| With the development of portable devices,intelligent furniture,electric vehicle and other fields,the comprehensive performance of lithium-ion batteries has been put forward higher requirements.The traditional polyolefin separator has some defect in porosity and thermal stability,which affected the safety and charge-discharge performance of lithium battery in the process of using.Lithium battery separator has become one of the main factors restricting the development of lithium battery technology.In this paper,ionic liquids was used as solvent,cellulose and nylon 6 were used as main membrane materials,the high quality separators with high porosity,uniform pore size distribution,high mechanical strength,strong affinity with electrolyte,high thermal safety and eco-friendly were prepared by blending,impregnation and crosslinking,and the properties and structure were regulated.The main works are as follows:Firstly,polyacrylonitrile?PAN?was dissolved in ionic liquid?[Emim]Ac?to determine the optimal dissolved temperature and time.Next,the separator was prepared of PAN modified cellulose/nylon 6 with polyvinylpyrrolidone?PVP K30?used as the porogen.The effects of regulating PAN concentration on the mechanical properties,liquid absorption,liquid retention,porosity and thermal stability of the separators were studied.The characteristics of the modified separator were investigated through the methods of SEM,N2-adsorption isotherms,thermogravimetric analysis,contact angle measurements and electrochemical characterization.The results showed that the optimal dissolved temperature and time of PAN in ionic liquid were 140?and 2h,respectively.The optimal composition of the casting solution in the ionic liquid was:3wt%?PAN?,4wt%?cellulose?,3wt%?nylon 6?,4wt%?PVP K30?.In this case,the tensile strength of the separator could reach 71.24MPa,and the elongation at break reached 33.7%.The electrolyte uptake,retention rate and porosity could reach 225.3%,66.7%and 55.7%,respectively.The maximum thermal shrinkage stress and the thermal shrinkage rate reached 1.27N and 2.0%.The electrochemical window increased to 4.5V and the ion conductivity reached 0.55*10-3S/cm.The related characterization indicated that the mechanical properties,thermal stability,pore distribution and electrochemical properties of the regulation separator were improved comparing with the unregulated separator,which meet the requirements of lithium battery industry.Secondly,the modified separator was prepared by impregnation.The cellulose/nylon6 separator was prepared with PVP K30 used as the porogen,and using ionic liquid?[Emim]Ac?as the solvent.Then the separator was impregnated in water-soluble polyimide?PI?.The effects of regulating PI solid concentration on the mechanical properties,liquid absorption,liquid retention,porosity and thermal stability of the separators were studied.The characteristics of modified separator were investigated through the methods of SEM,N2-adsorption isotherms,thermogravimetric analysis,contact angle measurements and electrochemical characterization.The results showed that the composite performance of modified separator was best when the solid content of PI was 40%.In this case,the tensile strength of the separator could reach 69MPa,and the elongation at break reached 35.3%.The electrolyte uptake,retention rate and porosity could reach 238.7%,69.4%and 54.2%,respectively.The maximum thermal shrinkage stress and the thermal shrinkage rate reached 1.38N and 1.5%.The electrochemical window increased to 4.7V and the ion conductivity reached 0.61*10-3 S/cm.The related characterization showed that the PI regulation separator had good performance in mechanical strength,pore diameter,affinity with electrolyte and thermal stability.Thirdly,the modified separator was prepared by crosslinking.The cellulose/nylon 6separator was prepared with PVP K30 used as the porogen,and using ionic liquid?[Emim]Ac?as the solvent.Then the separator was modified with glutaric dialdehyde used as cross-linking agent.The effects of regulating glutaric dialdehyde concentration on the mechanical properties,liquid absorption,liquid retention,porosity and thermal stability of the separators were studied.The characteristics of modified separator were investigated through the methods of SEM,FT-IR,XRD,N2-adsorption isotherms,thermogravimetric analysis,contact angle measurements and electrochemical characterization.The results showed that the optimal crosslinking conditions were:crosslinking time and temperature were 60min and 75?respectively,and the concentration of glutaraldehyde was 6%.In this case,the tensile strength of the separator could reach 75.42MPa,and the elongation at break reached 28.96%.The electrolyte uptake,retention rate and porosity could reach235.5%,68.9%and 53.6%,respectively.The maximum thermal shrinkage stress and the thermal shrinkage rate reached 1.42N and 1.8%.The electrochemical window increased to4.9V and the ion conductivity reached 0.65*10-3 S/cm.The results show that the comprehensive properties of the regulation separator have been improved.Comparing the comprehensive properties and the complexity of the preparation process of the separator which prepared by the above regulation methods,it is concluded that the separator prepared by PI regulation was the most ideal,and the preparation method was easier to realize. |
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