Study On The Performance Of Polyolefin Microporous Membrane For Lithium-ion Battery Prepared By TIPS Method

High density polyethylene (HDPE) is one of the most widely used materials of lithium ionbattery separator due to its excellent corrosion resistance and low price. HDPE separator ensures thesafety of lithium batteries because when temperature reached to130℃the micro-pores of separatorcould shutdown timely. The thermal stability of HDPE decreased caused by its low melting point. Inorder to reduce the thermal shrinkage of HDPE separator that we adopted nano-silicon (nano-SiO2)and ultra high molecular weight polyethylene (UHMWPE) to modified HDPE separator.Firstly, the thesis explore the optimum process of membrane preparation to studied the processcondition that effect on the thermal shrinkage, porosity and pore size of HDPE separator. Secondly,four different micro-porous membranes were prepared by thermally induced phase separation (TIPS)LP as a solvent. Finally, used n-hexane as extraction the crystalline, thermal stability, shrinkage afterextraction, porosity, pore size, water flux, the surface and cross-section morphology, thermalshrinkage and shutdown temperature of micro-porous membranes were characterized which couldstudy the effect of nano-SiO2and UHMWPE on performance and structure of membranes.The results showed that the optimum process condition of preparing micro-porous membranewere20℃water bath cooling and tempering treatment before and after extraction. It can obtain thatusing nano-SiO2and UHMWPE synergistic modified HDPE micro-porous membrane was better thansimple modification under the process parameters. The research showed that nano-SiO2couldimprove the crystalline and thermal stability of blend system and the residual rate of it in the blendmicro-porous membranes was59%. When the ratio of UHMWPE/HDPE fixed to5/95, HDPEmicro-porous membrane was modified by1wt%of nano-SiO2and5wt%of UHMWPE, thecomprehensive performance of the membrane was the best. Scanning electron microscopy (SEM)analysis showed that the pore size of blend membrane distribution was the most uniform and averagepore size was0.5um, and shrinkage after extraction, heat shrinkage rate, porosity, water flux andcrystallinity were13%,3.5%,54%,142,55.56%, respectively. Compared with pure HDPE membranethe shrinkage after extraction, heat shrinkage rate decreased by56%,67.2%, while the porosity, waterflux and crystallinity increased by46%,111%and34.5%.