Take a quick peek through the Tesla Motors archives, and I’m fairly certain you won’t find anything resembling an electric vehicle range extender like Fisker Karma or Chevy Volt. Go ahead, I’ll wait…
Wait, gasoline, in an electric vehicle? What kind of craziness would that be? Still, Tesla Motors CEO Elon Musk isn’t above range extending technology, as long as it isn’t fueled by dinosaurs or prehistoric plant life. In the Tesla Model S, one can see that special attention has been made to address range, which is a sticking point for many people considering the technology. The highest-range electric vehicle, under the Tesla Model S 85kWh, has a EPA-estimated range of just 103mi [the Toyota RAV4 EV], which is just 38% of the Tesla Model S 85kWh EPA-estimated range of 265mi.
Still, with class-leading electric vehicle range, and access to the expanding network of Tesla Superchargers, the Tesla Model S is somewhat limited. Given that the average American drives just thirty miles per day, most any of the electric vehicles available on the market would be a good choice, but what happens on your two-weeks vacation and you want to drive to [insert favorite destination not far enough to fly but too far to drive on even the Tesla Model S’ 265mi range and no Superchargers]? Do you rent a gasoline-powered conventional vehicle? Should you have opted for an extended-range electric vehicle [EREV] and burn gasoline to get you where you’re going?
Elon Musk’s engineers and patent application says stick with the pure electric vehicle and leave fossil fuels in the ground. The new patent is essentially a hybrid battery pack, part of which is lithium-ion, as we’re already familiar with seeing in electric vehicles, but the other half is a metal-air battery range extender. Modern lithium-ion battery technology has led to fairly reliable and long-lived battery packs that can be readily placed in long service in electric vehicles.
Metal-air batteries, on the other hand, are extremely energy-dense, up to 11.4kWh/kg in the case of lithium-air. Lithium-ion batteries are up to just 0.265kWh/kg. One could put a lighter, cheaper, and longer-range lithium-air battery into an electric vehicle, but it would have a significantly reduced lifespan, as metal-air batteries can only endure about one hundred cycles. Tesla Motors’ idea is to combine the two battery types into one electric vehicle, taking advantage of the strengths of each. The end result would be an electric vehicle, such as the Tesla Model S 85kWh, with an EPA-estimated range of 265mi, with an auxiliary metal-air battery to give it a couple hundred more miles of range.
In a final Tesla product, drivers would have the option of driving solely on the lithium-ion battery but, if the need arises, they can choose to use the metal-air battery as a range-extender. Drivers would have to be well aware that use of the metal-air battery would come at a price, the limited number of cycles. Such a design could bring electric vehicles even closer to conventional vehicles, in terms of range.
Image © US Patent Office