Electrospun sandwiched PVDF-HFP@UIO-66/PEO/PVDF-HFP@UIO-66 nanofiber separators with low temperature thermal shutdown for lithium-ion batteries

To address the issue of thermal runaway in lithium-ion batteries while simultaneously enhancing their electrochemical performance, this study fabricated a sandwich-structured composite separator of PVDF-HFP@UIO-66/PEO/PVDF-HFP@UIO-66 via electrospinning, which was further enhanced by impregnation with PMMA. In this design, the two outer PVDF-HFP@UIO-66 layers aim to improve electrochemical performance and mechanical stability, while the PEO core layer enables thermal shutdown at approximately 67 °C. The composite separator exhibits high ionic conductivity (3.25 mS cm −1 ), excellent thermal dimensional stability, and good mechanical strength (13.6 MPa). Cells assembled with this separator achieved an initial discharge specific capacity of 166.2 mAh g −1 at 0.5C, with a capacity retention rate of 97.9% after 100 cycles, significantly outperforming cells using a commercial separator (133.1 mAh g −1 , 96.9%). Accelerating rate calorimetry (ARC) tests further confirm its exceptional safety, delaying the time to reach the thermal runaway critical temperature by 194.1 min and raising that critical temperature by 4.5 °C. This work presents an effective strategy for designing battery separators that combine high safety with superior electrochemical performance.