Carbon embedded α-MnO2@graphene nanosheet composite: a bifunctional catalyst for high performance lithium oxygen batteries†
Carbon is essential for the oxygen electrode in non-aqueous lithium–oxygen (Li–O2) batteries for improving the electron conductivity of the electrode. However, it also leads to some side reactions when exposed to the Li2O2 product and the electrolyte, limiting the round-trip efficiency and coulombic efficiency of the batteries. In this paper, a carbon-embedded α-MnO2@graphene nanosheet (α-MnO2@GN) composite is introduced as a highly effective catalyst for Li–O2 batteries. X-ray photoelectron spectroscopy (XPS) analysis showed that the Li2CO3 by-product was significantly reduced due to the isolation of carbon with the electrolyte and Li2O2. Thus, the composite could deliver a reversible capacity of ∼2413 mAh g−1 based on the total mass of the composite with an extremely high discharge voltage of ∼2.92 V (only 40 mV lower than the thermodynamic potential) and a low charge voltage of ∼3.72 V at a current density of 50 mA g−1. The round-trip efficiency is calculated to be ∼78% with a coulombic efficiency of almost 100%.