Battery
Lithium metal-air batteries can store a tremendous amount of energy–in theory, more than 5,000 watt-hours per kilogram. That’s more than ten-times as much as today’s high-performance lithium-ion batteries, and more than another class of energy-storage devices: fuel cells. Instead of containing a second reactant inside the cell, these batteries react with oxygen in the air that’s pulled in as needed, making them lightweight and compact.