It is a version of what is known as a lithium-air battery, something that has been a desideratum of energy-storage research since the 1970s. In theory, such batteries could hold more than four times the energy per kilogram of lithium-ion batteries.  Building them, though, has proved taxing. As their name suggests, they draw in air.  The part they need is the oxygen, but other atmospheric components—water vapour and carbon dioxide in particular—often damage them.

Even versions using pure oxygen have problems. Using and recharging existing lithium-air batteries wastes a huge amount of energy.  They rapidly degenerate to the point where the battery can no longer be recharged.  The crucial difference between this and previous designs is no actual air is involved.  Instead, the cell is hermetically sealed and uses oxygen stored inside the battery itself, in a chemical called lithium superoxide (LiO2).  Because this compound is unstable, it is easily induced to surrender some of its oxygen.