One of the biggest hurdles lithium ion batteries face is to overcome is heat. Today’s electric cars use complex and bulky cooling systems to get rid of the heat, fact that also lowers the batteries’ storage capacity and put weight on the car, lowering its mileage per charge. A new type of battery chemistry that doesn’t overheat is now emerging from Leyden Energy‘s labs.
The four-year-old startup uses sodium imide instead of lithium hexafluorophosphate as the electrolyte and graphite instead of aluminum to build a battery whose performance doesn’t get affected by temperatures higher than 60 degrees Celsius.
One of the advantages of combining sodium imide and graphite in a battery is a charging capacity 50 percent higher than that of standard lithium ion units, up to 225 watt-hours per kilogram, compared to the 140 watt hours per kg of lithium iron phosphate, a battery known to withstand higher temperatures. Changing the current collector into graphite has been forced by the fact that sodium imide corrodes the aluminum.
“The key advance for Leyden is not the electrolyte. Their magic is, they are not using aluminum as the current collector,” says Venkat Srinivasan, a scientist at the Lawrence Berkeley National Laboratory, about Leyden‘s technology. “This change allowed them to change the electrolyte.”
The new sodium imide battery will first be used in laptops, and will feature a three year warranty, instead of the standard one-year. The reason for this is that the battery can be recharged up to 1,000 times, instead of 300.
Leyden Energy has received a $2.96 million grant from the state of California for further developing the technology and producing 10 electric car batteries per month. Motorcycle manufacturers like Brammo are also interested in the novel technology, citing its improved thermal management, essential in a bike-type application.
The company also says that electric cars will only have to use air-based cooling. Nissan Leaf currently uses this approach, and although it’s been said that’s not enough for the current lithium ion technology used, it seems to be enough for sodium imide-based batteries.