Electro-spun EVOH-SO₃Li/PU Composite Polymer Electrolyte

Polymer lithium ion batteries have drawn considerable attention due to theirgood electrochemical performance and miniaturization package. As the corecomponent of polymer lithium ion battery, polymer electrolyte determines thebattery’s quality. Porous polymer electrolyte has been studied greatly because ofits high electrolyte uptake and wonderful electrolyte retainability. Electro-spinning is considered an ideal method of preparing porous films, however, thepoor mechanical performance of them limit their practical application.We take EVOH-SO₃Li as the polymer electrolyte. Li ions were provided byEVOH-SO₃Li in li-ion transfer process, then the li-ion transference number couldbe improved; the charging time was shorten; at the same time the interfacestability between the polymer electrolyte and electrodes was enhanced. In thispaper, firstly EVOH-SO₃Li was synthesized, then EVOH-SO₃Li spinningsolution with terminated polyurethane pre-polymer （PUR） was blended, EVOH-SO₃Li/PUR composite membrane by electro-spinning was prepared. The purposeof introduction PUR is to form EVOH-SO₃Li/PU half interpenetrating network,in order to improve the mechanical properties of electro-spun film.Electro-spun parameters effect on the fiber morphology of EVOH-SO₃Lifilm were discussed. Scanning electron microscopy （SEM） was used toinvestigate microstructure of the films. The best electro-spinning conditions ofEVOH-SO₃Li system were determined: spinning solution concentration of40wt%, receiving distance of20cm, voltage of20kV, flow rate of0.3ml/h.PUR was added into EVOH-SO₃Li spinning solution, which was spun underthe optimum spinning conditions of EVOH-SO₃Li. EVOH-SO₃Li/PU compositemembrane was obtained under a certain temperature conditions. The compositemembrane was characterized by mechanical properties and SEM to determine the effects of PUR addition amounts on the tensile strength and micro structure. Theresults showed that the tensile strength was promoted with the increase of PURaddition amounts. When the mass fraction of PUR was6wt%, the mechanicalproperties were good; the microstructure of fiber was clear with fine fiberdiameter and uniform distribution. While the amount of PUR was increased, fiberdiameter trends became coarse, porosity decreased. With testing the above twokinds of composite membrane with FTIR, SEM, mechanical properties andelectrochemical performance, the results indicated that, compared EVOH-SO₃Lifilm with6wt%PUR doped EVOH-SO₃Li/PU composite membrane, tensilestrength increased from EVOH-SO₃Li film’s4.1MPa to10.3MPa; Porosityreduced from67%to66%. However the electrolyte uptake went up from393%to427%; Ionic conductivity was promoted from0.20×10-3s/cm to0.44×10-3s/cm;Lithium ion transference number increased from0.73to0.74; lithium iontransference number the existing system of polymer electrolyte was less than0.5;After100cycles, more than98%capacity of the battery remained.The results suggested that the addition of PUR effectively increased themechanical properties of the electrostatic spinning film, liquid absorption rate,ionic conductivity, slightly increased lithium ion transference number, good cycleperformance.