Molecular level structure and dynamics of electrolytes using ¹⁷O nuclear magnetic resonance spectroscopy

Electrolytes help harness the energy from electrochemical processes by serving as solvents and transport media for redox-active ions. Molecular-level interactions between ionic solutes and solvent molecules - commonly referred to as solvation phenomena - give rise to many functional properties of electrolytes such as ionic conductivity, viscosity, and stability. It is critical to understand the evolution of solvation phenomena as a function of competing counterions and solvent mixtures to predict and design the optimal electrolyte for a target application. Probing oxygen environments is of great interest as oxygens are located at strategic molecular sites in battery solvents and are directly involved in inter- and intramolecular solvation interactions. NMR signals from ¹⁷O nuclei in battery electrolytes offer nondestructive bulk measurements of isotropic shielding, electric field gradient tensors, and transverse and longitudinal relaxation rates, which are excellent means for probing structure, bonding, and dynamics of both solute and solvent molecules. This article describes the use of ¹⁷O NMR spectroscopy in probing the solvation structures of various electrolyte systems ranging from transition metal ions in aqueous solution to lithium cations in organic solvent mixtures.