Dual Protection of Li‐Metal Anode by Black Phosphorus‐Modified Separator via Modulating Solid Electrolyte Interphase and Eliminating Li Dendrites

Lithium metal batteries (LMBs) are highly valued due to their high energy density. However, LMBs are severely hindered by the unstable solid electrolyte interphase (SEI), which requires a rational design of interface engineering. Herein, a dual protection strategy of Li-metal anode is proposed via coating a black phosphorus (BP) layer on the separator. During the battery assembly process, few-layer BP nanosheets can be peeled off and uniformly modified on the lithium metal surface, due to the soft metallic properties of lithium, meanwhile, the remaining BP remains on the separator, so that they provide two types of protection during the initial formation and cycling processes, respectively. During initial lithiation, the stripped BP is converted to Li₃P, which is a beneficial component for stable and fast-dynamic SEI. In addition, when Li dendrites are dramatically generated under extreme conditions, the BP modified on the separator can melt Li dendrites owing to the high activity of their alloying reaction. Therefore, the BP-modified separator facilitates the large-scale application of Li metal, with generalisability in both ester and ether electrolytes. In the ester electrolyte, the lifetimes of Li||Li cells are prolonged to over 2200 h, and Li||LiFePO₄ cells exhibit a superior capacity retention of 78% after 500 cycles at 1 C.