Sensitive Detection of Dendritic Lithium Morphologies by Dynamic Nuclear Polarization.

Lithium metal batteries are a promising energy storage technology, but their commercialization is hindered by nonuniform lithium deposition, which is detrimental to the battery lifetime and safety. In particular, needle-like dendrites pose the greatest risk as they often lead to short-circuits; as such, it is essential to identify and mitigate their formation for enabling use of lithium metal anodes. Here we demonstrate that Overhauser dynamic nuclear polarization (DNP)- enhanced NMR, where the high polarization of the lithium conduction electrons increases the sensitivity of lithium NMR, is a powerful tool for determining the lithium morphology. By systematically controlling the deposited lithium structures within a polymer electrolyte system, we show that DNP enhancement correlates with morphology, allowing us to distinguish between micro- and nano-sized dendrites. Complementary electron paramagnetic resonance and electron microscopy measurements confirm the morphological interpretation. This work introduces a spectroscopic strategy for sensitively probing lithium dendritic structures with high specificity, offering a pathway to understand and control their formation across a range of battery systems and electrochemical formation conditions.