Preparation Of Microstructure-controlled Mo₂C Nanocrystals And Their Electrochemical Performance In Li-O₂ Batteries

With the growth of population and development of economy, there is huge increase in the demand of usable energy. Most counties rely heavily on the fossil fuels for the energy consumption, which are limited and non-renewable. Additionally, CO2 emissions from the combustion of fossil fuels are recognized as the main factor for the environmental pollution. Therefore, searching for the environmental friendly energy storage and conversion devices have become the target for the development renewable energies. Li-O2 battery has been attracted increasing attentions as a promising power source for electric vehicle due to its significant high specific energy (11400 Wh/kg). Currently, as the most common material for the O2 electrode in the Li-O2 battery, carbon-based material has been reported that it can react with the electrolyte and/or immediate, which results in the poor cyclability and rate performance.In this thesis, the Mo2C nanorod with legth of 200-300 nm was prepared via a simple liquid-phase method. With the limition capacity of 300 mAh/g at a current density of 100 mAh/g, the Li-O2 battery using Mo2C nanorod as O2 electrode material exhibited an overpotential of 0.62 V at the first cycle. The value is significantly lower than that of Li-O2 battery using Super P (1.33 V).Mo2C nanotube with a diameter of 300 nm was successfully prepared via a template method. The Mo2C nanotube show a mesoporous structure. The specific surface area of prepared Mo2C is 193.38 m2/g and the pore distribution is 3-30 nm. The Mo2C nanotube was empolyed as the oxygen electrode material for Li-O2 battery, which showed the excellent electrochemical performance. There is no significant capacity fade up to 30 cycles with a limitation capacity of 500 mAh/g at current densities of 100,200, and 300 mA/g. In addition, the overpotential was 0.46 V in an Li-O2 battery cycled at a current density of 100 mA/g, indicating that the employment of Mo2C can lower the overpotential and improve the battery performance. Based on the results, it is reasonable to propose that the mesoporous and tubular structure can facilitate the O2 diffusion, the Li+ migration and the electrolyte moisture.