In the internal structure of lithium batteries, there is a seemingly insignificant key component that plays a decisive role in battery performance and safety - the lithium battery separator. From the appearance, it is just a thin film, with a thickness usually ranging from a few micrometers to tens of micrometers, resembling a fraction of a human hair. However, its interior is full of hidden wonders, filled with a dense array of micro-pores with diameters at the nanometer level, which form a unique microstructure.

The main functions of lithium battery separators are twinning: Firstly, they act as a "physical barrier" between the positive and negative electrodes. By virtue of their non-conductive nature, they effectively prevent direct contact between the positive and negative electrodes, avoiding short circuits and laying a solid foundation for the safe operation of the battery. Secondly, it is a dedicated "high-speed channel" for lithium ions, allowing lithium ions in the electrolyte to freely shuttle between the positive and negative electrodes, ensuring the smooth progress of the battery's charging and discharging process. In simple terms, the separator is like a strict "traffic controller", allowing only lithium ions to pass through while keeping other "interfering factors" out.

From the perspective of material, given that the electrolyte of lithium batteries is mostly an organic solvent system, this requires that the separator material must have good resistance to organic solvents. At present, the mainstream separator materials for lithium batteries are high-strength film-like polyolefin porous membranes, among which polyethylene (PE) and polypropylene (PP) microporous separators are the most widely used. PE diaphragms have relatively excellent low-temperature resistance and are relatively soft in texture. PP diaphragms are more heat-resistant, have a lower density than PE, and also have a higher melting point and closed-cell temperature. In practical applications, to meet the strict requirements for battery performance in different scenarios, people often combine PE and PP to create double or triple-layer composite separators, such as the common three-layer PP/PE/PP separator, which integrates the advantages of both materials and greatly enhances the comprehensive performance of the separator.

Although lithium battery separators are small, they contain numerous advanced technologies and complex processes. They are one of the core components that ensure the efficient and safe operation of lithium batteries and play an indispensable role in promoting the vigorous development of the new energy industry.