In situ aluminide armored polyimide nanofiber separators with ultrahigh strength and high wettability for advanced lithium-ion batteries

Polyimide (PI) has been widely used in aerospace, electronic information, novel energy, and other industries due to its excellent high- and low-temperature, radiation, and chemical corrosion resistance. However, the use of electrospun PI separators in lithium-ion batteries (LIBs) is limited due to their poor electrolyte wettability and insufficient mechanical strength. Inorganic materials such as aluminide have typically been used in the coating composition of PI separators. To investigate the effects of different aluminide components, in this work, PI materials were prepared by the complexation–hydrolysis method and used as separators for LIBs. The physicochemical and electrochemical properties of the different nanofiber membranes were studied by adjusting the calcination temperature. The results showed that the sample with the highest tensile strength was 107.6 MPa, which is close to the commercial polyolefin separator. When the calcination temperature increased to 300 °C and then exceeded 400 °C, the aluminide shell initially transformed into thin boehmite and then into γ-Al2O3 phases. The mechanical properties of the nanofiber membranes were enhanced, and the wettability and electrochemical characteristics also improved to some extent. Furthermore, the nanofiber structure was destroyed at 500 °C and could not meet the long-term battery cycles. Therefore, when the calcination temperature was controlled between 300 °C and 400 °C, the aluminide-armored PI nanofiber membranes exhibited better comprehensive performance and were suitable for use as separators in LIBs, which was of great significance for improving the safety and stability of LIBs, especially power batteries.