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Afdhal Atiff Tan
Unlike EVs that placed batteries in the back seat and trunk, the Leaf's pack will reside under the floor. Source: Nissan
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From the Altra EV of a decade ago to today's Leaf, Nissan claims it has doubled its battery's energy density and power. In interviews, however, the automaker hasn't revealed if it is comparing today's number to the 1998 figure, which was 90 W-hr/kg, or to some earlier figure.
Most experts believe the new number is between 140-150 W-hr/kg. "I suspect that the ‘factor two' phrasing is being used loosely, in a marketing way," says David Swan, founder and president of DHS Engineering, a consulting engineering firm that designs and tests batteries. "Who's going to say, ‘We boosted it by a factor of 1.7?'"
Whatever the actual number, Nissan is enjoying the benefits of higher energy density. By pumping up the energy, the company's engineers were able to create a smaller battery. Instead of the 900-lb batteries that have been commonplace in previous EVs, the Leaf uses a 480-lb battery, with cooling and battery management included.
"Everybody is reaching for 200 W-hr/kg," Swan says. "But there's nothing shabby about 150."
Most experts believe the new number is between 140-150 W-hr/kg. "I suspect that the ‘factor two' phrasing is being used loosely, in a marketing way," says David Swan, founder and president of DHS Engineering, a consulting engineering firm that designs and tests batteries. "Who's going to say, ‘We boosted it by a factor of 1.7?'"
Whatever the actual number, Nissan is enjoying the benefits of higher energy density. By pumping up the energy, the company's engineers were able to create a smaller battery. Instead of the 900-lb batteries that have been commonplace in previous EVs, the Leaf uses a 480-lb battery, with cooling and battery management included.
"Everybody is reaching for 200 W-hr/kg," Swan says. "But there's nothing shabby about 150."
Donald Sadoway, professor of materials chemistry at MIT, offers this simple rule of thumb for determining the relationship between a battery's energy density and an EV's range: 1 W-hr/kg of storage capacity = 1 mile of range (if 30 percent of the vehicle's mass is tied up in its battery).
So what does that mean? It means that if a 3,000-lb vehicle has a 900 lb battery and a specific energy of 150 W-hr/kg, its range is 150 miles. The Nissan Leaf has a lower range largely because it uses a relatively small, 480-lb battery pack.
So what does that mean? It means that if a 3,000-lb vehicle has a 900 lb battery and a specific energy of 150 W-hr/kg, its range is 150 miles. The Nissan Leaf has a lower range largely because it uses a relatively small, 480-lb battery pack.
Performance Driving Range: 100 miles
(without AC or heater running)
Top Speed: 90 mph
Motor Type: ac synchronous
Motor Power: 107 hp (80 kW)
Motor Torque: 206.5 lb-ft (280 N-m)
Battery
Type: Laminated Lithium-ion
Capacity: 24 kW-hr
Power: 90 kW
Energy Density: 140-150 W-hr/kg
(Design News estimate)
Number of Modules: 48
Charging Times: At 440V, 25 min.
At 220V, 8 hours.
At 110V, 16-18 hours
Cost: $32,780
(minus a $7,500 federal tax credit)
(without AC or heater running)
Top Speed: 90 mph
Motor Type: ac synchronous
Motor Power: 107 hp (80 kW)
Motor Torque: 206.5 lb-ft (280 N-m)
Battery
Type: Laminated Lithium-ion
Capacity: 24 kW-hr
Power: 90 kW
Energy Density: 140-150 W-hr/kg
(Design News estimate)
Number of Modules: 48
Charging Times: At 440V, 25 min.
At 220V, 8 hours.
At 110V, 16-18 hours
Cost: $32,780
(minus a $7,500 federal tax credit)
The cost of a lithium-ion battery is still one of the auto industry's best-kept secrets. Experts say the figure could be as low as $500/kW-hr or as high as $1,000/kW-hr. A hotly debated and much-maligned study from the National Academy of Sciences even places the figure between $1,000 and $1,200/kW-hr. Whatever the real cost, though, EV proponents want the number to go down.
"Lithium-ion is still very expensive," says Jacob Grose, an analyst for Lux Research. "We believe the packs cost about $900/kW-hr, so if you have a 24-kW-hr pack, you're looking at a $22,000 battery cost. Even if your pack is $750/kW-hr, the battery cost is still $18,000."
Those costs could be especially important down the road, as consumers begin facing the prospect of buying replacement batteries for their aging EVs.
Ultimately, EV proponents hope production volume will dramatically reduce the cost of the batteries. Most experts agree that the packs - which include the battery cells, cooling systems and battery management - will dip to about $400-$500/kW-hr at greater scale. They'll probably not go much below that figure, however.
"Lithium-ion batteries for cell phones and laptops cost $300/kW-hr, and automotive batteries will always be more expensive because of the cooling," Grose says. "So you're not going to get much better than $500 unless there's a fundamental change in the way the batteries are made."
"Lithium-ion is still very expensive," says Jacob Grose, an analyst for Lux Research. "We believe the packs cost about $900/kW-hr, so if you have a 24-kW-hr pack, you're looking at a $22,000 battery cost. Even if your pack is $750/kW-hr, the battery cost is still $18,000."
Those costs could be especially important down the road, as consumers begin facing the prospect of buying replacement batteries for their aging EVs.
Ultimately, EV proponents hope production volume will dramatically reduce the cost of the batteries. Most experts agree that the packs - which include the battery cells, cooling systems and battery management - will dip to about $400-$500/kW-hr at greater scale. They'll probably not go much below that figure, however.
"Lithium-ion batteries for cell phones and laptops cost $300/kW-hr, and automotive batteries will always be more expensive because of the cooling," Grose says. "So you're not going to get much better than $500 unless there's a fundamental change in the way the batteries are made."
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