Metal air batteries have fundamental difference to other types of battery architectures, due to the fact that active material for one of the redox half-reactions is supplied from outside of the system. This ensures one of the main advantages of metal-air technology – high energy density, for example specific energy of Li/air battery is close to that of traditional gasoline. Aluminium-air and zinc-air batteries have in addition the great advantage of availability and low price of anode materials.
However, metal air batteries suffer from shortcomings, resulting from stability of intermediates and side reactions with the components of the air, bad reversibility of electrochemical processes, as well as kinetic limitations of cathodic reaction. This is why metal air batteries exist mostly as primary batteries and the commercialisation of secondary batteries requires solution of the challenging questions. A lot of those problems, however, could be tackled by choosing the right electrolyte.
Ionic liquids are potentially interesting alternatives to traditional aqueous and organic electrolytes for metal-air batteries and can offer following advantages:
- Increased safety, due to
- higher electrochemical and chemical stability, allowing use in more strenuous conditions
- ultralow vapour pressure, minimizing release to the environment and risk of overpressure-triggered exposures
- possible absence of toxicity
- High solubilizing power, allowing better solubility of intermediates and active material
- Tunability of properties, allowing fine tuning of the systems
- Compatibility with other system components