Are Batteries in Electric Cars Safe?

Automakers are pressing ahead with plans for hybrids and electric vehicles powered by lithium-ion batteries, but at what risk?

Next month will mark another important milestone on the road to cleaner, greener motoring: Mitsubishi Motor will begin mass-producing an electric vehicle, becoming the first major carmaker in the world to do so. By late July, the Tokyo-based automaker will deliver its $48,000 electric i-MiEV minicar to businesses and local governments. The car, which runs 160 kilometers on a charge, will be available to Japanese consumers in the coming months. They will pay just $33,000 thanks to a Japanese government subsidy, but likely won't drive their cars off dealers' lots until April 2010. "With the electric vehicle, we will challenge global players," Mitsubishi Motors President Osamu Masuko told reporters at the i-MiEV's official launch in Tokyo on June 4.

Other automakers have similar ideas. Subaru, a unit of Japan's Fuji Heavy Industries, plans to sell 170 of its $48,000 plug-in Stella electric cars this year. Nissan Motor will release its first model in 2010 and plans to start production in the U.S. by 2012. China's BYD Auto, which has been selling a plug-in gas-electric hybrid car to businesses since December, aims this year to release an electric vehicle that can go 300km to 400km when charged. The release of General Motors' long-awaited Chevrolet Volt plug-in hybrid is slated for late 2010. To help automakers fund their green car programs, the U.S. Energy Dept. on June 23 divvied up $8 billion in loans to Nissan, Ford Motor (F), and electric-car startup Tesla Motors.

Yet even as carmakers race to showcase these green vehicles, some experts are raising concerns about their safety. The worst-case scenario: thermal runaway, which can happen when a short circuit inside a battery sparks a chain reaction, causing overheating or a fire. In mobile phones, laptops, and other portable gadgets, thermal runaway can occur in 1 of every 5 million to 10 million cells, says Brian Barnett, a battery expert at technology firm Tiax in Cambridge, Mass. The incidence can be higher for the products of less experienced battery makers, he says. A laptop battery usually has six cells, but electric cars will likely rely on 75 or 80 cells, meaning they would be more susceptible to problems. Another difference: Cars move at high speeds and carry passengers. "It's not going to happen all that frequently, but the consequences could be catastrophic," says Barnett.

There's a big difference in power, too. And defects might not crop up right away. Laptops were on the market for years before the first reports surfaced about overheating products that burst into flames. Sony's (SNE) recall of millions of computer batteries took place just three years ago.

Nissan's Stress Tests

Carmakers insist that safety is a top priority. Nissan got an early start on battery research, collaborating with Sony to develop the first lithium-ion batteries for cars in the early 1990s. (Recently, Nissan has been working with Japanese tech conglomerate NEC) The carmaker is planning to make an initial 50,000 electric vehicles in 2010, and will quickly increase production to begin worldwide sales by 2012.

To test for safety, Nissan relies on a series of stress tests. In one, the battery is put to use in extreme heat and cold. In another, the battery is charged and depleted nonstop for weeks. To simulate crashes, engineers crush the battery cells with enormous force or pierce the cells in different spots with nails. The data will help Nissan make "extremely reliable" batteries, says Hideaki Horie, who heads Nissan's next-generation battery group.

To increase safety, manufacturers are reinforcing the frame around the batteries. The Mitsubishi i-MiEV's batteries (made by Kyoto-based GS Yuasa) are protected by both the car's rigid steel skeleton and a second anti-impact cage. On-board computers will help monitor the battery's condition.

Current gas-electric hybrids such as the Toyota Prius run on nickel metal-hydride batteries. Many carmakers and tech firms are betting that an array of new lithium-ion batteries will be better suited for electric vehicles because they store about twice the energy per charge compared to nickel-metal batteries of equal weight. Companies are also hoping that costs can be lowered.

Some industry executives concede that lithium-ion batteries might need more time before they're ready. Questions about the reliability of the batteries prompted Toyota (TM) to stick with nickel metal-hydride batteries in its third-generation Prius, which dealers in Japan began selling this month. Toyota is planning to lease a small number of plug-in Prius hybrids powered by li-ion batteries this year and is developing a fully electric car for 2012.

The Mass-Production Question

Developing a li-ion battery that's technically sound isn't the problem. Plenty of manufacturers already have the expertise to do that, says Koei Saga, a managing officer at Toyota in charge of hybrids. Safety becomes an issue when carmakers shift to high-volume production. "If we mass-produce, we have to be able to ensure 100% safety for every single product," Saga told reporters during a tour at a factory owned by Toyota's battery supplier, Panasonic EV Energy, earlier this month. To avoid defects, manufacturers must be meticulous in designing and building their plants—and that can cost a lot, Saga said. Perhaps tellingly, Toyota will only lease—not sell—its li-ion-powered plug-in Prius, and says it will limit initial production to 500 units.

Even if the battery works properly, other parts might fail. The vehicle's control system, which monitors energy storage and discharge, could go haywire. And unlike the two-year life span of batteries for mobile phones, car batteries need to last 10 years or longer. "In batteries for laptops or cameras, everyone just assumes that after using any portable gadget for a while the battery will wear down and may only recharge to two-thirds of its original capacity," says Nissan's Horie. "You can't design a car battery that way."

It's debatable whether carmakers can do enough real-world testing to ensure safety. It will take time for even the top manufacturers to gain confidence about mass-producing batteries. Some worry that the rush to build plug-ins and electric cars may come back to haunt automakers. Tiax's Barnett says there's no industry consensus about what causes batteries to overheat or catch fire, and that analyzing the debris after an accident might not help, either. Trying to replicate or test for a condition that's isolated to a few cells of a new type of battery, says Barnett, "represents a tremendous challenge for the battery industry."

That Nissan and NEC plan to mass-market globally li-ion EV battery packs by 2012 puts some experts at ease. "If there is any concern about its safety, they would absolutely not be able to say that," says Hideaki Miyata, a professor at the University of Tokyo's School of Engineering Department of Systems Innovation.

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