Preparation and application of a high-temperature–resistant EVOH-SO3Li/PI fiber membrane with self-closing pores

Abstract

A lithium ethylene-vinyl alcohol copolymer sulfate (EVOH-SO3Li)/polyimide (PI) composite fiber membrane prepared via high-voltage electrospinning and impregnation was used as a lithium-ion battery separator for research purposes. The polyamic acid spinning solution was synthesized from 3,3′′,4,4′′-benzophenone tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether. The PI fiber membrane was prepared via high-voltage electrospinning and thermal imidization, and EVOH-SO3Li was then coated on the surface of the PI fiber to prepare an EVOH-SO3Li/PI composite fiber membrane material (t-EVOH-SO3Li/PI). Overall, the EVOH-SO3Li/PI membrane exhibits excellent basic physical properties, given the clear three-dimensional network microstructure. When compared with EVOH-SO3Li/PI composite fiber membrane prepared via the cospinning method (s-EVOH-SO3Li/PI), its electrolyte uptake and tensile strength can increase to 739% and 17.56 MPa, respectively. Additionally, the EVOH-SO3Li/PI composite fiber membrane prepared via high-voltage electrospinning and impregnation exhibits better heat shrinkage stability, electrochemical performance, and high-temperature self-closing pores function. The electrochemical stability window, electrochemical impedance, and ionic conductivity correspond to 5.8 V, 310 Ω, and 3.753 × 10−3 S cm−1, respectively. Specifically, at 200°C, the internal pores can close effectively, and this is extremely important for the safety of lithium-ion batteries.