In Situ Derived Mixed Ion/Electron Conducting Layer on Top of a Functional Separator for High‐Performance, Dendrite‐Free Rechargeable Lithium‐Metal Batteries

Abstract Rechargeable lithium‐metal batteries (RLBs), which employ the Li‐metal anode to acquire notably boosted specific energy at cell level, represent the “Holy Grail” for “beyond Li‐ion” electrochemical energy storage technology. Currently, the practical use of RLBs is impeded by poor cycling and safety performance, which are derived from high chemical reactivity of metallic Li and uncontrollable formation and propagation of metal dendrites during repeated Li plating/stripping. In this study, a new strategy is demonstrated to stabilize the anode electrochemistry of RLBs by applying a Mg 3 N 2 ‐decorated functional separator onto the Li‐metal surface. An in situ conversion‐alloying reaction occurring at Li‐separator interface assists formation of a mixed ion/electron conducting layer that consists mainly of Li 3 N and Li‐Mg solid‐solution. The inorganic interlayer effectively suppresses parasitic reactions at Li‐electrolyte interface while simultaneously homogenizes Li + /e ‐ flux across the interface and therefore, contributes to dendrite‐free operation of Li‐metal anode. A Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 battery based on the functional separator delivers a reversible capacity of 129 mAh g ‐1 after 600 cycles at 0.5 C, which corresponds to a capacity retention of 75.9%. The preparation of functional separator is scalable and adaptive to battery manufacture, which brings new opportunities to realize high‐energy RLBs with long cycle life and improved safety.