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Mechanistic Understanding and Novel ...

Liang, Zhuojian.

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Mechanistic Understanding and Novel Cell Design for Reversible Lithium-oxygen Batteries.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Mechanistic Understanding and Novel Cell Design for Reversible Lithium-oxygen Batteries./
作者:	Liang, Zhuojian.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	126 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-08, Section: B.
Contained By:	Dissertations Abstracts International80-08B.
標題:	Alternative Energy. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13837764
ISBN:	9780438850620

Mechanistic Understanding and Novel Cell Design for Reversible Lithium-oxygen Batteries.
Liang, Zhuojian.

Mechanistic Understanding and Novel Cell Design for Reversible Lithium-oxygen Batteries. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 126 p.

Source: Dissertations Abstracts International, Volume: 80-08, Section: B.

Thesis (Ph.D.)--The Chinese University of Hong Kong (Hong Kong), 2018.

This item is not available from ProQuest Dissertations & Theses.

Lithium-oxygen (Li-O2) batteries have the potential to provide 2-5 times higher energy density compared to current commercial Li-ion batteries and is one of the most promising nextgeneration batteries to enable wide penetration of renewable energy and electric transportation. However, the application of Li-O2 batteries is hindered by critical challenges including low energy efficiency, low rate capability and most critically, limited cycle life. These challenges are intricately associated with the various instability factors of the Li-O2 chemistry. This thesis aimed to develop mechanistic understanding of the instability issue of Li-O 2 batteries and based on which propose novel cell designs to address the instabilities and achieve high-energy-density, efficient and truly reversible Li-O2 batteries. We developed a high-temporal-resolution online electrochemical mass spectrometry system to quantitatively analyze gas evolution from the cell in situ and generate direct evidence of the underlying reactions. Using this custom-built tool, the reaction mechanism of charging Li-O2 batteries with redox mediators was investigated. We revealed that the electrochemical pathway of Li 2O2 oxidation is intrinsically unstable, which leads to parasitic product generation. In contrast, mediator-assisted Li2O2 oxidation (chemical pathway) bypasses the formation of unstable intermediates and thereby suppresses instabilities. We further showed that the mediator's effectiveness in suppressing side reactions is much more pronounced at high charging rates owing to fast charge-transfer kinetics of the redox mediator. This study demonstrates that transforming electrooxidation of Li2O 2 to chemical oxidation of Li2O2 is a promising strategy to simultaneously mitigate reaction instabilities and achieve low overpotentials for Li-O2 batteries. To eliminate cathode decomposition in Li-O2 batteries, we proposed a novel strategy to protect the cathode during cell operation. We demonstrated that creating a dynamic O2 shield in the vicinity of the cathode using reduced discharge mediator effectively eliminates cathode degradation. A novel cell configuration is designed to manipulate the diffusion fluxes of reduced discharge mediator and O2, thereby forming a dynamic O2 shield which depletes O2 in the cathode and hence isolates the cathode from reactive oxygen species. With protection by the O2 shield, 98% of the by-products on cathode are eliminated, achieving a more than 10-fold increase in cycle life compared to conventional dual-mediator cells. This work demonstrates an effective approach to achieve efficient and long-life Li-O2 batteries. To guide further improvement of Li-O2 batteries protected by dynamic O2 shield, we developed a model of the diffusion and reaction processes to quantitatively analyse the discharge and charge stages. Simulation results reveal in detail the spatial and temporal evolution of key species including mediators, O2 and Li2O2 throughout cycling. The predicted behaviour is consistent with the experiment results. By providing different inputs of cell parameters to the model, we showed that the protection effect can be further enhanced by tuning the structural and operational parameters, especially by reducing O2 solubility. The model and simulation described in this work provides a quantified and intuitive tool for better understanding and further development of cathode-protected Li-O2 batteries.

ISBN: 9780438850620Subjects--Topical Terms:

1035473
Alternative Energy.
Subjects--Index Terms:

Energy storage

Mechanistic Understanding and Novel Cell Design for Reversible Lithium-oxygen Batteries.
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520 $a Lithium-oxygen (Li-O2) batteries have the potential to provide 2-5 times higher energy density compared to current commercial Li-ion batteries and is one of the most promising nextgeneration batteries to enable wide penetration of renewable energy and electric transportation. However, the application of Li-O2 batteries is hindered by critical challenges including low energy efficiency, low rate capability and most critically, limited cycle life. These challenges are intricately associated with the various instability factors of the Li-O2 chemistry. This thesis aimed to develop mechanistic understanding of the instability issue of Li-O 2 batteries and based on which propose novel cell designs to address the instabilities and achieve high-energy-density, efficient and truly reversible Li-O2 batteries. We developed a high-temporal-resolution online electrochemical mass spectrometry system to quantitatively analyze gas evolution from the cell in situ and generate direct evidence of the underlying reactions. Using this custom-built tool, the reaction mechanism of charging Li-O2 batteries with redox mediators was investigated. We revealed that the electrochemical pathway of Li 2O2 oxidation is intrinsically unstable, which leads to parasitic product generation. In contrast, mediator-assisted Li2O2 oxidation (chemical pathway) bypasses the formation of unstable intermediates and thereby suppresses instabilities. We further showed that the mediator's effectiveness in suppressing side reactions is much more pronounced at high charging rates owing to fast charge-transfer kinetics of the redox mediator. This study demonstrates that transforming electrooxidation of Li2O 2 to chemical oxidation of Li2O2 is a promising strategy to simultaneously mitigate reaction instabilities and achieve low overpotentials for Li-O2 batteries. To eliminate cathode decomposition in Li-O2 batteries, we proposed a novel strategy to protect the cathode during cell operation. We demonstrated that creating a dynamic O2 shield in the vicinity of the cathode using reduced discharge mediator effectively eliminates cathode degradation. A novel cell configuration is designed to manipulate the diffusion fluxes of reduced discharge mediator and O2, thereby forming a dynamic O2 shield which depletes O2 in the cathode and hence isolates the cathode from reactive oxygen species. With protection by the O2 shield, 98% of the by-products on cathode are eliminated, achieving a more than 10-fold increase in cycle life compared to conventional dual-mediator cells. This work demonstrates an effective approach to achieve efficient and long-life Li-O2 batteries. To guide further improvement of Li-O2 batteries protected by dynamic O2 shield, we developed a model of the diffusion and reaction processes to quantitatively analyse the discharge and charge stages. Simulation results reveal in detail the spatial and temporal evolution of key species including mediators, O2 and Li2O2 throughout cycling. The predicted behaviour is consistent with the experiment results. By providing different inputs of cell parameters to the model, we showed that the protection effect can be further enhanced by tuning the structural and operational parameters, especially by reducing O2 solubility. The model and simulation described in this work provides a quantified and intuitive tool for better understanding and further development of cathode-protected Li-O2 batteries.
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