Modification And Performance Of Polyvinylidene Fluoride Based Lithium Ion Battery Separator

As one of the four main materials of lithium batteries,separator directly affects the key performance of the battery,such as internal resistance,capacity,ratio and cycle.At the same time,it also has a vital impact on the safety of lithium batteries.How to solve the safety problem of lithium battery has become a bottleneck problem in the industry.The purpose of this paper is to prevent thermal runaway reaction of lithium-ion batteries by separator.The N-N dimethyl formamide（DMF）and tetrahydrofuran（THF）according to a certain proportion of mixed as mixed solvent,through coaxial electrospinning technology was successfully prepared PEI-PVDF coaxial electrospun fiberous membrane.By scanning electron microscopy,TEM Fourier transform infrared spectroscopy,experimental mechanics,absorbency,invasive,characterization of electrochemical experiments and test the PEI-PVDF coaxial electrospun fiber membrane microstructure,thermal properties,mechanical properties,absorption rate,infiltration performance and electrochemical stable performance,including electrochemical stability window,and conductivity.The experimental results show that it compared with that of conventional separators,the PEI-PVDF coaxial electrospinning fiber thin film has the following advantages,（1）it has a more uniform distribution of fiber diameter;（2）It has a better thermal stability;（3）It has better compatibility with electrolyte;（4）Greatly improve the electrochemical properties,conductivity can reach the magnitude of 10^-3,and higher than that of conventional separators,electrochemical stability window can not only reach the safety of the lithium battery using range,and higher than that of conventional separators;（5）The application of PEI-PVDF coaxial electrospinning fiber thin film in the lithium battery separator has great development and progress space.The lithium ion battery assembled with PEI-PVDF coaxial separator still show the specific discharge capacity of 107 mAhg^-1 at discharge current density of 8C.In the recovery at 0.2C rate,the specific capacity retained 95.4%of its original specific capacity.The coulombic efficiency of the batteries is 92.5%after 100cycles of charge and discharge.The characteristics of the high rate and high heat resistance of the PEI-PVDF separator.Polyethylene（PE）microspheres were prepared by solvent evaporation method.PVDF battery separators were prepared by electrospinning.PE microspheres were coated on the surface of PVDF non-woven membrane by spin coating.A high performance Lithium battery separator coated with the thermal-shutdown functional layer has been prepared.The shutdown temperature of the separator could be controlled by using the melting point of thermal-shutdown functional layer.Electrochemical and rate performance tests were performed on a battery equipped with a PVDF separator and PVDF/PE separator.The results showed that the resistance,rate performance and electrochemical stability of the battery are unaffected by the presence of the PE microspheres.The ionic conductivity and charge-discharge capacity of batteries with PVDF/PE separators were tested at high and room temperatures.The results showed that the ionic conductivity was 3.88×10^-3 S/cm at room temperature,and it decreased to 1.6×10^-4 S/cm at 110℃.This indicated that the melting of the microspheres closed the pores of the separator at high temperature and prevented the lithium ion from being transmitted.The discharge capacity of the battery at high temperature is 0.08 mAh,which is only 4.6%of the discharge capacity at room temperature.This showed that the separator can perform thermal shutdown of the battery at high temperatures to prevent thermal runaway of the battery and improve battery safety.