Control of thermodynamic affinity between CNT-based electrode and electrolyte for lithium-air battery

Abstract

Lithium-air batteries have been intensely researched for its super high theoretical energy density of 3500 Wh kg-1, which is even comparable to that of gasoline. Because the cathode of lithium-air battery needs high surface area, high electrical conductivity and chemical stability, carbon nanotubes have been one of the most widely used cathode materials. However, due to their hydrophobic surface nature and high van der Waals interaction between their walls, they tend to aggregates and show lack of wettability with electrolyte and as a result, the cell performance deceases. In order to overcome this problem, many methods of surface modification have been suggested, such as, covalent functionalization and non-covalent adsorption. However, such covalent functional groups or non-covalent surfactants could be easily attacked by superoxide radicals, limiting the cycle stability of Li–air batteries. Therefore, it came to our interest that, in order to show high performance in small electrolyte condition, the CNT-based electrode that has not only high wettability with electrolyte by surface modification, but also chemical stability by shielding with bigger stable molecule. In this research, we prepared 3,5-bis(trifluoromethyl)phenylmaleimide functionalized CNT films for the cathode of lithium-air batteries. The maleimide group increases the wettability between electrode and electrolyte by modification of solubility parameter of CNT and the 3,5-bis(trifluoromethyl)phenyl group protects the maleimide group from decomposition. The resulting materials delivered a high capacity and cycle stability as a cathode material in small electrolyte condition. Consequently, this research can provide straightforward strategies to commercialize the lithium-air battery.