Lithium air prototype cell.
Interesting article from IEEE Spectrum about the potential benefits of developing a usefully rechargeable lithium-oxygen cell (for use, most importantly, in electric cars) and the challenges that remain for that research. So-called “air batteries,” in which one of the reacting chemical species is atmospheric oxygen, are already widely employed, for instance, in hearing-aid batteries, which are commonly zinc-air cells with a piece of adhesive film that must be removed before use to allow atmospheric oxygen onto the cathode. The know-how to make lithium-air cells is available right now; the hard part is making the reverse process practical over many recharging cycles. [Thanks, Glen!]