Pushing Batteries Too Far?

What random defects say about the design process.


Reports of battery fires in consumer devices are not abating. The culprit in almost all cases is the lithium-ion battery.

In some cases, this is a manufacturing issue, where predictable intervals of failure can point to a breach in the membrane separating the anode and cathode or a metal particle contaminant that causes a short circuit. Those kinds of flaws are well understood, based upon how extensively a battery maker tests its products. With a 99.999966% (6 sigma) process, for example, the defectivity rate is expected to be 3.4 per million.

In contrast, there were roughly three dozen instances of failure with the Samsung Galaxy Note 7 batteries, according to numerous reports, out of an estimated 2.5 million devices sold worldwide. But the real issue is that the Note 7 fires were not predictable—or at least not without massive amounts of data that doesn’t exist until the device is in widespread use in the market. The reported failures involved a sequence of events that created unexpected stress on the battery.

Samsung is hardly the only maker of phones to experience these kinds of problems. Nokia recalled 46 million phones made in 2005 and 2006 due to battery overheating. And there are numerous reports of other consumer devices overheating, including hoverboards (now banned from most flights) and laptops.

It’s important to get this right in the smartphone/phablet/tablet market, though, because these are a critical component in the IoT’s development. For edge devices such as connected appliances and personalized medical equipment, the phone functions as the primary interface between the device and the user. It is, far and away, the best dashboard for managing these devices over the Internet. But as phone makers strive to pack even more features into their phones without expanding the size of the battery, they are pushing the physical limits of how much energy can be stored without potential problems.

The problem is that there is no way to check every possible combination of use cases and identify all of the corner cases for every device. There are too many of them. As of several years ago, most phone makers would run a suite of 60,000 to 80,000 possible scenarios for phones, and that was sufficient to guarantee the devices would work in most cases. In others, a reboot usually solved the problem, and in the worst case it required a software update, which is how Apple addressed its antenna issues in the iPhone 4.

But batteries are different. There are no software patches or simple fixes. And there are no serious alternatives. While other types of batteries show up in news reports from time to time, most of them have been sidelined as unstable. Lithium-ion batteries are still the best compromise—they have the highest discharge voltage, extremely low leakage, and they are virtually impossible to overcharge. But there also are limits to how far these batteries can be pushed. And no matter how many sigmas are added into a manufacturing process, there will still be unexpected failures.

Form vs. function is a critical metric for phone makers, but safety needs to be added as a third leg of that formula. There are physical limits to energy storage today, and it’s clear that we are now at the limit. It’s time to recognize that functionality is limited by the battery discharge, and that what used to be worst-case scenario planning is insufficient when it comes to the mobile devices.

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