Hydroxyl-Containing Polyimide Nanofiber Separator for High Performance Lithium-Ion Batteries

The present study focuses on the application of hydroxyl-containing polyimide (HPI) nanofiber membranes as separators in lithium-ion batteries. The fabrication of hydroxyl-containing polyimide nanofiber membranes was accomplished through electrostatic spraying, utilizing poly(amide acid) (PAA) solutions with varying solid contents (20%, 23%, 25%, 27%). A hydroxyl-containing diamine was selected as one of the monomers. SEM characterization indicates that the HPI-25 sample exhibits optimal nanomorphology and pore structure. As demonstrated in the relevant literature, the HPI separator displays relatively high levels of ionic conductivity (1.81 mS·cm–1 at 25 °C), which are 2.2 times those of the PP separator and 1.12 times those of the PI separator. It has been demonstrated that the strong polar modification of the hydroxyl group (−OH) leads to an increase in electrolyte wettability. Furthermore, the weak coordination of Li+...O–H has been shown to increase the lithium ion migration number to 0.79. In the LiFePO4 || Li battery system, the discharge specific capacity of HPI-25 can reach 161 mAh·g–1 after 200 cycles at a 1C rate. This finding demonstrates the pivotal role of selecting appropriate monomers with functional groups in determining the overall performance of polymer membranes.