Regulating the Helmholtz plane by trace ionic liquid additive for advanced Al-air battery

Abstract

Al-air batteries (AABs) are the next generation of alternative energy sources due to their high theoretical energy density, low cost, and environmental friendliness. Researchers have been interested in AABs with stable discharge in alkaline solution, long discharge time, and high conductivity. However, the uncontrolled self-corrosion of the Al anode and the severe hydrogen evolution reaction in alkaline electrolytes have been two major drawbacks hindering the commercial development of AABs. These shortcomings reduce the Al anode's utilization and significantly shorten the battery's service life. Herein, the Helmholtz plane structure was reconstructed using an ionic liquid additive called 1-aminopropyl-3-methylimidazolium bromide (AMIB) to regulate the electrochemical interface between the electrolyte and the Al anode. Electrochemical tests found that when 3 mM AMIB was added, the corrosion inhibition efficiency could reach up to 60 %. Further surface analysis and theoretical calculations showed that AMIB can form a dense and uniform protective layer on the surface of the Al anode substrate, which reduces the anode corrosion, lowers the active centers for hydrogen evolution on the Al surface, and reduces the hydrogen evolution rate. The full-cell studies found that the specific capacity of the cell increased from 1227 to 2564 mAh g−1, the energy density increased from 1546 to 3359 Wh kg−1, and the Al anode utilization increased from 41.2 % to 86.1 % as the AMIB addition to the alkaline electrolyte risen from 0 to 3 mM. This method of electrolyte regulation provides an efficient strategy for the commercial development of AABs.