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Redox-active polymers with large charge-storage density are candidates for electrode-active materials in next-generation energy storage devices, due to their swift charge-discharge capabilities and their inherent characteristics of redox reactions that occur without significant structural changes, leading to their highly energy-efficient and durable performance. Here we report poly(diphenanthrenequinone-substituted norbornene) (PQN) as a novel class of organic electrode-active material. A Li coin cell composed of the PQN/carbon composite electrode as the cathode exhibited 2.8 V (V vs. Li/Li+) and great cycle performance maintaining a capacity higher than 100 mAh/g for more than 100 cycles at 60 C (i.e. in 1 min charging and discharging). Among many types of o-quinone-containing polymers for Li-ion batteries reported so far, the present research provides the first example of introducing phenanthrenequinone as the pendant group per repeating unit of polymers, which proved to be especially advantageous in terms of robustness and cyclability by virtue of the fused-ring structure to protect the reactive positions of the o-benzoquinone. We also report that the functional group tolerance against many types of redox-active groups, which we have established for the initiator and the propagating end of norbornene derivatives, apply for the phenanthrenequinone-substituted monomer, giving rise to a reversible redox activity.Poly(diphenanthrenequinone-substituted norbornene) (PQN) was obtained with high molecular weight from few steps of monomer synthesis and ROMP for polymerization. The Li coin cell battery composed of the PQN/carbon composite electrode as the cathode exhibited 2.81 V and great cycle performance maintaining a capacity higher than 100 mAh/g for more than 100 cycles. more...