Effect of Al2O3 Coatings Prepared By RF Sputtering on Polyethylene Separators for High Power Lithium-Ion Batteries

Abstract

Most of the separators currently used in lithium-ion batteries (LIBs) are based on microporous polyolefin membranes such as polyethylene (PE) and polypropylene (PP). Such separators have excellent mechanical strength and chemical stability, but their thermal properties should be further improved to meet required level of safety for large-format LIBs. In order to achieve this goal, highly heat-resistive components including ceramic coated layers [1] and thermal resistive polymeric layers [2, 3] are introduced onto separator surfaces via dip-coating method, atomic layer deposition, and chemical vapor deposition method.In order to develop a novel and economical process with continuous processing, in this study, we introduced Radio Frequency (RF) sputtering method for fabricating aluminum oxide (Al2O3) ceramic coating layers onto PE separators. Coating thickness of Al2O3 layers was controlled as a function of RF sputtering power and coating time. We also evaluated morphological changes of PE separators in regard to sputtering time by measuring Gurley number, wettability, and ionic conductivity. The unit cells employing coated PE separators revealed similar level of cell performance compared to those of the unit cells employing bare PE separators. We believe that the improved wetting ability of ceramic coating layers successfully compensates pore-blocking effect. On the other hand, we verified that heat resistance of Al2O3 coated PE separators was remarkably improved out of a short sputtering time.