Engineering company Instrumental has uncovered the cause of Samsung’s exploding Galaxy Note 7 batteries.
Exploding Note 7 batteries were first reported in September this year. Samsung believed the issue was that too much tension was used in the manufacturing of its lithium-polymer batteries, and therefore issued replacement phones to customers. However, several weeks later, some of the batteries in the replacement phones also exploded, causing Samsung to cancel the entire product line.
Engineers from Instrumental procured a Note 7, and took the phone apart to examine its construction. What they found was that the battery was packed too tightly in the body of the device, meaning that any pressure from battery expansion or stress on the body itself could squeeze together layers in the battery, with the potential to cause an explosion.
“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,” wrote Instrumental’s chief executive Anna Shedletsky in a recent blog post.
“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.
“Any battery engineer will tell you that it’s necessary to leave some percentage of ceiling above the battery, 10 per cent is a rough rule-of-thumb, and over time the battery will expand into that space.”
According to Shedletsky, the Note 7 had no ceiling. The battery and adhesive was 5.2mm thick, resting in a 5.2mm deep pocket, when there should have been a 0.5mm ceiling.
Shedletsky believes that a smaller battery using standard manufacturing parameters would have solved the issue, however the battery life of the device would not have been able to compete with the iPhone 7 Plus, nor the device’s predecessor, the Note 5.