| With the increasingly serious energy crisis,the development of electric vehicle becomes more and more rapid,which demands the advancement of high performance lithium ion batteries.Separator,which is one of the key elements of the battery,has a direct impact on the battery performance improvement,especially the safety of lithium ion battery.Microporous membrane prepared by vapor induced phase transition has excellent pore structure,high porosity and high ionic conductivity,is often used for high-performance separator.Polyetherimide?PEI?,which has excellent dimensional stability,electrochemical stability,and excellent electrolyte wettability,is a promising candidates for separators of high performance lithium ion battery,and has attracted more and more researchers'attention in recent years.This article explores the influence of the solvent/non-solvent systems,the polymer concentration and the relative humidity on the microporous membrane structure in the phase transition process,and verifies the best solvent/non-solvent system is NMP/water system,and the microporous membrane's pore size decreases as the relative humidity and the polymer concentration are increased.Compared with the Celgard PP separator,PEI separator have the symmetrical uniform pore structure,higher porosity?>75%?,higher electrolyte uptake?>450%?and more excellent thermal stability which greatly improves the safety of the battery.Furthermore,the ionic conductivity of the 23%-PEI separatoris as high as 0.846×10-3 S cm-1,and interfacial resistance between the electrode and PEI membrane is smaller than that of Celgard PP membrane.The assembled cells adopting the prepared PEI membrane as separator have higher charge and discharge stability,and higher initial discharge specific capacity as high as 164 m Ah/g at 0.2C,have excellent rate capability and cycle performance with capacity retention closing to 100%after 50 cycles,showing very excellent electrochemical properties.To further enhance the thermal stability and ionic conductivity of the separator,and to improve their safety and practical application,adding inorganic components is selected.We successfully prepare the enhanced PEI-SiO2 composite membrane,which includes PEI-A?direct addition method?and PEI-B?indirect addition method?composite membrane.The result shows that composite membrane both maintain the previous morphology,the high porosity and high electrolyte uptake,and have the higher ionic conductivity,which is as high as 2×10-3 S cm-1,and interfacial resistance between the electrode and composite membrane is smaller than that of PEI membrane.The PEI-A composite membrane shows the better thermal stability;the PEI-B composite membrane shows the better electrochemical performance,the initial discharge specific capacity of the cell assembled with PEI-B composite membrane is 167.4 m Ah/g at 0.2 C.It demonstrates the membrane we prepared have a great prospect in the field of lithium-ion battery. |
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