Effect of Polybenzimidazole Addition to Three-Dimensionally Ordered Macroporous Polyimide Separators on Mechanical Properties and Electrochemical Performances

Li-metal batteries employing Li-metal anodes with the highest capacity density have attracted considerable attention. However, the Li-metal deposition is often nonuniform, which reduces the cycle performance of Li-metal batteries. The three-dimensionally ordered macroporous polyimide (3DOM PI) separator has provided much better Li deposition/dissolution cycle performance owing to its unique and ordered pore structure, but its low mechanical strength is an obstacle to practical use. In this study, we added polybenzimidazole (PBI) to increase the mechanical strength of the 3DOM PI separator. Both the 3DOM PI and 3DOM PI+PBI separators with pore sizes of 300 and 100 nm were prepared to investigate the effect of pore size on the mechanical strength of the separator. The 3DOM PI+PBI separators exhibited higher tensile strength, higher thermal stability, better Li deposition/dissolution cycle performance, and higher charge–discharge performance of the Li-metal battery than the 3DOM PI separators. Here, it was suggested that the increase in the mechanical strength of the separator prevented the compression of the pores in the separator by external pressure and provided a more uniform Li+ ion flux inside the separator.