Oxygen-enriched carbon nanotubes as a bifunctional catalyst promote the oxygen reduction/evolution reactions in Li-O2 batteries

Abstract The aprotic lithium-oxygen (Li-O 2 ) batteries based on carbon-based oxygen cathodes usually suffer from low round-trip efficiency. Here we adopt oxygen-enriched carbon nanotubes (CNTs) by acid etching treatment as the cathode, in which a low voltage plateau at ∼3.5 V during charge is exhibited and the initial round-trip efficiency is increased from 69.9% to 76.0%. An optimized integration of electrocatalytic property and electrical conductivity is crucial for the oxidized CNTs cathode to enhance the capacity and cycling performance. In particular, the surface oxygen groups can facilitate the electrocatalysis of O 2 with the enhanced oxygen reduction reaction activity and induce defective lithium peroxide (Li 2 O 2 ) formation due to their preferential adsorption of O 2 on the oxidized CNTs. Compared to the high crystalline Li 2 O 2 toroids, the defective Li 2 O 2 with poor crystallinity could be decomposed at a lower charge potential, contributing to the enhanced round-trip efficiency of Li-O 2 batteries.