For the great wide world of transportation, the lithium-ion battery is the shining city on the hill, that pivotal bit of technology that will have us whizzing around in silent cars banishing the evils of carbon dioxide. For aviation, lithium-ion is both an enigma and an opportunity.
To understand both, you need only to grasp three numbers: 50, 150 and 1700. The opportunity part resides in the first two numbers—a lead-acid battery’s energy density is about 50 Wh/kg, a third or less than that of the typical lithium-ion’s 150 Wh/kg. Now for the enigma. The 1700 is the Wh/kg energy content of gasoline, adjusted for the typical internal combustion engine’s 20 percent efficiency. The very best lithium-ion batteries can do at the moment is 400 Wh/kg and these don’t exist commercially yet. That means the practical electric airplane may be on the horizon, but it’s not around the corner.