it is both insoluble and insulating, it forms a deposit on the electrode surface that limits the cell performance. In this work we have demonstrated techniques that can be used to assess the performance of potential soluble redox catalysts. Based on their standard potentials and their Gibbs free energy of reaction ethyl viologen was identified as being a suitable redox catalyst of the ORR, while cobalt terpyridine (CoTerpy) was identified as being a suitable catalyst of both the ORR and the OER. However, experimental results showed that while ethyl viologen was an efficient mediator of the ORR CoTerpy was not able to mediate the ORR or the OER.

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Published date: 14 March 2016
Organisations: University of Southampton, Chemistry

Identifiers

Local EPrints ID: 393075
URI: http://eprints.soton.ac.uk/id/eprint/393075
PURE UUID: 241bedee-b870-4973-b03e-e9134cb5ca2f
ORCID for John Owen: ORCID iD orcid.org/0000-0002-4938-3693

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Date deposited: 22 Apr 2016 14:03
Last modified: 14 Jul 2018 00:37

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