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Addressing lithium‐dendrite problem caused by uneven lithium (Li) plating/stripping is crucial for improving cycle‐life and safety of Li‐metal batteries. Here we describe a simple chemical substitution method of 2Li+Mg(PF6)2=Mg+2LiPF6 to construct a highly stable Li−Mg alloy on Li metal anode. The self‐grown Li−Mg alloy exhibits homogeneous β‐phase bulk structure with flat and dense surface morphology. Systematic studies reveal that the obtained Li−Mg film acts as ion redistributor and surface stabilizer to protect Li metal anode by its low strain, fast conductivity, superior lithophilicity and excellent stability. Compared to the bare Li metal, symmetric cells assembled using Li−Mg‐protected Li exhibit better cycling performance with lower charge‐discharge overpotential. Notably, this Li−Mg film demonstrates great potential for Li‐metal batteries, it can effectively suppress Li‐dendrite growth and work effectively in LiFePO4//Li and LiNi0.8Co0.1Mn0.1O2//Li cells. This work provides a simple and effective strategy to construct Li‐ion redistributor and surface protector to guard Li anodes operating in high‐energy Li batteries.

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