"Electron transfer without redox:A new paradigm for energy storage"

Scott Warren: UNC Chapel Hill

Among the challenges facing humanity, the sustainable production, storage, and use of energy is among the most urgent.  In this talk, I will describe our laboratory’s work to develop a new device for energy storage: the fluoride-ion battery.  Compared to lithium-ion batteries, fluoride-ion batteries have been little explored, largely because no fluoride-ion liquid electrolyte was known.  This situation changed in 2018, when researchers at Caltech, JPL, and Honda reported the first stable liquid electrolyte for fluoride ions (Science, 362, 1144-1148, 2018).  Now, with a liquid electrolyte available, it becomes possible to develop and explore electrodes for a fluoride-ion battery.

This talk will focus on our lab’s discovery of a new class of materials – electrenes – and their use as an electrode in a fluoride-ion battery.  Electrenes are 2D (“layered”) materials in which a lattice site that would normally hold an anion instead contains a bare electron.  We have now developed electrochemical cells using Honda’s electrolyte in which a bare electron can be exchanged for a fluoride ion.  This exchange occurs without any change in the oxidation states of the surrounding atoms and is therefore the first example of an electrochemically controlled electron-transfer event that occurs without reduction or oxidation.  The realization of this phenomenon in the electride [Y₂C]²⁺·2e^- offers electrodes with capacities that are nearly double state-of-the-art lithium-ion batteries while also having almost no volume change.