Reduced Co3O4 nanowires with abundant oxygen vacancies as an efficient free-standing cathode for Li-O2 batteries

The growth mechanism and reversible formation/decomposition of the discharge products in Li-O-2 batteries, which play a vital role in the performance of these batteries, are greatly affected by the construction of the cathode. In this work, a free-standing cathode with reduced Co3O4 nanowires (r-Co3O4@Ni) is prepared by a facile hydrothermal calcination process followed by reduction with aqueous NaBH4. The cathode not only displays a high discharge capacity of 4448 mAh g(-1) but also performs stably for 162 cycles, which is nearly three times the number of cycles of an Li-O-2 battery with pristine Co3O4@Ni and even better than that with a RuO2-modified electrode (RuO2/Co3O4@Ni). The Li2O2 growth models of the three types of Co3O4 electrodes at different discharge stages are studied in detail to understand the catalytic processes occurring on the surface of the electrodes. As a conclusion, the superior properties of r-Co3O4@Ni are due to the enhanced surface growth of the discharge products, which is promoted by the abundant oxygen vacancies and conformally distributed active sites generated during NaBH4 treatment.