As one of the four main materials of lithium-ion batteries, the separator directly affects the safety of the battery. Its porosity, thickness, liquid absorption, and electrostatic value directly affect the electrical performance of the battery. As the energy density of lithium-ion batteries increases year by year, the amount of inactive materials is getting smaller and smaller, and the separators are getting thinner and thinner. This will bring great challenges to the safety of lithium-ion batteries. Here are a few Let’s take a brief look at the current research progress of diaphragms from this aspect.

　　As can be seen from the above figure, the various performance indicators of the diaphragm are mutually restrictive and affect each other. All diaphragm manufacturers are looking for the optimal combination. There is no diaphragm with the best indicators for all indicators, so it is necessary to improve the electrical performance. Find a balance point among the comprehensive evaluation indicators of safety performance and large-scale production. Since traditional diaphragms are getting thinner and thinner, it is necessary to apply glue or ceramics on the diaphragm to meet the needs of thermal stability and tensile strength.

　　Different coatings have different functions. At present, ceramic-coated separators have been stable and are in mass production. However, there are still problems such as failure to pass the short-circuit test, self-discharge problems caused by the falling off of ceramic particles, and problems caused by battery winding. The existence of problems such as core pulling and powder loss requires further improvement and research on the ceramic coating. At the same time, in order to improve the electrical performance, the glue coating and the separator of the coating are also being further studied.

　　Performance tests on ceramic separators show that the ceramic coating significantly improves the liquid absorption and retention properties of the separator, thus showing good cycle performance.

　　Simple separator heating experiments also show that the presence of the ceramic layer significantly improves the thermal shrinkage performance of the separator. There is no obvious shrinkage at 150°C, which also provides safety guarantee for high-energy-density batteries.

　　As for the future development of separators, it can also be seen from this trend chart that with the advancement of technology, separators are gradually transitioning from microporous to non-porous, and will eventually be replaced by solid electrolytes (solid electrolytes will be Special discussion, this article will not go into details), several new types of diaphragms will be introduced below.

　　The sandwich-structured non-woven composite separator prepared by hot pressing method significantly improves the shedding of the ceramic layer and the self-discharge of the battery.

　　The PI nanofiber membrane prepared by electrospinning not only improves the mechanical strength of the separator itself, but also significantly improves electrolyte absorption and ionic conductivity.

　　The sandwich-structured PI-PVDF-PI nanofiber separator melts PVDF at 160°C and blocks the micropores of PI, thereby realizing the closed-pore function and significantly improving the safety performance of the battery.

　　Judging from the technology roadmap announced by the expert group, it also matches the current technological development. High-security and high-stability diaphragms will be a research hotspot in the next seven or eight years.

　　References: 1. Power battery technology roadmap

　　2. High specific energy power battery seminar report

　　3. Development of lithium-ion battery separator technology Energy storage science and technology

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