Collaborative Research: Promoting Lithium Sulfides Redox Cycle via Atomically Dispersed Active Sites for Batteries

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Batteries play a key role in information technology, energy storage, and reduction in carbon emissions. The lithium-sulfur battery uses earth-abundant sulfur as the cathode material and delivers more energy than the current batteries, thus it is considered as one of the next-generation technologies. However, its chemistry of converting between sulfur and lithium sulfides is a very complex process and has fundamental problems that result in low capacity and short battery lifetime, such as the dissolution of intermediate products and their shuttling between the two electrodes. Recent evidence has shown the critical role of single-atom catalysts in promoting this conversion process and subsequently boosting the battery performance, but the fundamental understanding of the active catalytic sites and the reaction mechanism remains very elusive. This hinders the development of a catalyst-functionalized cathode structure with much improved performance. The current project will fill this knowledge gap, thus accelerating the development of a practical lithium-sulfur battery technology to serve the national interest in the key energy storage applications. The project will also result in societal boarder impacts. The knowledge gained on single-atom catalysts can be applied to other electrochemical systems. Graduate and undergraduate students, including those from underrepresented groups, will be trained in the fields of advanced material science and battery technology. The research outcomes will be incorporated into the elective courses. The research teams will reach out to the local communities, recruiting high school students to conduct research and delivering public lectures on the new battery technology to local public libraries. This collaborative fundamental research project will attain theoretical understanding and experimental validation of the structure-property correlation of atomically dispersed catalysts in promoting lithium sulfides redox cycle, and to transform these understandings into an optimized sulfur cathode design. The project hypothesizes that the electronic structure of the single-atom catalyst, which is determined by both the metal center and its local coordination, can be tuned for binding polysulfides and activating the Li-S and S-S bonds with an optimized strength, thus significantly improving the landscape of sulfides conversion while preventing polysulfides shuttling. To this end, combining theoretical calculations and modeling with in-situ/ex-situ experimental studies, this project will establish the structure-property correlation of single-atom catalysts in chemisorbing polysulfides and activating the Li-S and S-S bonds for conversion, and probe and visualize the evolution of the electrode morphology and its chemical distribution during cycling. The studies will thus provide insights on the choice of the metal center, its local coordination, and the electrolyte in the proximity, and reveal their impacts on the lithium sulfides redox cycle. These understandings of single-atom catalyst functions on sulfides binding and conversion, both thermodynamically and kinetically, assisted by advanced characterization tools, will then be leveraged to design advanced sulfur cathode structures, functionalized with single-atom catalysts, for demonstration of battery cells with much-improved performance.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.