Lithium-air batteries, which could give electric cars the same range as gasoline ones, are a step closer to becoming practical. Researchers at Yale and MIT have found a way to alleviate two of the batteries’ biggest problems—their inefficiency and inability to be recharged many times.

The researchers developed a nanostructured membrane that reduces the energy needed to recharge the battery, making it more efficient. The advance also allowed an experimental version of the battery to be recharged 60 times without losing storage capacity— roughly double the number of times as previous versions of the battery. (Electric car batteries should last roughly 1,000 recharge cycles.)  

Lithium-air batteries are attractive because of their huge theoretical energy storage capacity, which is, by weight, roughly 10 times higher than the conventional lithium-ion batteries  used in electric vehicles today. That means an electric car using such batteries could easily travel the 350-plus miles people expect from a tank of gasoline, and the battery could be much smaller and cheaper than conventional batteries. Some research groups have recently abandoned research on lithium-air batteries because they’ve had trouble getting the batteries to meet their potential. The advance from Yale and MIT shows that some key problems are being solved, although much work still remains before lithium-air batteries can be used commercially in electric cars.

Lithium-air batteries generate electrical current when lithium ions react with oxygen, forming lithium oxide. Recharging them involves reversing this reaction, breaking the bonds between lithium and oxygen atoms and freeing the oxygen. The problem is that lithium oxide forms a coating on one of the battery electrodes, covering up the catalysts needed to free the oxygen efficiently.

The researchers’ solution was to change the structure of lithium-air batteries, adding a membrane made of catalyst-coated polymer nanofibers. They showed that lithium oxide doesn’t form on the nanofibers, so the catalysts remain relatively exposed and effective.

The experimental battery uses pure oxygen. To realize the theoretical potential of lithium-air batteries would require developing a system that can work in air, which poses several challenges. For example, lithium ions tend to react with carbon dioxide in air, producing lithium carbonates that make the battery difficult to recharge.