Is there something in your garage, perhaps charging up right now, that has a shockingly high chance of unexpectedly erupting in a fireball?
We’re really not taking aim at electric cars or plug-in hybrids, and we’ll explain why shortly. We’re talking about hoverboards. For those whose minds still go to anything as cool as the “real” hoverboard from Back to the Future II—or the gloriously impossible, liquid-nitrogen-cooled surprise from Lexus last year—we salute you. It still pains us to see that tweens and Martha Stewart and made-in-China consumerism have bogarted the term, subbing in a cheap, ubiquitous, and critically flawed Segway-without-handles mobility device. One that is, it turns out, pretty dangerous.
Earlier this week, after trying for months to reel in this Wild West of a market with mere threats of seizure and detention, the Consumer Product Safety Commission (CPSC) announced the recall of more than a half a million of what we’ll regretfully henceforth call hoverboards. With this news, as car enthusiasts and likely gadget geeks, consider where your mind went: Well, if I have to worry about that hoverboard in the garage, do I ever have to worry about such incendiary risks in an electric car or plug-in hybrid?
In short, almost certainly not. Yes, both use lithium-ion cells, but there are too many differences—including discrete design and manufacturing differences—that separate the two.
“The vast majority of the hoverboards available on the market are cheaply made products, made to a bare-minimum price point,” says Sam Abuelsamid, senior analyst with Navigant Research. He suspects that hoverboard manufacturers made their battery choices to maximize power with minimal space and cost. Carmakers aren’t doing that; they’re taking a conservative approach with batteries and aiming for a longer life span and predictable performance across temperatures and conditions.
Lack of Quality Control, Heat Control = Inferno
And it’s not just the quality of the battery packs installed in these conveyances but the bare-minimum battery management systems that often fail to detect when the battery reaches a dangerously high temperature, either when charging or when rapidly discharging. Many of these personal-electronics batteries also provide a higher energy density than they safely should, said Abuelsamid, and aren’t made with the same care, precision, or quality control of automotive-grade cells, or even of the kind you’d find in top-tier personal devices from Apple or Samsung.
Specifically, the issue takes form in uneven heat distribution, often resulting from manufacturing or material flaws in the electrodes. Eventually the electrode fractures, shorting the cell. And at that point, with certain chemistries, the electrolyte can spontaneously ignite.
“Electrolytes are typically organic compounds that contain oxygen,” said Abuelsamid. “So once they ignite they tend to be self-sustaining.” And there you have your flaming fireball of a hoverboard, the star of social media in some cases, and in others a grave disaster in the making.
Doesn’t That Look Familiar Though?
On the surface, these hoverboard batteries may seem frighteningly familiar; some use pouch cells that aren’t much different than what’s used in Apple phones and tablets, or small cylindrical, 18650-format cells that look almost the same as the 7000-or-so of these that are crammed into each Tesla Model S sedan or Tesla Model X SUV.
Rest assured, what you see isn’t what you get. Those automotive-grade cells are very, very different: meticulously manufactured, carefully temperature-controlled lithium-ion and lithium polymer cells, with chemistries that have been very carefully selected to keep their cool.
The Nissan Leaf’s standard 24-kWh battery pack.
Automakers and suppliers design these systems to be extremely durable and compliant with federal safety standards. The packs are subjected to crash-testing, and designed to prevent intrusion. Temperature management also is one of the keys to automotive battery packs’ stability and longevity. It’s monitored even at the cell level in some packs, and cooling and conditioning systems help keep them stable and in their sweet spot, in the range of 30 to 50 degrees Celsius. That’s not only because it helps maximize capacity but because it helps prevent overcharging or complete discharge—both ways that cells can be damaged.
The Chemistry Set
Chemistries used for cars and electronics are constantly evolving—and, for the most part, safe and stable. While the previous Chevrolet Volt and some models of the current Leaf use manganese spinel chemistry, the upcoming Chevrolet Bolt, the new version of the Volt, and the latest 30-kWh Nissan Leaf use a nickel-manganese-cobalt (NMC) battery that offers more capacity and stability.
There have been a few exceptions. One of the earlier lithium-ion chemistries, lithium cobalt oxide, has been at the root of several higher-profile fire issues: Sony Vaio laptops some years ago, and the Boeing 787 Dreamliner more recently. Because of the presence of oxygen, in the event of an internal short batteries of this type were more likely to flare up. That chemistry was used in the Tesla Roadster, and while the pack in that model hasn’t been an issue in itself, Tesla has since moved on to a different chemistry for its Model S and Model X, and a distribution box has been found at root of the one (widely publicized) Tesla Model S fire.
Back in 2009, the CPSC looked into a series of claims of iPod-related fires and decided that there was no need for further action. Yet this time the noxious stench of burning plastic has been building for months, as all the major U.S. airlines banned hoverboards by earlier this year, and even the Department of Transportation issued a warning about their battery packs, requiring them to be treated as hazardous materials. By now, having hoverboards erupt in smoke and flames is such a common sight in American driveways that Saturday Night Live has parodied the phenomena.
In the spirit of shanzhai, lots of brands sound a little familiar, and these models all kind of look alike. The Swagway X1 is the very popular model with the highest recall volume (267,000 units). Segaway, another one of the hoverboard brands, is already marketing its boards as “fireproof.” For these hoverboards, which cost $300 to $900, typically, and can go nearly 10 miles on a charge in some instances, it’s not all that surprising that manufacturers skimped on the batteries—going for high energy density (and holiday-ready production) with, apparently, very little heat monitoring or charge control.
The gamble taken on the lifetime of the product is an important way to frame this hoverboard foul. While a smartphone might last a couple of years before being retired, and your kids might use the hoverboard for a summer before it’s forgotten in the back of the garage, cars are still expected to perform for eight or ten years. “Auto manufacturers can’t afford to have their cars exploding, or to pay out warranty claims on a $15,000 battery pack,” said Abuelsamid.
Ultimately, it sounds a lot like an entire industry, eager to compete at an impossibly low price point, shipped its product before fully testing it out.
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