Orientation gradient architecture of nanofibrous separator towards mechanical enhancement and ion transport acceleration for lithium-ion batteries

Designing rational structure is one of strategies as effective as supplementing proper materials for separator performance enhancement. Focusing on the nanofibrous separators that generally have high porosity but poor mechanical strength, in this work, we develop an architecture of orientation gradient along the thickness direction for polyacrylonitrile (PAN) nanofibrous membrane (OGP), which is facilely fabricated by sequential electrospinning with different collector rotating speeds. The obtained OGP separators not only share the advantages of PAN nanofibrous separator, such as high porosity, superior wettability and thermal stability, but also have considerable improvements in tensile strength and puncture resistance to compensate for its mechanical weakness. Meanwhile, when compared to the most commonly used nanofibrous separator with randomly oriented nanofibers, the OGP separators present more desirable lithium ion transport ability, including a larger amount of ions transported as well as a faster ion transport rate, thereby endowing the cell with superior cycling stability with a capacity retention 97.2% after 100 cycles at 0.5 C. Therefore, taking safety and battery performance into account, the as-prepared OGP nanofibrous membrane could be a promising separator candidate for lithium ion batteries.