Hyun-Seok Jeong

A novel poly(vinylidene fluoride-hexafluoropropylene)/poly(ethylene terephthalate) composite nonwoven separator with phase inversion-controlled microporous structure for a lithium-ion battery

We demonstrate a novel and facile approach to fabrication of a new composite nonwoven separator for a lithium-ion battery, which comprises a phase inversion-controlled, microporous polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) gel polymer electrolyte and a polyethylene terephthalate (PET) nonwoven support. The thermally stable PET nonwoven is chosen as a mechanical support and contributes to improving the thermal shrinkage of the composite nonwoven separator. The microporous PVdF-HFP gel polymer electrolyte serves as a pore size controller for the composite nonwoven separator. In order to provide a theoretical basis for this approach, an investigation of the phase diagram for coating solutions consisting of PVdF-HFP, solvent (acetone), and nonsolvent (water) is preceded. Based on this understanding of the phase behavior, the effects of phase inversion, more specifically, the water content in the coating solutions, on the morphology evolution of the composite nonwoven separators are identified. The phase inversion-governed microporous structures of the composite nonwoven separators play a crucial role in determining electrochemical performances of cells. The composite nonwoven separator is expected to be a promising alternative to a commercialized polyethylene (PE) separator, particularly in next-generation lithium-ion batteries necessitating superior battery safety and performance.

Effect of Microporous Structure of Al 2 O 3 /PVdF_HFP Ceramic Coating Layers on Thermal Stability and Electrochemical Performance of Composite Separators for Lithium-Ion Batteries

The internal short-circuit between cathodes and anodes has been known to be a critical concern for the safety failures of lithium-ion batteries, which is strongly influenced by the thermal stability of separators. In this study, to effectively suppress the internal short-circuit failures, we developed a new composite separator with the improved thermal stability compared to con- ventional polyolefin-based separators. The composite separators were prepared by introducing a ceramic coating layer (Al2O3/PVdF-HFP) onto both sides of a polyethylene (PE) separator. The microporous structure of ceramic coating layers is determined by controlling the phase inversion of coating solutions and becomes more developed with the increase of nonsolvent (water) content. This structural change of ceramic coating layers was observed to greatly affect the thermal stability as well as the electrochemical performance of composite separators, which was systematically discussed in terms of phase inversion.