Researchers at George Washington University have demonstrated a new class of high-energy battery, called a "molten-air battery," that has one of the highest storage capacities of any battery type to date. Unlike some other high-energy batteries, the molten-air battery has the advantage of being rechargeable.
Although the molten electrolyte currently requires high-temperature operation, the battery is so new that the researchers hope that experimenting with different molten compositions and other characteristics will make molten-air batteries strong competitors in electric vehicles and for storing energy for the electric grid.
This ability to store multiple electrons in a single molecule is one of the biggest advantages of the molten-air battery. By their nature, multiple-electron-per-molecule batteries usually have higher storage capacities compared to single-electron-per-molecule batteries, such as Li-ion batteries. The battery with the highest energy capacity to date, the vanadium boride (VB2)-air battery, can store 11 electrons per molecule. However, the VB2-air battery and many other high-capacity batteries have a serious drawback: they are not rechargeable.
The researchers experimented with using iron, carbon, and VB2 as the molten electrolyte, demonstrating very high capacities of 10,000, 19,000, and 27,000 Wh/l, respectively. The capacities are influenced by the number of electrons that each type of molecule can store: 3 electrons for iron, 4 electrons for carbon, and 11 electrons for VB2. In comparison, the Li-air battery has an energy capacity of 6,200 Wh/l, due to its single-electron-per-molecule transfer and lower density than the other compositions while a typical Li-Ion battery has a capacity of approx 600 Wh/l.