DNP-enhanced NMR of Lithium Dendrites: Selective Observation of the Solid–Electrolyte Interphase

Li metal anodes represent the ultimate energy density, but to address safety issues caused by dendrite formation, it is critical to understand the solid–electrolyte interphase (SEI) layer which forms on the metal surface. Dynamic nuclear polarisation (DNP) boosts sensitivity in NMR by harnessing the greater polarisation of unpaired electrons, however typical exogenous organic radicals are non-selective, could react with the SEI, and require cooling the sample to cryogenic temperatures. We instead exploit the inherent conduction electrons to hyperpolarise lithium metal at room temperature, utilising the Overhauser mechanism by which DNP was first discovered. This permits selective enhancement of the organic and inorganic SEI components, revealing their chemical nature and spatial distribution, via the ⁷Li, ¹H and ¹⁹F NMR spectra.