A Novel Organic "Polyurea" Thin Film for Ultralong-Life Lithium-Metal Anodes via Molecular-Layer Deposition.

Metallic Li is considered as one of the most promising anode materials for next-generation batteries due to its high theoretical capacity and low electrochemical potential. However, its commercialization has been impeded by the severe safety issues associated with Li-dendrite growth. Non-uniform Li-ion flux on the Li-metal surface and the formation of unstable solid electrolyte interphase (SEI) during the Li plating/stripping process lead to the growth of dendritic and mossy Li structures that deteriorate the cycling performance and can cause short-circuits. Herein, an ultrathin polymer film of "polyurea" as an artificial SEI layer for Li-metal anodes via molecular-layer deposition (MLD) is reported. Abundant polar groups in polyurea can redistribute the Li-ion flux and lead to a uniform plating/stripping process. As a result, the dendritic Li growth during cycling is efficiently suppressed and the life span is significantly prolonged (three times longer than bare Li at a current density of 3 mA cm-2 ). Moreover, the detailed surface and interfacial chemistry of Li metal are studied comprehensively. This work provides deep insights into the design of artificial SEI coatings for Li metal and progress toward realizing next-generation Li-metal batteries.