Synthesis and characterization of nano-scale vanadium oxides, vanadium phosphates as cathodes for lithium batteries

Progress in rechargeable lithium batteries for applications from small electronic devices to hybrid vehicles is intimately related to the successful research of advanced cathode materials. For improving the performance of lithium batteries, the search for cathode materials focuses on the investigation of insertion materials with a layered or open structure for reversible intercalation/deintercalation of lithium ions. Amongst insertion compounds, vanadium oxides and their derivatives with varied oxidation states (V5+, V4+ and V 3+) and desirable structures have attracted much attention. Onedimensional (1D) nanostructured building blocks such as nanorods, nanowires and nanoribbons, have attracted worldwide attention because of their distinctive geometries, outstanding physical and chemical properties and their potential applications in lithium batteries. Therefore, the investigation of nano-scale vanadium oxides with a layered structure is the subject of this thesis.;It was confirmed that the hydrothermal technique has advantages for the synthesis of vanadium oxides with layered structures. Here we present new methodology to control the morphology of vanadium oxides by using vanadium-polymer composite fibers, and form single-crystalline nanofibers with a layered structure through a hydrothermal treatment. By this synthesis method, two new layered vanadium oxides with dimensions ≤ 100 nm have been successfully obtained, vanadium oxide nanofibes (H0.48V4O10 · 2.0H2O) and lithium intercalated nanorods (Li 1.6H0.48V8O20 · 4.0H2O). The electrochemical performance of the nano-scale vanadium oxides as cathodes for lithium cells has been dramatically improved after the removal of interlayer water and hydronium ions. Additionally, the synthesis method has successfully produced nanoscale singlecrystalline VO2 (B) with an average width of 100 nm.;LiVPO4OH has been first synthesized hydrothermally by using vanadium pentoxide and lithium dihydrogen phosphate as starting materials. The pH value in the initial reaction solution plays an important role for the formation of lithium vanadium phosphate. The electrochemical behavior shows that the redox reaction of vanadium ions offers higher charge/discharge potentials in phosphates than in vanadium oxides, as expected for the inductive effect.