Event

Unifying ion transport mechanisms: insights into ion dynamics in heterogeneous media

Abstract:  The unification of knowledge regarding ion transport mechanisms in solid ion conductors, polymers, and liquid electrolytes remains an outstanding goal in enabling functional energy storage materials. Magnetic resonance modalities, such as NMR and PFG (pulsed-field-gradient) NMR, are important analytical tools in relating transport phenomena to local atomic and molecular structures. The power of these methods can be further unleashed by computational approaches, such as density functional theory (DFT) calculations and molecular dynamics (MD) simulations. This work details the development of electrophoretic NMR (eNMR) methodologies to directly quantify the direction and magnitude of ion and solvent motion with spectroscopic specificity in battery electrolytes. These measurements can provide direct insight into slow recharging rates that limit battery performance. We uncover solvent coordination and ion clustering phenomena that underlie unexpected bulk transport phenomena such as negative transference numbers and solvent segregation in mixed-solvent systems. The transition from liquid to polymer electrolytes implies changes in ion motion mechanisms, concomitant with evolution of solvation “shells” into “cages.” Solid electrolytes present a final case wherein ion transport can be uniquely enhanced by “paddlewheel” rotation of rigid cluster anions. Evidence of paddlewheel motion in antiperovskite electrolytes obtained by variable-temperature NMR provides a mechanism for fast cation transport. By probing the complexities of ion transport at the molecular level through the deployment of advanced magnetic resonance methodologies and computational simulations across classes of functional materials, we pave the way for improved energy storage technologies.

Bio:   Dr. David Halat completed a B.S. in Chemistry and a B.S. in Mathematics at Montana State University (USA), and his Ph.D. in Chemistry at the University of Cambridge (UK), working with Prof. Dame Clare Grey on 17O solid-state NMR of functional paramagnetic oxides. He then joined the groups of Prof. Jeffrey Reimer and Prof. Nitash Balsara at the University of California, Berkeley (USA), where his postdoctoral research has centered on advanced NMR techniques, such as pulsed-field-gradient and electrophoretic NMR methods, as probes of ion transport in concentrated Li-ion battery electrolytes.