Carbon embedded α-MnO2@graphene nanosheet composite: a bifunctional catalyst for high performance lithium oxygen batteries

Abstract

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%.