Researchers have demonstrated how several of the problems impeding the practical development of the so-called 'ultimate' battery could be overcome. Scientists have developed a working laboratory demonstrator of a lithium-oxygen battery which has very high energy density, is more than 90% efficient, and, to date, can be recharged more than 2000 times, showing how several of the problems holding back the development of these devices could be solved.

Lithium-oxygen, or lithium-air, batteries have been touted as the 'ultimate' battery due to their theoretical energy density, which is ten times that of a lithium-ion battery. Such a high energy density would be comparable to that of gasoline. But engineering a Li-air battery has been a challenge. Researchers have managed to overcome the remaining challenges: They were able to avoid electrode passivation, turn limited solvent stability into an advantage, eliminate the fatal problems caused by superoxides, achieve high power with negligible degradation, and even circumvent the problems of removing atmospheric water.

Researchers from the University of Cambridge have developed a lab-based demonstrator of a lithium-oxygen battery which has higher capacity, increased energy efficiency and improved stability over previous attempts.

Their demonstrator relies on a highly porous carbon electrode made from graphene and additives that alter the chemical reactions at work in the battery, making it more stable and more efficient.

The researchers developed uses a very different chemistry than earlier attempts at a non-aqueous lithium-air battery, relying on lithium hydroxide (LiOH) instead of lithium peroxide (Li2O2). With the addition of water and the use of lithium iodide as a 'mediator', their battery showed far less of the chemical reactions which can cause cells to die, making it far more stable after multiple charge and discharge cycles.

The researchers were able to reduce the 'voltage gap' between charge and discharge to 0.2 volts. A small voltage gap equals a more efficient battery – previous versions of a lithium-air battery have only managed to get the gap down to 0.5 – 1.0 volts, whereas 0.2 volts is closer to that of a Li-ion battery, and equates to an energy efficiency of 93%.

While the results, reported in the journal Science, are promising, the researchers caution that a practical lithium-air battery still remains at least a decade away. Issues that still have to be addressed include finding a way to protect the metal electrode so that it doesn’t form spindly lithium metal fibres known as dendrites, which can cause batteries to explode if they grow too much and short-circuit the battery.

Additionally, the demonstrator can only be cycled in pure oxygen, while the air around us also contains carbon dioxide, nitrogen and moisture, all of which are generally harmful to the metal electrode.

"While there are still plenty of fundamental studies that remain to be done, to iron out some of the mechanistic details, the current results are extremely exciting - we are still very much at the development stage, but we’ve shown that there are solutions to some of the tough problems associated with this technology," said Professor Clare Grey of Cambridge’s Department of Chemistry, the paper’s senior author.