Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen
<p>Lithium-oxygen batteries (LOBs) have attracted immense research interest as they have the highest theoretical energy density among the advanced battery systems. Achieving such high energy densities can substantially reduce the need for fossil fuels, enable greater use of renewable energy, a...
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| Formato: | Tese |
| Idioma: | English |
| Publicado em: |
2022
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| _version_ | 1826316931183935488 |
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| author | Zor, C |
| author2 | Bruce, P |
| author_facet | Bruce, P Zor, C |
| author_sort | Zor, C |
| collection | OXFORD |
| description | <p>Lithium-oxygen batteries (LOBs) have attracted immense research interest as they have the highest theoretical energy density among the advanced battery systems. Achieving such high energy densities can substantially reduce the need for fossil fuels, enable greater use of renewable energy, and revolutionise the transportation sector. However, due to the complexity of oxygen reduction and evolution reaction chemistries and reactivity of reduced oxygen species, LOBs still need significant improvement in their fundamental understanding to overcome the electrolyte and cathode stability issues.</p>
<p>In the Thesis, firstly, the redox mediated charging process was studied to understand the mechanism to enable fast charging with low overpotentials and side reactions. It is demonstrated that the redox mediated oxidation follows Marcus theory of electron transfer and the rate limiting step is the first 1-electron oxidation, Li<sub>2</sub>O<sub>2</sub> → LiO<sub>2</sub>. The kinetically dominant step is the LiO<sub>2</sub> disproportionation. It is also shown that the singlet oxygen (<sup>1</sup>O<sub2</sub>) yield does not correlate with the amount of degradation. This casts doubt on whether <sup>1</sup>O<sub>2</sub> is the main cause of degradation in LOBs.</p>
<p>Secondly, due to the discrepancy in <sup>1</sup>O<sub2</sub> and electrolyte degradation amounts, the stability of the common LOB salts and solvents towards <sup>1</sup>O<sub>2</sub> were tested. It is shown that tetraglyme-LiTFSI, one of the most widely used electrolytes, is stable towards <sup>1</sup>O<sub>2</sub> under chemical conditions. In the LOB literature, <sup>1</sup>O<sub>2</sub> is mainly detected and quantified using DMA, a <sup>1</sup>O<sub>2</sub> trap. Here, it is revealed that DMA can react with superoxide depending on the salt-solvent combination and DMAO<sub>2</sub>, the reaction product of <sup>1</sup>O<sub>2</sub> with DMA, can degrade into by-products depending on the solvent environment. </p>
<p>Finally, the stability of the electrolyte and the cathode towards <sup>1</sup>O<sub>2</sub> under electrochemical conditions and the real cause of faradaic efficiency loss are investigated. It is demonstrated that <sup>1</sup>O<sub>2</sub> is not the main source of degradation and fresh Li<sub>2</sub>O<sub>2</sub> surfaces is the culprit. This finding should redirect the focus of LOB research from avoiding <sup>1</sup>O<sub>2</sub> to developing electrolytes inert towards peroxide and peroxide-derived side products for an electro/chemically stable cell.
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| first_indexed | 2024-03-07T07:38:33Z |
| format | Thesis |
| id | oxford-uuid:ce27d3a8-0d85-4d2b-8145-bc805da7c7d6 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2025-02-19T04:30:37Z |
| publishDate | 2022 |
| record_format | dspace |
| spelling | oxford-uuid:ce27d3a8-0d85-4d2b-8145-bc805da7c7d62025-01-02T09:43:53ZUnravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygenThesishttp://purl.org/coar/resource_type/c_db06uuid:ce27d3a8-0d85-4d2b-8145-bc805da7c7d6BatteriesEnergy storageEnglishHyrax Deposit2022Zor, CBruce, P<p>Lithium-oxygen batteries (LOBs) have attracted immense research interest as they have the highest theoretical energy density among the advanced battery systems. Achieving such high energy densities can substantially reduce the need for fossil fuels, enable greater use of renewable energy, and revolutionise the transportation sector. However, due to the complexity of oxygen reduction and evolution reaction chemistries and reactivity of reduced oxygen species, LOBs still need significant improvement in their fundamental understanding to overcome the electrolyte and cathode stability issues.</p> <p>In the Thesis, firstly, the redox mediated charging process was studied to understand the mechanism to enable fast charging with low overpotentials and side reactions. It is demonstrated that the redox mediated oxidation follows Marcus theory of electron transfer and the rate limiting step is the first 1-electron oxidation, Li<sub>2</sub>O<sub>2</sub> → LiO<sub>2</sub>. The kinetically dominant step is the LiO<sub>2</sub> disproportionation. It is also shown that the singlet oxygen (<sup>1</sup>O<sub2</sub>) yield does not correlate with the amount of degradation. This casts doubt on whether <sup>1</sup>O<sub>2</sub> is the main cause of degradation in LOBs.</p> <p>Secondly, due to the discrepancy in <sup>1</sup>O<sub2</sub> and electrolyte degradation amounts, the stability of the common LOB salts and solvents towards <sup>1</sup>O<sub>2</sub> were tested. It is shown that tetraglyme-LiTFSI, one of the most widely used electrolytes, is stable towards <sup>1</sup>O<sub>2</sub> under chemical conditions. In the LOB literature, <sup>1</sup>O<sub>2</sub> is mainly detected and quantified using DMA, a <sup>1</sup>O<sub>2</sub> trap. Here, it is revealed that DMA can react with superoxide depending on the salt-solvent combination and DMAO<sub>2</sub>, the reaction product of <sup>1</sup>O<sub>2</sub> with DMA, can degrade into by-products depending on the solvent environment. </p> <p>Finally, the stability of the electrolyte and the cathode towards <sup>1</sup>O<sub>2</sub> under electrochemical conditions and the real cause of faradaic efficiency loss are investigated. It is demonstrated that <sup>1</sup>O<sub>2</sub> is not the main source of degradation and fresh Li<sub>2</sub>O<sub>2</sub> surfaces is the culprit. This finding should redirect the focus of LOB research from avoiding <sup>1</sup>O<sub>2</sub> to developing electrolytes inert towards peroxide and peroxide-derived side products for an electro/chemically stable cell. </p> |
| spellingShingle | Batteries Energy storage Zor, C Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title | Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title_full | Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title_fullStr | Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title_full_unstemmed | Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title_short | Unravelling the degradation pathways and charging mechanism in the Li-O2 battery: the role of singlet oxygen |
| title_sort | unravelling the degradation pathways and charging mechanism in the li o2 battery the role of singlet oxygen |
| topic | Batteries Energy storage |
| work_keys_str_mv | AT zorc unravellingthedegradationpathwaysandchargingmechanisminthelio2batterytheroleofsingletoxygen |