This might be why the Note 7 exploded

After watching the crisis unfold once, and then again, we’ve all wondered exactly what led to the Samsung Galaxy Note 7 exploding. Here’s why.

Samsung’s Galaxy Note 7 was set to be the phone of 2016. It had the best specs, best design, and unrivalled functionality. And then the worst happened.

All over the world, reports started rolling in stating that the Note 7 was exploding. After two recalls, Samsung finally killed it off.

The reason

Months later, the company has still not revealed why the Note 7 exploded. But an engineering consulting company, Instrumental, thinks they might have figured out why.

They believe that the Note 7’s issues can be attributed to a fundamental design problem with the phone itself. Everyone wants a thinner phone with a better battery. And, every year, tech companies have been pushing the boundaries of hardware design to bring us exactly that. It turns out that this demand for thinner phones and higher-capacity batteries could have been the downfall of the Note 7.

Instrumental’s findings

Instrumental acquired a Note 7 to test the device and attempt to determine what could have caused the battery explosions. “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. This causes more energy to flow and more heat, typically resulting 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 (eg, 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.

Faulty Design

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What’s interesting is that there is evidence in the design of an intellectual tension between safety and pushing the boundaries.

Samsung engineers designed out all of the margin in the thickness of the battery, which is the direction where you get the most capacity gain for each unit of volume. But the battery also sits within a CNC-machined pocket. This is a costly choice probably made to protect it from being poked by other internal components.

“Looking at the design, Samsung engineers were clearly trying to balance the risk of a super-aggressive manufacturing process to maximise capacity, while attempting to protect it internally.”

The report concludes by saying there was no competitive salvageable design. Which means Samsung would either have had to put a smaller battery in the device, and therefore have a high-end device without a battery suitable to get it through a day’s worth of use, or find another way to compromise the phone.

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