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An unsuitable Li-O2 battery electrolyte made suitable with the use of redox mediators

An unsuitable Li-O2 battery electrolyte made suitable with the use of redox mediators
An unsuitable Li-O2 battery electrolyte made suitable with the use of redox mediators
The unique properties of room temperature ionic liquids make them promising electrolytes for next-generation rechargeable batteries. Unfortunately, many promising ionic liquid electrolytes suffer degradation under the operation conditions of Li-O2 batteries. This work demonstrates that the addition of redox mediators can transform the reaction mechanism and suppress the degradation of the electrolytes in Li-O2 batteries. 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide (EMIMTFSI) is a room temperature ionic liquid that is widely being explored for battery applications, but its instability in the presence of reduced oxygen species (superoxide) limits application in Li-O2 batteries. The addition of redox mediators can suppress the degradation of EMIMTFSI in Li-O2 cells, leading to remarkable improvements in capacity and reversibility. In-situ Surface Enhanced Raman Spectroscopy and operando-pressure evaluation demonstrate that 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) is capable of suppressing the attack of superoxide species against EMIMTFSI, thus promoting the desirable 2-electron pathway to Li2O2 discharge product. A detailed evaluation of the gas evolution was carried out using online mass spectrometry. In spite of an efficient 2-electron oxygen reduction with the use of DBBQ additive, this effect did not translate into a substantial improvement in the oxygen evolution during charging. However, when a charge mediator was used in combination with DBBQ, a significant improvement in oxygen evolution could be observed. This work provides the first direct experimental evidence that redox mediators can enable the incorporation of electrolytes prone to degradation by the attack of superoxide species in practical and reversible Li-O2 batteries.
1932-7447
20241-20250
Padmanabhan, Vivek
edf1af56-581e-4653-9887-b98a99c0e314
Garcia-Araez, Nuria
9358a0f9-309c-495e-b6bf-da985ad81c37
Homewood, Thomas
10b9670e-7275-4f27-a98c-690d1a3472ad
Padmanabhan, Vivek
edf1af56-581e-4653-9887-b98a99c0e314
Garcia-Araez, Nuria
9358a0f9-309c-495e-b6bf-da985ad81c37
Homewood, Thomas
10b9670e-7275-4f27-a98c-690d1a3472ad

Padmanabhan, Vivek, Garcia-Araez, Nuria and Homewood, Thomas (2019) An unsuitable Li-O2 battery electrolyte made suitable with the use of redox mediators. The Journal of Physical Chemistry C, 123 (33), 20241-20250. (doi:10.1021/acs.jpcc.9b03403).

Record type: Article

Abstract

The unique properties of room temperature ionic liquids make them promising electrolytes for next-generation rechargeable batteries. Unfortunately, many promising ionic liquid electrolytes suffer degradation under the operation conditions of Li-O2 batteries. This work demonstrates that the addition of redox mediators can transform the reaction mechanism and suppress the degradation of the electrolytes in Li-O2 batteries. 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide (EMIMTFSI) is a room temperature ionic liquid that is widely being explored for battery applications, but its instability in the presence of reduced oxygen species (superoxide) limits application in Li-O2 batteries. The addition of redox mediators can suppress the degradation of EMIMTFSI in Li-O2 cells, leading to remarkable improvements in capacity and reversibility. In-situ Surface Enhanced Raman Spectroscopy and operando-pressure evaluation demonstrate that 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) is capable of suppressing the attack of superoxide species against EMIMTFSI, thus promoting the desirable 2-electron pathway to Li2O2 discharge product. A detailed evaluation of the gas evolution was carried out using online mass spectrometry. In spite of an efficient 2-electron oxygen reduction with the use of DBBQ additive, this effect did not translate into a substantial improvement in the oxygen evolution during charging. However, when a charge mediator was used in combination with DBBQ, a significant improvement in oxygen evolution could be observed. This work provides the first direct experimental evidence that redox mediators can enable the incorporation of electrolytes prone to degradation by the attack of superoxide species in practical and reversible Li-O2 batteries.

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acs.jpcc.9b03403 - Accepted Manuscript
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Accepted/In Press date: 15 July 2019
e-pub ahead of print date: 15 July 2019
Published date: 2019

Identifiers

Local EPrints ID: 433118
URI: http://eprints.soton.ac.uk/id/eprint/433118
ISSN: 1932-7447
PURE UUID: 3fe90537-5597-4870-bf98-89020508e897
ORCID for Vivek Padmanabhan: ORCID iD orcid.org/0000-0002-6088-312X
ORCID for Nuria Garcia-Araez: ORCID iD orcid.org/0000-0001-9095-2379

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Date deposited: 08 Aug 2019 16:30
Last modified: 07 Oct 2020 05:23

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Contributors

Author: Vivek Padmanabhan ORCID iD
Author: Thomas Homewood

University divisions

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