Study On Preparation And Properties Of Modified Cellulose Lithium Battery Separator

At present,the materials used to make lithium battery separator are mainly polyolefin materials such as polyethylene,polypropylene,etc.With the increasing capacity and power of the lithium battery,however,there are higher requirements on mechanical strength,thermal stability,uniform pore diameter distribution and porosity of the separator.Therefore,it is necessary to explore new diaphragm materials.High porosity,good electrolyte infiltration,low thermal shrinkage and high melting temperature are the development directions of lithium battery separator.In this paper,we use natural polymer cellulose as the main separator components,by blending and coating method to modify cellulose,and finally prepared the lithium battery separator.This research can effectively utilize cellulose biomass resources,and lay a foundation for the further development of lithium battery separator.The research is of great significance from the point of environmental protection and effective utilization of resources.Main works are as follows:Dissolved Polyvinylidene fluoride?PVDF?with PVP K30 as additive and using ionic liquid[Emim]Ac as solvent,PVDF/cellulose/PA6 lithium battery separator was synthesized by blending on the basis of cellulose/PA6 lithium battery separator,prepared by the research group early.The effects of PVDF content on the mechanical properties,liquid absorption,liquid retention,porosity and thermal stability were studied.The characteristics of modified separator were investigated through the methods of SEM and contact angle measurements.The results showed that the optimum temperature and time of ionic liquid dissolved PVDF were 100?and 2h,the solubility of ionic liquid to PVDF reached 6.28%.The content of PVDF in the casting solution was 1.5wt%,the comprehensive properties of the separator were the best.The mechanical strength of separator could reach 65.26MPa,the heat shrinkage rate,absorption rate,liquid retention rate and porosity could reach 2.1%,230%,67.2%and 53.3%,respectively.Compared with the cellulose/PA6 separator,the tensile strength,suction rate,retention rate and porosity of PVDF/cellulose/PA6 separator increased by 28.2%,6.5%,9.4%and 10.6%,and the thermal shrinkage rate decreased by 32.3%.The mechanical properties and thermal safety stability of separator were improved remarkably.SEM results showed there were irregular pore structure dispersed on the surface and the cross section of the composite membrane.It provided a guarantee for the liquid absorption rate and the liquid retention rate of the membrane.The contact angle test proved that the wetting property of the composite membrane was improved.Dissolved Cellulose acetate?CA?with PVP K30 as additive and using ionic liquid[Emim]Ac as solvent,CA/cellulose/PA6 lithium battery separator was synthesized by blending on the basis of cellulose/PA6 lithium battery separator,prepared by the research group early.The effects of CA content on the mechanical properties,liquid absorption,liquid retention,porosity and thermal stability were studied.The characteristics of modified separator were investigated through the methods of SEM and contact angle measurements.The results showed that the optimum temperature and time of ionic liquid dissolved CA were 100?and 2.5h,the solubility of ionic liquid to CA reached 11.82%.The content of CA in the casting solution was 1wt%,the comprehensive properties of the separator were the best.The mechanical strength of separator could reach 62.34MPa,the heat shrinkage rate,absorption rate,liquid retention rate and porosity could reach 2.4%,227%,66.1%and52.1%,respectively.Compared with the cellulose/PA6 separator,the tensile strength,suction rate,retention rate and porosity of CA/cellulose/PA6 separator increased by22.5%,5.1%,7.7%and 8.1%,and the thermal shrinkage rate decreased by 22.6%.The mechanical properties and thermal safety stability of separator were improved remarkably.SEM results showed there were irregular pore structure dispersed on the surface and the cross section of the composite membrane.It provided a guarantee for the liquid absorption rate and the liquid retention rate of the membrane.FT-IR results showed that the characteristic absorption peaks of cellulose and CA were reflected in the infrared spectra of composite membrane.The contact angle test proved that the wetting property of the composite membrane was improved.The cellulose membranes were prepared with PVP K30 as additive and using NaOH/Urea aqueous solution as solvent.Composite diaphragm was prepared by coating the surface with cellulose membranes as base membrane and using Nano-SiO₂/PVA as coating solution.The effect of coating on mechanical properties,thermal stability,liquid absorption,liquid retention and porosity of the membrane was investigated.The research results showed that the comprehensive properties of the composite membranes were obviously improved by the introduction of the coating.When the content of PVA was 6wt%and the content of nano-SiO₂ was 1wt%,the comprehensive properties of the separator were the best.At this time,the mechanical strength reached 35.58 MPa,the heat shrinkage rate,liquid absorption rate,liquid retention rate and porosity were 1.2%,228%,60.7%and 42.1%,respectively.SEM results showed there were irregular pore structure dispersed on the surface and the cross section of the composite membrane.It provided a guarantee for the liquid absorption rate and the liquid retention rate of the membrane.The TG test and contact angle test results showed that the thermal stability and wetting performance of composite diaphragm were significantly improved.The dissolution of cellulose in NaOH/Urea aqueous solution and ionic liquid was observed by transmission polarization microscope.It was found that the dissolution effect of ionic liquid system on cellulose was much better than that of NaOH/Urea aqueous solution.