Tuning the Morphology of Li2O2 by Noble and 3d metals: A Planar Model Electrode Study for Li-O2 Battery.

In this work, a planar model electrode method has been used to investigate the structure-activity relationship of multiple noble and 3d metal catalysts for the cathode reaction of Li-O2 battery. The result shows that the battery performance (discharge/charge overpotential) strongly depends not only on the type of catalysts but also on the morphology of the discharge product (Li2O2). Specifically, according to electrochemical characterization and scanning electron microscopy (SEM) observation, noble metals (Pd, Pt, Ru, Ir, and Au) show excellent battery performance (smaller discharge/charge overpotential), with wormlike Li2O2 particles with size less than 200 nm on their surfaces. On the other hand, 3d metals (Fe, Co, Ni, and Mn) offered poor battery performance (larger discharge/charge overpotential), with much larger Li2O2 particles (1 μm to a few microns) on their surfaces after discharging. Further research shows that a "volcano plot" is found by correlating the discharging/charging plateau voltage with the adsorption energy of LiO2 on different metals. The metals with better battery performance and worm-like-shaped Li2O2 are closer to the top of the "volcano", indicating adsorption energy of LiO2 is one of the key characters for the catalyst to reach a good performance for the oxygen electrode of Li-O2 battery, and it has a strong influence on the morphology of the discharge product on the electrode surface.