Developing metal-salen complexes as redox mediators for lithium-air batteries

开发金属-salen配合物作为锂空气电池的氧化还原介体

• 批准号: 2444464
• 金额: --
• 依托单位: University of Nottingham
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2444464
• 关键词: Developing; metal; salen; complexes; redox

The drive towards a greener, sustainable future is leading to increased research into next-generation energy storage devices. In due course, it is anticipated for renewable energy sources, such as solar and wind, to replace non renewable fuels as the major means of consumer energy production. However, their intermittency requires the use of electrical grid energy storage systems. As such, the development of efficient, sustainable energy storage devices is essential to further a greener future. One of the most promising is the lithium air battery, which offers ample competition to the current market leader, lithium ion batteries. The coupling of a lithium metal negative electrode and porous carbon, air-breathing positive electrode leads to a high theoretical gravimetric energy density of 3500 Wh kg 1 an order of magnitude greater than current lithium ion technology. The use of more abundant materials, such as lithium and carbon, is a monumental shift away from using less abundant, and more expensive transition metals in electrode structures. Furthermore, the cell chemistry relies on the reaction of lithium with oxygen, the latter of which is readily available from air. However, despite its high theoretical performance and sustainable design, there are significant issues to address before lithium-air batteries are commercialised. They suffer from sluggish reaction kinetics of the discharge/charge reactions; poor solubility and electrical conductivity of the discharge product, lithium peroxide (Li2O2); and passivation of the positive electrode by Li2O2. To tackle the electrochemical difficulties encountered in lithium air batteries, redox mediators can be added to the electrolyte. These are homogenous catalysts, which are capable of transferring electrons from the positive electrode to intermediate species in solution. In doing so, the rate performance of the cell during discharge/charge is significantly enhanced, and many of the issues outlined can be alleviated. This project will embark on developing a coherent mechanistic understanding of how redox mediators operate in lithium-air batteries. To do so, a class of molecule, known as metal salen complexes, will be used throughout the project. This class has been specifically chosen due to its high versatility in functionalisation. By modifying the structure of the molecule, its various properties can be fine-tuned, namely: the solvent reorganisation energy, binding site, and redox potential. It is expected by altering mediator structures and its properties outlined above, it will be forced to adopt an inner or outer-sphere electron transfer mechanism. Throughout the project, metal salen complex derivatives will be synthesised and initially screened for chemical and electrochemical stability in lithium-air battery electrolytes. Techniques such as cyclic voltammetry and nuclear magnetic resonance spectroscopy will be used to obtain mediator redox potentials, and mediator/electrolyte degradation. Chemical reaction of Li2O2 with mediators will be assessed, where techniques such as UV-Vis spectroscopy will be employed - promising mediators will be taken forward. Scanning electrochemical microscopy (SECM) will be employed to obtain kinetic information of Li2O2 in the presence of synthesised mediators. This technique will be coupled with others such as EPR and Raman spectroscopy to monitor formation of new intermediates or bonds. Finally, cell cycling will be employed to assess the stability of mediator in the presence of lithium metal; shuttling of mediator between electrodes; and performance of mediators in standard lithium-air cells.

为了实现更绿色、可持续的未来，人们对下一代储能设备的研究越来越多。在适当的时候，预计可再生能源，如太阳能和风能，将取代不可再生燃料，成为消费能源生产的主要手段。然而，它们的不稳定性需要使用电网能量存储系统。因此，开发高效、可持续的储能设备对于进一步实现更绿色的未来至关重要。其中最有前途的是锂空气电池，它为目前的市场领导者锂离子电池提供了充分的竞争。锂金属负电极和多孔碳、吸气正电极的耦合导致3500 Wh kg-1的高理论重量能量密度，比当前的锂离子技术大一个数量级。使用更丰富的材料，如锂和碳，是从在电极结构中使用不太丰富和更昂贵的过渡金属的巨大转变。此外，电池化学依赖于锂与氧的反应，后者很容易从空气中获得。然而，尽管锂空气电池具有高理论性能和可持续设计，但在锂空气电池商业化之前，仍有一些重大问题需要解决。它们具有放电/充电反应的缓慢反应动力学;放电产物过氧化锂（Li 2 O2）的溶解性和导电性差;以及正极被Li 2 O2钝化。 为了解决锂空气电池中遇到的电化学困难，可以将氧化还原介体添加到电解质中。这些是均相催化剂，其能够将电子从正电极转移到溶液中的中间物质。这样做，电池在放电/充电期间的倍率性能显著增强，并且可以缓解所概述的许多问题。 该项目将着手开发一个连贯的机制，了解氧化还原介质如何在锂空气电池中工作。为了做到这一点，一种被称为金属萨伦络合物的分子将在整个项目中使用。由于其在功能化方面的高度通用性，该类别已被特别选择。通过改变分子的结构，可以微调其各种性质，即：溶剂重组能，结合位点和氧化还原电位。通过改变介体的结构和性质，将迫使其采用内层或外层电子转移机制。在整个项目中，将合成金属salen络合物衍生物，并初步筛选其在锂空气电池电解质中的化学和电化学稳定性。技术，如循环伏安法和核磁共振光谱将用于获得介体氧化还原电位，和介体/电解质降解。将评估Li 2 O2与介质的化学反应，其中将采用紫外-可见光谱等技术-将采用有前途的介质。将采用扫描电化学显微镜（SECM），以获得动力学信息的Li 2 O2在合成的介质的存在下。这项技术将与其他技术如EPR和拉曼光谱相结合，以监测新的中间体或键的形成。最后，将采用电池循环来评估在锂金属存在下介体的稳定性;介体在电极之间的穿梭;以及介体在标准锂-空气电池中的性能。