Electro-spun EVOH-SO₃Li/Inorganic Nanocomposite Lithium-ion Battery Separator

Due to the scarcity of global resources, low carbon environmental protectionand sustainable development of energy has been widely concerned. Because thelithium ion battery have a small size, high energy, long cycle life, no memoryeffect, safe and reliable, and can quickly be charged and discharged, etc, moreand more focus has been gotten by the researchers, all the applications areas aremore widely. The EVOH sulfonic acid lithium is a semicrystalline polymer thathas excellent blocking performance. It has both processing performance likepolyethylene, and is strong hydrophilic, which can become an excellent batteryelectrodes diaphragm material. With fiber diameter in tens of nanometers tohundreds of nanometers by electro-spinning, the diaphragm has a well-proportioned microporous structure. Doped inorganic nanoparticles cancompaensate the defect of the lithium ion battery diaphragm in the mechanicalproperty, heat-resistant quality, ionic conductivity, ionic conductivity. Therefore,the research of electro-spun EVOH-SO₃Li/inorganic nanocomposite lithium-ionbattery separator has important theoretical significance and application value.Tert-butyl alcohol lithium reacted with polyethylene-vinyl alcohol （EVOH）to form EVOH alcohol lithium polymer，then EVOH-SO₃Li grafted polymerwas synthesized by addition reaction of1,3-propane sulfonic acid ester andEVOH alcohol lithium polymer，and doped with nano-SiO₂and Al₂O₃withdifferent proportion, respectively. The non-woven EVOH-SO₃Li/SiO₂andEVOH-SO₃Li/Al₂O₃were prepared by electro-spinning，and their morphologiesand composition points were tested, in order to inorganic nano-particles existedon non-woven fiber filaments with good morphology. By consolidating the testedresults of physical properties, chemical stability and thermal properties,analyzing the impact of doping on each performance, the optimum amount ofnano-doped SiO₂and Al₂O₃were3wt%and2wt%, respectively.The electrochemical properties of the non-woven film EVOH-SO₃Li/SiO₂ with wt=3%, EVOH-SO₃Li/Al₂O₃with wt=2%, EVOH-SO₃Li non-woven filmand commercial diaphragm （pp diaphragm） were tested, to analyze the impact ofnanoparticles doped to the electrochemical properties of the non-woven films.The results suggested that: the electrochemical window of non-woven filmEVOH-SO₃Li/SiO₂and EVOH-SO₃Li/Al₂O₃were stable; stability limit voltagewere5V and4.8V, respectively. They meet performance requirements well forthe battery separator. Ionic conductivity and lithium ion transference number ofthe EVOH-SO₃Li/SiO₂non-woven film were σ=0.52×10-3S/cm and t+Li=0.91; theEVOH-SO₃Li/Al₂O₃non-woven film were σ=0.44×10-3S/cm and t+Li=0.88;EVOH-SO₃Li non-woven film were σ=1.90×10-4S/cm and t+Li=0.92, respectively,which indicated that nano-doped inorganic particles can improve the ionicconductivity of non-woven fabrics, whitout effect on lithium ion transferencenumber, and their performance were higher than σ=9.87×10-5S/cm and t+Li=0.75of the commercial membrane （pp diaphragm）. At room temperature, the charge-discharge cycles of the diaphragm were tested，cycled after100cycles，it stillremained more than97%of the initial capacity, indicated that the battery hasexcellent cycle performance. They meet performance requirements well for thebattery separator.This paper shows that the non-woven film doped by nano inorganic particlescan be prepared by electrospinning, and its performance can meet therequirements of a lithium ion battery separator. Performances of porosity,expansion and contraction rate, heat resistance and ion conductivity were allincreased. The porosity increased by30%, liquid absorption rate increased bymore than150%, melting point increased by25to40℃, thermal decompositiontemperature increased by about30℃, ionic conductivity enhanced by nearlyan order of magnitude.