Application Of Manganese Oxide-Based Catalyst In Rechargeable Lithium-Air Batteries

Owning to the high energy density (3458 Wh kg-1) and environmental friendly properties, rechargeable lithium-air batteries are becoming one of the most promising energy storage systems. However, there still exists some hardships for the application of rechargeable lithium-air batteries:high overpotential, low energy efficiencies, inferior cyclability, side-reactions and so on. Developing high electrochemical activity and low cost cathode catalyst is the critical solution to solve the problems. Manganese oxides were widely utilized as the cathode catalyst in rechargeable lithium-air batteries due to the advantage of the environmental friendless, low cost, and large element abundance. Considering the relative low electrochemical catalytic activity of manganese oxides, some technique methods are implied to improve the performance of rechargeable lithium-air batteries. In this thesis, the in-situ electrochemical lithiation and composite with selected metal oxides were developed to enhance the catalytic performance, which are summarized below:(1) Herein, We demonstrate that sealed Li-MnO2 cells with manganese dioxide as the cathode, after their depletion, can be further operated efficiently as rechargeable Li-air batteries when exposed to air. The novel electrochemical lithiation measurement is applied to synthesize the cathode catalyst in rechargeable lithium-air batteries for the first time to obtain various lithiation manganese dioxides. We further disclose the correlation between electrocatalytic properties for ORR/OER and the degree of lithiation of MnO2. In particular, Li0.50MnO2 delivers high discharge capacity (10823 mAh gcarbon-1) and durable cyclability (over 190 cycles) in rechargeable Li-O2 batteries.(2) The performance of rechargeable lithium-air batteries is influenced by the structure and the morphologies of the cathode catalysts. The Co3O4 nanorods were in-situ prepared on the nickel foam as the precursor, then the MnO2 nanoplates were compounded on them by the hydrothermal method. The hydride metal oxides exhibit excellent ORR and OER performance with the overvoltage around 0.72 V. Moreover, the hierarchical porous catalysts provide amount of active sites and confined structure to increase the performance of rechargeable lithium-air batteries. We further investigate the size effect of the discharge production Li2O2 and found that the overpotential for the charging process decrease with smaller discharge production.