Co₃O₄-precious Metal As A Bi- Functional Catalyst For Lithium- Oxygen Batteries

Li-O2 (Li-air) batteries can provide a theoretical energy density of 3505 Wh kg-1,which is greatly higher than the theoretical energy density of current Li-ion batteries,584 Wh kg-1 for LiCoO2/C system. Despite recent advances, where long-term cycling of Li-O2 battery could be achieved, great challenges still remain to develop practical Li-air batteries. The performance of Li-O2 battery is largely limited by the inherent shortcomings of Li2O2, the discharge product. And the parasitic reactions will lead to the formation of undesirable by products, for instance Li2CO3, and the accumulation of by products on cycling will result in performance degradation and eventual failure of the battery.The main purpose of this work is to find an efficient catalyst, in order to improve the performance of Li-O2 battery by optimizing the discharge and charge product. In this work, Co3O4 and Pt/Co3O4 nanowires growing directly onto Ni foam are prepared by hydrothermal route. Morphology and constraction are observed by XRD, XPS, TEM and SEM. Electrical performance is analysted through CV, EIS and Cycling test, while we also use SEM, TEM and XPS to analysis the discharge and charge products.detailed work are as following.(1) In this work, the growth of Co3O4 nanowires, Pt/Co3O4 nanowires and different morphologies of Pd/Co3O4 on Ni foam was realized by a facile hydrothermal route. By dealing with different experimental conditions, we find three factors that influence the sybthesis of Co3O4, which are the time of the hydrothermal reaction, the temperature of annealing and the concentration of the precursor.(2) The catalytic activity of Pt/Co3O4 nanowires directly onto Ni foam is researched for Li-O2 batteries. Li-O2 battery with Pt/Co3O4 cathode shows remarkably improved electrochemical performance compared with that with Co3O4 cathode. The Pt/Co3O4 catalyzed Li-O2 battery can sustain a stable cycling over 50 times at a capacity of 500 mAh g-1. We found that Pt can direct the uniform deposition of a fluffy, thin Li2O2 layer on the surface Pt/Co3O4 nanowires by obsercing the discharge and charge products. This crystallization behavior of Li2O2 alleviates and delays the passivation of the electrode and reduces the side reactions by decreasing the charge overpotentials. This work provides a method to develop efficient catalytic cathode with directed Li2O2 growth on catalyst while avoiding the use of binder and carbon.(3) Co3O4 with Pd/TEGDME are designed as a bi-functional catalyst in both liquid phase and solid phase in Li-O2 battery by adding Pd to the electrolyte TEGDME. The Co3O4 with Pd/TEGDME catalyzed Li-O2 battery can sustain a stable cycling over 60 times at a capacity of 500 mAh g-1. SEM imagines show that the discharge product is uniform, without any aggregation. Meanwhile, the mapping analysis indicates Pd nano-particles are transporting from the electrolyte to the surface of anode during discharge reaction, and turning back in charge. This work provides a method to a bi-functional catalyst in both liquid phase and solid phase in Li-O2 battery with a better electrical performance.