GOALI: Development of Next Generation MXene-based Li-S Batteries with Practical Operating Temperatures

过去和现在，锂离子电池一直是用于交通和个人电子产品储能的主力。虽然这项技术已经被证明是相当强大和有用的，但它的主要缺点之一是它们储存的能量。在过去的十年里，另一种电池技术得到了广泛的研究，那就是锂硫(Li-S)电池。在其他条件相同的情况下，假设一些障碍可以克服，锂-S电池的储能容量将是目前锂离子电池的2-3倍。由此推论，如果一辆电动汽车目前的续航里程是200英里，如果它配备了锂-S电池，它的续航里程将是400-600英里。锂-S电池需要克服的两个重要障碍是：电极之间的电解液的性质和它们的快速褪色。在这个项目中，研究人员将与行业合作伙伴一起解决这两个问题。目前，对锂S电池的研究大多使用高挥发性的电解液(乙醚)，这些电解液在室温以上运行时会带来安全风险。此外，由于除气安全方面的考虑，这种电解液的添加剂具有严格的运输法规。在这个项目中，研究人员将使用目前用于锂离子电池的相同电解液，这种电解液具有良好的安全记录，可以在高于室温的温度下使用。第二个问题是骑自行车导致的运力迅速下降，这是另一个挑战。为了解决这个问题，研究人员将研究新的二维材料(比如原子水平的纸张)来固定S，从物理和化学上防止它在电池电极之间穿梭，从而导致它们褪色。在更广泛的影响方面，研究人员通过与一家大型电池公司和一家最终用途重型汽车公司合作，将确保研究的产业相关性。如果成功，这项技术可能会带来更持久的电池，创造新的就业机会，并确保美国成为能源储存领域的主要参与者。通过为攻读博士和本科生参与研究的研究生提供培训和研究机会，将实现更广泛的教育影响。这个根本性的目标项目将解决Li-S电池性能的两个关键障碍，一是可以在更高温度下工作的电解液，二是缓解多硫化物穿梭损失造成的容量损失。该项目将研究一种新的材料来容纳硫磺，S终止的MXenes。MXen是2011年在Drexel发现的二维(2D)碳化物和/或氮化物，具有金属导电性。初步结果表明，MXenes是为数不多的同时允许对S进行物理和化学限制/固定的材料平台之一，从而减少/最小化多硫化物穿梭效应。MXenes的金属导电性和“双固定化”策略将使其在碳酸盐电解液中稳定运行，同时仍能使70wt.%的S在7 mg/cm2的负荷下和83%的有效S利用率(1400mAhg)--所有这些都是达到500Wh/kg的应用目标所必需的先决条件。S-Mxene阴极的合成、制备和氧化还原活性研究将与碳酸盐电解液工程相结合，通过降低亲电性来进一步抑制可能发生的不利的多硫化物-碳酸盐反应。将进行死后和手术中光谱和显微镜研究，以阐明S终止的MXene宿主中的准固态氧化还原途径，检测S-碳酸盐相互作用中多硫化物或其他不良副产物的存在。单元级纽曼型建模，识别极限现象，将进一步指导材料设计。该GALI项目的最终目标是与行业合作伙伴合作，开发可在高沸点商用碳酸盐电解液中稳定工作的S负载和S使用的锂S电池，用于重型电池电动汽车。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智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The workhorse of energy storage for transportation and personal electronics has been, and remains, the lithium-ion battery. And while that technology has proven to be quite robust and useful, one of its major drawbacks is the amount of energy they store. An alternate battery technology that has seen extensive research in the last decade is lithium-sulfur (Li-S) batteries. All else being equal and assuming some hurdles can be overcome, the Li-S battery would have 2-3 times the energy storage capacity of current lithium-ion batteries. It follows that if an electric car’s current range is 200 miles, its range if equipped with a Li-S battery would be 400-600 miles. Two important hurdles that need to be overcome for Li-S batteries are: the nature of the electrolyte between the electrodes and their rapid fade. In this project, the researchers, together with industry partners, will address both problems. Currently, most of the research in Li-S batteries make use of electrolytes (ether) that are highly volatile and pose safety risks when operated above room temperature. Moreover, additives to this electrolyte comes with serious transport regulations due to degassing safety concerns. In this project, the researchers will make use of the same electrolyte that is currently being used for Li-ion batteries, which has an excellent safety record and can be used at temperatures higher than room temperature. The second problem of the rapid fade in capacity with cycling is another challenge. To solve that problem the researchers will study new 2-dimensional materials (think sheets of paper at the atomic level) to immobilize the S, both physically and chemically, to prevent it from shuttling between the battery electrodes that leads to their fade. In terms of broader impact, the researchers, by partnering with a major battery company and an end-use heavy-duty automotive company, will ensure industrial relevance of the research. If successful, this technology could lead to longer lasting batteries, creating new jobs and ensuring that the United States becomes a major player in the energy storage field. Educational broader impact will be achieved by providing training and research opportunities for graduate students pursuing PhDs and undergraduates’ involvement in the research. This fundamental GOALI project will address two key barriers for Li-S battery performance, an electrolyte that can operate at higher temperatures and mitigation of capacity loss due to polysulfide shuttling loss. The project will study a new class of materials to host sulfur, S-terminated MXenes. MXenes are two-dimensional (2D) carbides and/or nitrides discovered at Drexel in 2011 that exhibit metallic conductivity. Preliminary results have shown that MXenes are one of the few material platforms that allow both physical and chemical confinement/immobilization of S, thus reducing/minimizing the polysulfide shuttle effect. The MXenes’ metallic conductivity and “dual-immobilization” strategy will allow stable operation in carbonate electrolytes, while still enabling 70 wt.% S, with 7 mg/cm2 loadings and 83% effective S utilization (1400 mAh/g) – all necessary pre-requisites to approach the application targeted 500 Wh/kg. The cathode research on synthesis, fabrication, and study of redox activity of S-MXene cathodes will be integrated with carbonate electrolyte engineering to further suppress possible adverse polysulfide-carbonate reactions by reducing the electrophilicity. Post-mortem and in-operando spectroscopic and microscopic studies will be conducted to elucidate the quasi-solid-state redox pathways in S-terminated MXene hosts, detect the presence of polysulfides, or other undesired side products, from S-carbonate interactions. Cell-level Newman-type modeling, identifying limiting phenomena will further guide material design. The ultimate objective of this GOALI project - in collaboration with industry partners - is to develop Li-S batteries with practical S-loadings and S-utilizations that stably operate in high boiling point commercial carbonate electrolytes for application in heavy-duty battery electric vehicles.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.