Preparation Of PI/PEI Composite Porous Membrqne And Study On The Surface Silvering Of Polyimide Nanofiber

Polyimide(PI)possesses many excellent properties because of its main chain equipped with unique imide ring,such as thermostability,high insulation,outstanding tensile behavior and radiation hardened.It is widely used in aerospace,national defense,military industry,communications,electronic appliances and other fields in various forms such as films,foams,fibers,and coatings.The PI nanofiber membrane prepared by electrospinning owns the advantages of both PI material and nanofiber material,and then the fiber membrane is combined with other materials to prepare a multifunctional composite nanofiber material.In this paper,the PI/PEI composite membrane is obtained by coating porous polyetherimide(PEI)on the surface of the PI nanofiber membrane,which is used as LIBs separator to improve the safety performance of the battery.The surface of PI nanofiber membrane is coated with nano silver by the method of direct ion exchange reduction to obtain a conductive PI/Ag composite nanofiber membrane,which is used as an electromagnetic shielding material with excellent mechanical flexibility,conductivity and high electromagnetic interference shielding performance.The tightly bounded PI/PEI composite membrane is prepared by the simple method of coating PEI on the surface of the PI nanofiber membrane.With the introduction of PEI,a cross-linked structure of the PI nanofiber layer was formed,and its tensile strength was significantly increased from 13.7 MPa to 73.4 MPa.Compared with commercially available Celgard separators,this new composite membrane has satisfactory wettability to electrolytes,significant flame retardancy and excellent thermal dimensional stability(without any shrinkage at 150?).In particular,the PEI layer can be fully closed(over 260?),which gives the LIBs a self-protection function in the event of overheating.The PI/PEI composite membrane battery has a capacity of 142.9 mAh·g-1 at 5C,much higher than the Celgard PP separator(118 mAh·g-1),and shows excellent cycle stability.These properties prove the potential of PI/PEI composites as high-safety separators for lithium-ion batteries.With PI nanofibers as the core,the direct ion exchange reduction method was used to prepare conductive PI/Ag composite nanofiber membranes.The effects of reduction times and reducing agent concentration on the morphology of silver particles and the conductivity of the fiber membrane were studied.It is used as an electromagnetic shielding material to explore the influence of conductivity and thickness on electromagnetic shielding performance.The results show that as the conductivity and thickness increase,the electromagnetic shielding performance increases.When the number of ion exchange-reduction is 7 times,the electromagnetic shielding efficiency It reaches 42 dB and meets the two important technical requirements of light weight and flexibility required by electromagnetic interference shielding materials in practical applications.It is proved that PI/Ag composite conductive nanofiber membrane is an electromagnetic shielding material with excellent performance and strong practicability.