Synthesis And Modification Of The Coating Polypropylene Separators Used For Lithium-ion Batteries

Separator is an important component of lithium-ion batteries(LIBs).The polypropylene(PP)separator has the advantages of low cost,high mechanical strength,and high chemical stability.However,it has some disadvantages,such as poor thermal stability,poor electrolyte wettability and so on.In this dissertation,three coated PP separator was prepared and modified.The relationship between the performance and synthesis condition of the coated separator was investigated by using many advanced experimental methods,such as scanning electron microscopy,infrared measurement,electrochemical impedance spectroscopy,charge-discharge test.The main results are as follows:1.The coated PP separator was prepared by using a impregnating method from the oil-based mixture solution of the poly(vinylidene fluoride-hexafluoropropylene)(PVDF-HFP),poly(methyl methacrylate)(PMMA)and Al PO₄,which ionic conductivity is 1.03×10^-3S cm^-1(higher than that of PP matrix(3.8×10^-4S cm^-1)).The electrochemical stability window is in the potential zone of 2.0?5.15 V(vs.Li⁺/Li).The diffusion coefficient of lithium ions is 1.52×10^-9cm²s^-1.The heat shrinkage of the coated separator is less than 50%in size while heated at 170? for 30 mins.The coin cells composed of coated separators and Li Ni_0.50Co_0.20Mn_0.30O₂cathodes exhibit the discharge capacities of 213 m Ah g^-1(1st cycle)and 191 m Ah g^-1(40th cycle)in the voltage range of 2.5?4.6 V.The cells exhibit the discharge capacities of 183 m Ah g^-1(1st cycle)and 168 m Ah g^-1(40th cycle)at the 1 C rate at 55?.2.The coated PP separator was prepared by using a coating method in the water-based mixture solution of the hydroxypropyl methyl cellulose(HPMC)and Al PO₄,which ionic conductivity is 1.09×10^-3S cm^-1.The electrochemical stability window is in the potential zone of 2.0?5.15 V(vs.Li⁺/Li).The diffusion coefficient of lithium ions is6.23×10^-9cm²s^-1.The heat shrinkage of the coated separator is less than 51%in size while heated at 170? for 30 mins.The coin cells composed of coated separators and Li Ni_0.50Co_0.20Mn_0.30O₂cathodes exhibit higher electrochemical performance than that of PP matrix under the condition of high voltage(2.5?4.6 V),high temperature(55?)or low temperature(-22?).3.The coated PP separator was prepared by using a coating method in the water-based mixture solution of the lauramidopropyl hydroxy sulfobetaine(LHSB),konjac glucomannan(KGM)and Si O₂,which ionic conductivity is 9.7×10^-4cm²s^-1.The electrochemical stability window is in the potential zone of 2.0?5.0 V(vs.Li⁺/Li).The diffusion coefficient of lithium ions is 9.99×10^-10cm²s^-1.The heat shrinkage of the coated separator is less than 71.5%in size while heated at 170? for 30 mins.The coin cells composed of coated separators and Li Ni_0.50Co_0.20Mn_0.30O₂cathodes exhibit higher electrochemical performance than that of PP matrix under the condition of high voltage(2.5?4.6 V)and low temperature(-22?).