JOINT STUDY ON DEVELOPMENT OF NEW INERCALATION ELECTRODES

本研究旨在开发新型插层电极。采用乳状干燥法、水热法等软化学技术和射频溅射法等干法制备了金属氧化物电极。采用液相电化学还原技术合成了碳电极。研究了所制备的插层材料的晶体结构和电化学特性。此外，我们还对锂在金属氧化物晶体结构中的扩散行为进行了理论研究。主要研究结果如下：1)采用乳化干燥法制备了高Al掺杂量的LiAL_xMn_<2-x >o_4尖晶石化合物。制备的混合氧化物具有良好的充放电特性，容量可达120 mAh/g-oxide。2)采用磁控溅射技术制备了由LiMn_2O_4阴极和V_2O_5阳极组成的新型全固态锂二次电池。该二次电池在3.5 ~ 0.3 V电压范围内表现出优异的充放电性能，电池容量为18 μA/cm^2.3)。碳粉由三种不同形式的碳组成：石墨、无定形碳和碳纳米结构。这三分之一的平均直径为10纳米，并自组织成长长的绳索。4)考虑锂离子扩散系数对锂离子浓度的依赖性，提出了锂离子在基体中插入/脱嵌过程的新理论方法。将该理论模型应用于锂在Nb_2O_5晶格中的扩散。

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.