Preparation And Properties Of Lithium-air Batteries Ruthenium Oxide Composite Electrode

Lithium-air(Li-O2) batteries have very high theoretical specific energy, hence recently attracted a great deal of attentions because of the main application in eco-friendly electrochemical vehicles. However, there are many shortcomings hinder the commercialization of lithium-air battery, such as large overpotential, poor rate performance, low cycle life. There are also many challenges in Li-O2 batteries development and research, such as charge-discharge reaction mechanism, protected lithium sheet, decomposition of the electrolyte, structural design of the air electrode, the choice of catalyst etc.In this thesis, the catalytic oxygen reduction reaction(ORR) of lithium-air battery and the oxygen evolution reaction(OER) of the double-effect catalyst were explored for the target. RuO2 was used as the main catalyst for lithium-air batteries. Different morphologies of RuO2/MWNTs composites were prepared with lquid co-deposition and hydrothermal. Method has been chosen due to better catalytic properties of the catalyst preparation. Moreover nanoscale MnO2 and RuO2 particles simultaneously load on the surface of MWNTs. We use XRD, SEM, TEM and other methods of physical and chemical properties of the composites were characterized. Finally, the assembled Li-O2 battery electrochemical performance testing, we get the following conclusions:1. RuO2 which was prepared byhydrothermal reaction of RuO2/MWNTs composites has a good degree of crystallinityand a smaller particle size. In addition, the RuO2/MWNTs composites which were prepared by hydrothermal reactionhave good electrochemical performance. At a current density of 0.1 mA/cm2, the cut-off voltage of 2.3~4.0 V, the battery discharge capacity was 2033 mAh/g; At a current density of 0.2 mA/cm2, the battery discharge capacity was 1534 mAh/g, when the current density increased to 0.4 mA/cm2, the battery discharge capacity decay to 896 mAh/g.As the charge-discharge current density increases, the charge-discharge capacity significantly reduced, overpotential increases, electrode polarization increases. At a current density of 0.1 mA/cm2, thebattery discharge capacity after three cycles was 1808 m Ah/g, and the capacity retention rate was 88.9%.When the cycle test was conducted with a larger current density, a current density of 0.3 mA/cm2, capacity cut off 400 mAh/g, the battery can be recycled 50 times, at the same time thebatterycharge and discharge capacity is almost unchanged and overvoltage is small.2. The MnO2-RuO2/MWNTs composite nanomaterials was prepared by hydrothermal method further synthesized. At a current density of 0.1 mA/cm2, the battery has a large discharge plateau 2.88 V, a small charging platform 3.32 V, and overpotential is 0.44 V. the battery discharge capacity is 5736 mAh/gcarbon.The battery discharge plateau higher than RuO2/MWNTs 0.06 Vand has a good discharge capacity.In addition, the Li-O2 battery also has good cycle characteristics, at a current density 0.3mA/cm2, capacity cut off 1000 mAh/gcarbon(380 mAh/g), the battery cycle up to 65 times. This indicates that the MnO2-RuO2/MWNTs composites has better ORR catalytic activity.3. Electrochemical performance of Li-O2 battery is closely related to the morphology and size of the catalyst particles, smaller catalyst particles showed a greater discharge capacity. MnO2 can further improve Li-O2 battery discharge potential and increase the discharge capacity and cycle characteristics of lithium-air batteries. However, excess catalyst will reduce the pore volume of the electrode material and increase the electrochemical impedance of the Li-O2 battery.