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Alkali metals are attractive anode materials for advanced high-energydensity battery systems because of their high theoretical specific capacities as well as low electrochemical potential. However, severe dendrite growth as well as high chemical reactivity restrict their practical application in energy storage technologies. Herein, we propose a facile scalable solution-based approach to stabilize Li and Na anodes via the facile process of immersing the Li/Na metal in a nonhazardous ionic liquid 1-butyl-2,3-dimethylimidazolium tetrafluoroborate for several minutes at room temperature before battery assembly. This produces a dense and robust artificial fluoride layer, formed in situ by the reaction of the ionic liquid and Li/Na metal. As a demonstration, a homogeneous and compact LiF coating on the Li metal anode was fabricated via our method and it can effectively suppress the growth of Li dendrites and the continuous decomposition of electrolytes during cycling. As a result, the LiFcoated metallic Li anode achieves an enhanced cycling lifespan of over 700 h with low overpotential (∼22 mV) at 1 mA cm −2 , as well as a very high Coulombic efficiency of up to 98.1% for 200 cycles at 1 mA cm −2 . Furthermore, the successful achievements of the dendrite-free Na deposition show the versatility of room-temperature surface fluorination for potential battery applications.

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