New rechargeable batteries for electric vehicles

Researchers have developed new molten air rechargeable batteries for electric vehicles that have a significantly higher storage capacity than lithium batteries.

While electric vehicles offer many advantages, at least  one barrier stands in the way of their large-scale adoption: ‘range anxiety’.  

Researchers at George Washington University, led by Stuart Licht, have developed a novel solution, and they’re calling it the “molten air battery.” These new rechargeable batteries, which use molten electrolytes, oxygen from air, and special ‘multiple electron’ storage electrodes, have the highest intrinsic electric energy storage capacities of any other batteries to date.  Their energy density, durability and cost effectiveness give them the potential to replace conventional electric car batteries, said Licht.      

The researchers started with iron, carbon or vanadium boride for their ability to transfer multiple electrons. Molten air batteries made with iron, carbon or vanadium boride can store three, four and 11 electrons per molecule respectively, giving them 20 to 50 times the storage capacity of a lithium-ion battery, which is only able to store one  electron per molecule of lithium.

“Molten air introduces an entirely new class of   batteries,” Licht said.  Rechargeable molten batteries (without air), such as a molten sulphur battery, have been previously investigated, but are limited by a low storage capacity. The new molten air batteries, by contrast, offer the best   of both worlds: a combination of high storage capacity and reversibility. As the name implies, air acts as one of the battery electrodes, while simple nickel or iron electrodes can serve as the other.      

‘Molten’ refers to the electrolyte, which is mixed with reactants for iron, carbon or vanadium boride, then heated, until the mixture becomes liquid. The liquid electrolyte covers the metal electrode and is also exposed to the air electrode. The batteries are able to recharge by electrochemically reinserting a large number of electrons. The rechargeable battery uses oxygen directly from the air, not stored, to yield high battery capacity.     

The high activity of molten electrolytes is what allows this charging to occur, according to Licht.