Metal Ion Transport in Microporous Metal-Organic Frameworks for Energy Storage Applications

Part 1: NON-TECHNICAL SUMMARY The prevailing commercial lithium-ion batteries (LIBs) contain a flammable liquid electrolyte that can lead to major safety hazards. Replacing the liquid electrolyte with a nonflammable solid can alleviate these issues, but current batteries using solid electrolytes are unable to maintain high storage and fast charging capabilities. This project, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, leverages a unique class of porous materials called metal-organic frameworks (MOFs), which are made of metal and organic components that are precisely arranged in an ordered network, as promising solid electrolytes. By selecting appropriate metal ions and organic compounds, the desired chemical and physical properties of the MOF can be tuned to improve battery performance. The expected outcome of this project is the acquisition of foundational knowledge to design solid electrolytes that are safe replacements to existing liquid electrolytes. Such advances are necessary for developing reliable next-generation batteries for portable electronics, electric transportation, and electric grid management. Additionally, through education and outreach activities this project promotes public scientific discourse through the training of early-career researchers in effective scientific communication, an accessible chemistry video series on battery research, and on-site research opportunities for high schoolers and community college undergraduate students. This project thus advances the frontier of energy storage devices, promotes public engagement in science and technology, and aligns with the national interest of a secure energy future. Part 2: TECHNICAL SUMMARY A major bottleneck in advanced energy storage technologies is related to challenges of the electrolyte. The prevailing commercial lithium-ion batteries (LIBs) contain liquid electrolytes that are flammable and can lead to major safety hazards. Owing to the increasing demand of high-capacity, high-power batteries, safety challenges with liquid electrolyte are exacerbated with scaling to large battery packs and to other more reactive chemistries, such as replacing Li graphite anodes in LIBs with Li metal anodes. Solid-state electrolytes can alleviate these issues, but they are limited by low ion conductivity and poor interfacial stability. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, leverages the diversity and modularity of a class of microporous metal-organic frameworks (MOFs), which are known for their molecular sieving properties for gas separation, as solid-state ion conductors. The objectives are to 1) elucidate the mechanism of Li+ transport in a Ca-based squarate MOF, 2) apply mechanistic insights obtained to other metal squarate MOFs to evaluate the role of microporosity on metal ion diffusion, and 3) evaluate the interfacial stability of squarate MOFs and their ability to facilitate reversible Li deposition. In the long term, the researchers plan to build a multidimensional map that connects structural and chemical factors of microporous MOFs to metal ion transport. The acquired knowledge informs the rational design of solid-state electrolytes for Li-based energy storage devices. This project also enhances public access to science, technology, engineering, and mathematics (STEM) through the training of early-career researchers in effective scientific communication, an educational video series entitled, ″Meet a Chemist,″ and on-site research opportunities for local high school students and undergraduates from community colleges. 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.