Directly grown Co3O4 nanowire arrays on Ni-foam: structural effects of carbon-free and binder-free cathodes for lithium-oxygen batteries

Abstract

The problem of carbon and binder decomposition, degrading the performance levels of the cathodes used in lithium oxygen (Li-O-2) batteries, remains unsolved. For this reason, using carbon and binder-free cathodes may be an ideal approach to remedy this problem. Here, we have developed a carbon free-and binder-free cathode for Li-O-2 batteries based on vertically grown Co3O4 nanowire (NW) arrays on Ni-foam and demonstrated the suppression of this type of decomposition. The highly organized texture and high catalytic activity of the cathode provide high capacity with a reduced overvoltage. Interestingly, the charge voltage profile changed with the discharge rate, which is associated with the variation in the phase and local distribution of the discharge products. At a low discharge rate, a morphology resembling the pointed tip of a brush was observed, indicating that the crystalline discharge products were concentrated on the skin of the cathode, causing the deformation of the NW array. At a high discharge rate, a more uniform distribution of the quasi-amorphous discharge products was favored, resulting in a relatively stable voltage profile with cycling. These findings suggest the importance of the electrode structure and discharge product distribution during the design of carbon- and binder-free cathodes.