Electronic And Ionic Conductivity Enhanced MoO₃Nanobelts With Improved Electrochemical Performance

Lithium ion batteries have dominated the portable electronic markets and have potential application in the electric vehicles (EV) or hybrid electric vehicle (HEV) due to their advantages of high operation voltage, high energy density, long cycle performance. Molybdenum-based nanostructured materials have sparked a worldwide interest because of their unique optical, electronic and mechanical properties and potential applications in nanodevices and functional materials. Especially in the field of lithium ion batteries, molybdenum trioxide has attracted tremendous attention due to its high capacity, stability, low cost and safety.However, the electrochemical performance of molybdenum trioxide is not satisfying, mainly because of its low electronic conductivity and ionic conductivity. The low electronic conductivity will impact the rate performance of electrode materials; viz. the capacity reduction under high current densities is very severe. The low ionic conductivity means that the barriers for lithium ion migration in molybdenum trioxide is significant, influencing its capacity, and will result in the slip and distortion of the crystal structure of molybdenum trioxide, leading to the fast decay of molybdenum trioxide in capacity during cycling. Therefore, how to improve the electronic conductivity and ionic conductivity of molybdenum trioxide, to simultaneously improve the electrochemical performance of molybdenum trioxide, is the primary aim of this manuscript.In this dissertation, peroxomolybdic acid sol was chosen as the precursor, and performed several methods to improve the electronic and ionic conductivity to obtain better-performed electrode nanomaterials. Modern testing methods were used to study the preparation, structure and properties of as-synthesized molybdenum nano-materials. The obtained main results are as follows:(1) Using the as-prepared uniform molybdenum trioxide nanobelts and reduced graphene oxide with functional groups to prepare the wrinkled-graphene enriched molybdenum trioxide nanobelts, characterize the as-synthesized wrinkled-graphene enriched molybdenum trioxide nanobelts with AFM, SEM, Raman spectra, etc., to analyze the structure and morphology of the materials, and illustrate the growth mechanism.(2) Testing the electrochemical performance of the wrinkled-graphene enriched molybdenum trioxide nanobelts, especially concentrate on the performance of high-rate and stability test, and after graphene wrinkled the performance of molybdenum trioxide nanobelts has increased significantly.(3) Using the surfactant to reduce the molybdenum trioxide nanobelts, and using alkali metal ions to get the alkali metal ion intercalated molybdenum trioxide nanobelts. Use the ICP, TEM, SAED measurements to characterize the intercalation mechanism and lattice variation.(4) Using the electrochemical measurements to test the property of the as-synthesized materials. It is demonstrated that after the alkali metal ions intercalation, the cycling performance of molybdenum trioxide nanobelts has increased significantly, and with the increasing of the radius of alkali metal ions, the electrochemical performance has changed regularly. The mechanism is discussed based on the computational simulation results.