Pore Structure and Performance Modulation of Polypropylene Lithium-ion Battery Diaphragm Based on Dry Bi-directional Stretching
ZHANG Jiaheng1,2, ZHANG Long1,*, SONG Sainan2, LI Guangquan2,*
1 School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China 2 PetroChina Company Limited Lanzhou Chemical Research Center, Lanzhou 730060, China
Abstract: Safety and electrochemical efficiency are dependent on the performance of lithium-ion battery diaphragms. Dry bi-directional stretching is a common method for preparing high-performance polypropylene (PP) diaphragms, but systematic studies on its process parameters remain limited. This study investigates the effects of key process parameters, such as stretching temperature, multiplicity, and speed, on the pore structure, air permeability, and mechanical properties of PP diaphragms produced by dry bi-directional stretching. The diaphragms were analyzed using scanning electron microscopy (SEM), pore size distribution testing, and mechanical property testing. The results show that stretching temperature significantly affects both the uniformity of the pore structure and the mechanical properties. The optimal stretching temperature is 90 ℃ for longitudinal stretching and 130 ℃ for transverse stretching. Increasing tensile multiplicity improves pore uniformity, with optimal performance achieved at a 3×3 multiplicity. However, excessive multiplicity leads to insufficient pore expansion. Tensile speed significantly impacts the densification and orientation of pore walls, with optimal diaphragm performance achieved at 15 mm/min. The diaphragm, prepared under optimal process parameters, exhibits a porosity of 45%, permeability of 337 s/100 mL, longitudinal tensile strength of 43 MPa, transverse tensile strength of 21 MPa, and puncture strength of 0.07 N/mm. The study shows that the dry bi-directional stretching process parameters significantly affect the pore structure and performance of polypropylene separators for lithium-ion batteries. This provides both a theoretical foundation and practical gui-dance for preparing high-performance diaphragms.
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2026, Vol. 40 
