High-stability core-shell structured PAN/PVDF nanofiber separator with excellent lithium-ion transport property for lithium-based battery.

The ion transport channel constructed by the separator is crucial for the practical performance of Li-ion batteries, including cycling stability and high rate capability under high current. Traditional polyolefin separator is the storage of electrolyte, which guarantees the internal ion transport process. However, its weak interaction with electrolyte and low cationic transport capacity limit the application of lithium ion battery in large current. In this study, a kind of core-shell structured polyacrylonitrile (PAN)/polyvinylidene fluoride (PVDF) nanofiber separator composed of PAN core and PVDF shell was prepared by coaxial electrospinning technique. As a result, the mechanical strength of PAN/PVDF nanofiber separator is increased from 0.6 MPa of PVDF to 3.6 MPa for PAN core. Furthermore, PAN/PVDF nanofiber separator exhibits an improved lithium-ion transference number (0.66), which is resulted from F functional groups of PVDF shell. It is believed that the interactions between the lithium ion and F functional group could construct a fast ion transport channel. The LiCoO/Li half-cells assembled with PAN/PVDF exhibited higher discharge capacity (5C) than those cells using pristine PVDF, PAN separators and polyethylene (PE) separator. It is worth mentioning that the cells with PAN/PVDF separator also have excellent cycle stability. This study provides a new idea about separator-design strategy for high-performance lithium-based battery.