Improved battery capacity and cycle life in iron-air batteries with ionic liquid

Abstract

Hydrogen releasing and electrode passivation are the major factors resulting in low cycling stability of Fe-air batteries with battery capacity deterioration. Here we introduce a new approach to restrain these drawbacks by adding ionic liquid (1-ethyl-3-methylimidazolium L-(+)-lactate, abbrev. EML) as an electrolyte additive to suppress both hydrogen releasing and passivation formation on the electrode surface during battery discharge. By utilizing hydrogen volume, electrochemical, and battery capacity measurements, the impact of ionic liquid EML on the performance of the Fe-air battery has been clearly demonstrated. The introduction of EML as an electrolyte additive allows for the inhibition of hydrogen releasing with an efficiency of over 97%. The nature of ionic liquid EML enables to prevent the passive layer formation on the Fe electrode surface by forming iron (II) lactate instead of iron oxides. As a result, a Fe-air battery with ionic liquid EML achieves capacity retention after 1000 cycles higher than 94% with a nominal capacity of 0.416 Ah g−1 at C/5. This approach provides a promising direction for the future development of ionic liquids as electrolyte additives that can be used to improve the cycling life of Fe-air batteries.