Disproportionation in Li-O_2 Batteries Based on a Large Surface Area Carbon Cathode

摘要

In this paper we report on a kinetics study of the discharge process and its relationship to the charge overpotential in a Li-O_2 cell for large surface area cathode material. The kinetics study reveals evidence for a first-order disproportionation reaction during discharge from an oxygen-rich Li_2O_2 component with superoxide-like character to a Li_2O_2 component. The oxygen-rich superoxide-like component has a much smaller potential during charge (3.2-3.5 V) than the Li_2O_2 component (～4.2 V). The formation of the superoxide-like component is likely due to the porosity of the activated carbon used in the Li-O_2 cell cathode that provides a good environment for growth during discharge. The discharge product containing these two components is characterized by toroids, which are assemblies of nanopartides. The morphologic growth and decomposition process of the toroids during the reversible discharge/charge process was observed by scanning electron microscopy and is consistent with the presence of the two components in the discharge product The results of this study provide new insight into how growth conditions control the nature of discharge product, which can be used to achieve improved performance in Li-O_2 cell.