CAREER: Probing Polysulfide Redox Chemistry in Tunable Metal-Organic Frameworks for Energy Storage

尽管锂离子电池已经彻底改变了便携式设备和电动汽车的发展，但它们仍然受到低电荷存储容量和高成本的限制。硫锂电池利用廉价的硫材料，其储存能力是目前锂离子电池的10倍，是极具吸引力的储能装置。然而，锂硫电池寿命短，导致电池更换频繁。该职业奖项目由材料研究部固态和材料化学项目支持，通过使用金属有机框架（mof）作为评估电池内部硫化学的定义良好的模型系统，阐明了迄今为止阻碍锂硫电池采用的关键电化学过程。mof是一种多孔材料，由有序排列的连接金属离子和有机化合物的网络组成。金属离子和有机连接体可以很容易地改变，从而产生一系列具有不同结构和化学功能的材料。通过这种方式，可以操纵mof来模拟电池环境，以揭示化学机制。PI和她的研究小组推进了锂硫电池重要电化学挑战的基础知识，并发现了新的电池材料。可替代的高密度能量存储设备，如锂硫电池，可以应用于较小的便携式设备，远程电动汽车和可靠的电网管理。通过这个项目，PI还促进了当地小学生、研究生和博士后在科学话语中的参与，特别是在能源领域。此外，PI还设计了一个新的互动课程，将其纳入现有的课后项目，为巴尔的摩市中心的小学生提供服务。这个动手演示系列旨在激发五年级学生评估他们作为消费者和未来科学家在能源技术进步中的作用。该项目的科学和教育价值推动了储能技术的前沿，促进了研究人员和年轻学生之间的公众参与，并与可持续能源未来的国家利益保持一致。从本质上讲，当今现代电池的所有降解过程都涉及复杂界面上的不良反应。本项目使用分子功能化技术在几何和原子定义良好的化学系统上建立材料设计标准。金属有机框架（MOFs）用于阐明影响多孔材料中电荷输运的因素，并制定新的策略来促进锂硫（Li-S）电池中高效的多硫氧化还原。锂- s电池的能量密度可以达到锂电池的10倍，硫是地球上丰富且价格合理的。然而，锂硫电池的商业化受到多硫化物溶解和硫利用不完全导致循环性能不稳定的挑战。这个CAREER项目由材料研究部固态和材料化学项目支持，利用mof的可调性和模块化来解耦结构和化学变量，以获得锂- s电池中潜在电荷传输和氧化还原过程的基础知识。利用Zr mof作为强大的模型系统，Thoi研究小组致力于1)确定孔隙结构、离子扩散和多硫化物氧化还原特性之间的结构-性能-功能关系；2)加入氧化还原活性成分来控制电子和离子传输；3)嵌入化学锚来捕获多硫化物，以获得其氧化还原化学的机理。对结构-性质关系的原子理解为新型功能硫电极的设计提供了标准。所获得的基础知识也使未来用于电化学应用的新型电荷导电材料的开发成为可能，从而将mof的应用范围从传统的气体存储和分离扩展到电子设备。这个职业奖项目还促进了当地小学生、研究生和博士后在科学话语中的参与，特别是在能源领域。一个名为“EnergyNOW!”的示范系列是为参加课后STEM项目的五年级学生开发的，目的是让学生检查他们与能源的关系。每节课都包括一个激发科学探究的问答环节，一个包含角色扮演和/或实验的演示，以及一个鼓励解决问题和决策的实践活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Part 1: NON-TECHNICAL SUMMARYAlthough lithium ion batteries have revolutionized the development of portable devices and electric vehicles, they are still limited by their low charge storage capacity and high cost. Lithium sulfur batteries, which utilizes inexpensive sulfur materials, are attractive energy storage devices with up to 10 times the storage ability of current lithium ion batteries. However, lithium sulfur batteries have short lifetimes, leading to frequent battery replacement. This CAREER award project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, elucidates the critical electrochemical processes that have so far hindered the adoption of lithium sulfur batteries by using metal-organic frameworks (MOFs) as a well-defined model system for evaluating the sulfur chemistry inside a battery. MOFs are porous materials that are composed of a network of connected metal ions and organic compounds arranged in an ordered fashion. The metal ions and organic linkers can be easily changed to generate a series of materials with different structures and chemical functionalities. In this way, MOFs can be manipulated to simulate battery environments for uncovering chemical mechanisms. The PI and her research group advance the fundamental knowledge on an important electrochemical challenge to Lithium sulfur batteries, and discovery of new battery materials. Alternative high-density energy storage devices, such as lithium sulfur batteries, may enable applications in smaller portable devices, long-range electric vehicles, and reliable electric grid management. Through this project the PI also promotes engagement between local elementary school students, graduate students, and postdoctoral fellows in scientific discourse, particularly in the area of energy. Additionally the PI designs a new interactive curriculum for incorporation into an existing afterschool program that serves inner-city elementary school students in Baltimore. This hands-on demonstration series aims to provoke 5th graders to evaluate their role in the advancement of energy technologies as consumers and future scientists. The scientific and educational merits of this project advance the frontiers of energy storage technologies, promote public engagement between researchers and young students, and align with the national interest of a sustainable energy future.Part 2: TECHNICAL SUMMARYEssentially all degradation processes in today's modern batteries involve poorly understood reactions at complex interfaces. This project uses molecular functionalization techniques on geometrically and atomically well-defined chemical systems to establish materials design criteria. Metal-organic frameworks (MOFs) are used to elucidate factors that influence charge transport in porous materials and develop new strategies to promote efficient polysulfide redox in lithium sulfur (Li-S) batteries. Li-S batteries can reach up to 10x the energy density of LiBs and sulfur is earth-abundant and affordable. However, the commercialization of Li-S batteries is challenged by unstable cycling performance due to polysulfide dissolution and incomplete sulfur utilization. This CAREER project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, takes advantage of the tunability and modularity of MOFs to decouple structural and chemical variables to acquire fundamental knowledge of the underlying charge transport and redox processes in Li-S batteries. Using Zr MOFs as robust model systems, the Thoi research group works to 1) identify structure-property-function relationships between pore structure, ion diffusion, and polysulfide redox properties, 2) incorporate redox-active components to control electron and ion transport, and 3) embed chemical anchors to trap polysulfides for obtaining mechanistic insights into their redox chemistry. Atomistic understanding of structure-property relationships provides design criteria for new functional sulfur electrodes. The fundamental knowledge acquired also enables the development of new charge conducting materials for electrochemical applications in the future, thus extending the application of MOFs beyond traditional gas storage and separation to electronic devices. This CAREER award project also promotes engagement between local elementary school students, graduate students, and postdoctoral fellows in scientific discourse, particularly in the area of energy. A demonstration series, entitled “EnergyNOW!” is developed for 5th grade students in an afterschool STEM program, with the objective of having students examine their relationship with energy. Each lesson includes a Q&A segment that stimulates scientific inquiry, a demonstration that involves role play and/or an experiment, and a hands-on activity that encourages problem-solving and decision-making.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.