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Safety is one of the most factors for lithium-ion batteries (LIBs). In this work, a novel kind of ceramic separator with high safety insurance is proposed. We fabricated the core-shell nanofiber separators for LIBs by atomic layer deposition (ALD) of 30 nm Al2O3 on the electrospinning nonwoven fiber of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The separators show a pretty high heat resistance up to 200 °C without any shrinkage, an excellent fire-resistant property and a wide electrochemical window. Besides, with higher uptake and ionic conductivity, cells assembled with the novel separator shows better electrochemical performance. The ALD produced separators exhibit great potential in elaborate products like 3C communications and in energy field with harsh requirements for safety such as electric vehicles. The application of ALD on polymer fiber membranes brings a new strategy and opportunity for improving the safety of the advanced LIBs.

TiO2 nanoparticles with oxygen vacancies (B-P25) prepared by NaBH4 reduction method were coated onto PE separator to construct an active ceramic layer. The effect of the functional layer was carefully studied especially the interaction between oxygen vacancies on B-P25 and species in the liquid electrolyte. The B-P25 not only improves the affinity between the separator and electrolyte, but also improves the lithium ion transference number of the electrolyte, from 0.28 to 0.50. Based on the infrared spectroscopy results, it was found that B-P25 weakened the coordination between Li+ and EC, and partially desolvated the Li+-EC complex. Further theoretical calculation showed that the oxygen vacancies are more likely to adsorb EC molecules and indirectly promote the dissociation of Li+-EC, so that partially solvated Li+ has a stronger mobility and a higher lithium ion conductivity in the electrolyte. Therefore, B-P25 as an active layer assembled in LiFePO4 half-cell has better rate performance.