In situ formation of a LiF and Li-Al alloy anode protected layer on a Li metal anode with enhanced cycle life

Development of next-generation high-energy lithium (Li) metal batteries is hindered by uncontrollable growth of Li dendrites and the unstable Li/electrolyte interface during repeated Li plating/stripping. To overcome these issues, artificial protection for Li metal prior to assembling the cell/battery is needed. Here we show a facile approach to in situ coating of a protected layer on the Li metal anode by directly placing a PVDF-HFP/AlF₃ modified Celgard separator on its surface. We find that AlF₃ can react with highly reactive Li metal and produce a LiF coating on Li metal in situ. This LiF-rich SEI layer can effectively passivate the highly active Li anode surface and suppress the lithium dendrite growth, forming a uniform structure on the Li/electrolyte interface that reduces interfacial impedance. Owing to the enhanced interface stability, the Li‖Li cell presents a stable polarization voltage for approximately 600 h compared with the blank cell (45 h). The Li‖LiFePO₄ cell with the composite separator has a high capacity retention of 78.3% after 300 cycles at the 3C rate, exhibiting an improvement in the cycling life of high energy-density Li metal batteries.