Electrochemical Evaluation of Lithium Metal Batteries Using Separators with Different Pore Sizes

Lithium metal batteries (LMB)-laminate-type full cells were prepared by combining a high-concentrated electrolytes lithium bis(fluorosulfonyl)imide (LiFSI)/ethylene carbonate (EC) and the 3-Dimensionally Ordered Macroporous (3DOM) Polyimide (PI) separator, and the cycle characteristics were compared with the full cell using the conventional polypropylene (PP) + polyethylene (PE) separator, which is widely used in lithium ion batteries. The capacity of the laminate-type cell using the PP + PE separator decreased to half of the initial capacity after 50 cycles, while the cell using the 3DOM PI separator kept its initial capacity and showed stable performance even after 50 cycles.We also investigated pore size effect of the 3DOM separators on cycle characteristics. The cell using 2500 nm pore size 3DOM separator showed quickly decreasing capacity after the first cycle, while those cells using 300 nm and 1000 nm pore size 3DOM separator maintained their initial capacities and showed highly reversible charge-discharge performances.It was revealed from those results that the highly concentrated electrolytes are available to use with the 3DOM separators and the cycle characteristics of the LMB full cell strongly depends on the pore size. Both the separators with too large or too small pores resulted in short-circuit with lithium dendrites.