Study On Preparation And Properties Of EVOH-Li/TPU Lithium-ion Battery Separator

With the concept of environmental protection gradually getting popular,the new energy lithium-ion battery as a clean and green energy has attracted researchers’attention.Meanwhile,it is the power source of mobile phones,laptops,new energy vehicles and other equipment.The safety,endurance and multiple rate charging and discharging capabilities have attracted people’s attention.As the key component of lithium-ion battery,the performance of the separator also needs to be improved.And it needs to have good safety performance,excellent electrochemical performance and other characteristics.In this paper,the composite separator of lithium-ion battery was prepared with EVOH-Li and TPU as raw materials by mixed-spinning and co-spinning.And then its chemical structure and micro morphology were characterized.Its thermal stability,porosity,electrolyte uptake,mechanical properties and electrochemical properties were tested.The main work is as follows:First,EVOH-Li was prepared,and then EVOH-Li and TPU were blended to form a lithium-ion battery separator.That is to say,the two polymers were mixed in a certain proportion to form a spinning solution,and then spun into a separator.The results show that when the mass ratio of EVOH-Li and TPU is 3:1 and the concentration is 30%,the three-dimensional network structure of the nonwoven fabric has the best morphology and comprehensive properties,among which,the macro size has no obvious change after heat treatment at 120℃for 2 hours,the fracture stress is 5.46 MPa,the elongation at break is 61.19%,the porosity is 81%,the electrolyte uptake is 306%,the ionic conductivity is 5.42×10^-4S/cm,and the interface has the best properties The impedance is about 430Ω,and the electrochemical stability window is 4.8 V.Secondly,EVOH-Li and TPU separators were spun respectively to determine the optimal spinning ratio.Then,two kinds of spinning solution were prepared into lithium-ion battery separator by co-spinning,that is,two kinds of polymer were dissolved in solvent,and the non-woven fabric was made on a collecting drum by two spinning outlets at the same time.Then the properties of the nonwoven fabric were tested.When the concentration of EVOH-Li was 30%and the concentration of TPU was 25%,the nonwoven fabric showed a uniform three-dimensional network structure.Through the comparative study of EVOH-Li single spin film,TPU single spin film,EVOH-Li/TPU mixed Film and EVOH-Li/TPU co-spin film,it is found that the performance of the co spin film is the best,among which,after heat treatment at 120℃for 2 hours,the macro size and micro morphology have no obvious change;the maximum stress value is 6.09 MPa,the elongation at break is79.26%,and the higher elongation at break can prevent the lithium dendrite from penetrating the separator and increase the lithium-ion battery.The results show that the porosity is 84%,the electrolyte uptake is 321%,and the high porosity and electrolyte uptake provide a good basis for the excellent electrochemical performance of lithium-ion batteries.The ionic conductivity is 6.65×10^-4S/cm,the interface impedance is 219Ω,and the electrochemical window is 5.0 V.The results show that the performance of the separator prepared by mixed-spinning and co-spinning is better than that of EVOH-Li or TPU.Among them,the EVOH-Li/TPU lithium-ion battery composite separator prepared by the co-spinning method has the best performance than the composite separator prepared by the mixed-spinning method.