Technology firm Instrumental has issued a report which says aggressive design caused the Samsung Galaxy Note 7 battery explosions.
When the 5.7-inch phablet was announced in early August, it was touted as the most impressive Android smartphone of the year for its myriad of features, including iris scanning, improved stylus, waterproofing and quick wireless charging.
When the first Samsung Galaxy Note 7 battery exploded in early September, Samsung said this was due the lithium polymer battery manufacturing process. It issued a recall and offered to replace devices.
However, when the replacement phones started to heat up and smoke, Samsung decided to cancel the entire product line.
Anna Shedletsky, Instrumental CEO, says the company started following the news closely and saw several excuses given by Samsung sources. These included tension in the cell fabrication, squeezing the layers too much during processing, and poorly positioned insulation tape, which were all battery-related.
However, Shedletsky did not understand why Samsung would cancel a whole product line if it was only a battery part issue and could have been salvaged by a re-spin of the battery.
"We believe there was more in play: that there was a fundamental problem with the design of the phone itself," says Shedletsky.
Instrumental helps hardware companies find and fix issues caused by workmanship, part quality, processes and design.
To prove the explosions were due to bad design, Instrumental put the Galaxy Note 7 through a series of tests (with a fire extinguisher nearby).
The firm found the design of the smartphone compresses the battery, even during normal operation.
Shedletsky says this was a surprising insight as: "When batteries are charged and discharged, chemical processes cause the lithium to migrate and the battery will mechanically swell. Any battery engineer will tell you that it's necessary to leave some percentage of ceiling above the battery."
She said 10% is a rough rule-of-thumb as the battery will expand over time. The two-month-old smartphone Instrumental tested had a 5.2mm thick battery resting in a 5.2mm deep pocket.
This is important because the Note 7's lithium-polymer battery is comprised of four layers: a lithium cobalt oxide positive layer, a negative graphite layer, and two electrolyte-soaked polymer separator layers. If the positive and negative layers touch, more heat and energy will flow directly into the electrolyte, which normally results in an explosion, says Shedletsky.
Therefore, "compressing the battery puts pressure on those critical polymer separator layers that keep the battery safe".
"Samsung stated 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," explains Shedletsky.
"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."
Shedletsky says Samsung engineers were probably trying to push boundaries.
"For something that is innovative and new, you design the best tests that you can think of, and validate that the design is okay through that testing. Battery testing takes a notoriously long time (as long as a year for certain tests), and thousands of batteries need to be tested to get significant results.
"It's possible that Samsung's innovative battery manufacturing process was changing throughout development, and that the newest versions of the batteries weren't tested with the same rigor as the first samples."
Shedletsky says a smaller battery using standard manufacturing parameters would have solved the explosion and swelling issue. However, "a smaller battery would have reduced the system's battery life below the level of its predecessor, the Note 5, as well as its biggest competitor, the iPhone 7 Plus".
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