Current progress in the development of Fe-air batteries and their prospects for next-generation batteries

With the ever-growing dependency on electronic devices as well as the rapid development of electric vehicles, the demand for large-scale energy storage systems has risen significantly. Besides lithium-ion batteries, one alternative source of energy that has attracted tremendous attention is metal-air batteries as they possess high theoretical energy densities compared to other forms of batteries. Metal-air batteries employ metals such as iron, zinc, tungsten, or aluminum as the negative working electrodes and oxygen from the air as the positive working electrode. As the theoretical capacity of the metal-air batteries is determined by the negative electrodes, development is more focused on the metal electrode. Commonly, a metal-air battery in a liquid state with an alkaline aqueous solution as the electrolyte has a number of drawbacks, such as irreversibility of hydroxide ions conduction, fast capacity decay, electrode deformation, as well as hydrogen evolution during the charging process. As technology is moving toward Internet-of-Things and lightweight wearable devices, the bulkiness as well as weight of the batteries have never been more crucial. Therefore the heavier and leakage-prone liquid electrolyte-based metal-air batteries are deemed inappropriate for use as wearable devices. Therefore an alternative method to overcome both electrolyte leakage and hydrogen evolution is to utilize a solid electrolyte in an all-solid-state metal-air rechargeable battery. In this chapter, brief fundamentals of metal-air batteries focusing more on the Fe-air battery, current progress, and its future outlook will be discussed. The development of all-solid-state Fe-air batteries and their potential will also be mentioned.