Preparation Of Polyimide Nanofiber Membrane And Its Application As Lithium Battery Membrane

In recent years,the rapid development of lithium battery industry,and the research on anode and cathode materials of lithium battery is quite mature.Meanwhile,the research on polymer electrolyte and membrane has also been increasing gradually.The most commonly used polyolefin separator in the market,due to its disadvantages such as low absorption of electrolyte and poor thermal stability,Many methods,such as polymer grafting modification and inorganic ion addition,have emerged to improve the properties of polyolefin.Or use nonwoven membrane to improve the porosity of the separator;Or new composite membranes such as inorganic-polymer composite,polymer-polymer composite to replace the polyolefin separator.In order to find better heat resistance,mechanical strength,electrochemical stability and other comprehensive properties of the separator to replace the existing polyolefin separator.This research is divided into two parts.The first part is to prepare a GO/PI separator with good thermal conductivity as the basic material and GO as the reinforcing material,which has good electrochemical performance after battery assembly test.In the second part,a three-layer PVDF/PI/PVDF composite nanofiber membrane was prepared,and ZIF-67 particles were grown in situ on the PVDF/PI/PVDF membrane surface.After the composite membrane was assembled,the battery had good electrochemical performance.(1)Firstly,the viscosity and electrical conductivity of spinning solutions with different concentrations of PAA and GO/PAA is investigated,and the optimal spinningconditions is determined through pre-experiments,Finally,the membrane with the best morphology is prepared.The results show that when the PAA solution concentration is23%,the nanofiber membrane prepare when GO accounted for 0.2% of the PAA mass fraction had the best morphology.Thus,GO/PI fiber membrane is obtained after GO/PAA fiber membrane is thermally aminated.TG analysis showed that the thermal decomposition temperatures of PI and GO/PI are both higher than 500℃,and their morphology stay the same after heating at 200℃ for 1h.The ionic conductivity of GO/PI membrane is calculated as 2.04041 ms /cm,GO/PI membrane oxidation decomposition voltage up to 4.9V,the first charge and discharge capacity is 154.4mAh/g,The discharge capacity at 2C is 120.3mAh/g,After 100 cycles at 0.2C multiplier,the battery is still maintained at 94.9% of its initial capacity.In summary,the GO/PI diaphragm can be used as a lithium battery.(2)Secondly,Secondly,the above-mentioned PI is used as the core layer,PVDF as the surface layer,and the three-layer composite membrane PVDF/PI/PVDF is heat pressing to form a slight adhesion between the fibers.Then,ZIF-67 particles are in situ grown on PVDF fibers to obtain the ZIF-67/PVDF/PI composite membrane.When the mass fraction of ZIF-67 reaches 90% of PVDF,the composite membrane can maintain its original morphology at 200℃,The mechanical strength reached12.4mpa,the electrolyte absorption rate is 370%,and the oxidation decomposition voltage reached 5.3V.The ionic conductivity is 1.6ms /cm,the initial discharge capacity at 0.1C is 199.2mAh/g,and the decentralized electric capacity at 5C ratio is 123.7m Ah/g.At the same time,72.74%of the initial capacity is maintained after 100 charges and discharges at 0.5C multiplier.Considering the ZIF-67/PVDF/PI separator is more suitable for the use of high-performance batteries.