Preparation and Properties of PP/PAN/Cotton Fibers Composite Membrane as Lithium-Ion Battery Separator with Thermal Shut-Off Function

The lithium-ion battery separator plays roles of separating the positive and negative electrodes and providing ion channels, and at the same time, it can play a more important role in the safety of the lithium-ion battery. In this work, a modified PP (polypropylene)/PAN (polyacrylonitrile)/cotton fibers composite membrane with a thermal shut-off function was prepared by a wet-laid process. The results are as follows: When the fibers’ mass fraction was 50%, the composite membrane had the best combination properties, with a tensile strength of 1.644 KN·m−1, the porosity was 63%, and it had good wettability with an aspiration height of 39 mm and a liquid absorption rate of 269%. The thermal shrinkage of the composite membrane was less than 4% after thermal treatment under 160 °C. More importantly, the DSC curve showed that the modified PP/PAN/cotton fibers composite membrane had a thermal shut-off function with the temperature between 110 °C and 160 °C. After thermal treatment under 160 °C for 1 h, the ionic conductivity of the fiber membrane decreased to 0.32 mS·cm−1 from 1.99 mS·cm−1. Electrochemical performance tests showed that the button battery using the fiber composite membrane had a slightly better initial discharge, capacity retention and cycle performance at different rates than the button battery equipped with the PP membrane. The results show that the modified PP/PAN/cotton fibers composite membrane improves the safety and electrochemical performance of lithium-ion battery.