Heavily n-Dopable π-Conjugated Redox Polymers with Ultrafast Energy Storage Capability

We report here the first successful demonstration of a "π-conjugated redox polymer" simultaneously featuring a π-conjugated backbone and integrated redox sites, which can be stably and reversibly n-doped to a high doping level of 2. 0 with significantly enhanced electronic conductivity. The properties of such a heavily n-dopable polymer, polyN, N'-bis (2-octyldodecyl) -1, 4, 5, 8-naphthalenedicarboximide-2, 6-diyl-alt-5, 5'- (2, 2'-bithiophene) (P (NDI2OD-T2) ), were compared vis-à-vis to those of the corresponding backbone-insulated polyN, N'-bis (2-octyldodecyl) -1, 4, 5, 8-naphthalenedicarboximide-2, 6-diyl-alt-5, 5'-2, 2'- (1, 2-ethanediyl) bithiophene (P (NDI2OD-TET) ). When evaluated as a charge storage material for rechargeable Li batteries, P (NDI2OD-T2) delivers 95% of its theoretical capacity at a high rate of 100C (72 s per charge-discharge cycle) under practical measurement conditions as well as 96% capacity retention after 3000 cycles of deep discharge-charge. Electrochemical, impedance, and charge-transport measurements unambiguously demonstrate that the ultrafast electrode kinetics of P (NDI2OD-T2) are attributed to the high electronic conductivity of the polymer in the heavily n-doped state.