Multi-functional groups decorated composite nanofiber separator with excellent chemical stability in ester-based electrolyte for enhancing the lithium-ion transport

As various heat-resistant polymer separators come out, although they possess better thermal stability and superior affinity to liquid electrolyte than commercial polyolefin separator, the porous structure and chemical stability of these novel separators should be paid more attention. In this work, we prepare a thin polyacrylonitrile/cellulose acetate (PAN/CA) composite nanofiber separator and discuss the importance of chemical stability in the ester-based electrolyte. The addition of CA decreases the PAN/CA fiber diameter from 310 nm to 210 nm. However, CA containing a lot of ester groups is easy to be dissolved by liquid electrolyte for the property of similarity and compatibility. Hence, the obtained PAN/CA composite nanofiber separator is treated via alkaline hydrolysis process, and some ester groups are transformed to be hydroxyl groups. Noteworthily, hydroxyl-rich PAN/CA composite nanofiber separator not only remains stable in electrolyte, but also possesses an improved lithium-ion transport property for reducing concentration polarization effect. As a result, the LiCoO2/Li half cells employing the hydroxyl-rich composite nanofiber separator exhibits better capacity retention (118.5 mAh g−1 after 300 cycles) and superior rate performance (143.1 mAh g−1 at 3C). Therefore, this multi-functional groups decorated composite nanofiber separator with excellent chemical stability is a candidate for next-generation lithium-based battery.