Particle size-dependent, tunable porous structure of a SiO2/poly(vinylidene fluoride-hexafluoropropylene)-coated poly(ethylene terephthalate) nonwoven composite separator for a lithium-ion battery

Abstract

We demonstrate a new silica (SiO₂) nanoparticle/polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP)-coated polyethylene terephthalate (PET) nonwoven composite separator for a lithium-ion battery as a promising alternative to a commercialized polyethylene (PE) separator. A distinctive feature of the nonwoven composite separator is its porous structure, i.e. well-connected interstitial voids formed between close-packed SiO₂ nanoparticles interconnected by PVdF-HFP binders. More notably, this unusual porous structure of the nonwoven composite separator can be tuned by controlling the SiO₂ particle size (herein, 40 nm and 530 nm SiO₂ powders are exploited). Such morphological variation of the nonwoven composite separator has a crucial influence on separator properties such as porosity, electrolyte wettability, and ionic conductivity. The PET nonwoven is employed as a physical support to prevent thermal shrinkage of the nonwoven composite separator. Based on this understanding of the separator characteristics, the effects of the SiO₂ particle size-dependent, tunable porous structure of nonwoven composite separators on the electrochemical performance of cells are investigated. In comparison to a nonwoven composite separator containing 530 nm SiO₂ particles as well as the conventional PE separator, the nonwoven composite separator incorporating 40 nm SiO₂ particles provides superior cell performance owing to facile ion transport and retarded growth of cell impedance during cycling.