We report 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. 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.
 We will also discuss its application as the active electrode material in aqueous batteries.