Boeing has made big news in recent weeks, but for all the wrong reasons. The Federal Aviation Administration (FAA) grounded Boeing’s flagship airplane, the fuel-efficient, next generation 787 Dreamliner. The problem isn’t its innovative carbon fiber construction, but rather a less heralded technologic leap: lithium ion batteries. In the span of one week a battery caught fire while a plane was at the gate in Boston and another forced an emergency landing and evacuation in Japan when it overheated. This marks the first grounding of an airplane type since the DC-10 in 1979.
Inevitably, news stories appeared connecting the 787’s battery troubles to past laptop battery fires and electric vehicles (EVs), reflexively highlighting the 2011 Chevy Volt fire that occurred following crash testing.
Yet these stories fail to note that the batteries found in EVs are distinctly different from those in consumer electronics or the 787. Sure, they are all lithium-ion batteries, but that’s where the similarities end. There are different chemical ingredients for each application. Painting all lithium ion batteries with the same brush is no different than saying a Corvette and a Silverado are both simply Chevrolets.
The batteries found in the 787, as well as in most consumer electronics, are made of lithium cobalt oxide (LiCoO2), prized for its high energy density. This characteristic is a good fit for electronics and aerospace where space and weight, respectively, are major design constraints. The drawback is that cobalt oxide batteries are less thermally stable than other chemistries. When these batteries overheat (whether from overcharging, uneven charging, a manufacturing defect, or physical damage) they can more easily enter thermal runaway, where exothermic chemical reactions create a positive feedback loop that creates more and more heat. Combine that heat generation with the lithium ion battery ingredients—a flammable organic electrolyte and a readily available source of oxygen (remember the O2 in the LiCoO2?)—and it is easy to see how the batteries can catch fire.
There is a history of lithium ion batteries catching fire in electronics. A spate of fires resulted in the recall of millions of lithium ion batteries for laptops in 2006 and again in 2008. The cause was tiny shards of metal introduced in the manufacturing process that short circuited cells. Even more troubling, lithium ion batteries have been implicated in, but not proven to cause, two fatal cargo plane accidents in the last seven years: a UPS 747 and an Asiana 747. Each flight was carrying shipments of lithium ion batteries and suffered fires that originated in the cargo hold. The incidents at the heart of the 787’s grounding are not even the first problems the program has faced with lithium-ion batteries. A sub-contractor’s facility where they designed and manufactured battery-charging electronics for the 787 program burned down while testing a battery. The cause was an improper test setup, but the scale of the damage highlights the risks in the technology.
Unlike electronics and aerospace batteries, electric vehicles do not use LiCoO2 chemistry, specifically because of its safety concerns. (Some 2,500 early Tesla Roadsters used LiCoO2 batteries designed with multiple safeguards, but the company has since switched to batteries with more stable chemistries.) Automakers have intentionally traded less energy density for better safety and lower cost (cobalt is expensive). Most electric vehicles or plug-in hybrids on the road use a lithium-manganese-spinel (LiMn2O4) chemistry. Some are adding a nickel-manganese-cobalt chemistry developed at Argonne National Lab to increase energy density.
Though the lithium-manganese chemistry is more stable, it is not immune from the risk of overheating. Automotive design features focus on avoiding conditions that commonly cause battery incidents. The battery is located between the axles and outside of the collision zone, just like a fuel tank. Many electric vehicles contain an active cooling system that maintains the battery temperature and extends its life. Monitoring systems for cell voltage, current, and temperature help avoid unsafe conditions such as overcharge or uneven charging. Finally, passive interrupt controls can electrically disconnect cells as a last line of defense if something does start to go wrong. Battery chemistry and design is evolving as automakers and their suppliers strive for safer, cheaper, and more energy-dense chemistries and design.
Does more stable lithium ion chemistry combined with the robust design of automotive batteries mean a 787-style battery meltdown will never occur in an EV? Of course not. The precise reason that lithium-ion batteries are used—their high energy density—increases the odds of a sudden energy release (aka fire). But that doesn’t mean electric vehicles are any less safe than internal combustion vehicles. For the last one hundred years cars have been carrying around gasoline, which has more than twice the energy density of lithium ion. Automakers have been able to minimize, but not eliminate (see the Ford Pinto) the risk of fire due to fuel leaks. In fact, I might prefer the on-road safety record of current automotive lithium-ion batteries, which have had zero reported fires in over 500 million miles driven. By comparison, gasoline vehicles have averaged nearly 65,000 vehicle fires that caused 300 fatalities per year between 2008 and 2010.
What really worries me is the laptop computer on which I’m writing this blog post.
Image 1 copyright Boeing
Image 2 courtesy Shutterstock.com
Image 3 copyright General Motors