H-Bond Cross-Linked Polyimide Nanofiber-Modified Polyethylene Composite Separators for Lithium-Ion Batteries

H-bond cross-linked polyimide (HPI) nanofiber-modified polyethylene (PE) composite separators with high thermal stability, excellent electrolyte wettability, and improved electrochemical performance are prepared by electrospinning and alkaline hydrolysis processes. Due to the high thermal stability of the layer of HPI nanofiber, the dimension stability of the HPI@PE separator is greatly enhanced compared to the PE separator, without obvious thermal shrinkage at 200 °C. In comparison to the PE separators, lithium-ion batteries (LIBs) assembled with the HPI@PE composite separators show better cycling performance and rate capability, which are ascribed to the high polarity and developed porosity of the HPI nanofiber layer, which gives the separator excellent electrolyte wettability (electrolyte uptake and retention are 204 and 65%, respectively), low bulk resistance (3.1 Ω), and high ionic conductivity (0.46 mS cm–1). Therefore, the assembled Li/HPI@PE/LiCoO2 cell achieves a specific capacity of 105.5 mA h g–1 as well as a capacity retention of 80.7% after 200 cycles at the discharge rate of 1 C. These results indicate that the prepared HPI@PE separator is applicable toward safe, long-life, and high-rate LIBs.