Preparation And Performance Investigation Of Molybdenum-Based Composite Materials For Li-CO₂ Batteries

With the dual benefits of CO₂ fixation and energy storage/conversion,Li-CO₂batteries are considered a significant way to balance the continuous release of CO₂.However,due to the slow kinetics of carbon dioxide reduction reaction and precipitation reaction,Li-CO₂ batteries have a series of problems such as large overpotential and poor cycle performance.The construction of efficient cathode catalysts is an important prerequisite for realizing the above transformations.Molybdenum-based materials,such as molybdenum carbide（Mo₂C）with excellent conductive properties and molybdenum oxide（Mo O₃）with high chemical stability,are expected to be positive catalyst materials for reducing the overpotential and improving the rate performance of Li-CO₂ batteries.This thesis systematically studies the effect of nanostructure design on the electrochemical performance of materials.The details of the study are as follows:To solve the degradation of battery performance caused by the dissolution of powder catalyst,a flexible self-supporting thin film electrode of Molybdenum carbide/carbon cloth（Mo₂C/C）was designed and fabricated.The results show that carbon cloth provides fast carrier transportation channels,and Mo₂C effectively reduces the discharge/charge overpotential.The Mo₂C/carbon cloth thin film self-supported electrode can maintain 40 times of stable constant current discharge/charge under the same conditions,the energy efficiency can reach 81%,and the charge-discharge potential difference is only 0.63 V,which is significantly better than the Mo₂C powder cathode catalyst.Its excellent electrochemical performance derive from the synergistic effect of the high electrical conductivity of the carbon cloth material,the excellent adsorption capacity of Mo₂C,and fully exposed active sites of the material.In order to further improve the cycle life of Li-CO₂ batteries,molybdenum oxide/carbon nanotube composites（Mo O₃/CNTs）were constructed by chemical vapor deposition and atomic layer deposition techniques as positive catalysts for Li-CO₂ batteries.The large specific surface area and high conductivity of carbon nanotubes can provide larger deposition space and fast electron/ion transport channel for discharge products,and improve the electrochemical reaction kinetics.The Mo O₃shell layer structure can provide protection for carbon nanotubes and enhance the cyclic stability of electrode materials.At the same time,this benefit from the advantages mentioned above,the discharge capacity of Mo O₃/CNTs composite electrode can reach 30.25 m Ah cm^-2,and maintain 300 cycles of discharge/charge stably.Flexible full batteries assembled from the Mo O₃/CNTs electrode as catalytic cathode can light up the light-emitting device.Excellent electrochemical performance is maintained even when bent 180 degrees.This method can provide reference for the synthesis and design of high performance molybdenum base materials and the development of Li-CO₂ battery electrode.