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.