The synthesis of the D-A-type polymers containing benzo[1,2-b:6,5-b′]dithiophene-4,5-dione unit, their composites with carbon, and the lithium storage performances as electrode materials

Abstract

Two novel donor-acceptor (D-A)-conjugated polymers, poly[(thiophene-2,5-yl)-((benzo[1,2-b:6,5-b′]dithiophene-4,5-dione)-2,7-yl)] (PTDT) and poly[((2,3-dihydrothieno[3,4-b] [1, 2]dioxine)-5,7-diyl)-((benzo[1,2-b:6,5-b′]dithiophene-4,5-dione)-2,7-diyl)] (PTDO), have been synthesized with the same acceptor unit of benzo[1,2-b:6,5-b′]dithiophene-4,5-dione and different donor units of thiophene (Th) and 3,4-ethylenedioxothiphene (EDOT), respectively. And then, two composites (PTDT@C and PTDO@C) are made by coating the polymers on the surface of active carbon with an in situ method, which are used as the electrode materials of lithium-ion battery. The reversible capacities of PTDT@C and PTDO@C are 246.9 and 322.3 mAh g−1 at 0.1 A g−1 after 300 cycles running, respectively. By deducing the capability contribution of pure carbon, the theoretical capacities of the pure polymers are calculated to be 596 and 991 mAh g−1, respectively, for PTDT and PTDO, which correspond to the lithium storage number of 6.7 and 13.3, respectively, for the least repeating unit of the polymers. With the help of theoretical calculations, the underlying mechanisms for the different electrochemical performances of the polymers are discussed and revealed. The structure-activity relationship discussed in this work may provide the design principle for the construction of the D-A-type polymers used as high-capacity electrode materials for organic rechargeable batteries.