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.

Despite the potential of incorporating electron-withdrawing cyano functional groups in organic cathode materials for sodium-ion batteries, a systematic understanding of the effect of the functionality on the redox properties and electrochemical performance is still limited to be explored. Herein, the electrochemical performance parameters as well as the Na-involved electrochemical redox characteristics for a series of chloranil derivatives with one to four cyano functional group(s) are explored using the computational modeling approach to assess their potential as organic cathode materials. It is highlighted from this study that the incorporation of cyano functional groups would improve both the redox potential and theoretical charge capacity, exhibiting the highest open-circuit redox potential (4.16 V vs Na/Na+) and theoretical charge capacity (386.5 mAh/g) for the chloranil derivative with four cyano functional groups. To be noted, the resulting values are comparable to those for top-ranking organic cathode materials in sodium-ion batteries. It is further verified that the beneficial effect of the cyano functional group on both the redox potential and theoretical charge capacity would lead to its positive impact on the theoretical energy density. These indicate that all the three parameters, namely, redox potential, charge capacity, and energy density, would be improved with the number of cyano functional groups. Further investigation reveals that the redox properties of chloranil derivatives would be strongly correlated with their electronic properties and solvation as well as their structural variations. Notably, the redox activity of a chloranil would be continuously weakened by the gradual change in electron affinity during the discharging process but a drastic increase in solvation would be a critical factor causing its cathodic deactivation. All the findings would assist us to establish a design approach for promising organic cathode materials in sodium-ion batteries.

Despite the creativity in designing materials based on bio-inspired organic compounds and their potential structural diversity, the incorporation of such materials into cathodes has attracted scarce attention, principally due to intrinsically weak redox activities. Herein, a large number of DNA/RNAinspired derivatives are systematically designed, and their electrochemical redox properties are explored with the aim of understanding structurepotential-performance relationship. Four striking conclusions can be drawn from this study. First, charging energy describing the 1st reduction step is a decisive parameter for the open-circuited adiabatic redox potentials of the compounds in the fully charged states, indicating that reorganization energy in the 2nd reduction step has a negligible impact. Second, both the charging and reorganization energies contribute cooperatively to the discharging potentials. Third, the compounds become cathodically inactive at the end of the discharging process owing to a sudden increase in solvation energy; thus, the compounds exhibit "three-stage discharging behavior". Fourth, the charge/energy-storage capability shows a critical dependence on Li binding mechanism, which is in turn correlated with the afore-mentioned core factors, leading to exceptional performance for a guanine derivative (1190 and 1586 mWh g −1 ). These findings will aid in advancing the development of bioinspired cathode materials for high-performance Li-ion batteries.

No abstract

Although environmentally benign organic cathode materials for secondary batteries are in demand, their high solubility in electrolyte solvents hinders broad applicability. In this study, a bridging fragment to link redox‐active sites is incorporated into organic complexes with the aim of preventing dissolution in electrolyte systems with no significant performance loss. Evaluation of these complexes using an advanced computational approach reveals that the type of redox‐active site (i. e., dicyanide, quinone, or dithione) is a key parameter for determining the intrinsic redox activity of the complexes, with the redox activity decreasing in the order of dithione>quinone>dicyanide. In contrast, the structural integrity is strongly reliant on the bridging style (i. e., amine‐based single linkage or diamine‐based double linkage). In particular, owing to their rigid anchoring effect, diamine‐based double linkages incorporated at dithione sites allow structural integrity to be maintained with no significant decrease in the high thermodynamic performance of dithione sites. These findings provide insights into design directions for insoluble organic cathode materials that can sustain high performance and structural durability during repeated cycling.