APS Doctoral Defense – Connor Slamowitz

Zoom Link: https://unc.zoom.us/j/96843452539

Meeting ID: 968 4345 2539

Title:

DESIGN OF FLUORIDE-ION BATTERIES BASED ON ELECTRON-ANION EXCHANGE

Abstract:

The large-scale adoption of wind and solar power calls for battery technologies that achieve higher storage capacities at lower cost. Although lithium-ion batteries have been widely adopted, other ions, including Na⁺, Zn²⁺, Mg²⁺, Al³⁺, and Cl^– continue to provoke scientific interest because of competitive theoretical capacities, lower costs, and   resource abundance. Among these alternatives is F^–, which has favorable characteristics because of its small charge density and light weight. Fluoride-ion batteries (FIBs) have been relatively unexplored, however, because electrolytes that are highly conductive at room temperature were only recently discovered. With this discovery, there is now an increased motivation for systematically exploring electrodes for the FIB. These advances in electrolytes and electrodes have led to our development of a new class of electrodes that reversibly intercalate fluoride ions: electrides.

Electrides are ionic crystals that have lattice sites occupied by a bare electron, often called an “anionic electron” because the site has a negative charge. Some electrides crystallize in a layered structure and in these materials, the electrons lie in planes, sandwiched between layers of cations. Employing layered electrides in fluoride-ion batteries capitalizes on the transport characteristics of layered materials and the high electrochemical potential of the anionic electrons. In addition, layered electrides allow us to probe a fundamentally new mechanism for electron transfer: one in which an anionic electron is exchanged directly for a fluoride without reduction or oxidation of the host atoms. The realization of this exciting mechanism leads to electrodes with large capacities and little volume change upon intercalation. We have introduced the name “electrochemical electron-anion exchange” (EAX) to describe this new mechanism.

Here, we describe how the electride, Y₂C, led to the prediction of the EAX mechanism in the Y₂C–Y₂CF₂ material system. We highlight our calculations and experiments that provide the first evidence for electron transfer without reduction or oxidation during the electrochemical fluorination of Y₂C at room temperature. To further improve cycling performance, we design 1) aliovalently doped Y₂CF₂ to improve the ionic conductivity of our electrode, 2) artificial solid-electrolyte interphases to improve the chemical stability of Y₂C at its surface, and 3) high surface area amorphous electrodes that enhance electrode composite interactions while driving fast fluoride diffusion. These design principles lead to large capacity electrodes that cycle repeatedly without reduction or oxidation.

The discovery of EAX and high-capacity electrodes is the beginning of a fascinating era in the development of the fluoride-ion battery. These advances, combined with the development of new fluoride electrolytes, are leading to exciting scientific and technological progress.

Short Bio

Connor graduated with a BS in Nanoscience and a minor in International Business from Virginia Tech in 2020. As an undergraduate researcher, Connor studied the electronic and electrochemical properties of Metal Organic Frameworks under Dr. Amanda Morris. Connor then worked at Luna Innovations as a Materials Engineering Intern where he developed functionalized paints, polymers, and composites for the Department of Defense. In the Warren Lab, Connor’s research involves the fabrication of next-generation electrodes using newly discovered materials to create high-performance batteries.