Fabrication of coaxially electrospun PEI@PVDF-HFP fibrous membrane as flame-retardant and anti-shrink separator for lithium-ion battery

•A core–shell structured PEI@PVDF-HFP nanofiber membrane is successfully prepared.•The separator has outstanding electrolyte uptake, anti-shrink and flame-retardant performance.•The assembled battery shows high safety and excellent electrochemical properties. A novel core–shell nanocomposite fiber membrane was fabricated in this work by coaxial electrospinning using poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) as shell material and polyetherimide (PEI) as core material. The PEI core has good heat resistance and mechanical strength, serving as a stable skeleton support. At the same time, the gel shell is conducive to enhancing the electrolyte affinity, thereby promoting the rapid transmission of Li+. As a result, the Li/LiCoO2 batteries with the fabricated separator present an excellent first discharge capacity of 178.8 mAh g−1 at 0.2C and capacity retention rate of 89.7 % after 200 cycles. Even running at high temperature (65 °C), the PEI@PVDF-HFP separator still enables a steady charging/discharging performance. Therefore, the PEI@PVDF-HFP nanocomposite separator can be an extraordinary candidate for high-safety lithium-ion batteries.