Molten Air Battery - A Hot One for a Long Ride

Scientists at George Washington University have invented a new class of high energy, rechargeable battery with one of the highest intrinsic energy storage capacities to date. This is what they call molten air battery.

This battery uses a molten form of electrolyte at high temperature- north of 700 C. Experiments with iron, carbon and VB2 ( Vanadium Bromide) have produced volumetric energy capacities of 10000, 19000 and 27000 Wh/liter respectively- much higher than that of gasoline and way beyond 6200 Wh/liter storage capacity of Li-air batteries.

The secret to these high energy capacities lies in the number of electrons per molecule that the materials used can store, viz., for Iron it is 3, for Carbon it is 4 and for VB2 (Vanadium Boride) it is a whopping 11!

The rechargeable molten cathode uses Oxygen directly from the air, instead of stored one, as is the case with some other approaches. With no Oxygen to store, the weight of the battery is reduced and a higher capacity is achieved.

Operating a battery at high temperatures, something in the neighborhood of 700 C, is rather unusual but poses no big challenge as other high temperature batteries have already been successfully tested in Electric Vehicles. Search is, however, on for electrolytes with lower melting temperatures.

Application areas for this type of batteries are widespread and growing. Grid scale energy storage needs high capacity batteries. Areas far away from the electric grid with small populations where electric supply becomes too costly, can also benefit from these. There are medical devices in need of high capacity batteries.

Over the years widespread electric vehicle adoption is facing the challenge of increasing the distance a car can travel on a single charge. This range anxiety is a serious issue. With high capacity batteries, Electric vehicles are poised for a long ride on just one charge.

So far the foundations of this new class of battery has been demonstrated. Various parameters, such as increasing the charging rate, lowering the operating temperatures, increasing the current densities, etc. are still to be investigated and optimized before we can see these batteries in commercial applications.