Nanofibrous Composite Separator for Lithium-Ion Batteries with High Safety

Thermally stable separators, particularly those with a multifaceted and ultrawide range of thermal protection functions, are essential to the long-term safe operation of lithium-ion batteries (LIBs). In this work, we fabricate a sandwiched nanofibrous composite separator (PPPA) that integrates comprehensive thermal protection capacities of heat storage, shutdown, dimensional stability, and flame retardancy together, via a facile combination of coaxial-electrospinning polyacrylonitrile and poly(butylene succinate) nanofibrous membrane (PAN@PBS), spraying a mixture of poly(ethylene glycol) (PEG) and ammonium polyphosphate (APP), and folding techniques. The resultant PPPA separator is able to offer a fibrous network, high porosity, and superior electrolyte affinity. Meanwhile, the thermal protection of the PPPA separator starts with the phase-change heat storage of PEG at 60 °C. Then, the shutdown can be activated at 115 °C by the outer PBS melting of coaxial nanofibers, while the inner PAN maintains dimensional stability up to 250 °C. Further, self-extinguishing will occur in the event of fire due to the existence of APP. Moreover, PEG phase-change leakage of the composite separator can be overlooked due to the hydrogen bonds between PEG and APP and the entrapment of the upper and lower fibers. Furthermore, the PPPA separator demonstrates electrochemical performance that is on par with a commercial polyolefin separator, with higher ionic conductivity (2.49 mS cm–1) and lithium-ion transference number (0.32), as well as a cell discharge capacity retention of 92.4% after 100 cycles at 1 C. Therefore, given its excellent safety and satisfactory performance, PPPA composite separators are anticipated to be a potential separator for LIBs.