See the invisibles: Inspecting battery separator defects via pressure drop

Separator defects critically impact safety, reliability and performance of energy storage devices. However, there is a lack of cost-effective and rapid approach being able to inspect separator defects. Here, for the first time, we successfully correlate the airflow resistance of battery separator at extremely low flow rates (0.5-30 mm/min.) with various artificial defects (e.g. pinhole, micro-crack). It is demonstrated that the present method can not only inspect defects, but is also sensitive to the type, number and size of defects on the separator with a threshold down to sub-micron range. Specifically, by varying the airflow rates, we establish the relationship between defect quantity/size and airflow resistance. It is found that the higher the flow rate, the more sensitive the airflow resistance to the defects. Moreover, the defected separators show obviously negative effects on the battery performance, such as short-circuit, rapid capacity decay, etc. These results indicate that the pressure drop testing at extremely low flow rates is a very facile, economical and non-destructive method for evaluating separator defects and porous structures, which is in critical need by the quality and/or failure analysis of battery separators and separator coatings.