Electrochemical Mass Spectrometric Study Of Cathode Materials For Lithium-oxygen Batteries

Energy source is the material foundation of human society, always a hot scientific research field. Recently, lithium-oxygen batteries processing higher theoretical energy density of 5200 Wh?kg-1 have been considered as the promising next generation energy storage device.However, there are numerous scientific challenges, which provide great opportunities and challenges to the research and application of rechargeable lithium-oxygen batteries, such as poor cycle life and low round-trip efficiency. Some achievements have been made on the development of cathode materials(electrocatalysts) to address these issues. There are many unknown mechanisms in the electrochemical process of ORR/OER for lithium-oxygen batteries. So advanced in-situ and ex-situ characterization techniques are very important tools to clarify these mechanisms and scientific problems in lithium-oxygen batteries. Different electrochemistry mass spectrometry(DEMS) is a powerful research tool to in situ study mechanisms of a broad range of electrode reactions by identifying and quantifying reaction products and intermediates. In this thesis, we have been set up DEMS to focus on the application of on-line electrochemistry mass spectroscopy to investigate the stability and electrocatalysis performance of cathode materials. The results are detailed as follows:Commercial Super P carbon black(SP), SP treated by HNO3(HNO3-SP) and SP treated by high temperature sintering(HT-SP) were used as three types of carbon cathode materials.In conjunction with DEMS, the evolution of gaseous product during charging process was shown that HT-SP was more suitable for Li-O2 batteries. High-temperature thermal treatment process can reduce the oxygen species amount on carbon surface. Then we introduced Co O mesoporous spheres into carbon materials cathode. DEMS result was that CO2 was predominantly evolved from the battery during charge. Co O does not act as electrocatalysts during Li2O2 decompositon, but promote some parasitic reactions. Another electrocatalyst was Ni Co2O4, which exhibits a remarkable electrocatalytic activity for Li-O2 batteries. In this work, mesoporous Ni Co2O4 nanoflakes were synthesized to research that the influence of the amount of catalyst on the Li-O2 battery performance.Recent studies have focused on carbon free cathode materials to address carbon decomposition under the high voltage. Here we report the preparation of carbon-free Ni@Ni O electrode, and its application as cathode materials for rechargeable Li-O2 batteries. Li2O2 prefilled Ni@Ni O electrode and isotope labeled Li213CO3 prefilled Ni@Ni O electrode were obtained,which electrochemically decomposed separately to generate O2 at lower voltage and13CO2 at the potential of 4.5 V. It is considered to be a promising catalyst for Li-O2 batteries.