Current electric vehicle range is limited by how much energy you can stuff into them, that is, the energy density of the battery pack, which also explains range anxiety.
For example, gasoline has an energy density of about 12.8 kWh/kg (kilowatt-hours per kilogram), which gives, even at just 25% maximum internal combustion engine efficiency, extensive range. The Scion iQ, for example, has a range of over 300 miles per tank of gas, and can be refueled in minutes at practically any gas station in the world. The only electric vehicle to offer that range is the Tesla Model S 85 kWh, and takes at least 45 minutes to fully recharge on a limited number of Tesla Superchargers. It also costs 400% more.
The problem with adding even more range to an electric vehicle, however, has to do with energy density of the energy storage medium. The Panasonic 18650 lithium-ion cells used in the Tesla Model S have an energy density of just 225 Wh/kg (watt-hours per kilogram), just 1.8% the energy density of gasoline. One could add more kWh to the battery pack to increase range but, at one point, the extra range would be canceled out by the extra weight, that is, a victim of the law of diminishing returns. What’s needed is a rechargeable battery technology with higher energy density.
Researchers have been developing, with varying degrees of success, on high-density batteries. Even Tesla Motors has suggested using metal-air batteries, which could greatly expand electric vehicle range, but there’s one problem, that they cannot be recharged. Researchers at George Washington University, with the support of the National Science Foundation, may have cracked the rechargeability problem with molten-air battery packs. The new battery, using iron (FeO2), carbon (CO2), or vanadium boride (VB2O2), in a molten electrolyte, can hold between 11 and 50 times more than the typical lithium-ion battery. If researchers can get the internal temperature down below 600 °C, it could prove to be a significant boost for electric vehicle range.
At 50 times the energy-density of lithium-ion, a VB2O2 molten-air battery energy-density actually approaches that of traditional automotive fuels. A Nissan Leaf with a molten-air battery could theoretically top 7,000 miles. The average driver would have to charge twice a year at that rate, perhaps eliminating the need for public-access charging stations. Electric vehicle range anxiety would be a quaint notion! “Hey, you remember back when we used to worry about how close the Supercharger was? Oh, those were the days.”
Photo credit: Major Nelson