A phase separation method toward PPTA-polypropylene nanocomposite separator for safe lithium ion batteries

The building of separators with high thermal stability and security is important for lithium ion batteries. A novel, simple and successive process, which aims at coating poly-p-phenylene terephthamide (PPTA) onto commercial polypropylene (PP) separators, has been demonstrated. Without any additional binder, the PPTA nanofiber coating layer sticks to the porous PP separators by physical anchoring, endowing the composite separators with modified wettability toward electrolytes and heat resistance. Meanwhile, migration routes for lithium ions are guaranteed by the porous structure controlled by the self-assembly of the fibrillar units during the nonsolvent induced phase separation. The cells equipped with the composite separators show better cycling performances. Moreover, the system based on the composite separators shows a sharp drop in ion conductivity after heat treatment at 200 degrees C for a certain period, indicating the shutdown effect of the composite separators, which can contribute to additional safety of lithium ion batteries. (C) 2018 Wiley Periodicals, Inc.