Ford Says Li-On Batteries to Outshine Very Reliable Nickel-Metal
Probably the biggest worry people have about electric cars is projected battery life—it’s a top purchase consideration. The fear is this: A few years down the road, their pack will fail and the dealer will be holding out his hand for $20,000. First of all, this isn’t likely to happen because most EV batteries are warranted for eight years or 100,000 miles (it’s 10 years and 150,000 miles in California emission states).
Low Failure Rates
And it’s also not likely to happen because batteries in hybrids and electrics have proven incredibly durable. A Consumer Reports test of 2001 and 2002 Toyota Priuses with 200,000 miles found spot-on performance, including from their battery packs. Obviously, we don’t have much long-term data on lithium-ion batteries yet, but Ford says it’s figured out how to simulate that—with a rigorous protocol called the Key Life Test that mimics 15 years of wear in just 10 months.
The company has performed real-world testing on nickel-metal packs—some new, others with high mileage—and used lab data to extrapolate how much better lithium batteries would perform under the same conditions. As the chart above shows, lithium should degrade at a much slower rate, perhaps 20 percent better.
Great Expectations for Li-Ion
“We’re very confident that lithium-ion is going to greatly exceed the capability of nickel-metal-hydride,” says Kevin Layton, Ford’s director of electrified power engineering. “And in our testing, nickel-metal cells and packs [taken from such cars as the Ford Escape Hybrid]—some with more than 250,000 miles on them—have performed flawlessly.” California’s Escape taxis have collectively almost 100 million miles on them. Ford has put 50 million hybrid battery cells on the market, and only six have failed.
Anand Sankaran, a Ford technical leader for energy storage and hybrid systems, said the company takes batteries, as well as individual cells, and “accelerates their failure modes.” That means subjecting them to 140 degrees Fahrenheit in Phoenix, and minus-40 degrees in Manitoba, as well as water immersion tests and other challenges.
Li-ion has obvious benefits over NiMH, including 25 to 30 percent size reduction with three times the power output per cell. Some companies are sticking with nickel-metal for hybrids and li-ion for battery electrics, but the trend is plainly in lithium’s favor. Durability is still the critical question, so we’re awaiting the first hard data on that. Projections like Ford’s are interesting, but what’s really going to matter is what happens in the field.
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