The phone was switched off and not charging, its owner said, when it began to overheat in his pocket. He was on a Southwest Airlines plane in Louisville, Kentucky, waiting to leave for Baltimore. It was October 5, 2016. He threw the phone to the floor and it started to smoke. Everyone got off through the main cabin door before take-off.
It was a Samsung Galaxy Note 7.
And it was supposed to be one of the safe ones. The owner had bought it on September 21, as a replacement, and he said its box carried the mark Samsung had added to tell the new phones from the old.
A month earlier, the fix had looked simple. The Note 7 had gone on sale in August, at $850 to $890 in the US, and its batteries had started catching fire. On September 2, Samsung said it had found “a battery cell issue,” counted 35 cases worldwide and stopped sales. By the formal US recall on September 15, there were 92 reports of overheating there, including 26 burns and 55 cases of property damage, among them fires in cars and a garage. Owners were offered a new Note 7 with a different battery, made by a different supplier.
Then the replacements started smoking too. After the plane, more reports came in. Samsung stopped sales and exchanges, and on October 11 it announced a final decision to halt production. In the US alone, the recall now covered about 1.9 million phones.
The full answer came on January 23, 2017, at a press conference in Seoul, with three outside firms that had run their own investigations: UL, Exponent and TÜV Rheinland. There had been two problems, one in each battery.
In battery A, from the first recall, the negative electrode was bent in the upper right corner of the cell. Exponent traced this to a pouch that did not leave enough room for the electrodes inside, and found the damage in every one of these cells it and Samsung examined.
Battery B, from the second recall, failed differently. Welding on its positive tab left sharp burrs tall enough to push through the insulation tape and the separator, until the tab touched the negative electrode. Some cells had no insulation tape at all. Exponent reported that the first B cells it examined showed no deficiencies; cells made after that initial look carried the new defect.
UL listed one design choice for both batteries: a thinner separator, which it said could mean poorer protection and less tolerance for manufacturing defects.
Samsung did not name the suppliers that day. It said it was “taking responsibility for our failure to ultimately identify and verify the issues arising out of battery design and manufacturing.” The recall and the end of the phone were estimated to have cost it $5.3 billion.
The same day, Samsung unveiled an 8-point battery safety check. One of the eight was an X-ray. Another took the battery apart: “We disassemble the battery to assess its quality, including the battery tab welding and insulation tape conditions.”