Hierarchical tunnel design for rapid transport of ion in solid state materials

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1. We established the solid state method for synthesis of vanadium cobalt oxide, CoV_3O_8, which has tunnels for one dimensional ionic transport. It was examined as electrode material for lithium ion battery. The electrochemical reaction of CoV_3O_8 with lithium was found to proceed as follows. First lithium intercalated in CoV_3O_8. Second an amorphous substance was generated. Finally a crystalline substance, whose XRD peaks can be indexed on the basis of a face centered cubic cell, was generated. On the other hand, charge can be done. Therefore, discharge-charge cycles were possible. In particular, high coulombic efficiency near unity in the second cycle or later was observed. Measurement and analysis of open circuit potentials at various lithium insertion levels indicated that such reversible discharge-charge was due to lithium insertion in the amorphous substance and extraction out of that.2. Hexagonal tungsten trioxide (h-WO_3), which has tunnels in its structure, is a metastable … More phase of WO_3. The tunnel accommodates various kinds of ions and provides them transport path. Amorphous peroxopolytungstic acid (PPTA), which is one of solid state acids, is a significant precursor of hexagonal tungsten trioxide. We analyzed structure of this material using X-ray absorption measurements. As a result, we acquired knowledge concerning correlation of polyhedral variation with temperatures of thermal treatment. For instance, corner shared polyhedra became dominant, compared to edge shared ones with increase in temperature. The polymerization of the polyhedra and change in coordination number of W-O were clarified. Furthermore, the evolution of structural change from PPTA to h-WO_3 was observed.3. Ba_2In_2O_5 is known to have oxygen vacancy in high concentration, which allows oxide ionic conduction. We synthesized various Ba_2In_2O_5-derivative oxides and studied their properties. BaIn_<1-x>M_xO_<3-δ> (M = Fe and Co) was found to be a good electronic and oxide ionic conductor. A single chamber fuel cells using high oxide ionic conductor BaLaInO_<5.5> were constructed. The relationship between fuel supply conditions and performance of the cell was studied in detail. Less