| Research Abstract |
Secondary batteries with high energy and power densities is expected for further development of electric vehicles and many other electric instruments. Objective of the present work is developing novel organic materials for high performance secondary batteries. First we examined electron transfer between a thiol (2,5-dimercapto-1,3,4-thiadiazole, DMcT) and a conducting polymer (polyaniline, PAn). As a result, it was found that the reversible electron transfer is possible between them. We have already found that the DMcT-PAn composite can serve as a high energy density cathode material for a secondary battery. However, charging current and discharging current of the battery were not high enough for the practical use. Then, we used a copper current collector for the composite cathode instead of a conventional carbon current collector. In the first few cycles, dissolution of the copper current collector was seen during the charging process. Simultaneously, an increase in the discharge capacity was seen. Since the charge-discharge capacity can exceed the theoretical capacity, which is calculated from amounts of DMcT and PAn, dissolved copper ion (s) must function as cathode active material. This suggests that some complex is formed between copper ion (s) and DMcT.Charging/discharging currents were high enough for the practical use. Although we have no clear evidence for the complex formation at present, we observed some change in the visible spectrum of a Cu (ClO_4)_2 solution upon addition of DMcT.Complex formation of Cu (I) and Cu (II) with DMcT has been reported as well as other transition metal ions. Other thiadiazoles also form complexes with copper and other metal ions. The complexes should be promising as cathode materials for secondary batteries.
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