Electrochemical properties of lithium ethylene-vinyl alcohol copolymer sulfate/polyimide Li-ion battery separator composite by electrospinning

Polyamic acid(PAA) spinning solution was fabricated by using benzophenone-3,3',4,4'-tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether as raw materials, and the polyimide(PI) fiber membranes were prepared by high-pressure electrospinning and thermal imidization. Then, lithium ethylene-vinyl alcohol copolymer sulfate(EVOH-SO₃Li)/PI li-ion battery separator composites were prepared by introduction of EVOH-SO₃Li fiber on both sides of PI membranes surface through high-pressure electrospinning and heating pressure treatment. The performance of EVOH-SO₃Li/PI li-ion battery separator composite was characterized by FTIR, SEM, universal tensile tester, contact angle meter and IM6 electrochemical workstation. The results show that EVOH-SO₃Li/PI separator has a clear three-dimensional network structure. Compared with PI separator, the absorption rate and tensile strength of modified EVOH-SO₃Li/PI separator composites increase to 521% and 12.83 MPa although the porosity reduces. The excellent thermal shrinkage rate, closed-cell at high temperature and electrochemical performance were exhibited. Then, the electrochemical window increases from 5.5 V to 5.8 V, the bulk resistance decreases from 360 Ω to 315 Ω, and the ion conductivity increases from 2.416×10^-3 S/cm to 3.672×10^-3 S/cm.