Study On Preparation Of Modified Cellulose Membrane Used For Lithium Battery Separator In Ionic Liquids

Lithium battery is becoming the hotspot of energy storage technology as its high energy density,no memory effect,high output power,high output voltage,wide working temperature and long life cycle characteristics.As one of the core material of lithium batteries,the main function of separator including the flowing aspects: separate the positive and negative electrodes to prevent the battery from short circuit,maintain the electrolyte to form ion channels,and the micro pores shrink or close to limit the current increase to protect the battery when the battery internal become too high.At present,the domestic battery separator mainly rely on imports,major of the market is occupied by imported products.Therefore,study and produce the high thermal stability with qualified separator in quality indicators can effectively promote the development of the domestic battery separator industry.In present work,by using cellulose as main component,the cellulose modified lithium battery separators were prepared by using blending and impregnation method.The solubility of cellulose and nylon were studied by using ionic liquids as the solvent.The morphology,crystal form and thermal stability of regenerated cellulose membrane and nylon membrane were characterized by using scanning electron microscope,X ray diffraction and microcomputer differential thermal balance.The results showed that the solubility of cellulose and nylon in ionic liquids were 17.96% and 11.58%,respectively.The optimum temperature and time of cellulose and nylon dissolved in ionic liquids were 90?,150? and 2h,3h,respectively.The surface of regenerated cellulose membrane was more dense and no large holes appeared on the membrane surface,the crystalline shape of regenerated cellulose changed from cellulose ? to cellulose?,and the regenerated cellulose had good thermal stability within 260?.There were network connected tiny holes appeared on the surface of regenerated nylon membrane,the crystalline shape of regenerated nylon was not changed,and the regenerated nylon had good thermal stability within 360?.Using non-woven fabric as the base material of membranes,non-woven fabric based lithium battery separators were prepared by L-S phase inversion method.Ionic liquids was used as the solvent and polyvinylpyrrolidone(PVP K30)was used as polymer additives.The effects of cellulose content,nylon content and additive content on the mechanical property of separators were discussed.The absorption rate,liquid retention rate and porosity of separators were tested.The blend membranes were characterized by tensile testing,scanning electron microscope,FT-IR,X ray diffraction and microcomputer differential thermal balance.It was found that the optimal preparation condition of blend membrane was: 4 wt%(cellulose),3 wt%(nylon),4 wt%(additive PVPK30).Under the experimental conditions,the mechanical strength of separator could reach 63.12 MPa,absorption rate,liquid retention rate could reach 254.2% and 88%,the porosity of separator could reach 53.4%.FT-IR results showed that the characteristic absorption peaks of cellulose and nylon were reflected in the infrared spectra of cellulose/nylon blend membrane,there was good compatibility between the two components of the blend membrane.SEM results showed there were irregular holes dispersed on the surface and the cross section of the blend membrane.SEM and DSC results indicated that cellulose had favorable compatibility with nylon.XRD results showed that the crystalline phases of cellulose and nylon did not change after blending.TG results showed that the blend film had good thermal stability.The cellulose/nylon modified lithium battery separator,which not using non-woven as the base material of the blend membrane,was prepared by using waterborne polyurethane as the impregnation solution.The effects of waterborne polyurethane solid content on the mechanical property,absorption rate,liquid retention rate and porosity of modified separator were discussed.The structure,morphology and thermal stability were characterized.The results showed that the mechanical strength of modified separator could reach 43.93 MPa when the solid content of waterborne polyurethane was 30%.Under above condition,the absorption rate,liquid retention rate and porosity were 214.7%,67.1% and 43.2%,respectively.ATR-FTIR results demonstrated that the blend membrane was modified successful,SEM images showed that the surface and cross section of the modified separator still existed micro porous,TG results showed that the modified separator had good thermal stability.Thermal stability test indicated that the heat shrinkage rate of the separator was only 2.8% under 200?.