“As the size of the cell increases, the chance of something happening increases because you have an increased amount of material being exposed” says Dr. K.M. Abraham. “[Lithium-ion batteries] are not as forgiving as far as design and construction are concerned. If you have quality control issues, it can be very bad.”
Dr. Abraham is a battery consultant and professor at Northeastern University in Boston and has been researching lithium-ion batteries since 1976.
Lithium-ion batteries are extremely power dense, delivering a lot of electricity from a relatively compact package. To do this they need extremely thin sheets of the plastic material to separate the cathodes and anodes inside the battery. The large 32 volt battery like those found in the 787 is made up of eight 3.7 volt cells. Dr. Abraham says the design and construction of a battery is critical so that these separators are not damaged during manufacturing or during a battery’s use.
“I always consider the separator as a major source for a problem” Dr. Abraham says of the sheets that are 25 microns thick, around the same thickness as cellophane.