Solvent-free, oxidatively prepared polythiophene: High specific capacity as a cathode active material for lithium batteries

Polythiophene (PTH) was prepared by the chemical polymerization of thiophene under ambient, solvent-free conditions in the presence of FeCl3. This PTH was characterized by FTIR, UV-vis, NMR, and XRD. The NMR spectrum showed a PTH oligomer consisting of both aromatic thiophene and hydrogen-saturated tetrahydrothiophene moieties. The insoluble PTH was studied as a cathode active material for rechargeable lithium batteries with LiN(CF3SO2)2 (LiTFSI), 1,2-dimethoxyethane (DME), and 1,3-dioxolane (DOL) as electrolytes. Charge-discharge tests were conducted at room temperature. The discharge specific capacity, for levels above 400 mA h g−1, was obtained. The detected stable specific capacity and isolated, conjugated structure indicate that the charge-discharge mechanism was different from a classical 'doping-dedoping' process. We tentatively propose that the high specific capacity of PTH results from multi-electron electrode reactions on S atoms.