Development of active materials of nonaqeous lithium secondary battery, based on its discharge and charge mechanisms.

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The discharge and charge mechanisms of metallic oxides, metallic sulfides, and conducting polymers in nonaqueous solvent were investigated in order to develop the positive active material of lithium secondary batteries. These reactions proceeds with the insertion and deinsertion of <Li^+> ion, <ClO(_4^-)> , <BF(_4^-)> , or <PF_6^-)> . In this study, the diffusion behavior of <Li^+> ion and <ClO(_4^-)> etc. in solid phase of active material were examined by using a potential step method.Rutile and anatase <TiO_2> thin films were prepared by rf-supptering method. Anatase <TiO_2> films was heated at 400゜C to increase its crystallinity. Diffusion coefficients of lithium in <TiO_2> films were estimated, assuming one-dimensional finite diffusion. Diffusion coefficient increased with decreasing of crystallinity of <TiO_2> film. Therefore, amorphous like <TiO_2> must be suitable for active material of lithium secondary battery. <MoS_2> were also investigated, which has a layer structure. In this case, solvated <Li^+> ion intercalated into <MoS_2> layer, resulting in large polarization caused by diffusion resistance of <Li^+> ion. Therefore, the solvent for the electrolyte must not strongly interact with <Li^+> ion.Diffusion behavior of anions in polyacetylene and polyaniline were studied and the diffusion coefficients of <ClO(_4^-)> , <BF(_4^-)> , and <PF(_6^-)> were obtained to be the order of 1x <10^(-14)> <cm^2> <s^(-1)> . This means that the discharge and charge reactions are limited by diffusion process of anions in polymer. Therefore, thin film of polyaniline was prepared by electrochemical polymerization and was examined its discharge and charge characteristics. Such film electrode indicates the good performance as active material of lithium secondary battery. This is because the diffusion path for anion in polymer becomes short.