For the roads to start filling up with electric cars, batteries will need to get much cheaper—as much as 80 percent cheaper by some estimates (see “How Improved Batteries Will Make Electric Vehicles Competitive”). Two recent advances that make an experimental type of battery much more practical could lead to such cost savings.

Researchers have for years been working on a type of battery that uses lithium metal in one electrode and sulfur in the other. In theory, this kind of battery could store three to five times as much energy as a conventional lithium-ion battery (see “Revisiting Lithium-Sulfur Batteries”).