Mechanisms of capacity degradation in reduced graphene oxide/α-MnO2nanorod composite cathodes of Li–air batteries

Abstract

The electrochemical performance of rechargeable Li–air batteries containing a reduced graphene oxide (rGO)/α-MnO₂ composite and neat α-MnO₂ electrode is studied. The rGO/α-MnO₂ composite exhibits a specific capacity as high as 558.4 mA h g⁻¹ at a current density of 100 mA g⁻¹, indicating its potential to make a good cathode material. The composite electrode also presents a relatively moderate degradation of capacities with increasing cycles, compared to the neat α-MnO₂ electrode. rGO functions as the conducting medium to connect the α-MnO₂ nanorods, thus improving the Li ion transfer. The mechanisms responsible for the capacity degradation in the composite electrodes are studied after a series of interrupted charge/discharge cycles, detecting Li₂O₂ and LiF as the main reaction products formed on the electrode surface. In particular, the LiF layer is identified to be an important component of reaction products, which serves as a barrier to reactions between the Li ions and electrons with the electrode, giving rise to detrimental effects on the cyclic and capacity performance of Li–air batteries.