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Two Advances Point Toward a Cheaper Electric-Car Battery

Lithium-sulfide batteries could store far more energy than lithium-ion ones.

Better battery: This scanning electron microscopy image shows lithium sulfide particles used by researchers at Stanford University to make an improved lithium sulfide battery.

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”). But lithium metal is highly reactive when exposed to water and can form root-like structures inside batteries over time; these structures can join positive and negative electrodes, causing short circuits and even fires. So many researchers have begun turning their attention to a similar battery that doesn’t require lithium metal.

In the new type of battery, the sulfur electrode is replaced with a lithium-sulfide material—a compound that contains both lithium and sulfur. This becomes the source of the lithium, so the lithium metal is no longer required and can be replaced with graphite—a material used in lithium-ion batteries today—or with a material such as silicon.

The trouble is, lithium sulfide is electrically insulating, which slows down charging and reduces the amount of energy the battery can deliver. But two recent papers, one from Stanford and the other from Lawrence Berkeley National Laboratory, offer ways to make lithium-sulfide batteries more practical.

These research papers demonstrate low-cost methods for making lithium-sulfide batteries with high-energy storage capacities. The work could lead to commercial batteries that store more than three times as much energy as the lithium-ion batteries currently used in electric vehicles, says Yuegang Zhang, a staff scientist at Lawrence Berkeley National Laboratory.

Earlier this year, Yi Cui, a materials science professor at Stanford, showed a way to overcome the inherent limitations of lithium-sulfide batteries by charging the battery at a higher voltage than usual for its first charge. This changes the chemistry of the electrode, getting around the conductivity problem.


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