Preparation of Dendrimer-Sulfur Composites and their Application to Positive Active Material for Lithium Secondary Battery

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A higher-power and thinner secondary battery will reduce the weight of potable electrical equipment, such as a cellular telephone and portable computer. Organosulfur compounds, such as 2, 5-dimercapto-1, 3, 4-thiadiazole (DMcT), which have polymerizable sulfur groups, are one of the most promising candidates of positive active materials for a high-energy storage secondary battery. We prepared new-type disulfide polymers that have a hyperbranch backbone and cyclic disulfide structures at the terminal of each branches. Their electrochemical behavior in an organic electrolyte and possibility as positive active material were investigated. Branched polyesters with cyclic disulfide structure were prepared from branched polyester and lipoic acid which has cyclic disulfide moiety. The structure of the polymers was identified from the results of FTIR, NMR, and MALDI-TOFF MASS spectroscopy. The electrodes with the hyperbranch polymers in the organic electrolyte solution (for example, the electrolyte solution form propylene carbonate, 1, 2-dimethoxyethane, and LiClO_4) showed electrochemical responses based on the cyclic disulfide. The redox potential and behavior of the disulfide bonds in the hyperbranch polymer depended on its branched structure. The capacity of the test cell with the positive electrode based on the compound was 27.9 - 54.8 Ah kg^<-1>.