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bitshifter writes with a story from Science Daily:

Chemists at the Waterloo University have discovered the key reaction that takes place in sodium-air batteries that could pave the way for development of the so-called holy grail of electrochemical energy storage.

Unlike the traditional solid-state battery design, a metal-oxygen battery uses a gas cathode that takes oxygen and combines it with a metal such as sodium or lithium to form a metal oxide, storing electrons in the process. Applying an electric current reverses the reaction and reverts the metal to its original form.

In the case of the sodium-oxygen cell, the proton phase catalyst transfers the newly formed sodium superoxide (NaO₂) entities to solution where they nucleate into well-defined nanocrystals to grow the discharge product as micron-sized cubes. The dimensions of the initially formed NaO₂ are critical; theoretical calculations from a group at MIT has separately shown that NaO₂ is energetically preferred over sodium peroxide, Na₂O₂ at the nanoscale. When the battery is recharged, these NaO2 cubes readily dissociate, with the reverse reaction facilitated once again by the proton phase catalyst.

Chemistry says that the proton phase catalyst could work similarly with lithium-oxygen. However, the lithium superoxide (LiO₂) entities are too unstable and convert immediately to lithium peroxide (Li₂O₂). Once Li₂O₂ forms, the catalyst cannot facilitate the reverse reaction, as the forward and reverse reactions are no longer the same. So, in order to achieve progress on lithium-oxygen systems, researchers need to find an additional redox mediator to charge the cell efficiently.

Another battery technology "only a few years from the market"?