Samsung announced that problems with battery design and manufacturing were the causes of the Note 7’s catastrophic failure, leading to the recall of nearly 4.3 million devices last fall due to spontaneous combustion, at a cost of at least $5 billion.
Koh said that Samsung set up a special test facility to replicate the conditions that led to the Note 7 fires. Samsung tested more than just the batteries, though, running tests on the Note 7’s software, fast charging technology, USB type C port, iris scanner, + waterproofing features.
None of these issues were found to be related to the combustion problem, however.
The investigators instead found, as many outside observers had predicted, that the problems lay in the lithium ion batteries, both the “Battery A” from the original devices and the “Battery B” that was rushed into replacement phones.
A combination of design + manufacturing mistakes at companies A and B, which were respectively identified as Samsung SDI and ATL by The Wall Street Journallast week, meant that the original batteries + the replacement ones issued had their own unique fire risks.
Samsung and the investigators did not name “Company A” or “Company B,” though. (neither Samsung SDI nor ATL have yet issued statements.)
Sajeev Jesudas, President of UL’s Consumer Business Unit, described the problems found in the original batteries and the replacement ones. The original, Battery A, was deformed on the upper left and right hand corners when placed inside its casing, and the deformation was exacerbated by thin separators and the battery’s high energy density. The stress this put on Battery A meant that the separator could not keep the aluminum and copper foils from touching, which can cause an internal short circuit.
That is, because there wasn’t enough space around the corners, the battery folded up on itself and its internal safeguards wore away to the point of catastrophic failure.
In contrast, Battery B showed internal short circuits in different spots. And Battery B samples met Samsung’s current, temperate, and voltage safety standards. But, these batteries were found to often lack insulation tape and also have improperly welded joints. Battery B suffered less from design flaws than from manufacturing mistakes that were not caught in quality control before shipping out.
This was likely due to Battery B being hurried out as a replacement for Battery A by Samsung, to keep the Note 7 on the market. And ATL just couldn’t handle the demand, according to USA Today. That said, separator thinness and high power density also put stress on Battery B, given that it shared Battery A’s design, a design that originated not with SDI or ATL, but Samsung itself.