INSIGHT STUDY OF BIFUNCTIONAL REDOX MEDIATORS INTERPLAYING WITH SUPEROXIDE INTERMEDIATES IN LI-O2 BATTERIES

锂氧电池中双功能均相催化剂与超氧化物中间体相互作用的深入研究

吴思思

11655005

博士

哲学博士

材料科学与工程

卢周广

2021-12-17

2022-07-02

新加坡国立大学

新加坡

While profound studies have been carried out in the past three decades, Li-O2 battery remains at the infant stage and falls far behind commercialization despite its ultrahigh energy density. The sluggish reaction kinetics, which is one of the culprits of the low energy efficiency and poor rate performance, has drawn particular attention to the advancement of electrocatalysts. However, challenges relating surface passivation and heterogeneous catalysts’ deactivation by Li2O2 precipitation remain, leading to the rise of homogeneous catalysts (redox mediators, RMs). Despite the efficient homogenous catalysts, their interplay pertaining to reactive LiO2 intermediates remains vague. Given the instability and short life span of LiO2 intermediates in low donor number solvents, strategies that tune the solubility of them and increase the attainable capacity are imperatively anticipated to contribute to a stably rechargeable Li-O2 battery with high energy density. Therefore, this thesis aims to probe different bifunctional redox mediators from the aspect of interplay with LiO2 intermediates in low DN solvents and capacity. Chapter 1 presents a comprehensive background and review of redox mediators for Li-O2 batteries. Chapter 2 introduces the experimental methods applied in the thesis. Chapter 3 demonstrates a bifunctional redox mediator, duroquinone (DQ), as both electron and superoxide shuttles, which enhances the solvation of LiO2 intermediates and increases the capacity. On revealing the catalytic pathway of DQ, direct correlation between its role of superoxide shuttle and the promoted solution reaction route is well established by monitoring the change of lifetime of LiO2 intermediates via electron paramagnetic resonance (EPR) spectroscopy. Chapter 4 reveals another type of bifunctional redox mediator, EV, which exhibits the reverse effect on the LiO2 intermediates as a superoxide quencher. Contradictory to the common knowledge, the promotion of surface reaction route by the presence of such superoxide quencher does not lead to premature death, providing a new direction for screening for efficient redox mediators and increasing the battery stability. Finally, Chapter 5 concludes the thesis and proposes future research direction for redox mediators for rechargeable Li-O2 batteries.

得益于其超高的理论能量密度，锂空气电池在过去的三十年中被高度重视和深入研究。然而三十年过去了，锂空气电池的研究进展仍处于实验室水平，离商业化程度尚有非常大的空间。对于锂空气电池而言，缓慢的反应动力学是低能量效率和低速率性能的罪魁祸首之一，从而引发人们对电化学催化剂的特别关注。然而，放电过程中过氧化锂的生成和堆积仍会导致正极表面钝化和固态催化剂的失活，严重降低了锂空气电池的比容量。针对这一问题，均相催化剂进入人们的视线。 均相催化剂于2013年首次被运用在锂空气电池中。虽然许多均相催化剂已被证实对催化氧还原反应有着不错的效果，但它们与活性LiO2中间体之间的相互作用仍不明确。鉴于LiO2中间体在低供体数溶剂中的不稳定性所导致的容量受限，研究人员针对其溶解度选择了一些功能性的添加剂，以助于实现具有高能量密度且循环稳定的锂空气电池。 然而，添加剂的存在依然具有一定的局限性和安全隐患。因此，本论文旨在对调节LiO2中间体溶解度和寿命的双功能均相催化剂进行催化机理的探索和其催化性能的研究。 第一章介绍了锂空气电池的基本内容和均相催化剂的研究综述。第二章介绍了本论文采用的实验方法和设计思路。第三章以杜醌为例，展示了一类能作为超氧介质的双功能均相催化剂。该类催化剂能增强LiO2中间体的溶剂化从而增加锂空气电池的容量。通过电子顺磁共振（EPR）光谱监测LiO2中间体的寿命变化，很好地建立了其超氧介质功能与促进溶液反应路线之间的直接关联。第四章以乙基紫精为例揭示了另一种双功能均相催化剂，该类催化剂作为超氧化物猝灭剂对LiO2中间产物表现出相反的作用。与常识相矛盾的是，这种超氧化物猝灭剂的存在促进了表面反应途径的同时并未导致锂空气电池的容量衰减。该工作为筛选功能性的均相催化剂和提高电池稳定性提供了新的方向。最后，第五章对全文进行了总结，并对二次锂空气电池均相催化剂的研究前景进行了展望。

Li-O2 battery redox mediator LiO2 oxygen reduction reaction

锂空气电池 均相催化剂 超氧化锂 氧还原反应

English

Wu SS. INSIGHT STUDY OF BIFUNCTIONAL REDOX MEDIATORS INTERPLAYING WITH SUPEROXIDE INTERMEDIATES IN LI-O2 BATTERIES[D]. 新加坡. 新加坡国立大学,2021.