Development of plasma-treated polypropylene nonwoven-based composites for high-performance lithium-ion battery separators

Separators have drawn substantial attention because of their important role in achieving the safety and good electrochemical performance of lithium-ion batteries. In this study, we report a new type of composite membrane prepared by a combination of fluorinated polypropylene (PP) nonwoven fabric, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and SiO2 nanoparticles. 2, 2, 3, 3, 4, 4, 5, 5-Octafluoropentyl methacrylate (OFPMA) is first grafted on the surface of PP nonwoven by plasma treatment to improve the nonwoven's adhesion with PVdF-HFP. Two kinds of composite separators have been prepared by using the different PP nonwovens together with PVdF-HFP and SiO2 nanoparticles. They were separately designated as PHS for commercially raw PP nonwoven system and PHS-n for OFPMA-modified PP nonwoven systems (n means plasma treatment time). The morphology, electrolyte uptake, ionic conductivity and electrochemical properties of the composite separators have been analyzed by scanning electron microscope (SEM) analysis, impedance measurement, charge-discharge cycle and Crate tests, respectively. The results indicate that PHS-10 composite separator using the modified PP nonwoven treated by plasma for 10 min exhibits much better properties than PHS separator, including an improved mechanical property, thermal stability, electrolyte uptake (290 wt%) and ionic conductivity (1.76 mS cm(-1)). More importantly, the LiFePO4/Li half-cell assembled with PHS-10 composite separator displays a good C-rate performance, which shows an enhancement in the chemical stability and discharge capacity. The capacity keeps above 150 mA h g(-1) after 100 charge-discharge cycles. These performances endow this composite membrane as a promising candidate for high-performance lithium-ion battery separators. (C) 2015 Elsevier Ltd. All rights reserved.