Samsung’s Note 7 release and subsequent is quickly becoming a legendary blunder in the smartphone industry. The Korean electronics giant is still conducting an internal investigation of the battery fires that plagued this device during its short life. But manufacturing technology company Instrumental has gotten its hands on a Note 7 to do a detailed third-party analysis. The verdict? Samsung’s aggressive design tolerances are the culprit, not the battery itself.
The Note 7 was getting universally excellent reviews several months ago as it hit the market. However, it wasn’t long before Samsung’s fortunes took a turn for the worse. Reports of battery fires started accumulating by the dozen until Samsung had to admit there was something wrong with the Note 7. Carriers stopped selling the device and Samsung started a recall program to replace phones. The new batteries in these replacement phones didn’t stop the fires, though. After less than two months on sale, Samsung discontinued the Note 7 and began the process of refunding buyers in order to collect all outstanding phones.
That made it difficult for Instrumental to get its hands on a Note 7, but it managed to track one down. With the phone (and a fire extinguisher) in hand, it tore the device down in hopes of learning what made it so volatile. The engineers at Instrumental claim that Samsung’s aggressive pursuit of high battery capacity and sleek, compact design were at odds and caused an unacceptably high failure rate.
Samsung packed a 3500mAh battery into a very small space in the Note 7. It apparently intended to protect it internally with the help of a CNC-machined pocket. However, the battery simply did not have enough clearance. A lithium ion battery should have 0.5mm of clearance on all sides, but in order to push the Note 7’s design, there was as little as 0.1mm of clearance on the top and 0.3mm on the side.
This is important because lithium-ion batteries swell slightly during normal use. If there’s enough space, the battery won’t be damaged. However, the Note 7’s battery would have been compressed during use, or even from slight flexing of the device (such as being in your pocket while you sit down). The battery itself was already extremely dense, with the positive and negative electrodes separated by a thin polymer layer. The pressure exerted by the casing as the battery expanded could easily be enough to bring the electrodes into contact, leading to high heat generation and fire.
The gist of Instrumental analysis is simply that Samsung pushed the design too far. If the battery had a bit more space, there might not have been any issues. Replacing the battery with identical units in the first recall didn’t address the fundamental design issues, so the fires continued. Samsung has yet to release its own findings, so we’ll have to wait and see if its engineers agree.