As one of the four main materials of lithium-ion battery , its existence directly affects the safety of the battery. Its porosity, thickness, liquid absorption and electrostatic value directly affect the electrical properties of the battery. As the energy density of lithium-ion batteries increases year by year, the amount of inactive materials is less and less, and the separator is getting thinner and thinner. This will bring great challenges to the safety of lithium-ion batteries. In one aspect, let's take a brief look at the current research progress of the diaphragm.
As can be seen from the above figure, the various performance indicators of the diaphragm are mutually constrained and mutually influential. All diaphragm manufacturers are looking for the optimal combination. There is no diaphragm with the best index, so the electrical performance is required. Find a balance between safety performance and comprehensive evaluation indicators for large-scale production. As conventional diaphragms become thinner and thinner, it is necessary to apply glue or ceramics to the diaphragm to meet the thermal stability and tensile strength requirements.
Different coatings have different functions. At present, ceramic coated diaphragms have been stabilized and mass-produced. However, there are still short-circuit tests, self-discharge problems caused by ceramic particles falling off, and battery winding. The existence of the core pulling and powder dropping problems requires further improvement and research on the ceramic coating, and in order to improve the electrical properties, the coating and the coated separator are further studied.
Tests on the performance of ceramic diaphragms show that the ceramic coating significantly improves the liquid absorption and liquid retention of the separator, thus exhibiting good cycle performance.
The simple diaphragm heating experiment also shows that the presence of the ceramic layer significantly improves the thermal shrinkage of the separator, and there is no obvious shrinkage at 150 ° C, which also brings a safety guarantee for the high energy density battery.
As for the development of the future diaphragm, it can be seen from this trend graph that as the technological level progresses, the diaphragm gradually transitions from micropores to non-pores, and will eventually be replaced by solid electrolytes (solid electrolytes will do The panel discussion, which is not covered here, will introduce several new types of membranes.
The non-woven composite membrane of the sandwich structure prepared by the hot pressing method significantly improves the peeling of the ceramic layer and improves the self-discharge performance of the battery.
The PI nanofiber membrane prepared by the electrospinning method not only improves the mechanical strength of the separator itself, but also significantly improves the absorption of the electrolyte and the ionic conductivity.
The sandwich-structured PI-PVDF-PI nanofiber separator melts PVDF at 160 °C and blocks PI micropores, thereby achieving the function of closed cells and significantly improving the safety of the battery.
Judging from the published technical roadmap of the expert group, it is also compatible with the current technological development. The high security and high stability diaphragm will be the research hotspot in the next seven or eight years.
References: 1. Power Battery Technology Roadmap
2. High specific energy battery seminar report
3. Development of Lithium Ion Battery Membrane Technology Energy Storage Science and Technology
Author: Lithium Union president
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