Anna Shedletsky, CEO and Founder of Instrumental Inc.
We acquired a Galaxy Note 7 and with a fire extinguisher close at hand, tore it down. We used an Instrumental station to document the process. What we found was surprising: the design can compress the battery even during normal operation.
Why does this matter? The Note 7’s lithium-polymer battery is a flattened “jelly-roll” consisting of a positive layer made of lithium cobalt oxide, a negative layer made of graphite, and two electrolyte-soaked separator layers made of polymer. The separator layers allow ions (and energy) to flow between the positive and negative layers, without allowing those layers to touch. If the positive and negative layers ever do touch, the energy flowing goes directly into the electrolyte, heating it, which causes more energy to flow and more heat — it typically results in an explosion. Compressing the battery puts pressure on those critical polymer separator layers that keep the battery safe. Samsung stated that these separator layers may have been thin to start with due to aggressive manufacturing parameters. Add some pressure due to normal mechanical swell from the battery or accumulated stress through the back cover (e.g. from being sat on in a back pocket), and that pressure could be enough to squeeze the thin polymer separator to a point where the positive and negative layers can touch, causing the battery to explode.
The whole article is full of technical and manufacturing jargon, Samsung design and engineering team will should be able to learn a thing or two from the article.
The kicker will be the last paragraph. Keep in mind that this is coming from a former Apple Watch System Product Design Lead and Manager.
[H/T to Unbox]
The design and validation process for a new product is challenging for everyone. In this case, Samsung took a deliberate step towards danger, and their existing test infrastructure and design validation process failed them. They shipped a dangerous product. That this is possible at one of the top consumer electronic companies in the world is humbling — and demonstrates the need for better tools. Instrumental is building them.
Last modified: December 6, 2016