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SummaryTo overcome limited information on organic cathode materials for lithium-ion batteries, we studied the electrochemical redox properties of pyrenetetrone and its nitrogen-doped derivatives. Three primary conclusions are highlighted from this study. First, the redox potential increases as the number of electron-withdrawing nitrogen dopants increases. Second, the redox potentials of pyrenetetrone derivatives continuously decrease with the number of bound Li atoms during the discharging process owing to the decrease in the reductive ability until the compounds become cathodically deactivated exhibiting negative redox potentials. Notably, pyrenetetrone with four nitrogen dopants loses its cathodic activity after the binding of five Li atoms, indicating remarkably high performance (496 mAh/g and 913 mWh/g). Last, the redox potential is strongly correlated not only with electronic properties but also with solvation energy. This highlights that pyrenetetrone derivatives would follow two-stage transition behaviors during the discharging process, implying a crucial contribution of solvation energy to their cathodic deactivation.

Doping capability is primitively governed by the energy level offset between the highest occupied molecular orbital (HOMO) of conjugated polymers (CPs) and the lowest unoccupied molecular orbital (LUMO) of dopants. A poor doping efficiency is obtained when doping directly using NOBF4 forming a large energy offset with the CP, while the devised doping strategy is found to significantly improve the doping efficiency (electrical conductivity) by sequentially treating the NOBF4 to the pre‐doped CP with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquino‐dimethane (F4TCNQ), establishing a relatively small energy level offset. It is verified that the cascade doping strategy requires receptive sites for each dopant to further improve the doping efficiency, and provides fast reaction kinetics energetically. An outstanding electrical conductivity (>610 S cm−1) is achieved through the optimization of the devised doping strategy, and spectroscopy analysis, including Hall effect measurement, supports more efficient charge carrier generation via the devised cascade doping.

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In efforts to design organic cathode materials for rechargeable batteries, a fundamental understanding of the redox properties of diverse non-carbon-based functionalities incorporated into 9,10-anthraquinone is lacking despite their potential impact. Herein, a preliminary investigation of the potential of anthraquinones with halogenated nitrogen-based functionalities reveals that the Li-triggered structural collapse observed in the early stage of discharging can be ascribed to the preference toward the strong Lewis acid–base interaction of N–Li–X (X = F or Cl) over the repulsive interaction of the electron-rich N–X bond. A further study of three solutions (i.e., substitution of NX2 with (i) BX2, (ii) NH2, and (iii) BH2) to the structural decomposition issue highlights four conclusive remarks. First, the replacement of N and/or X with electron-deficient atom(s), such as B and/or H, relieves the repulsive force on the N–X bond without the assistance of Li, and thus, no structural decomposition occurs. Second, the incorporation of BH2 is verified to be the most beneficial for improving the theoretical performance. Third, all the redox properties are better correlated with electron affinity and solvation energy than the electronegativity of functionality, implying that these key parameters cooperatively contribute to the electrochemical redox potential; additionally, solvation energy plays a crucial role in determining cathodic deactivation. Fourth, the improvement to the Li storage capability of anthraquinone using the third solution can primarily be ascribed to solvation energy remaining at a negative value even after the binding of more Li atoms than the other derivatives.