Fast assemble of polyphenol derived coatings on polypropylene separator for high performance lithium-ion batteries

Improving the wettability of liquid electrolyte to polyolefin separators plays a significant role in the fabrication of high performance lithium-ion batteries. Herein, we report a facile surface coating method to enhance the wetting capacity of commercially available polypropylene (PP) separator. Natural polyphenol tannic acid (TA) and sodium periodate are selected as the coating precursor and inorganic trigger, respectively. Coating formation is initiated by the absorption of tannin molecules on the separator surface and then triggered by a single contact (5 min) with sodium periodate solution. After being modified, wettability of the separator can be significantly enhanced without damaging its original advantage properties, which accordingly resulted in higher electrolyte uptake and better interfacial compatibility. Furthermore, the LiCoO2/graphite full cells assembled with the modified separator displays an excellent cycle stability with coulombic efficiency exceeding 99.9% and superior rate performance. The ease, low cost and scalability of this coating process, combine with the general surface binding affinity of polyphenol, making this surface modification technique suitable to upgrade other inert substrates for various applications.