Synthesis of Metal-Substituted Manganese Dioxides by Soft-Chemistry Method and Application to Active Electrode Materials in secondary cells

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The present research has aimed to synthesis several metal-substituted manganese dioxides by soft-chemistry routes, such as aqueous solution, hydrothermal, emulsion drying, and spray-drying methods. The chemical compositions and crystal structures of the prepared manganese dioxides were examined, and furthermore the electrochemical characteristics of the prepared manganese oxides were investigated as new cathode materials for secondary lithium batteries. The main results were as follows.1.New hollandite-type Co-doped α-K_<0.12>(Mn_<1-x>Co_x)O_2 (x=0〜0.12) and orthorhombic LiMn_<1-x>M_x,O_2 (O<x≦0.14 in M=Co,O<x0.1.5 in M=Fe) have been synthesized by aqueous solution and hydrothermal methods, respectively. The crystal structure, surface fine structure, structural variation with lithium intercalation, and lithium diffusion behavior in the crystal lattice were examined.2.The layered Li excess Li_<1+x>Ni_<0.5>Mn_<0.5>O_2 and its Ti-substituted LiNi_<0.5>Mn_<0.5-x>Ti_xO_2 (x=0〜0.3) have been synthesized by an emulsion-drying method. The structural analysis of the prepared layered materials was carried out by X-ray diffraction, newtron diffraction and X-ray absorption spectroscopic methods. These prepared materials showed a high discharge capacity of 170〜180 mAh/g oxide during 50 cyclings.3.The layered Li_<1-x>(Ni_<1/3>Co_<1/3>Mn_<1/3>)_xO_2(0≦x≦0.17) has been prepared by a spray-drying method, and the electrochemical characteristics and structural stability have been investigated. The crystal lattice parameter decreased with increasing the amount of Li excess (x-value), and at x=0.17 the highest discharge capacity of 179 mAh/g was obtained during 50 cyclings, due to the enhanced structural stability