The Research On Performance Of Separator Via Electrostatic Spinning Technique

At present,rechargeable lithium-ion batteries?LIBs?play an important role in our daily life because of many merits,such as high energy/power density,long cycle life,and no memory effect,et al.They have been widely applied in portable electronic devices,such as laptops and mobile phones.And recently,LIBs are being used as motive power for,energy-storage and transportation applications,including passenger vehicles,such as electric vehicles,indicating a promising direction of the development of lithium ion batteries.As an important part of lithium ion battery,the separator can avoid the battery internal short circuit,allow the electrolyte ions free shuttle migration,and prevent electronic transportation through the separator.At present,polyolefin separator,such as polypropylene?PP?and polyethylene?PE?prepared through the dry/wet process are widely used due to their excellent mechanical strength and stable chemical performance.However,the poor resistance to high temperature,low porosity and poor liquid wetting performance severely affect their application in high power lithium ion battery.Therefore,to ensure the safety and high performance of the battery,appropriate separator must be chosen.Electrostatic spinning technology is a novel membrane-making technology developed rapidly in recent years.As applying a high voltage electric field on the polymer solution or melt polymer,a nanofibre film was formed on the receiver plate.This film has a 3D space structure with high specific surface area,porosity and liquid absorption rate.This thesis tries to use electrostatic spinning membrane method to design serial lithium-ion battery separator,and their physical and electrochemical properties were characterized.1.Take high heat resistant material polyacrylonitrile?PAN?as the inner core material,high lyophilic poly(vinylidene fluoride-hexafluoropropylene copolymer?PVDF-HFP?as the outer shell material,a core-shell structured PAN@PVDF-HFP separator was prepared via the electrostatic spinning process.Results show that the spinning complex membrane is excellent than commercial PE separator in heat-resistance,porosity,lyophilic,ionic conductivity and electrochemical window,etc.CR2032 coin cells were used to test the electrochemical performance of the separator?cathode:LiFePO4,anode:graphite,electrolyte:=8:1:1?discharge specific capacity of the cell with PAN@PVDF-HFP separator decreases from 159.4mAh g^-1 to 158.4 mAh g^-1 at 0.1 C rate after 100 cycles,with a capacity retention of 99.4%.While that with PE membrane is only 96.2%.And the discharge specific capacity of the former is 43.4%higher that the later at 10 C rate.2.Boehmite/PAN composite fiber membrane was prepared by the electrostatic spinning process.Results show that separator mixed with boehmite,displayed lyophilic,lithium ionic conductivity and the electrochemical window of the composite membrane was improved to some extent.CR2032 coin cells were used to test the electrochemical performance of the separator.The discharge specific capacity of the PAN/BM membrane is 25%higher that the pure PAN membrane at 10 C rate.3.PVDF HFP/BM composite fiber membrane was prepared using the electrostatic spinning method.CR2032 coin cells were used to test the electrochemical performance of the separator.After 200 cycles at 0.2 C rate,discharge specific capacity of the cell with PVDF-HFP/BM separator is 388.4 mAh g^-1,41%higher than that with pure PVDF-HFP membrane.And the discharge specific capacity of the former is 89.7 mAh g^-1 at 4 C rate.While that of the later is only 44.6 mAh g^-1.