Tuning the Morphology and Crystal Structure of Li2O2: A Graphene Model Electrode Study for Li–O2 Battery

The performance and the cyclability of the Li–O2 batteries are strongly affected by the morphology and crystal structure of Li2O2 produced during discharge. In order to explore the details of growth and electrochemical decomposition of Li2O2, and its relationship with the cell performance, graphene films were used as model carbon electrodes and compared with electrodeposited Pd nanoparticles (NPs) on graphene. Multiple methods, including transmission/scanning electron microscopy (TEM/SEM), Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and coin cell charge/discharge test, were employed for material characterization and reaction monitoring. The results showed that the presence of Pd NPs significantly changed the growth, morphology, and crystal structure of Li2O2 and reduced the charge overpotential by 1060 mV. All of these changes are ascribed to the stronger binding energy between LiO2 and the Pd surface, resulting in the generation of amorphous Li2O2 with higher ionic conductivity of Li+ and O22–, which in turn improve the cell charging performance.