Grain Boundary Orientation Impacts on Internal Resistance in Solid State Lithium Ion Conductors

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Freeing the U.S. from reliance on fossil fuels is important for national security and economic prosperity. Efficient transition from fossil fuels to electricity will require the ability to rapidly and safely charge batteries in minutes rather than hours. Solid-state batteries have promise to accomplish this task because of their inherent safety, but they are currently unable to charge and discharge at sufficient rates. This project will study the features of electrolytes in solid-state batteries that hinder charge and discharge rates. The knowledge gained will allow engineering of improved electrolytes to achieve faster rates. The project also will develop educational outreach materials designed to illustrate the scientific process and will focus on experimental failures. They will show how failed experiments are a key component of the scientific process and that society’s knowledge is built over time upon the lessons learned.The goal of this fundamental research project is to determine the features that lead to resistance in ionic conduction across grain boundaries in perovskite-structured lithium ion conductors and to categorize ionic resistances by specific grain boundary orientations. Epitaxial lithium ion conducting films will be prepared by pulsed laser deposition on single crystal, bicrystal, and large-grained polycrystalline insulating substrates. The grain and grain boundary orientations will be assessed via electron backscatter diffraction and the ion conductivity measured across the individual grain boundaries using microcontact electrochemical impedance spectroscopy. The nature of resistance to ionic conduction will be assessed to determine whether the origin is structural or electronic in nature. With the ionic conductivity of different grain boundary orientations determined, cross-sectional scanning transmission electron microscopy will be employed to measure the local chemical compositions and structures. These parameters will then be used to determine the mechanisms that lead to grain boundary resistances in solid-state lithium ion conductors. Using this information, the features and grain alignments that lead to high and low ion conductivities across grain boundaries will be established, which may then be used to design a microstructure that minimizes the populations of high resistivity boundaries in the conduction path. The end result will be a step toward realizing high power fast charge and discharge solid-state lithium ion batteries.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.