Elucidating Surface Adsorption of Lithium Ions on Electrode Materials Using ⁷Li Dark-State Exchange Saturation Transfer NMR Spectroscopy

Interfacial chemistry plays a central role in the development of next-generation high-energy Li-ion electrode materials. Yet, the rational design of new surface treatments that serve as beneficial solid electrolyte interphases is hindered by the challenges involved in probing their interfacial ion transfer properties. Here, we demonstrate how ⁷Li Dark-State Exchange Saturation Transfer (DEST) NMR can be used to directly measure the Li-ion surface adsorption process at the solid-liquid interface. The development of an optimized model system composed of monodisperse submicron particles allowed for comparison between different surface functionalities, enabling the characterization of state-of-the-art electrode coating layers in terms of their Li-ion affinity. Numerical simulations based on Bloch-McConnell equations enable a quantitative analysis of the surface exchange rates and binding properties, cementing DEST as a valuable tool for elucidating the structure-function relationship in electrode materials.