In the structure of lithium batteries, battery separator refers to a layer of separator material between the positive and negative electrodes of the battery. It is a very critical part of the battery and has a direct impact on the safety and cost of the battery. Its main function is to isolate the positive and negative electrodes and prevent the electrons in the battery from passing freely, so that the ions in the electrolyte can pass freely between the positive and negative electrodes. The performance of the separator determines the interface structure and internal resistance of the battery, which directly affects the battery's capacity, cycle and safety performance. According to the differences in physical and chemical properties, lithium-ion battery separators can be divided into several categories: woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, rolled membranes, etc. Although there are many types, the main commercial lithium-ion battery separator materials are polyethylene and polypropylene microporous membranes. Polyolefin materials have excellent mechanical properties, chemical stability and relatively low prices. Therefore, polyolefin microporous membranes such as polyethylene and polypropylene have been used as lithium-ion battery separators in the early stages of lithium-ion battery research and development.

