Study on Diffusion of Lithium Ion in Solid and Development of Lithium Secondary Battery

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Electronically conductive polymers, such as polyacetylene, have attracted considerable attention due to their potential application to lithium secondary battery. The diffusion coefficients of various anions, BF^-_, C10^-_, and PF^-_, in polyacetylene was estimated. The diffusion of polyacetylene was treated by a cylindrical finite diffusion model. The diffusion coefficients of the anions were estimated as 2-4x10^<-14> cm^2s^<-1>. This results suggested that the rate determining step on charge or discharge of polyacetylene electrode was the anion diffusion process.The discharge reaction of FeOCl was investigated and the discharge products have been identified by XRD and EPMA. At high concentrations of lithium, FeOCl co-intercalated by lithium and solvent gradually decomposed to yield Fe and other compounds. On the other hand, FeOCl modified by the intercalation of basic organic compounds, such as 4-aminopyridine or 2-vinylpyridine, is high enough to stabilize the structure of FeOCl during the discharge.Ultra-thin, uniform, pinhole-free solid polymer electrolyte films of approximately 1 mum thickness were prepared by the complexation of plasma-polymerized tris(2-methoxyethoxy)vinylsilane with lithium perchlorate. Room temperature conductivities greater than 10^<-6> S cm^<-1> (10^2 OMEGA cm^2: resistance per unit area) were observed.A thin solid-state lithium battery was fabricated using thin film of TiS_2 (10-15 mum) prepared by chemical vapor deposition (CVD) as a cathode active material, a thin solid polymer electrolyte film (-2 mum) prepared by plasma polymerization, and a thin film of lithium deposited by thermal evaporation.