Formulating the Dual‐Function Separator‐Enabled Homogenizing Ion Flux in Nonflammable Phosphate toward High Stable Lithium Metal Batteries

The high‐energy lithium metal battery employing a nonflammable phosphate electrolyte is an attractive strategy to resolve the notorious safety trouble. Unfortunately, the sluggish ion dissociation and transport kinetics, strong interaction of Li + ‐phosphates, and uncontrollable secondary reaction between the electrode and electrolyte interfaces severely impedes the cycling stability of lithium metal batteries. Herein, the dual‐function separators with fast ion dissociation and transport capability are designed to enable the homogeneous and efficient ion flux in nonflammable phosphate electrolyte. By virtue of the regulating effect of the designed dual‐function separator, the homogeneous distribution of the ion field and electric field are constructed, thus reducing the concentration polarization among nonflammable phosphate electrolyte and weakening the parasitic reaction of the metallic lithium anode and nickel‐rich cathode with the electrolyte. The Li||Li symmetrical cells exhibit remarkable cycling stability of above 1000 h at 2 mA cm −2 . Moreover, the Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) battery exhibits above 90% capacity retention after 300 cycles at 1C. Furthermore, stable bidirectional electrode‐electrolyte interfaces are also realized after cycling. This approach holds great promise for regulating the ion flux in nonflammable electrolyte, and would encourage more separator engineering design to optimize ionic transport behavior.