Behind Ford's lithium-ion decision

But Ford engineers now say their decision to use lithium-ion was based on accelerated lab tests showing lithium-ion would actually be more durable than nickel-metal hydride over a long lifetime. The tests, combined with mountains of field performance data on nickel-metal hydride, convinced them that they could predict the eight- or 10-year future of a chemistry that didn't even have five years worth of reliable field data.

"We are really confident that our Key Life Tests are mimicking the duty cycle of some of our most stringent and abusive customers," Kevin Layden, Ford's director of electrification programs and engineering, told Design News. "Given that, we feel lithium-ion will be better than nickel-metal hydride. We expect it to be absolutely stellar."

Ford's confidence in lithium-ion is based on so-called Key Life Tests. The tests predict that the working capacity (y-axis) of lithium-ion batteries (green line) will be greater over a high-mileage lifetime (x-axis) than that of nickel-metal hydride (yellow line). Past field data for nickel-metal hydride (blue dots) has shown that the testing results are conservative -- that is, batteries generally do better in the field than they do on tests.
(Source: Ford Motor Co.)

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