Combined Electrochemical, XPS, and STXM Study of Lithium Nitride as a Protective Coating for Lithium Metal and Lithium-Sulfur Batteries

Li3N is an excellent protective coating materialforlithium electrodes with very high lithium-ion conductivity and lowelectronic conductivity, but the formation of stable and homogeneouscoatings is technically very difficult. Here, we show that protectiveLi(3)N coatings can be simply formed by the direct reactionof electrodeposited lithium electrodes with N-2 gas, whereasusing battery-grade lithium foil is problematic due to the presenceof a native passivation layer that hampers that reaction. The protectiveLi(3)N coating is effective at preventing lithium dendriteformation, as found from unidirectional plating and plating-strippingmeasurements in Li-Li cells. The Li3N coating alsoefficiently suppresses the parasitic reactions of polysulfides andother electrolyte species with the lithium electrode, as demonstratedby scanning transmission X-ray microscopy, X-ray photoelectron spectroscopy,and optical microscopy. The protection of the lithium electrode againstcorrosion by polysulfides and other electrolyte species, as well asthe promotion of smooth deposits without dendrites, makes the Li3N coating highly promising for applications in lithium metalbatteries, such as lithium-sulfur batteries. The present findingsshow that the formation of Li3N can be achieved with lithiumelectrodes covered by a secondary electrolyte interface layer, whichproves that the in situ formation of Li3N coatings insidethe batteries is attainable.