Eco-Friendly Aluminum-Air Batteries as a Possible Alternative to Lithium Systems

Lithium battery technology currently dominates the electrical vehicle market and it is expected will dominate over the next decade as it is mature enough to rapidly deliver new electrochemical devices. However, several issues related to safety and large scale availability of Lithium have determined in recent years the development of a new research field, known as "beyond Lithium", in the attempt to identify innovative systems for electric energy storage based on different metal anodes. In this context, metal-air batteries are the most promising electrochemical devices able to provide high theoretical energy and power densities and also, if properly conceived, to satisfy the sustainability characteristics imposed by modern legislations. Among the various metals considered as anode in metal-air batteries, Aluminum is the material with the most satisfactory parameters of economy/ecology and electrochemistry at the same time. The technological challenge in the research on Al-air batteries consists in obtaining sustainable electrochemical devices with practical values of energy and power density, that are competitive with those of current lithium-ion systems. Above all, to make these batteries electrically rechargeable in aqueous electrolytes, taking into account that the re-deposition of the Aluminum during the charging phase is hampered by competitive reactions which consume current before the reduction potential of aluminum is reached. In this paper we present our recent results on quasi-solid-state Aluminum-air batteries realized with new electrolytes based on aqueous solutions at different pH and natural polysaccharides. We show that gel solid electrolytes in primary Al-air cells are able to provide 70 mAh cm-2 as cell capacity at discharge current of 10 mA cm-2. We finally remark some differences between alkaline and acidic electrolytes and their impact on primary cell electrochemical performance.