High rate and long cycle life in Li-O₂ batteries with highly efficient catalytic cathode configured with Co₃O₄ nanoflower

The reaction mechanism of non-aqueous Li-O₂ batteries is based on the deposition and decomposition of Li₂O₂. The polarization of Li-O₂ batteries can be rapidly increased by operation under a high rate condition, resulting in the early capacity fade of the cells. Therefore, a well-designed catalyst with a unique structure and excellent catalytic ability is an important way to boost the round-trip performance of Li-O₂ batteries, especially under high current density. In this work, a unique nanoflower structure assembled with Co₃O₄ nanosheets is synthesized by using 2-methylimidazole (2-MIM) as a structural directing agent. X-ray photoelectron spectroscopy (XPS) and Raman spectra reveal abundant oxygen vacancies on the surface of the Co₃O₄ nanoflower, which are beneficial for oxygen reduction and evolution reactions and long round-trip lifetime. Density functional theory results demonstrate that Co₃O₄ catalyst with oxygen vacancies could promote the wetting of Li₂O₂ on substrate and formation of a Li₂O₂ nanofilm, thereby boosting the discharge capacity of Li-O₂ batteries. On account of the synergistic effect of abundant oxygen vacancies, the unique structure, and excellent oxygen evolution reaction, Co₃O₄ nanoflower-based cells could deliver ultralong lifetime of 276 and 248 cycles with a discharge capacity of 1000 mAh g⁻¹ under charge/discharge current densities of 0.5 A g⁻¹ and 1 A g⁻¹, respectively. This study has shed light on a new strategy for catalyst preparation for long lifetime Li-O₂ batteries.