Nissan, led by enthusiastic CEO Carlos Ghosn, has emerged as a surprise leader in the push toward electrification of the automobile. What is so remarkable about this is Nissan was not even part of the EV conversation two years ago. Now the company is poised to be the first major manufacturer to mass-produce electric vehicles.
The Nissan Leaf is slated to appear in a handful of test markets by the end of the year, putting the company neck-and-neck with General Motors and the Chevrolet Volt expected at about the same time. Nissan’s sudden change in focus was the result of Ghosn’s personal vision and his willingness to force it through his company from the top down. The impatient CEO recently told Bloomberg, “The engineers will always tell you, ‘Wait a little more,’ and if you keep playing this game, you never launch any product.”
Sheer force of will from a charismatic leader can accomplish great things when matched with a company that has a good reputation for execution. Cars, however, are complicated pieces of engineering, and an electric vehicle presents numerous fresh challenges to Nissan engineers. Intense pressure from the top may have created a sense of urgency, but it also appears to have driven the company to take some shortcuts.
First, Nissan overpromised on the realistic range by consistently quoting a number tied to the most optimistic benchmark, the LA4 cycle. Drivers who stick to stop-and-go traffic on city streets in temperate climates may indeed consistently see 100 miles of range, but most drivers will see significantly less in a mix of city and highway driving. Driving in California, the country’s top market for electric vehicles, involves a lot of time on highways where the 65 mph speed limit is rarely observed. The LA4 cycle Nissan quotes mostly stay below 30 mph with one two-minute “sprint” at 55 mph every 22-minute cycle.
It also appears Nissan has cut corners on the most critical aspect of electric vehicle technology — the battery pack. The key engineering trade-off Nissan has made is opting not to include active thermal management, where the temperature of the pack is controlled by an HVAC system similar to what cools the passenger cabin on a hot day. Instead, Nissan has opted to use only an internal fan that circulates the air within the sealed pack to evenly distribute the heat, which escapes by passive radiation through the pack’s external case.
Thermal management in lithium-ion battery packs is critical to the long-term performance and quality of the battery. The manganese oxide pack is sensitive to high temperature and the primary consequence is that the pack will degrade more rapidly than one with active thermal management. This problem will be worse in hotter climates such as Phoenix, which Nissan has selected as one of its launch cities.
Mark Perry, Nissan’s director of product planning for the United States, dismissed the importance of active thermal management.
“We don’t need thermal management for the U.S., but we are looking at the technology for Dubai and other locations like that…. We’ve gone on the record saying that the pack has a 70 to 80 percent capacity after 10 years,” he told Wired.com. Pressed on whether that is realistic for a passively cooled manganese oxide pack, Perry said yes.
“If it wasn’t our pack and it wasn’t our engineers and we weren’t working on it for 17 years … we wouldn’t make the statement if we weren’t confident in our ability to do so,” he said.
But we heard a different story from Paul Hawson, a Nissan product planner who worked on the Leaf, when the automaker brought the Leaf to the Wired offices in November. Asked why Nissan chose not to use active thermal management, Hawson explained the engineers experimented with it but found it required a central tunnel on top of the pack. That would intrude on cabin space, splitting the rear bench into two seats with a hump in the middle. Nissan, he said, decided to use only passive cooling to preserve passenger space.
Asked to confirm that, Perry insisted Hawson had misunderstood the question and said, “We don’t make sacrifices in performance. The electric vehicle is the number one priority at Nissan.”
General Motors has taken a different approach with the battery in the Chevrolet Volt. Although it uses a similar lithium manganese chemistry, GM opted to use an active liquid cooling system. Doing so ensures optimal power and lifespan, said Tony Posawatz, vehicle line director for the Volt.
“Thermal management [with lithium manganese batteries] has bookend issues to manage: minimized power at low temperatures and life reduction at high exposure to higher temperatures,” he said. “If you want to replace your battery every four to five years and someone is willing to pay for [a replacement battery], either the customer or the manufacturer, a modest or minimal HVAC system may work.”
The Volt actively manages both low-temperature and high-temperature conditions.
“Additionally, we cycle the battery in a much friendlier way than our BEV competitors which need an 85 percent state-of-charge window to get their miles and this EV range begins degrading after day one of usage,” Posawatz added, referring to the fact that the Volt only cycles through 8 kilowatt-hours of the pack’s 16-kilowatt-hour capacity, which also contributes to longer life. Even with these conservative engineering approaches, Posawatz said, “our 10-year target still yields a battery with 70 to 75 percent of the capacity at the end of life.”
Nissan’s confidence on this matter aside, early purchasers of the Leaf should consider taking the company up on its offer to lease the battery, which would leave any financial risk of early battery degradation where it belongs — with Nissan.
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