(2kw) Migrating Solvation Structures in Li-Ion Battery Electrolytes Revealed By Electrophoretic NMR

The rapid (dis)charge capability of Li-ion batteries, an important metric for electric vehicle adoption, strongly depends on transport of ions and solvent within the electrolytic phase. Electrophoretic NMR (eNMR), can directly quantify the direction and magnitude of cation (⁷Li), anion (¹⁹F), and solvent (¹H) motion under an applied electric field in Li-ion battery electrolytes. We report ¹H eNMR measurements of solvent velocity in model LiTFSI/tetraglyme electrolytes that reveal cation–solvent coordination, complementing molecular dynamics (MD) snapshots. These changes in the velocity of the solvent, a neutral species, underlie concentration-dependent trends in the cation transference number as measured by eNMR. We further corroborate MD solvation motifs in LiTFSI/tetraglyme by rationalizing concentration-dependent ¹H NMR shifts through hybrid functional DFT calculations. We explore a theoretical extension of our work wherein transference numbers can in principle be estimated using the measured velocity of a single species. Finally, we extend eNMR measurements to multivalent systems, i.e., polyanionic electrolytes dissolved in carbonate-based solvents, where we measure negative cation velocities that suggest Li⁺ moves the “wrong way”. Methodological extensions of eNMR will yield spatiotemporal velocity measurements to probe specific solvation structures, aiding in bottom-up design of high-transference electrolytes.

Teaching Interests

Sustainable energy, battery and fuel cell science, and polymeric, ceramic, solid-state and/or hybrid materials chemistry, applications of spectroscopy, diffraction and scattering.