A simple method to prepare a polydopamine modified core-shell structure composite separator for application in high-safety lithium-ion batteries

• Average tensile property of PVDF-HFP-PDA is 11.2 MPa.
• PVDF-HFP-PDA only suffers less than 15% of thermal shrinkage at 200 °C.
• Batteries with the PVDF-HFP-PDA show stable cyclic and good rate performance.

In this work, we report a simple dip coating method to grow a thin polydopamine (PDA) layer on the surface of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) nano-fibers as the composite separator for application in high-safety lithium-ion batteries. A thin adherent PDA film uniformly distributed on the surface of PVDF-HFP nano-fibers, formed a unique core-shell structure. Compared with pure PVDF-HFP nonwoven membrane, the PDA coating PVDF-HFP composite membrane (PVDF-HFP-PDA) not only exhibits much higher thermal stability, but also shows enhanced mechanical strength and tensile strength, which are very important for the assemble and long-term performance of the batteries. The ionic conductivity of the PVDF-HFP-PDA composite membrane is 1.40 mS cm−1 which is much higher than 0.80 mS cm−1 of the polypropylene (PP) separator. The lithium-ion batteries with PVDF-HFP-PDA composite membrane show excellent cyclic stability and good rate performance. The PVDF-HFP-PDA composite membrane is suitable for applications in secondary lithium-ion batteries due to its advantages mentioned above.

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