Zwitterion-Decorated Silica Nanoparticle Networks in Ionic Liquid Electrolytes

Tufts University, Medford MA

Investigators

Abstract

Part 1: Non-technical Summary Safe, reliable batteries are critically needed for future mobile devices and wearable electronics. Both lithium and sodium ion-based batteries can provide high operating voltages and large energy densities, but many of the ion-transporting electrolyte materials used today are flammable and may present a safety hazard if the battery fails. A class of room temperature molten salts, known as ionic liquids, can eliminate flammability concerns, but a fundamental challenge remains in how to promote the selective motion of the targeted cations (Li+, Na+) over that of the other ions also present in the electrolyte. This project, supported by the Solid State and Materials Chemistry program and the Polymer program in the Division of Materials Research at NSF, aims to address this challenge by creating inorganic oxide materials that are coated with zwitterionic chemical groups. Zwitterionic groups contain an equal number of both positively- and negatively-charged atoms, separated by a distance of just a few bond lengths, which are known to interact strongly with electrolyte ions as well as with one another. This project tests the hypothesis that zwitterion-decorated oxide nanoparticle networks can selectively enhance Li+ and Na+ transport in ionic liquid-based electrolytes. The research generate needed insights into the design of safer future battery electrolytes and reveal new fundamental information about zwitterion-ion interactions in nonaqueous, ion-dense electrolytes. A new K-12 outreach activity is also developed as part of this project. The activity will inform pre-college students about future energy storage technologies, connect them to the research findings of this study, and foster their interest in pursuing a career in science or engineering. Part 2: Technical Summary The primary objective of this project is to selectively enhance the transport of Li+ and Na+ ions within ionic liquid electrolytes using organic zwitterionic (ZI) functional group-decorated silica nanostructured networks. Two different manifestations of this unique materials class will be pursued: (1) ZI group-decorated oxide nanoparticles (ZIONs), and (2) ZI group-functionalized mesoporous oxide networks (zwitterionosilicas). A key hypothesis of this study is that ZI group-functionalized silica nanostructures assembled into a continuous three-dimensional network within an ionic liquid electrolyte can enable a substantial improvement in selective alkali metal cation transport (Li+ or Na+) compared to that in the liquid electrolyte itself, while also creating a robust composite gel electrolyte layer that can prevent leakage. By spatially defining the region of ZI group/alkali metal cation interaction to be located along the exposed surfaces of the ZIONs or zwitterionosilicas, it is posited that this approach can effectively maximize the ability of ZI units to enhance Li+/Na+ conductivity within these inherently safer electrolytes. This project, funded by the Solid State and Materials Chemistry program and the Polymer program in the Division of Materials Research at NSF, encompasses the synthesis of ZIONs and zwitterionosilicas featuring different ZI chemistries and the measurement of relevant ion transport metrics for their combinations with ionic liquid electrolytes. Additionally, the work provides mentored undergraduate and graduate research experiences for a diverse group of students, supporting their goals of future employment in U.S. industrial research and development, academia, and national laboratories. 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.