JOINT STUDY ON DEVELOPMENT OF NEW INERCALATION ELECTRODES

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The present joint study aimed to develop new intercalation electrodes. The metal oxide electrodes have been synthesized by using soft-chemistry techniques such as an emulsion-drying method and hydrothermal method, and a dry preparation technique of r.f.-sputtering method. The carbon electrode has been synthesized by using liquid electrochemical reduction techniques. We have examined the crystal structure and the electrochemical characteristics of the prepared intercalation materials. Furthermore, we have performed the theoretical study on the lithium diffusion behavior in the crystal structure of the metal oxide. The main research results are as follows.1) LiAL_xMn_<2-x>O_4 spinel compound with high Al doping amount has been prepared by using the emulsion-drying method. The prepared mixed oxide showed excellent charge-discharge characteristics with high capacity of 120 mAh/g-oxide.2) New all-solid-state Li secondary cell consisting of LiMn_2O_4 cathode and V_2O_5 anode has been fabricated by using magnetron sputtering technique. This secondary cell showed excellent charge-discharge behavior at the cell voltages between 3.5 and 0.3 V with the capacity of 18 μA/cm^2.3) Carbon fine powders were obtained by the electrochemical reduction of liquid ternary system lithium-sodium-potassium carbonate at 450 ℃ using Ni electrodes. The carbon powders are found to consist of three different forms of carbon : graphite, amorphous carbon and carbon nanostructures. This third has an average diameter of 10 nm and is self-organized into long ropes.4) A new theoretical approach of the intercalation/deintercalation process of lithium cations into host materials is proposed taking into account of the dependence of the lithium diffusion coefficient on lithium concentration. This theoretical model was applied for the lithium diffusion in Nb_2O_5 crystal lattice.