Polyimide/Metal–Organic Framework-5 Separator with Excellent Electrolyte Wettability and Thermal Stability for High Performance Lithium-Ion Battery

The safety and performance of lithium-ion batteries (LIBs) are closely related to the separator. Commercial polyolefin separators hinder electrochemical performance and may result in safety issues at high temperatures due to insufficient thermal stability and electrolyte wettability. In this work, a polyimide (PI)/metal–organic framework-5 (MOF-5) composite separator was prepared via in situ polymerization and electrospinning. The tensile strength of the PI/MOF-5 composite membrane was superior to that of the PI membrane by 104%. The outstanding flame retardancy of the PI/MOF-5 composite separator significantly enhances the safety of lithium-ion batteries, especially in high-temperature environments. The PI/MOF-5 separator demonstrated a high number of lithium-ion transferences (tLi+ = 0.79). The cell using the PI/MOF-5 separator exhibited excellent cycling performance, with an initial discharge capacity of 174.7 mA h/g at a current density of 0.5 C, which is 140.8 and 46.6% higher than that of the LIB coin cell with a polypropylene (PP) separator and PI separator, respectively. After 200 cycles at a current density of 0.5 C, the specific discharge capacity of the battery using the PI/MOF-5 separator still maintained 89.02% of the initial specific discharge capacity, which is higher than that of the PP and PI separators. Consequently, the outstanding properties of the PI/MOF-5 composite separator indicate its potential in high-performance lithium-ion batteries.