MrSeb writes "As part of IBM's Battery 500 project — an initiative started in 2009 to produce a battery capable of powering a car for 500 miles — Big Blue has successfully demonstrated a light-weight, ultra-high-density, lithium-air battery. In it, oxygen is reacted with lithium to create lithium peroxide and electrical energy. When the battery is recharged, the process is reversed and oxygen is released — in the words of IBM, this is an 'air-breathing' battery. While conventional batteries are completely self-contained, the oxygen used in a lithium-air battery comes from the atmosphere, so the battery itself can be much lighter. The main thing, though, is that lithium-air energy density is a lot higher than conventional lithium-ion batteries: the max energy density of lithium-air batteries is theorized to be around 12 kWh/kg, some 15 times greater than li-ion — and more importantly, comparable to gasoline."