Lithium battery separator: a nano-barrier that guards safety
main content
In the complex system of lithium battery, diaphragm is the key component to ensure safety and performance. The thin film, which is only 5-25 microns thick, is designed to block direct contact between positive and negative electrodes while allowing lithium ions to pass through efficiently. With the improvement of battery performance requirements for electric vehicles and energy storage systems, diaphragm technology has become a research hotspot in the field of materials science and engineering. This paper will analyze the core technology of lithium battery separator from three dimensions of material properties, functional principles and technological innovation.
1. Polyolefin diaphragm: classic material system
Polyolefin materials dominate the market due to their excellent chemical stability and controlled pore structure:
Polyethylene (PE) : through the dry unidirectional stretching process to form micropores, porosity 40%-50%, pore size 0.1-1 microns. Its melting point is about 130 ° C, triggering the obturator effect at 135 ° C, blocking ion transport to prevent thermal runaway.
Polypropylene (PP) : the diaphragm aperture prepared by wet process is more uniform, the melting point is increased to 160℃, and the mechanical strength is 20% higher than that of PE, but the infiltration of the electrolyte is slightly weaker.
Multi-layer composite structure: PP/PE/PP three-layer design combines the low melting point of PE and the high strength of PP, and improves the thermal stability by 30%.
2. Ceramic coated diaphragm: safety performance upgrade
The coating of 2-4 micron inorganic ceramic layers (such as Al₂O₃ and SiO₂) on the surface of polyolefine-based films has achieved three breakthroughs:
High temperature resistance: the thermal shrinkage rate is reduced from 90% of PE to 5% at 200℃ to avoid internal short circuit caused by high temperature melting;
Mechanical strength improvement: ceramic particles make the diaphragm puncture strength reach 500gf (conventional PE is 200gf), effectively inhibit lithium dendrite penetration;
Interfacial stability optimization: the ceramic layer adsorbs electrolyte decomposition products, and the cycle life is extended to more than 800 times.
Conclusion
From the industrial base of polyolefin to the technological leap of ceramic coating, the development history of lithium battery separator confirms the role of material innovation in promoting energy technology.
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