The Study Of PPEK Electrospun Membranes As Lithium Ion Battery Separators

Separator is an important part of lithium ion battery and plays an important role in battery's capacity,service life,safety performance and so on.The frequently-used separator is a polyolefin separator which is prepared by a dry process or a wet process.Polyolefin separator has some disadvantages,such as low porosity,poor electrolyte uptake,and poor thermal dimensional stability.These disadvantages limit the performance of lithium ion battery and easily cause safety problems of the battery.Therefore,it is necessary to prepare a separator which has high electrolyte uptake,good electrolyte wettability and good thermal dimensional stability.Poly?phthalazinone ether ketone??PPEK?has good high temperature resistance,which can impart high temperature resistance performance to the separator and improve the safety of lithium ion battery.Electrospinning is a simple and controllable method.Electrospun membrane has many advantages,such as uniform structure,high porosity and high electrolyte uptake.In this study,poly?phthalazinone ether ketone??PPEK?with good high temperature resistance performance is selected as the polymer matrix.Electrospinning is selected as the manufacturing process.The main research work is as follows:1.There are unsaturated Si-O bonds and hydroxyl groups on the surface of SiO₂,and the polarity is strong.SiO2 can enhance the electrolyte affinity,thermal dimensional stability and ionic conductivity of the separator.In order to improve the porosity,electrolyte uptake and electrochemical performance of the separator,SiO2 is chosen as the modification species.Micromorphology,porosity and electrolyte uptake,electrolyte wettability,thermal dimensional stability,mechanical property,electrochemical performance,battery cycle and rate performance of PPEK electrospun membranes with different content of SiO2 are investigated.The experimental results show that with the increase of SiO₂ addition,the porosity,electrolyte uptake,thermal dimensional stability and ionic conductivity of electrospun membranes are improved.When the addition amount of SiO₂ is 6 wt%,the electrospun membrane shows good microscopic morphology and meets the requiremnet of mechanical property,and the porosity and electrolyte uptake rate of which are 179%and1031%,respectively.The thermal shrinkage rate of the electrospun membrane is 0 after heat treated at 200°C for 1 h,which shows it had a good thermal dimensional stability.In addition,it also has good electrochemical performance,battery cycle and rate performance.2.Electrospun membrane needs to have a good mechanical property when it is used as a separator.In order to improve the mechanical property of the electrospun membrane,a method of solvent vapor treatment is adopted.Micromorphology,porosity and electrolyte uptake,electrolyte wettability,thermal dimensional stability,mechanical property,electrochemical performance,battery cycle and rate performance of PPEK electrospun membranes after different solvent vapor treatment time are investigated.The experimental results shows that the mechanical properties of the electrospun membranes improve with the increase of the solvent vapor treatment time,and the porosity and electrolyte uptake are decreased.However,due to the porous structure of the electrospun membranes,the porosity and electrolyte uptake are still much higher than the commercial PP separator.The thermal shrinkage rate of the electrospun membrane is 0 after heat treated at 200°C for 1 h,which shows it had a good thermal dimensional stability.When the solvent vapor treatment time is36 h,the PPEK electrospun membrane shows an excellent comprehensive performance,and the mechanical property improves effectively,while maintaining high porosity and electrolyte uptake,electrochemical performance,battery cycle and rate performance.